0

IN THIS VOLUME


Design Engineering

2005;():1-16. doi:10.1115/IMECE2005-79083.

A detailed nonlinear finite element analysis (FEA) model of a radial-ply truck tire, 295/75R22.5, has been developed using explicit FEA simulation software, PAM-SHOCK. For the validation of the model, the tire model predictions of contact patch area, vertical stiffness, and cornering characteristics, such as cornering force and aligning moment versus slip angle, at different vertical loads are in good agreement with available physical measurements. For complete vehicle simulations, a simplified rigid ring tire model is required for efficient analysis throughput. The behavior of such a tire model can be verified and improved by comparing responses with the developed FEA model. Moreover, the in-plane and out-of-plane tire parameters needed for the simplified rigid ring tire model could be virtually determined at various vertical loads by testing the FEA tire model instead of performing expensive tire parameters measurements. The in-plane and out-of-plane tire parameters are implemented into a simplified rigid ring tire model to perform durability tests. The durability tests are conducted to examine dynamic behaviors by using the FEA truck tire and the rigid ring tire models during running on a water drainage ditch at various vertical tire loads. The ditch is 12.0-cm (4.72-in) deep and lies in 45-degree angle against tire traveling direction. The dynamic responses such as vertical displacement, forces, and moments at tire center are predicted using both tire models. The results obtained from both models are in reasonable agreement.

Commentary by Dr. Valentin Fuster
2005;():17-22. doi:10.1115/IMECE2005-79128.

A general three-dimensional nonlinear model is formulated to study the liquid slosh inside a partly filled cylindrical tank with and without baffles, while subjected to lateral and longitudinal acceleration fields arising from braking and turning maneuvers of a tank vehicle. The analyses are performed to investigate the significance of resulting destabilizing forces and moments caused by transient fluid slosh using the FLUENT software. The analyses are performed under varying magnitudes of maneuver-induced planar braking-in-a-turn accelerations and different fill volumes. The influence of baffles is further investigated under time varying longitudinal and lateral accelerations. The deviations in transient lateral and longitudinal forces, as well as the roll, pitch and yaw moments imposed on the tank structure, are obtained with respect to the corresponding quasi-static solutions. The results show that the magnitudes of transient forces and moments are significantly larger than those obtained from steady-state or kineto-static solutions. The addition of baffles tends to limit the magnitudes of slosh forces not only in the longitudinal direction but also along the lateral axis.

Topics: Fluids , Turning , Braking , Sloshing
Commentary by Dr. Valentin Fuster
2005;():23-30. doi:10.1115/IMECE2005-79129.

The Integration Framework for Architecture Development (IFAD) is an integrated framework that provides fast and consistent discipline analysis results and identifies discipline consequences corresponding to vehicle design changes. This information is valuable for balancing and integration in the early design phase. In this paper, the IFAD framework is utilized to conduct an example multi-objective multi-disciplinary optimization to evaluate vehicle performance trade-offs for a hypothetical vehicle. We consider design changes on high-level geometrical dimensions including front overhang, rear overhang and vehicle width at rocker. We also study vehicle configurations including choice of materials and tires and choice of powertrains. A commonly used multi-objective genetic algorithm (MOGA) technique, Non-dominated Sorting Genetic Algorithm (NSGAII [1]) is chosen because of the mixed types of design variables involved (i.e., continuous design variables representing high-level geometrical dimensions and discrete design variables representing vehicle configurations such as powertrain selection and material choice). Vehicle performance analyses in a range of disciplines such as geometry, aerodynamics and energy are carried out automatically through IFAD. The use of response surface modeling (RSM) is desired due to the large number of evaluations typical for a MOGA application. A comparison of the engineering performance trade-offs based on two different sets of performance objectives is presented.

Commentary by Dr. Valentin Fuster
2005;():31-40. doi:10.1115/IMECE2005-79170.

Performance testing is an important step in the development of any vehicle model. Generally, full-scale field tests are conducted to collect the dynamic response characteristics for evaluating the vehicle performance. However, with increases in computational power and the accuracy of simulation models, virtual testing can be extensively used as an alternative to the time consuming and costly full-scale tests, especially for severe maneuvers. Validation of the simulation results is critical for the acceptance of such simulation models. In this paper, a methodology for validating the vertical dynamic performance of a virtual vehicle has been discussed. The dynamic performance of a multi-wheeled combat vehicle model specially developed using a multi-body dynamics code was validated against the measured data obtained on the U.S. Army Aberdeen Test Center’s (ATC) test courses. The multi-wheeled combat vehicle variant computer simulation model was developed in TruckSim, a vehicle dynamic simulation software developed by the Mechanical Simulation Corporation. Prior to validating the model, the vehicle weights, dimensions, tires and suspension characteristics were measured and referenced in the specially developed computer simulation model. The data for the tire and suspension characteristics were acquired from the respective leading manufacturers in the form of look-up tables. The predictions of the vehicle vertical dynamics on different road profiles at various vehicle speeds were compared with the field test results. The time domain data for the vertical acceleration at the vehicle center of gravity, pitching, vehicle speed and the suspension/damper displacement were compared to analyze the feasibility of using the computer simulation models to predict the vertical dynamic performance of the vehicle. Based on the results it was found that the particular combat vehicle computer simulation model is capable of predicting the vertical dynamic performance characteristics.

Commentary by Dr. Valentin Fuster
2005;():41-52. doi:10.1115/IMECE2005-79355.

This paper focuses on laboratory implementation of a semiactive seat suspension with application of magneto-rheological (MR) dampers. We firstly introduce the nonlinear dynamics phenomena induced with the skyhook control that is now widely applied from structural vibration suppression to commercialized vehicle suspensions. However, superharmonic dynamics has not been clearly addressed in such vibration control systems. This paper tries to explain how superharmonics are created with skyhook controls through testing data analysis. Furthermore, in order to avoid this dynamics issue, this study implements a nonlinear model-based adaptive control into this MR damper based seat suspension. Based on a nonparametric MR damper model, the adaptive algorithm is expanded mathematically, and the system stability is discussed. Then in the following sections, this paper describes implementation procedures such as modeling simplification and validation, and testing results. Through the laboratory testing, the adaptive suspension is compared to two passive suspensions: hard-damping (stiff) suspension with max current of 1A to the MR damper, and low-damping (soft) suspension with minimum of 0A, while broadband random excitations are applied with respect to the seat suspension resonant frequency in order to test the adaptability of the adaptive control. Furthermore, mass and spring rate are assumed known and unknown for this adaptive controller to investigate the capability of this algorithm with the simplified model, respectively. Finally the comparison of testing results is presented to show the effectiveness and feasibility of the proposed adaptive algorithm to eliminate the superharmonics from the MR seat suspension.

Commentary by Dr. Valentin Fuster
2005;():53-61. doi:10.1115/IMECE2005-79698.

In the automotive industry, temporal, financial and human constraints require continuous improvements in the design process of new vehicles, by delivering relevant specifications and providing reliability and robustness in design. In order to analyze factors like behaviors of drivers and types of roads and guarantee the reliability of car components, measurements of forces from wheels are stored when the vehicle is tested on tracks and used by customers. The measurements represent the time history of multi-dimensional forces on the four wheels in the longitudinal, vertical and transversal directions. They are applied on structures (suspensions or motoring for instance) during the design life of the vehicles. The context of this paper is the fatigue analysis of multi-input loadings. The study will be focused on random and possibly correlated multi-input processes, representing multidimensional forces. The goal of this paper is to present an approach to generate simple multi-input loadings equivalent to measurements in terms of damage. The simple loadings have to be equivalent for any arbitrary structure, satisfying the reliability requirements imposed by the car manufacturer.

Commentary by Dr. Valentin Fuster
2005;():63-72. doi:10.1115/IMECE2005-79714.

In this paper, a nonlinear position tracking controller is derived based on feedback linearization to globally linearize the nonlinear dynamics of an electrohydraulic actuator with nonlinear state feedback. A detailed computer model is developed for a four-post road simulation system with a transit bus as the test vehicle. Using this model, comparisons are conducted between the proposed nonlinear decentralized controller and a traditional linear decentralized controller. Previously introduced interaction measures suitable for time domain analysis of nonlinear systems confirm that, for the test vehicle considered, load plate position loop interactions are quickly eliminated by either the linear or nonlinear decentralized position controllers. The performance of the road simulator as gauged by a position tracking error metric for a typical rough road profile is improved by over 60% across all actuators and response matching of sprung mass vertical acceleration PSD is likewise improved by over 50% when using the nonlinear decentralized controller.

Commentary by Dr. Valentin Fuster
2005;():73-78. doi:10.1115/IMECE2005-79820.

A regression-based energy method is developed for rapid estimation of the overall passenger-compartment interior noise (dBA) and Articulation Index (AI) in a vehicle of prescribed architecture when the vehicle travels on a particular road at a particular speed. The method is developed for use in the early vehicle design stage when only limited vehicle architecture design information are known. Regression analyses from a database of vehicle on-road tests and vehicle wind-tunnel tests are used to identify the energy transfer functions that represent the prescribed vehicle architecture. Energy excitation from both tire-road interaction and aerodynamic loads is then used to predict the interior dBA and AI responses. Comparisons of the predicted versus measured dBA and AI responses show reasonable agreement for car and wagon-type vehicles, although limited architecture data somewhat underestimates the actual response in certain vehicles

Commentary by Dr. Valentin Fuster
2005;():79-87. doi:10.1115/IMECE2005-79868.

Two different methods for approximating the fatigue damage of broad banded non-Gaussian random loads using the rainflow cycle count method are evaluated using loads measured on a truck. Results for Gaussian loads are summarized, and transformations for non-Gaussian loads are discussed. One of the two methods is based on the spectral moments of the process, and the results are obtained as a linear combination of an upper and lower bound. The second method is based on the assumption that the sequence of turning points of the load can be considered a Markov chain, for which results can be obtained. Measurements performed on different markets are used to study the two methods. Results are presented in terms of expected damage and amplitude spectra. Problems and possible improvements of the models are discussed.

Topics: Stress
Commentary by Dr. Valentin Fuster
2005;():89-96. doi:10.1115/IMECE2005-79996.

The effect of cargo shifting on the braking efficiency of a freight truck is investigated thorough development and analysis of an analytical model of the cargo-vehicle system together with the tie-down system. Braking efficiency is characterized in terms of the stopping distance, as a function of the cargo securement method (direct and indirect) and deck vibration caused by varying levels of road roughness. The relative movement of the cargo with respect to the deck causes decoupling of the cargo and the vehicle masses. The effective braking forces are thus applied to a reduced total mass. An important phenomenon that influences the cargo-vehicle interaction derives from the decoupling of the cargo and vehicle masses during the shifting of the cargo, leading to a situation in which the braking forces are applied to a reduced mass. The vehicle performance with a rigidly fixed cargo is also evaluated for comparison purposes. Results show that the indirectly restrained cargo produces the minimum stopping distances, irrespective of the road roughness, while the maximum stopping distances are attained for the directly restrained cargo.

Commentary by Dr. Valentin Fuster
2005;():97-101. doi:10.1115/IMECE2005-79998.

Friction between cargo and vehicle’s deck has been considered among the supplemental means for securing cargo. Although friction coefficients have been determined as a function of different influencing factors, such measurements have been performed under laboratory controlled conditions that simplify vehicle vibration and cargo-deck stiffness and contact characteristics. In this paper a methodology is proposed to quantify cargo-deck friction coefficients under realistic field conditions throughout the kinematical analysis of the stopping of the cargo-carrying vehicle by effects of dragging the cargo on the vehicle’s platform. The vehicle is located on an inclined road segment while the cargo is lashed to a fixed point on the road, in such a manner that the vehicle can travel a certain distance before the lashing becomes tensioned and the cargo starts stopping the vehicle. While average values for friction coefficients correlated well with those reported in the literature, standard deviations represented up to 33% of such average values.

Topics: Friction
Commentary by Dr. Valentin Fuster
2005;():103-108. doi:10.1115/IMECE2005-80002.

Road safety is influenced by the dynamic performance of heavy trucks during emergency maneuvers that involve abrupt changes in direction and velocity. In this context, rating of trucks performance under such situations becomes crucial to promote safer roads. Present test methods to evaluate trucks performance during braking and lane change maneuvers involve substantial monetary and time investments, and are limited to certain critical trucks and cargo. A more general methodology to evaluate a wider range of vehicles under diverse situations is thus necessary. In this paper the conceptual design of a truck testing facility is proposed to characterize and compare the dynamic performance of the vehicles under emergency maneuvering, as a function of the components’ properties, payload conditions and overall truck design. The equipment consists of a moving platform on which the vehicle is mounted, including load cells to measure tire loads. The motion of the platform can simulate steering maneuvers by providing lateral and yaw excitations.

Commentary by Dr. Valentin Fuster
2005;():109-115. doi:10.1115/IMECE2005-80029.

The Mahalanobis-Taguchi System is a diagnosis and predictive method for analyzing patterns in multivariate cases. The goal of this study is to compare the ability of the Mahalanobis-Taguchi System and a neural network to discriminate using small data sets. We examine the discriminant ability as a function of data set size using an application area where reliable data is publicly available. The study uses the Wisconsin Breast Cancer study with nine attributes and one class.

Commentary by Dr. Valentin Fuster
2005;():117-126. doi:10.1115/IMECE2005-80200.

Extraordinary developments in virtual crash testing research have been achieved during the past decade. Advancements in hardware and software technology along with improvements in computation mechanics and increased number of full-scale crash tests contributed positively to the development of more realistic finite element models. Use of complex finite element codes based on computational mechanics principles allowed the virtual reproduction of real world problems. Regarding roadside safety, the design phase was, until now, based on the use of simplified analysis, unable to describe accurately the complexity of vehicle impacts against safety hardware. Modeling details, such as geometry, constitutive laws of the materials, rigid, kinematic and other links between bodies, definition and characterization of contact surfaces are necessary to build an accurate finite element model for an impact problem. This set of information is needed for each different body involved in the event; making the development of a complete model very much demanding. Once a part (subset) of the entire model has been accurately validated against real experimental data, it can be used again and again in other analogous models. In this paper, finite element model of a unique Heavy Goods Vehicle (HGV) was developed and partially validated using actual crash test data. Development of this particular vehicle model was important since this vehicle is extensively used in Europe to test the structural adequacy of high containment level (H4a) safety barriers according to EN 1317 standard. The HGV model studied reproduces a FIAT-IVECO F180 truck, a vehicle with 4 axles and a mass of 30,000 kg when fully loaded. The model consisted of 12,337 elements and 11,470 nodes and was built for and is ready to use with LS-DYNA finite element code from Livermore Software Technology Corporation. Results of the validation study suggest that the developed HGV model shows promise and can be used in further studies with confidence. Improvements such as, steering mechanism in front axes and suspension system is currently underway to make model more realistic.

Topics: Design , Vehicles
Commentary by Dr. Valentin Fuster
2005;():127-132. doi:10.1115/IMECE2005-80438.

Accidents occur when the circumstances (i.e. the inputs) leading up to an accident map through the physical processes involved, to produce an undesirable result, namely the accident (i.e., the outputs). What the accident reconstructionist has to work with is the evidence left behind, and he then strives to determine the circumstances that led to the accident, based upon that evidence. In accident investigation there is often a deficit of physical evidence, and it is impossible, based on the available physical evidence alone, to pinpoint the circumstances that led to the accident. In practice, computer programs are often used to run simulations to find a set (or sets) of circumstances that is consistent with the evidence, and then the discovered set (or sets) of circumstances is presented as the answer. But this approach ignores some important questions related to whether the mapping being used (e.g., the computer simulation) is invertible and whether the circumstances leading to the evidence can be identified in a unique way, or whether the mapping is not invertible and the most that can be achieved is to identify whole sets in the input space of circumstances that might have led to the accident. Analysis offers the tools to probe such questions.

Topics: Accidents
Commentary by Dr. Valentin Fuster
2005;():133-142. doi:10.1115/IMECE2005-80484.

This study presents a compact hydro-pneumatic strut design with enhanced working area to reduce the design pressure requirements for suspension applications. The two struts are interconnected in the roll plane to realize enhanced roll properties of the suspension. The feedback effects of the interconnecting pipes on the suspension stiffness and damping properties are derived and discussed. The influences of fluid compressibility on the effective ride and roll properties are also investigated. Asymmetric and variable damping valves are further introduced to realize adequately damped and soft ride, and high low speed damping in the roll mode. Fundamental properties of the proposed interconnected configurations are derived and compared with those of the unconnected struts with an anti-roll bar, in terms of suspension vertical stiffness, roll stiffness, and vertical and roll mode damping. Parametric studies are also performed to study the role of interconnecting parameters on the essential suspension properties. The results indicate that interconnected suspension with inherent enhanced roll stiffness and damping characteristics offers significant potential to improve the dynamic roll performance of heavy vehicles, while retaining soft vertical ride. The effectiveness of the proposed concept is further illustrated through simulation results attained under two different deterministic excitations.

Commentary by Dr. Valentin Fuster
2005;():143-149. doi:10.1115/IMECE2005-80729.

In this paper, a comprehensive evaluation method for vehicle handling based on the driver’s subjective evaluation to different vehicle configurations has been studied by using development driving simulator tests. An objective evaluation index is developed which consists of several individual evaluation indices affecting vehicle handling. A series of weighting factors corresponding to individual evaluation indexes are found by using the Genetic Algorithm to reach the best agreement between the objective evaluation and the average of subjective evaluation of the drivers. Simulator test scheme has been designed and carried out with 14 vehicle configurations, and subjective evaluation has been made for easy handling of vehicle by a group of drivers. A driver/vehicle close-loop system model has been established which can predict the vehicle motion of handling and stability. Vehicle design parameters and control parameters of its control system have been optimized by using the driver/vehicle close-loop system model and objective evaluation index.

Topics: Design , Vehicles
Commentary by Dr. Valentin Fuster
2005;():151-159. doi:10.1115/IMECE2005-80816.

The effects of spot weld model on the numerical simulation of spot welded closed top-hat section sheet metal beams subjected to quassistatic and impact loading conditions were investigated using coupled experimental-numerical approach. Strength tests were performed to find the stiffness curves of spot weld in lap-shear, cross-tension (opening load), in-plane rotation (torsion) and peel specimens. The specimens were made from plain carbon steel and high strength low alloy steel sheets of three representative thicknesses. The local weld properties obtained from these tests were used to model a spot weld using different element types available in LSDYNA. These models were used in the numerical simulation of the beams subjected to static and dynamic axial crushing and static bending. The results obtained from the numerical analyses were validated by experiments on spot welded top-hat section sheet metal beams.

Commentary by Dr. Valentin Fuster
2005;():161-168. doi:10.1115/IMECE2005-81143.

The paper presents a new family of sensors that can be produced at a relatively low cost and that can measure the 3 forces and 3 moments acting at a point of a structure. The final aim of the research work is to develop measuring hubs and general purpose 6-axis load cells able to enhance the active safety of vehicles by providing information on forces and moments acting at the tyre/suspension system or on different vehicle subsystems, in the low frequency range (up to 100 Hz). Measuring hubs and general purpose 6-axis sensors have been manufactured and tested. The paper presents the concept, the construction issues and the performances of such devices. All of the presented measuring devices are based on a special statically determined structure. Twelve strain gauges measure the deformations at special locations and six signals (linearly related to the forces and moments) are filtered, amplified and digitally converted before they are stored or transmitted to a remote receiver. The sensitivity and the accuracy of such measuring devices are sufficient to exploit them to enhance the active safety of road vehicles.

Topics: Force , Sensors , Design , Vehicles
Commentary by Dr. Valentin Fuster
2005;():169-174. doi:10.1115/IMECE2005-81183.

This paper has studied the variable steering ratio for steering-by-wire (SBW) based on the 29 DOF vehicle dynamic model, which kept the steering gain of vehicle constant. And the steering ratio varied with the vehicle velocity and hand wheel angles. We have proposed three control strategies for SBW including front wheel control, yaw rate feedback control and yaw rate & acceleration feedback control. We compared these three control methods by simulation and simulator tests. We have researched the forward and feedback control methods in the four wheels (4WS) for SBW system. And compared with 2WS for SBW and the classical 4WS. The results indicated that 4WS for SBW could improve the vehicle handling.

Topics: Wire
Commentary by Dr. Valentin Fuster
2005;():175-184. doi:10.1115/IMECE2005-81269.

Body mount system is utilized for isolating dynamic load and vibration into the cab from the rest of vehicle system. The behavior of the mount system not only depends on the performance of individual mounts but also on the complete system configuration. A systematic approach is proposed for optimal design of the truck body mount system. Design variables include the mount locations and mechanical properties of each individual mount. First, an advanced component mode-based substructuring method is utilized for developing reduced-order models of the cab body and the other related subsystems, such as the chassis frame, from the original detailed finite element models. An optimization procedure is then developed, which can be used to determine the geometric distribution of the mounts and their mechanical characteristics (e.g., dynamic stiffness and damping) for minimizing vibration amplitudes at the given locations in the body structure over a frequency range of interest. To determine the optimal mount distribution, a path variable is introduced at the interface of cab and frame, which allows each individual mount moving along the chassis frame in the permitted range. The optimal mount location design problem is thus transformed to an equivalent problem that determines the optimal path variables of each mount. MATLAB codes are developed for the mount system design problem. An example mount system design is given to illustrate the effectiveness and efficiency of the proposed approach, in which the mount stiffness and the mount locations are optimized simultaneously. The developed optimization tool can be extended for optimizing other general mounting systems, such as an engine mount system.

Topics: Design , Trucks
Commentary by Dr. Valentin Fuster
2005;():185-191. doi:10.1115/IMECE2005-81355.

This paper presents the results of vibration isolation analysis for the pump/motor component of hydraulic hybrid vehicles (HHV). The hybrid subsystem can potentially improve the fuel efficiency of the vehicle by recovering some of the energy that is otherwise wasted in friction brakes. High pressure hydraulic fluid “assists” the engine in the initial acceleration period. Noise and vibration are an issue with these systems due to the variable hydraulic loads that are applied to the regenerative hybrid element. This study looks into the possibility of reducing the transmitted noise and vibration to the vehicle’s chassis by using smart magnetorheological (MR) dampers. MR dampers utilize MR fluid which is made of pure iron particles suspended in a carrier fluid. MR fluids deliver variable yield stress under the effect of a controllable electromagnetic field. To this end, an MR damper is modeled and simulated. In the simulation both shock and vibration loads are considered. The simulation results are compared with the performance of regular elastomer isolators. It is shown that the MR damper can effectively reduce the vibration for different working cycles of the regenerative system.

Commentary by Dr. Valentin Fuster
2005;():193-200. doi:10.1115/IMECE2005-81557.

Hybrid vehicles are gaining increasing popularity in recent years, and there are three major types of hybrid systems, hybrid hydraulic, hybrid electric, and hybrid fuel cell. The hydraulic system offers great advantages for vehicles operating in stop-and-go conditions because the reversible hydraulic pump/motor can capture large amounts of energy when the brakes are applied, and this energy is released through the hydraulic pump/motor to propel the vehicle. The key component in this new system is a HLA (Hydraulic Launch Assist) unit, which employs an advanced hydraulic hybrid power train system. Technical challenges with hydraulic hybrids include packaging and noise issues. HLA is an over 600 lbs system, and to fit it into a traditional designed vehicle, as well as to fit possibly multiple candidate platforms, the design of a sub-frame that can mount the HLA to the vehicles is a critical task. Because HLA system development is an on-going work, different structural problems emerge during this process. Therefore, an efficient design system is necessary to address the problems in the up-front design stage. Function-Oriented Material Design (FOMD) with special topology optimization techniques, such as multi-domain multi-step topology optimization, is a tool suitable for this task. The theoretical background is described and sub-frame design process is summarized in this paper. The effectiveness of the design system is demonstrated through design examples. The design method and procedure proposed in this paper is applicable to other vehicle structural design problems, which will reduce the design cycle and achieve the required functionalities in an efficient way.

Commentary by Dr. Valentin Fuster
2005;():201-208. doi:10.1115/IMECE2005-81660.

This paper develops two analytical models that describe the yaw dynamics of a farm tractor and can be used to design or improve steering control algorithms for the tractor. These models are verified against empirical data. The particular dynamics described are the motions from steering angle to yaw rate. A John Deere 8420 tractor, outfitted with inertial sensors and controlled through a PC-104 form factor computer, was used for experimental validation. Conditions including different implements at varying depths, as would normally be found on a farm, were tested. This paper presents the development of the analytical models, validates them against empirical data, and gives trends on how the model parameters change for different configurations.

Commentary by Dr. Valentin Fuster
2005;():209-214. doi:10.1115/IMECE2005-82101.

This paper presents the mathematical development of and simulation results for a full vehicle model with parametric uncertainties operating over unprepared terrain. The vehicle is modeled as a rigid multi-body dynamic system, consisting of chassis and four suspension and tire subsystems. The vehicle parameters considered uncertain are the suspension damping and the tire stiffness. The terrain profile is also modeled as a stochastic function. The uncertainties are explicitly represented using polynomial chaos decompositions. The computational technique presented in this study is more efficient than the traditional Monte Carlo approach, in modeling nonlinear multi-body dynamic systems with uncertainties. The numerical results presented here are very promising. The general computational tools discussed in this paper can be applied directly to any area that involves multi-body dynamic models, e.g., robotics, autonomous mechanical systems, actuator dynamics, and automatic control of systems with uncertainties.

Commentary by Dr. Valentin Fuster
2005;():215-224. doi:10.1115/IMECE2005-82153.

This paper presents the development of an active front steering (AFS) control system and normal force control (NFC) scheme utilizing fuzzy reasoning to track neutral steer yaw rate. The performance of the stand-alone controllers is compared with an integrated chassis management scheme combining the two. The simulation results indicate that the NFC by the active suspension as a stand-alone system shows improvement in vehicle handling response. The integrated chassis control scheme utilizing the steering and suspension controllers is proven to be more effective in attaining the desired performance that would not be attained individually.

Topics: Force , Vehicles , Tires
Commentary by Dr. Valentin Fuster
2005;():225-231. doi:10.1115/IMECE2005-82338.

This paper describes the optimization of the parallel hybrid electric vehicle (HEV) component sizing using a genetic algorithm approach. The optimization process is performed over three different driving cycles including the European ECE-EUDC, American FTP and TEH-CAR cycles in order to investigate the influence of the driving pattern on the optimal HEV component sizes. Hybrid Electric Vehicles are considered as a solution to the world’s need for cleaner and more fuel-efficient vehicles. HEVs use a combination of an internal combustion engine and an electric motor to propel the vehicle. Proper execution of a successful HEV design requires optimal sizing of its key mechanical and electrical components. In this paper, genetic algorithm is used as the optimization approach to find the best size of internal combustion engine, electric motor and energy storage system. The objective is minimization of fuel consumption and emissions while vehicle performances, like acceleration and gradeability are defined as constraints. These constraints are handled using penalty functions. Simulation results reveal that the HEV optimal component sizing is independent from the driving pattern. However, the amount of fuel use and emissions are extremely dependent on the driving cycles. In addition, the results show, while the performance constraints are within the standard criteria, the reduction in fuel consumption and emissions are achieved.

Commentary by Dr. Valentin Fuster
2005;():233-241. doi:10.1115/IMECE2005-82558.

Scaled passenger vehicles in conjunction with computer simulation have proven to be a valuable tool in determining rollover propensity. In this study, vehicle properties are varied to see their impact on roll stability and a stability threshold is derived empirically using simulation. The stability threshold is validated by scaled vehicle experiments. This is made possible with the lower cost and increased safety of using a scaled vehicle versus full size passenger vehicles. A simple electronic stability control (ESC) is then developed to keep the scaled vehicle within the stability threshold. The ESC is tested using varying vehicle properties with a constant vehicle model to see how these property changes affect the ESC’s effectiveness to prevent rollover. The ESC is then implemented with an Intelligent Vehicle Model (IVM) which updates the controller’s vehicle model as vehicle properties such as loading conditions change. This study shows that an IVM greatly increases the success of ESC in keeping the vehicle in the stability region.

Topics: Vehicles
Commentary by Dr. Valentin Fuster
2005;():243-253. doi:10.1115/IMECE2005-79451.

This report describes the state of design observed at NASA and collaborative research between NASA and Stanford University into improving design practices. Just as there are many types of missions and projects, there are many types of design practices and reviews at NASA. Through exploration of the NASA life-cycle across the organization and deeper case studies of specific missions, the goal of this work is to identify best practices and lessons learned from NASA’s review experience, benchmark against industry techniques, and develop methodologies to improve the process. By introducing design process error-proofing methods based on FMEA and QFD into the NASA framework, more robust corrective actions and solutions can better detect and prevent design errors. This paper demonstrates the methods through retroactive exploration and implementation on the Mars Climate Orbiter.

Topics: Design , Errors
Commentary by Dr. Valentin Fuster
2005;():255-263. doi:10.1115/IMECE2005-79453.

Design errors are a major source of quality loss in industry today. “Design Process Error-Proofing” seeks to prevent errors during product development by adapting quality management techniques. Poka-yoke solutions used in manufacturing and operation aim to prevent mistakes from occurring or detect them immediately after they are committed. The goal of design process error-proofing is to extend this strategy and develop innovative structured methods and tools that understand, predict, and prevent design errors. Because the research topic is fairly new, case studies are used to both explain and demonstrate the usefulness of solutions. Through a series of design initiatives at leading global organizations, important lessons were identified in the treatment of design errors. This paper discusses these error-proofing strategies and results.

Commentary by Dr. Valentin Fuster
2005;():265-274. doi:10.1115/IMECE2005-79713.

Plastic components are vital components of many engineered products, frequently representing 20–40% of the product value. While injection molding is the most common process for economically producing complex designs in large quantities, a large initial monetary investment is required to develop appropriate tooling. Accordingly, injection molding may not be appropriate for applications that are not guaranteed to recoup the initial costs. This paper extends previous work [1] with component cost and lead-time models developed from extensive industry data. The application is an electrical enclosure consisting of two parts produced by a variety of low to high volume manufacturing processes including CNC machining, fused deposition modeling, selective laser sintering, vacuum casting, direct fabrication, and injection molding with soft prototype and production tooling. The viability of each process is compared for production quantities of one hundred, one thousand, and ten thousand. The results indicate that the average cost per enclosure assembly is highly sensitive to the production quantity, varying in range from US$0.35 per enclosure for ten thousand assemblies produced via injection molding to US$49.30 per enclosure for one hundred assemblies produced via fused deposition modeling. The results indicate the cost and lead time advantages of the alternative processes; a flow chart is provided to assist process selection in engineering design.

Commentary by Dr. Valentin Fuster
2005;():275-289. doi:10.1115/IMECE2005-79961.

In the present paper, we explore issues in handling equality constraints in multiobjective robust design optimization (RDO) problems. Satisfying an equality constraint exactly under uncertainty can be a challenging task. The challenge of handling equality constraints is compounded in multiobjective RDO problems. Modeling the tradeoffs between the mean of the performance and the variation of the performance for each design objective in a multiobjective RDO problem is a complex task by itself. Equality constraints add to this complexity because of the additional tradeoffs that are introduced between constraint satisfaction under uncertainty and multiobjective performance. Satisfying equality constraints at their mean values, an approach typically followed, could lead to undesirable results. In this paper, we study the implications of equality constraint satisfaction in a multiobjective RDO problem, and provide a new problem formulation approach to resolve the above discussed tradeoffs. We illustrate that the proposed formulation can be used as an effective multiobjective design space exploration tool, with emphasis on equality constraint satisfaction under uncertainty. We present numerical examples to illustrate our theoretical developments.

Topics: Design , Optimization
Commentary by Dr. Valentin Fuster
2005;():291-297. doi:10.1115/IMECE2005-79971.

This paper is focused on 2400 liter waste container design, made by Contenur España; using computer aided engineering tools (CAE) and T.I.I.P. team experience, (University of Zaragoza, Spain). The goal was to produce a new plastic container concept, including all its elements, indicating assembly operations and selecting the plastic injection machine required for each part. Final cost should be reduced under other company’s prices. Several requisites were established at the beginning of the design stage: material type, European regulations on the product dimensions and testing procedures, an easy assembly, simple storage and low transport fares.... This work exposes several points of view around the complete design and work steps: feasibility analysis, aesthetical and structural design, detail drawing, injection molding definition, service tests, and final assembly. Methodology followed in this big product is described, collecting several fields’ experience. The final result is shown and four patents recognize this wide technical work.

Commentary by Dr. Valentin Fuster
2005;():299-305. doi:10.1115/IMECE2005-80058.

This paper presents a methodology for constructing spherical four-bar mechanisms with an emphasis on utilizing simpler machining processes and part geometries. By building each link out of easily created pieces instead of a single complex shape, a mechanism can be quickly prototyped and tested. The paper discusses the benefits and some of the issues that need to be addressed by this approach. Significant areas of concern include link design and tolerancing issues.

Topics: Mechanisms
Commentary by Dr. Valentin Fuster
2005;():307-317. doi:10.1115/IMECE2005-80191.

Various measurement methods have been proposed to measure the tooth shape parameters of profile-shifted spur and helical gears. This study proposes an over-balls measurement technique based on the tooth form equations of the profile-shifted spur and helical gears. The relations between the over-ball distance and the tooth parameters, i.e. the profile-shifted factor and the pressure angle, are derived for the two gears. The effect of the ball size on the accuracy of the measurements is investigated. An algorithm is proposed to extract the profile-shifted factor and the pressure angle from the measured over-ball chordal lengths. A good agreement is found between the calculated data and the measured results. Hence, the proposed inverse measurement method provides a feasible approach for obtaining highly accurate estimates of the tooth shape parameters of profile-shifted spur and helical gears.

Topics: Gears , Shapes , Spur gears
Commentary by Dr. Valentin Fuster
2005;():319-327. doi:10.1115/IMECE2005-80733.

Severe competition in plastic product manufacturing industry is driving the product design toward first-part-correct. Up to now, plastic product design is mainly evaluated by computer-aided-engineering packages to justify the plastic moulding processes including flow, packing and cooling. At the same time, product designers rely on their experience to justify the possibility of forming products, including parting/de-moulding direction and layout design, as there is rarely practical solution on those perspectives. This paper proposes a methodology to evaluate plastic product design based on downstream mould conceptual design probability. Several aspects of the conceptual mould design, from parting direction, undercut, draft angle to overall layout are studied. A novel undercut detection algorithm which extends the Z-Map to two sets of faces and sub-cells is proposed, and a hybrid parting direction detection mechanism is worked out. A prototype system is developed to help product designers to evaluate their designs based on the mould conceptual design perspectives. The system is tested with dozens of industrial parts and results show that the system can help the plastic part and mould designers to evaluate the designs before they are finalized.

Commentary by Dr. Valentin Fuster
2005;():329-333. doi:10.1115/IMECE2005-80809.

Tolerance analysis of mechanical assemblies requires the identification of locations of potential part interference, and determining whether the allowable geometric variation permitted by the part tolerances will cause part interference. Current commercial assembly modelers (and much of the classic work in assembly research [1-3]) require that the degrees of freedom between parts in an assembly be fully constrained prior to analysis. This method relies on the kinematics of the assembly contacts to determine whether the parts will assembly without interference. Our method — GapSpace — does not require these constraints in determining if interference-free assembly is possible [4]. Less restrictive, and thus less costly, tolerances can be used in assemblies where the specific relationships between surfaces is not predetermined. One difficulty we’ve had in implementing this GapSpace method is overcoming the constraints imposed by commercial modeling systems [5]. In this paper we report our success in implementing the GapSpace techniques in one such modeling system. Included in this system are additional user menus and interfaces which allow the identification of “fitting conditions” and analysis of the tolerances placed on the assembly components.

Commentary by Dr. Valentin Fuster
2005;():335-343. doi:10.1115/IMECE2005-80929.

In today’s marketplace, most products must better satisfy customers’ needs in the shortest time and be competitively priced. In this context, the reuse of knowledge about the targeted product is critical for developing potential product platforms. One can facilitate the reuse of existing knowledge to achieve a desired design by establishing a method that considers the layout of modules (or components) with identified flow interfaces, volume and the fundamental functional description. The problem grows with the number of candidate modules and with information-rich descriptions. The proposed REUSE (Reuse Existing Unit for Shape and Efficiency) Method greatly facilitates this search by filtering candidates based on their similarity to desired characteristics and their performance efficiency. By reusing existing information from components and modules, this approach allows the detailed specification of cost (e.g., investment and production cost for a module) along with other desired characteristics. This method applies to the complete product realization enterprise from conception through product launch. It also enables traceability of design decisions to help capture rationale and justification. A case study involving a family of cameras illustrates the proposed method.

Commentary by Dr. Valentin Fuster
2005;():345-354. doi:10.1115/IMECE2005-81179.

Today, a noticeable trend in the US industries is the growing reliance of companies on their supply chain to provide competitive components/sub-assemblies with the desired functionality to not only meet current needs and demands but also the anticipated ones of the future. Supplier consolidation through reduction of the total number of suppliers is being widely practiced by many companies. The increasing dependence on a few key suppliers makes supplier selection critical to a company’s success. Another distinct industry trend is shortening of product and technology lifecycles along with market demands for greater product variety. The direct implication of these trends is continually changing product architectures, which the manufacturers and their suppliers have to manage effectively. Thus, manufacturers need to base their supplier selection process on the robustness of suppliers to deliver components that are compatible with changing product architectures along with the other criterion such as price, reliability, quality, delivery time, etc. Supplier robustness, in the context of this paper, is defined as supplier ability to effectively cater to varying product architectures at minimum supplier costs. The current paper proposes an Ant Colony Optimization (ACO) based methodology for robust supplier selection by extending the robust engineering techniques to the supply chain domain. Taguchi’s quality loss concept is used to evaluate how well the individual components/subsystems supplied by the suppliers’ cost-effectively meet the customer needs. The objective is to select suppliers capable of meeting varying product architecture needs over a given planning horizon at optimal costs. The proposed methodology is demonstrated using an example of a cell phone product family.

Topics: Architecture
Commentary by Dr. Valentin Fuster
2005;():355-364. doi:10.1115/IMECE2005-81191.

Service centers can be viewed as facilities wherein service calls from customers relating to various service families cascade into work packages involving a set of service tasks. A service family is defined as a set of service type variants that have similar or common service tasks and hence may use a common set of resources (called the resource platform) over a given time horizon. In this paper, we present a methodology for determining cost-effective and robust resource platform configuration(s) for a given set of service families offered by a service center. The robust resource platform would be able to handle demand fluctuations from various service types within reasonable limits over a given planning horizon. Several successful studies have been reported in the manufacturing domain on successful application of product platforms to generate customizable product variants with cost advantages. In this paper, we extend the product platform concept to the service domain. The critical parts of the proposed Service Resource Platforming System (SRPS) methodology are: (1) generate rough cut resource selection using dynamic programming and create a resource schedule using linear programming; (2) generate final resource selection using uncertainty linear programming model proposed by Ben-Tal et al. (2003); and (3) construct resource platform using resource sub-sequence clustering concept. The objective for the rough cut and final resource selections is the maximization of the difference between the benefits and costs associated with in-house service processing and outsourcing. The proposed SRPS methodology is applied to an industry motivated problem.

Commentary by Dr. Valentin Fuster
2005;():365-370. doi:10.1115/IMECE2005-81508.

A wide variety of products are manufactured from raw materials that are in the form of sheets or plates. Once the product is designed, parts are unfolded or flattened into flat blanks, which are nested onto the raw material for cutting. Optimization of nesting and packing problems has been an active research field for many years, and many good algorithms have been created. These algorithms have a fundamental limitation, however, in that they assume the set of blanks to be nested is fixed. In this work we relax this assumption, and by linking a parametric CAD system, a part-unfolding module and a sheet-nesting module that all intercommunicate, nests are created which maintain the parametric dimensions of the assembled product. Given a nest of the set of required blanks, dimensions of the blanks are optimized for a particular objective, such as maximizing raw material utilization or minimizing total use of raw material, subject to assembly, part dimension, part and blank dimension constraints. Once optimized, these blank dimensions are returned to the CAD system to update the product model. Through the use of this system, a designer can simultaneously optimize all the dimensions within a product to minimize manufacturing costs early in the design phase while maintaining acceptable product performance. This paper will demonstrate a prototype of this DFM system, discuss issues such as performance improvement through randomized trials, and suggest how additional design objectives (e.g., strength to weight ratio, stiffness, etc.) can be integrated with the reduced manufacturing cost objective.

Commentary by Dr. Valentin Fuster
2005;():371-380. doi:10.1115/IMECE2005-81846.

A Design Repository has been created in an effort to archive existing products and the components in each product. With this function-based archiving system, designers can retrieve design information on existing products to assist in a new design project. The use of product families has emerged as an approach to exploit commonality for more efficient product development. However, the Design Repository does not contain explicit design information on platforms and modules. This paper describes information for the design of a platform and proposes a new data structure that organizes the information for augmenting the Design Repository. An information flow model for the development of a single product is modified to describe the flow of information needed for product platform design. The information flow model and associated data structure has been shown to be effective in representing three common product families: the Black & Decker Firestorm tool set, Kodak single-use cameras, and the IceDozer family of ice scrapers. With this data structure implemented into the existing repository, designers can find useful information on how to create different products based on the a common platform.

Topics: Design
Commentary by Dr. Valentin Fuster
2005;():381-388. doi:10.1115/IMECE2005-82024.

This paper describes the challenges faced by companies to manage warranty performance during product development. Understanding and reducing warranty cost often focuses exclusively on the analysis of product failures. However, warranty costs can also be incurred by events such as misaligned customer expectations that do not involve a product failure, per se. Many experts agree that effective management of system reliability and reliability validation during product development is a key to achieve superior time to market and life cycle quality. The paper first surveys the challenges faced by various organizations ranging from consumer electronics to aircraft engines to experimental high-energy physics accelerators. From the survey emerge some key and common issues that these companies face: identification of failure events; reliability modeling and prediction; prototyping and validation testing. The paper then reviews the current state of the art to identify areas for improvements as well as needed integrations in order to develop a comprehensive framework that will be useful to product developers to manage and predict warranty performance during product development. This framework extends and integrates three areas: 1) extend scenario-based FMEA to include the diagnosis and repair of failure events as part of the scenario; 2) use of Bayesian methods to integrate field data, product development data and engineering judgments; 3) generate costs models that allow tradeoff studies between product design, service model design and warranty policies. The paper concludes by presenting a future research agenda.

Commentary by Dr. Valentin Fuster
2005;():389-399. doi:10.1115/IMECE2005-82093.

Most simplified manufacturing processes generally result in two-dimensional features. However, most products are three-dimensional. Devices that could be manufactured through simplified manufacturing processes, but function in a three-dimensional space, would be highly desirable — especially if they require little assembly. Compliant ortho-planar metamorphic mechanisms (COPMMS) can be fabricated through simplified manufacturing processes, and then metamorphically transformed into a new configuration where they are no longer bound by the limitations of ortho-planar behavior. The main contributions of this paper are the suggestion of COPMM definitions, an investigation into the morphing process, and the description of a COPMM design process. This work also contributes a case study in designing COPMMs to meet particular design objectives.

Commentary by Dr. Valentin Fuster
2005;():401-410. doi:10.1115/IMECE2005-82137.

This paper introduces a methodology that guides the modularization of work task for global engineering. Global engineering is a new collaboration model of co-developing engineering design systems with distributed teams. We consider the decision of allocating subsystem designs to engineering teams as modularization of work tasks. Previous efforts have reviewed the different approaches to analyzing product modularization, but few studies have investigated developing a methodology that focuses on process applications. We begin this paper with an overview of current modularization methods and of the definitions of Global Engineering. Then we present the three-step modularization methodology in detail: 1.) decompose the design system and its functional specifications by a flow down technique, 2.) identify the couplings between the system parts and the functional requirements, and plot the interactions in a matrix, and 3.) modularize design work based on the identified couplings for worksharing. As a case study, we apply the method to a vehicle interior design. We conclude the paper by discussing the case study findings and the appropriate application of this analysis. We also explain the methodology’s limitations and propose future research opportunities.

Topics: Project tasks
Commentary by Dr. Valentin Fuster
2005;():411-423. doi:10.1115/IMECE2005-82342.

The increased use of 3D CAD systems by product development organizations has resulted in large databases of assemblies; this explosion of assembly data will continue in the future. Currently, there are no effective content-based techniques to search these databases. Ability to perform content-based searches on these databases is expected to help the designers in the following two ways. First, it can facilitate reuse of existing assembly designs, and thereby reducing the design time. Second, a lot of useful Design for Manufacturing and Assembly (DFMA) knowledge is embedded in existing assemblies. Therefore a capability to locate existing assemblies and examine them can be used as a learning tool by the designers to learn from the existing assembly designs and hence transfer the best DFMA practices to new designers. This paper describes a system for performing content-based searches on assembly databases. We identify templates for comprehensive search definitions and describe algorithms to perform content-based searches for mechanical assemblies. We also illustrate capabilities of our system through several examples.

Topics: Databases
Commentary by Dr. Valentin Fuster
2005;():425-435. doi:10.1115/IMECE2005-82886.

In this paper we continue our development of a structured methodology for product platform development suited to the early design stages. In addition to the previous focus on differences between new and mature products, we now consider how platform development is influenced by the morphology of a product. Purely physical products (e.g., a vacuum cleaner) often pose fewer challenges when undergoing platform design. However, products such as software, service offerings, or process-oriented solutions require adapting previous platform methods in order to accommodate the “amorphous” nature of the system. This paper includes a review of the recent literature in this area, and presents the authors latest platform methodology from the perspective of product morphology and maturity. Illustrative examples are used throughout.

Commentary by Dr. Valentin Fuster
2005;():437-441. doi:10.1115/IMECE2005-79102.

In the last decade, Lead Zirconate Titanate Oxide (PZT) thin-film actuators have received increasing attention because of their high frequency bandwidth, large actuation strength, fast response, and small size. The PZT film thickness is usually less than several microns as opposed to hundreds of microns for bulk PZT patches that are commercially available. As a result, PZT thin-film actuators pose unique vibration issues that do not appear in actuators with bulk PZT. Two major issues affecting actuator performance are the frequency bandwidth and the resonance amplitude. As an electromechanical device, a PZT thin-film actuator’s bandwidth and resonance amplitude depend not only on the lowest natural frequency ωn of the actuator’s mechanical structure but also on the corner frequency ωc of the actuator’s RC-circuit. For PZT thin-film actuators, the small film thickness implies large film capacitance C and small ωc . When the size of the actuator decreases, frequency ωn increases dramatically. As a result, improper design of PZT thin-film actuators could lead to ωc ≪ ωn substantially reducing the actuator bandwidth and the resonance amplitude. This paper is to demonstrate this phenomenon through calibrated experiments. In the experiments, frequency response functions of a fixed-fixed silicon beam with a 1-μm thick PZT film are measured through use of a laser Doppler vibrometer and a spectrum analyzer. The silicon beam has multiple electrodes with a wide range of resistance R and corner frequency ωc . The experimental results confirm that the actuator bandwidth and resonance amplitude are substantially reduced when ωc ≪ ωn .

Commentary by Dr. Valentin Fuster
2005;():443-452. doi:10.1115/IMECE2005-80007.

The hydrodynamic loading on silicon microcantilevers vibrating in different fluids close to (finite gap) and away from (infinite gap) a surface is analyzed numerically. Analytical techniques available to predict the hydrodynamic loading are restricted to simple cantilever geometries in fluids of infinite extent and are inaccurate for the higher modes of vibration. In this paper a finite element model developed in ADINA 8.1 (a fluid-structure interaction software, [1]) is used to overcome the shortcomings of the analytical models. Selective modal excitation of the cantilever in a fluid yields the corresponding modal frequency and damping factor. The numerical model benchmarks favorably with previously published experimental and analytical results. Detailed numerical analyses are performed in ADINA for variable gap lengths for a rectangular microcantilever for the first and second bending modes and the first torsional mode. Different cantilever geometries are also investigated. The results expose the physics of dissipation in the surrounding fluid and are expected to be of immediate interest to the Atomic Force Microscopy (AFM) and microcantilever biosensor communities.

Commentary by Dr. Valentin Fuster
2005;():453-460. doi:10.1115/IMECE2005-80019.

Electrostatic microactuators are used extensively in MEMS sensors, RF switches, and microfluidic pumps. Due to high bandwidth operation, however, reduction of residual vibration using feedback control is diffcult to implement. This paper designs, proves stability, and simulates a feedforward repetitive controller for an electrostatic microbridge. Squeeze film damping ensures boundedness of the distributed transverse displacement. Offline processing using repetitive control algorithm updates a waveform generator’s parameters based on measured response to reduce errors between the desired and actual displacement distribution. Simulations show a 36% reduction in midspan overshoot.

Commentary by Dr. Valentin Fuster
2005;():461-467. doi:10.1115/IMECE2005-80446.

The use of an interdigitated electrode configuration for tunable MEMS resonators is investigated. The tuning concept utilizes a shunt capacitor concept based on the fact that the mechanical compliance (stiffness) of the system is a function of both the mechanical properties and the electromechanical coupling of the piezoelectric element. Since the electromechanical coupling is dependant on the electrical impedance of the piezoelectric element and its shunt circuit, the circuit conditions applied to the piezoelectric tuning element can be varied in such a way as to tune the vibrational frequency of the resonator [1]. By utilizing an interdigitated electrode design to elicit the d33 response of the piezoelectric, a greater electromechanical coupling is achievable, corresponding to a wider range of tunability. In this paper, a model of the resonator is presented and then used in a study to determine the parameters which result in the highest range of tunability for the resonator.

Topics: Electrodes
Commentary by Dr. Valentin Fuster
2005;():469-474. doi:10.1115/IMECE2005-80474.

There has been recent interest in the utility and physical information content of higher harmonics in Atomic Force Microscopy: theoretically as a way to better understand the dynamical behavior of the cantilever-sample system and experimentally both as feedback signals to enhance scanning stability under liquid and as indicators of the properties of the tip-sample interaction force such as the Hamaker constant and Young’s Modulus. However, the great majority of investigations of cantilever motion have assumed the cantilever position detection system to be linear in cantilever position when in fact it is not. The output of both beam-bounce and interferometric detection systems are nonlinear and this nonlinearity leads to harmonic distortion of the output signal. Importantly, the magnitude of this distortion can easily be equal to or greater than the actual harmonic components of the cantilever motion, thus rendering attempts to use harmonic signals for feedback or as keys to the reconstruction of the tip-sample interaction force non-quantitative. We examine both beam-bounce and interferometric detection systems theoretically and experimentally, discuss the various sources of nonlinearity in each, and propose a simple technique for minimizing the harmonic distortion and extracting the real harmonic components of the cantilever motion from the distorted output signal.

Commentary by Dr. Valentin Fuster
2005;():475-483. doi:10.1115/IMECE2005-81153.

Robust manufacturing methods are needed for nanocomponent assembly, and one must understand the physics to optimize the processing and to develop control schemes to deal with the inherent uncertainty. We are studying field induced assembly of a new class of semiconducting metal oxides — nanobelts — that have been demonstrated for chemical sensing. We have demonstrated the integration of nanobelts with electrodes to make sensors by dielectrophoresis (DEP). The SnO2 nanobelts (width ~ 100–300 nm, thickness ~ 30–40 nm) were suspended in ethanol and introduced into a microchannel, and were assembled across the electrodes. Modeling suggests that attraction should occur at all frequencies over this range. Targeted experiments were performed to quantify surface and material properties for input to the modeling, and FEMLAB simulations were performed to validate the model. The goal of the modeling is to optimize the assembly of nanostructures in a manufacturing process at the wafer-scale.

Commentary by Dr. Valentin Fuster
2005;():485-491. doi:10.1115/IMECE2005-81156.

Current methods to study atomic force microscope (AFM) cantilever dynamics use model simplification or are based on the non-trivial solution of the equation of motion. As an alternative method, transfer function analysis gives a more complete description of system dynamics. In this work a transfer function study of two different AFM configurations, the point force and base driven cantilever, is presented. Exact analytical expressions of the infinite dimensional transfer function are derived for cantilever deflection and slope along the cantilever. Frequency response and transfer function infinite product expansion are obtained for the case where system outputs are set at the free end of the cantilever. The frequency response reflects the full complexity of cantilever dynamics affected by the presence of an infinite number of poles and zeros. An analytical expression for all the zeros and poles of the system is obtained. From the frequency response and pole-zero investigations it is shown how cantilever actuation and output measurement affect AFM operation and cantilever dynamics modelling. Transfer function analysis of AFM cantilevers opens the possibility of model based AFM operation to increase imaging and manipulation performance.

Commentary by Dr. Valentin Fuster
2005;():493-497. doi:10.1115/IMECE2005-81206.

Microcantilever based biochemical sensors rely on accurately detecting the selective binding of small amounts of the target analyte to a functionalized microcantilever. Commonly, the added mass of the bound analyte is detected by measuring accompanying shift in cantilever resonant frequency. In this paper we explore the possibility of using Anderson or mode localization in coupled oscillator arrays as a potentially more sensitive method for detecting the added mass. According to this method, the eigenvectors of an array of coupled, nominally identical cantilevers are expected to be extremely sensitive to small disorder such as that introduced by the added mass of the target biochemical analyte. A simple lumped parameter model of the cantilever array is used to establish theoretical feasibility of the method. The effects on the eigenvector sensitivity of initial statistical variability introduced due to inherent manufacturing tolerances are investigated. Experimental results are presented for a two cantilever array laser fabricated out of gold foil, and the results compared to theoretical expectations. Both the theoretical and experimental results indicate that added mass induced shifts in eigenvectors of such arrays can be orders of magnitude more sensitive than the resonance frequency shifts.

Commentary by Dr. Valentin Fuster
2005;():499-506. doi:10.1115/IMECE2005-81217.

There is strong experimental evidence for the existence of strange modes of failure of MEMS devices under shock. Such failures have not been explained with conventional models of MEMS. These failures are characterized by overlaps between moving microstructures and stationary electrodes, which cause electrical shorts. This work presents a model and simulation of MEMS devices under the combination of shock loads and electric actuation, which will shed the light on the influence of these forces on the pull-in instability. Our results indicate that the reported strange failures can be attributed to early dynamic pull-in instability. The results show that the combination of a shock load and an electric actuation makes the instability threshold much lower than the threshold predicted considering the effect of shock alone or electric actuation alone. Several results are presented showing the response of MEMS devices due to half-sine pulse, triangle pulse, and rectangular pulse shock loads of various durations and strengths. The effects of linear viscous damping and incompressible squeeze-film damping are also investigated.

Commentary by Dr. Valentin Fuster
2005;():507-515. doi:10.1115/IMECE2005-81264.

The feedback perspective of dynamic AFM provides a powerful tool to investigate the non-linear system dynamics from a system theoretic point of view. Including the higher order dynamics of the extended cantilever beam in the model the contact resonances can be reproduced faithfully without the need to solve the partial differential equation of motion directly. The investigation of the non-linear dynamics provides valuable insight into the generation of higher harmonics in dynamic AFM. However, the light lever detection scheme is widely used in dynamic AFM. This means that — strictly speaking — the tip-deflection is not a measurable quantity: the local deflection angle is measured but not the deflection itself. Additionally, time-delays may be introduced into the system influencing the dynamic behavior. Apart from system inherent time delays, a delayed force feedback is often used in order manipulate the system’s resonance characteristics (quality factor). Such an active control of the oscillatory behavior of the cantilever used in atomic force microscopy (AFM) allows one to tune the quality factor to purpose. For experiments requiring a high force sensitivity an enhancement of the quality factor is desirable whereas in time critical experiments additional damping may be needed. In order to control the quality factor a feedback signal is used that approximates the time derivative of the system state within the bandwidth of interest.

Commentary by Dr. Valentin Fuster
2005;():517-522. doi:10.1115/IMECE2005-81392.

This paper explores dynamically deriving the mechanical properties of a substrate. A method is presented in which a phase locked loop (PLL) is used to find the resonance frequency of a mechanical model consisting of an oscillating probe and a material substrate. This is done by first presenting an accurate PLL which is stable for nonlinear systems. The relationship between the system frequency and the stiffness of the material substrate is derived theoretically. The stiffness of the substrate is obtained by combining the theoretical result and the converging resonance frequency from PLL.

Commentary by Dr. Valentin Fuster
2005;():523-528. doi:10.1115/IMECE2005-81441.

Intracytoplasmic Sperm Injection (ICSI) is regarded as one of the most useful assisted reproductive technology (ART). During ICSI, a single spermatozoon is mechanically injected into cytoplasm of an oocyte using a glass needle, called a micro-injection pipette. The micro-injection pipette is usually controlled by a micromanipulator for the precise movement. In the case of rodent ICSI the Piezo-driven pipette is needed. However, one undesirable aspect of the Piezo-driven pipette is that the technicians have to use mercury in the micro-injection pipette in order to achieve consistent results. It is commonly held that the large density of mercury strongly affects the pipette vibration. In this work, we analyze the effect of mercury on the vibration characteristics of the Piezo-driven pipette. The pipette is modeled as a cantilever beam immersed in a viscous liquid. The forces on the pipette by the surrounding liquid include both inertial force and viscous force. The steady state response of the pipette is obtained by the finite element method together with the numerical integration method. We investigate the pipette dynamic responses when different fluids are used as the plug inside the pipette and as the fluid surrounding the pipette. Based on the analysis, we conclude that the effect mercury has on the vibration is not the main reason that it facilitates the ICSI.

Topics: Vibration
Commentary by Dr. Valentin Fuster
2005;():529-539. doi:10.1115/IMECE2005-81701.

A nonlinear autoparametric resonance based microresonator concept is explored in this study. The concept is illustrated by modelling an electrostatically actuated T-beam structure, with the first two modes of the structure in 1:2 internal resonance. The response of the system to primary resonance of the first and second mode is presented. When the second mode is resonantly actuated, the second mode in turn excites the first mode due to 1:2 internal resonance and the nonlinear coupling between the two modes. The structure therefore oscillates in first mode with half the frequency of excitation voltage. This is a unique feature of this microresonator, and as a result of this feature, the resonator can serve as a filter as well as a mixer in RF MEMS devices. When the first mode is excited, the structure oscillates in both the first and the second mode and thus has an output signal with frequency twice the input signal. The response also showed Hopf-bifurcations for higher actuation voltages.

Commentary by Dr. Valentin Fuster
2005;():541-548. doi:10.1115/IMECE2005-81824.

Two-dimensional (2D) nanofabrication processes such as lithography are the primary tools for building functional nanostructures. The third spatial dimension enables completely new devices to be realized, such as photonic crystals with arbitrary defect structures and materials with negative index of refraction [1]. Presently, available methods for three-dimensional (3D) nanopatterning tend to be either cost inefficient or limited to periodic structures. The Nanostructured Origami method fabricates 3D devices by first patterning nanostructures (electronic, optical, mechanical, etc) onto a 2D substrate and subsequently folding segments along predefined creases until the final design is obtained [2]. This approach allows almost arbitrary 3D nanostructured systems to be fabricated using exclusively 2D nanopatterning tools. In this paper, we present two approaches to the kinematic and dynamic modeling of folding origami structures. The first approach deals with the kinematics of unfolding single-vertex origami. This work is based on research conducted in the origami mathematics community, which is making rapid progress in understanding the geometry of origami and folding in general [3]. First, a unit positive “charge” is assigned to the creases of the structure in its folded state. Thus, each configuration of the structure as it unfolds can be assigned a value of electrostatic (Coulomb) energy. Because of repulsion between the positive charges, the structure will unfold if allowed to decrease its energy. If the energy minimization can be carried out all the way to the completely unfolded state, we are simultaneously guaranteed of the absence of collisions for the determined path. The second method deals with dynamic modeling of folding multi-segment (accordion style) origamis. The actuation method for folding the segments uses a thin, stressed metal layer that is deposited as a hinge on a relatively stress free structural layer. Through the use of robotics routines, the hinges are modeled as revolute joints, and the system dynamics are calculated.

Commentary by Dr. Valentin Fuster
2005;():549-557. doi:10.1115/IMECE2005-81922.

We consider the bending of two nanotubes coupled together with van der Waal forces acting transverse to the axis, and subject to axial loads. The nanotubes are modeled as elastica while the interaction forces are derived from a Lennard-Jones 12-6 potential. The elastica are assumed to be a fixed distance apart at their ends, not necessarily equal to the equilibrium distance as identified from the Lennard-Jones potential. Therefore, the equilibrium configuration is not necessarily straight. As the compressive axial force increases, the beams can undergo buckling instability and the critical load depends not only on the material properties of the structure, but the geometry of the system as well. The continuum model is subjected to a Galerkin reduction to develop a reduced set of equations that can be used to calculate the equilibrium configuration of the system as well as the stability of these configurations. We show that the buckling instability in this model is significantly affected by the presence of the interaction force as well as the separation of the nanotubes at their ends.

Commentary by Dr. Valentin Fuster
2005;():559-569. doi:10.1115/IMECE2005-82556.

This paper presents the controller design and implementation of a high-precision 6-degree-of-freedom (6-DOF) magnetically levitated (maglev) positioner. This high-precision positioning system consists of a novel concentrated-field magnet matrix and a triangular single-moving part that carries three 3-phase permanent-magnet linear-levitation-motor armatures. Since only a single levitated moving part, namely the platen, generates all required fine and coarse motions, this positioning system is reliable and low-cost. Three planar levitation motors based on the Lorentz-force law not only generate the vertical force to levitate the triangular platen but control the platen’s position and orientation in the horizontal plane. All 6-DOF motions are controlled by magnetic forces only. The platen is regarded a pure mass system, and the spring and damping coefficients are neglected except for the vertical directions. Single-input single-output (SISO) digital lead-lag controllers are designed and implemented on a digital signal processor (DSP). This 6-DOF fully magnetically levitated positioner has a total mass of 5.91 kg and currently exhibits a 120 mm × 120 mm travel range. This positioner is highly suitable for semiconductor-manufacturing applications such as wafer steppers. Several experimental motion profiles are presented to demonstrate the maglev stage’s capability of accurately tracking any planar and 3-D paths.

Commentary by Dr. Valentin Fuster
2005;():571-581. doi:10.1115/IMECE2005-83153.

The focus of this paper is on the nonlinear dynamics and control of the scan process in noncontacting atomic force microscopy. An initial-boundary-value problem is consistently formulated to include both nonlinear dynamics of a microcantilever with a localized atomic interaction force for the surface it is mapping, and a horizontal boundary condition for a constant scan speed and its control. The model considered is obtained using the extended Hamilton’s principle which yields two partial differential equations for the combined horizontal and vertical motions. Isolation of a Lagrange multiplier describing the microbeam fixed length enables construction of a modified equation of motion which is reduced to a single mode dynamical system via Galerkin’s method. The analysis includes a numerical study of the strongly nonlinear system leading to a stability map describing an escape bifurcation threshold where the tip, at the free end of the microbeam, ‘jumps-to-contact’ with the sample. Results include periodic ultrasubharmonic and quasiperiodic solutions corresponding to primary and secondary resonances.

Commentary by Dr. Valentin Fuster
2005;():583-584. doi:10.1115/IMECE2005-79213.

Most of the practical engineering structures contain holes and cutouts of different sizes designed as parts of basic design, as in joints and assemblies, and for maintenance purposes. It is well known that holes and cutouts cause serious problems of stress concentrations due to the geometry discontinuity. These problems are even more serious in structures made of composite materials since the materials exhibit anisotropic behavior, and the structures are more sensitive to stress concentrations due to their brittle behavior. Because of its importance, engineers want to determine the effects of stress concentration, predict the failure and strength, and develop methods to reduce these effects. The stress distribution in the notched composite laminate is very sensitive to the size of the hole and the eccentricity of the hole from its desired location. In practice, many times during manufacturing the drilled hole is slightly offset from the desired location, and further there is variability in the size of the hole. These variations have a random distribution over the ensemble of laminates. In addition, composite materials display significant variability in their mechanical properties. As a result of the above-mentioned variabilities, the stress distribution in the laminate becomes stochastic in nature. In this circumstance, it becomes appropriate that the analysis of the notched laminates be carried out based on a stochastic approach and that the design is performed based on reliability requirement.

Commentary by Dr. Valentin Fuster
2005;():585-598. doi:10.1115/IMECE2005-79233.

The present study is concerned with the “Free Flexural Vibrations Response of Composite Mindlin Plates or Panels with a Centrally Bonded Symmetric Double Lap Joint (or Symmetric Double Doubler Joint). The plate “adherends” and the plate “doublers” are considered as dissimilar, orthotropic “Mindlin Plates” with the transverse and the rotary moments of inertia. The relatively, very thin adhesive layers are taken into account in terms of their transverse normal and shear stresses. The mid-center of the bonded region of the joint is at the mid-center of the entire system. In order to facilitate the present solution technique, the dynamic equations of the plate “adherends” and the plate “doublers” with those of the adhesive layers are reduced to a set of the “Governing System of First Order ordinary Differential Equations” in terms of the “state vectors” of the problem. This reduced set establishes a “Two-Point Boundary Value Problem” which can be numerically integrated by making use of the “Modified Transfer Matrix Method (MTMM) (with Interpolation Polynomials)”. In the adhesive layers, the “hard” and the “soft” adhesive cases are accounted for. It was found that the adhesive elastic constants drastically influence the mode shapes and their natural frequencies. Also, the numerical results of some parametric studies regarding the effects of the “Position Ratio” and the “Joint Length Ratio” on the natural frequencies for various sets of support conditions are presented.

Commentary by Dr. Valentin Fuster
2005;():599-600. doi:10.1115/IMECE2005-79275.

One of the more formidable problems in composite research is the study of delamination and other failure modes in the vicinity of a circular hole in a laminate, e.g., a circular cut-out in a structure. In this problem, the singularity varies around the periphery of the hole as well as through the thickness of the laminate. Under tensile loading, the early failure modes in this problem consist of transverse cracks in various layers, so that delamination occurs only after other damage is precipitated, followed by fiber breakage leading to failure. A literature review of past work clearly shows that mechanical testing with simultaneous AE monitoring is a fruitful technique to study damage accumulation in composite systems. The acoustic-ultrasonic (AU) testing combines the high sensitivity of ultrasonics to internal damage and the method of acoustic emission technique to characterize elastic waves. As damage accumulates in the specimen along the wave path, the net internal damping increases and changes the wave parameters such as peak amplitude, duration, etc. accordingly. Additionally, a range of experimental results over the last decade has further shown that the mechanical deformation and electric resistance of carbon fiber reinforced polymers are coupled, so that the material is inherently a sensor of its own damage state. The monitoring of electric resistance and capacitance changes, linked to the modifications of the conduction paths in the composite, allows the detection of damage growth. It seems logical that a natural extension of these different approaches is the determination of damage mode, e.g., fiber breakage, matrix cracking or delamination, and damage size and position, based on combined measurements from these techniques. These multiple techniques will serve a two-fold purpose, namely, enable comparison as well as complement each other in case of incomplete damage mapping from one set of sensors For this study, we will consider carbon fiber-reinforced toughened bismaleimide, (IM7/5250-4) quasi-isotropic laminate coupons 12” long, 4” wide with hole at the center under tension. Figure 1 shows the damage which occurs around a 0.75” hole in a [45/0/-45/90]s graphite epoxy laminate obtained by radiography after unloading the test specimen from an applied stress of 50 Ksi. The failure stress for this laminate was 56.4 Ksi. Damage in the form of ply cracks in the 90, 45, and −45 plies and delamination around hole edges is clearly evident. The radiograph taken after unloading from a 50 Ksi stress level clearly shows the location and extent of damage, but contains no specific information about the sequence and the timing of damage events. Figure 2 shows stress-strain curves obtained from strain gages mounted at various distances away from the hole edge along with the far-field value. The stress-strain curves provide useful information regarding the initiation as well as the growth of the damage, as evidenced by jump in strain levels and onset of nonlinearity. Damage initiation is first picked up by the strain gage which is mounted closest to the hole edge at a stress level of 21 Ksi. Subsequently, other strain gages begin to sense damage growth as the applied stress level increases. The strain gage data provides useful information regarding initiation, growth and severity of damage, but it is difficult to assign specific damage modes and their location to the measurements. This example clearly demonstrates the needs, with the associated benefits, of the multiple sensor approach. In this work, three different hole sizes (0.25”, 0.5” and 0.75”) will be investigated. This example problem will enable us to examine the combined effects of cut-outs, matrix cracking, delamination and fiber breakage on the ability of various NDE techniques to assess damage. The development and growth of damage in the composite laminate with a hole under compression will be markedly different than in tension. Under compression, the major damage modes are fiber buckling and delamination, and will also be investigated.

Commentary by Dr. Valentin Fuster
2005;():601-602. doi:10.1115/IMECE2005-79421.

Single-Lap Joint (SLJ) and three-point end-notched flexure (ENF) joint configurations were used to bond 1” × 1/8″ (25.4mm × 3.175mm) aluminum 2024 T-4 adherends using a range of 3M™ high performance pressure sensitive adhesives (Adhesives 69, 73 and 85) and VHB™ acrylic foam tapes (Foam 41, 50, 52). Batches of bonded specimens were subjected to two types of aggressive environments simulating extreme service conditions: freeze-thaw cycling from 10°F to 50°F at 6 cycles per day (ASTM C666 Procedure A) for 21 days with samples immersed in water; heat-cool cycling (with 90% of maximum recommended temperature by the manufacturer of both acrylic foam and adhesive transfer tapes attained at 70% relative humidity) and 3 cycles per day for 21 days. Electrochemical Impedance Spectroscopy (EIS) and Fast Fourier Transform (FFT) based impulse frequency response vibration Non-Destructive Evaluation (NDE) techniques were used to monitor overall bond integrity.

Commentary by Dr. Valentin Fuster
2005;():603-604. doi:10.1115/IMECE2005-79425.

A range of 3M™ VHB™ acrylic foam tapes and high performance adhesive transfer tapes were used to bond 1” × 1/8″ (25.4 mm × 3.175 mm) aluminum 2024 T-4 adherends in single-lap joint (SLJ) and three-point end-notched flexure (ENF) configurations. Three types of 0.045” thick double-coated acrylic foam tapes: Foam 41, 50 and 52 (firm, soft and softer), and three types of adhesive transfer tapes: Adhesives 69, 73 and 85 (0.005”, 0.01” and 0.005” thick, respectively) were used for this study. The samples were subjected to two types of aggressive environments simulating extreme service conditions: freeze-thaw cycling from 10°F to 50°F at 6 cycles per day (ASTM C666 Procedure A) for 21 days with samples immersed in water; heat-cool cycling (with 90% of maximum recommended temperature by the manufacturer of both acrylic foam and adhesive transfer tapes attained at 70% relative humidity) and 3 cycles per day for 21 days. Initially the impulse-frequency response vibration and electrochemical impedance spectroscopy (EIS) techniques were used for monitoring bond quality nondestructively and selecting the best out of 250 fabricated samples. After obtaining baseline data, the specimens were subjected to quasi-static lap-shear and dynamic impact loading to compare their lap-shear failure loads and shear energy along with the impact load and energy absorbed.

Commentary by Dr. Valentin Fuster
2005;():605-612. doi:10.1115/IMECE2005-79752.

The behavior of bolted joints in component systems with relatively small fastening systems, critical materials or with high loading level often shows significant yielding effects with reduction of preload. Thus, poor reliability or even failures are possible. This problem requires an adaptation of the established analytical engineering design methods. A new approach with consideration of over-elastic behavior and preload history is proposed. Examples refer to magnesium components, contact pressure and tightening with angular control.

Commentary by Dr. Valentin Fuster
2005;():613-620. doi:10.1115/IMECE2005-79762.

The need for the best material behavior at any location within high performance component systems leads to diversified material combinations. One example is the material mixture in today’s vehicles: steel, aluminum, magnesium, plastics, fibers, glass and other solids. These combinations need new or modified fastening technologies, because traditional techniques like welding or bolting up to now are mainly focused on single material joints. Besides this, the loading level during operation of the components increases continuously, so the behavior of the involved fastening systems under operating conditions also has to be known. Fastening systems with light metals show a significant thermal induced change of clamping/preload. This paper gives an overview with some optimized exemplary fastening systems from the automotive sector which could be partly transferred to other industry branches. The paper also emphasizes that various details of designing fastening systems are decisive for reliability and stability.

Commentary by Dr. Valentin Fuster
2005;():621-623. doi:10.1115/IMECE2005-81188.

The Qualcomm OmniTRACS™ Antenna Communications Unit (ACU) is a mobile transceiver which when installed on trucks allows two-way communication between drivers and fleet logistic centers. A global positioning device (GPS) inside the ACU shows controllers the geographical location of the truck and its cargo. The ACU is deployed in frequently harsh, inhospitable regions of the world and as such must operate reliably when exposed to diverse climatic conditions such as high humidity encountered in the Amazon River basin, extreme heat typical of deserts in the American southwest and while operating in northern Alaska where the terrain is rugged and winter temperatures reach −40C.

Commentary by Dr. Valentin Fuster
2005;():625-636. doi:10.1115/IMECE2005-81422.

The joining of composite materials used in airframe structures has always presented a challenge to the structural engineer. As part of a Survivable Affordable Repairable Airframe Program (SARAP) agreement, research on three advanced joining concepts was conducted to identify and validate designs that would provide improved structural efficiency when compared to conventional joining methods. The first involves using finger joints in thin laminates to produce a joint with high specific strength compared to typical joining methods. The second utilizes a derivative of needling for stabilized dry fabric pre-forms to improve through-the-thickness laminate and joint properties. The third concept focuses on compression preload to improve the performance of a typical lap joint. Within each concept, coupon or element tests were used to validate the performance of these alternative configurations. This paper presents both analytical predictions and test results documenting the effects of these improved joining methods.

Commentary by Dr. Valentin Fuster
2005;():637-653. doi:10.1115/IMECE2005-79191.

Methods of Spur Gear Root Stress determination were analyzed by comparing an experimentally proven method to documented theoretical methods. The methods evaluated were German DIN standards, AGMA standard, JGMA standard, and Cornell method. The Cornell method was used as a benchmark for comparison of other methods. Each method was used to calculate root stresses in a spur gear system. The gear system variables were torque and rotational speed. Seven different torque settings and four different rotational speeds were used in the analysis, giving 28 different system settings for analysis. The system was modeled using a NASA computer program, Dynamic Analysis of Spur Gear Transmission (DANST) developed by one of the authors. The stresses in the tooth root were calculated from the dynamic forces at 121 points along the involute tooth profile during a two-gear mesh. The study has shown that the stresses calculated using AGMA could predict the stresses calculated using the Cornell method of stress calculation. The JGMA method calculates the maximum root stress of the gear system within three percent of the Cornell method. The study showed that AGMA, and JGMA methods could be as effective at calculating the root stresses as the Cornell method.

Topics: Stress , Gears , Spur gears
Commentary by Dr. Valentin Fuster
2005;():655-662. doi:10.1115/IMECE2005-79230.

A typical ground imitating tank is analyzed regarding it as the thin-walled structure composed of plates (skins) and beams (reinforcement) using finite element method (FEM). Through moving the location of reinforcements, make the skins close with the flanges of the reinforcements in order to imitate actually the connection of the skins and the reinforcements. The thickness of plates, the size and the geometry shape and the location of reinforcements are taken as parameters to be optimized. In calculation, not only consider effects of the oil-weight, the extra-pressure in tank and the dead weight of the tank on the stresses and displacements of the tank, but also analyze the effects of the inertia forces produced due to the rotation of the tank on the stresses and displacements. Displacement, stress and deformation distributions of the ground imitating tank under the three typical flying postures imitated are given.

Commentary by Dr. Valentin Fuster
2005;():663-671. doi:10.1115/IMECE2005-79232.

Presented is an approach for obtaining whole-field stress distributions of a bi-material rectangular plate, which is composed of plate I and plate II with a fixed boundary and subjected to external loads, using elasticity mechanics theory. There are two cracks at the edges of the interface of plate I and plate II, which are called as bilateral interface cracks. In the analysis, the effects of the ratio of Young’s modulus of material I (plate I) and to that of material II (plate II) and the ratio of the crack length to the width of the plate on the stress distributions in the vicinity of the interface were examined. Stress Intensity Factor (SIF) and normalized SIF equations were also calculated through the stresses in the vicinity of the crack tips.

Commentary by Dr. Valentin Fuster
2005;():673-682. doi:10.1115/IMECE2005-79234.

Stress functions expressed from Fourier series, suitable for arbitrary stress boundary conditions, were derived using method of variable separation. General displacement expressions containing the displacement of rigid body were also derived. A method of solving mixed boundary problems (in which external forces acting at a part of the whole boundaries are known and displacements at the rest boundaries are known) was presented. As an example, a rectangular plate, one side of which was fixed and objective side was subjected to a concentrated force, was analyzed. In addition, characteristics of stress distributions in the regions of stress concentration were questioned. It was found from the presented results of calculation that describing stress concentration with the singular stress at a point was unworkable. Describing stress concentration with the average stress in the feature size instead of the singular stress at a point was operative and reflected objectively practical stress and displacement boundary conditions. The concept of feature-size-factor was introduced.

Commentary by Dr. Valentin Fuster
2005;():683-688. doi:10.1115/IMECE2005-79312.

In Japan, with the recent increase in wind power generator installations, the incidence of lightning damage to FRP blades is increasing. Lightning damage is a significant issue in Japan since lightning in Japan seems severer than that in Europe or the US. In Kochi, Japan, six 600-750 kW grade generators have been installed, and some have been damaged by lightning several times. To resolve this problem, the Kochi University of Technology received a request in 2002 from the Kochi prefectural government for research into lightning protection. After surveying the literature and questioning related organizations such as NREL and Toray USA, experiments to protect against lightning damage to FRP blades of wind power generators were planned. Half size models and two 1/4 parts of a full size 250kW blade were prepared as specimens for this research. The method investigated to protect against lightning damage was metal coating. The aim being to protect against blade failure by using metal coating in actual field situations; by using a 1/2 size model and the full size blade specimens in an experimental situation. As in previous experiments, these ones were mainly conducted in the Toshiba Hamakawasaki High Voltage High Power Testing Laboratory. This Testing Laboratory is one of the biggest test laboratories for experiments involving high voltages and large currents.

Commentary by Dr. Valentin Fuster
2005;():689-696. doi:10.1115/IMECE2005-79320.

It is common knowledge that a bolt is apt to loosen due to slippage between the contact surfaces of joined parts. Loosening tests using real parts enable precise scrutiny of real phenomena under the influence of multiple factors such as slip distance, surface roughness, and coefficient friction. However, estimating the influence of the individual factors is very difficult because the friction forces of real contact surfaces are compiled based on variations in friction coefficients, meaning friction is not stable. Therefore, the effects of factors were investigated using Finite Element Analysis (FEA) to control friction coefficients. The procedures were as follows. Assuming a joined structure consisting of a bolt, nut, and washer, bolt axial tension was generated through constant movement of a washer in the bolt’s axial direction, following which the washer was constantly vibrated in one direction transverse to the bolt axis. This vibration generated displacements equivalent to the degree of slippage between the two clamped parts. During vibration, the rotating angles of the bolt and the contact pressure of the threads and bearing surfaces were calculated. The results were as follows. The vibrating displacements of a washer have considerable influence on the rotational loosening of a bolt. In cases where there was only minor displacement of the washer vibrations, the rotational loosening angle rapidly decreased, although the loosening did not cease completely. Therefore, the magnitude of what is called “critical slip” was not confirmed under the conditions of this study. In addition, the friction coefficient has a significant influence on the rotational loosening of a bolt. When the respective friction coefficient values of the threads and bearing surfaces are not balanced, rotational loosening cannot continue. Surface roughness readily affects contact pressure, so it tends to make the contact pressure localized. In particular, high-pressure areas were affected by several projections set on the threads. However, under those conditions the rotational loosening did not differ greatly from the results of the fine surface models subject to the same vibrating amplitude and friction coefficient. Consequently, the localized contact pressure had little evident effect on loosening. Above all, FEA reproduced the loosening of the bolt, and the reference made in this analysis is useful.

Commentary by Dr. Valentin Fuster
2005;():697-702. doi:10.1115/IMECE2005-79431.

The safe structural design of boiler waterwalls with various loadings such as dead weight, fluid pressure, gas pressure and thermal differences is an extensive problem demanding the use of sophisticated computation methods due to the complexity of the geometric structure and the large size of the walls. To evaluate the operating reliability of boiler waterwalls, it is essential to know not only overall behavior of the whole structure but also the stress states at the critical zones. In this paper, the structural soundness for the Korea standard 500MW boiler waterwalls is preliminary examined. The equivalent orthotropic plate model is used to investigate the structural behavior of boiler waterwalls under thermal differences. Submodeling technique for part model of boiler waterwalls is proposed to accurately compute stresses of waterwalls at the critical zones under gas pressure. The computed stresses are combined and finally compared with the allowable stress limits according to the criteria of ASME Code.

Commentary by Dr. Valentin Fuster
2005;():703-711. doi:10.1115/IMECE2005-79550.

The anisotropic nature of the laminate composites creates a unique opportunity and also a great challenge for tailoring its properties according to the design requirements. In this work investigating the strength of laminate composite, a nonlinear finite element analysis was used to simulate the stress concentration in a two dimensional element caused by a central circular hole subjected to the biaxial loading. The effects of elastic and plastic deformation of a metallic material, fiber orientation and stacking order of a laminated composite on stress concentration were investigated. This evaluation provides a clear indication and a key step in understanding failures initiated by stress concentration which may lead to the growth of a crack. Comparison between the effects of the hole both on a metallic material and on a fiber-reinforced laminate exposes a totally different situation. In general, the stress concentration depends largely on the material properties, the layer stacking order, and the orientation.

Commentary by Dr. Valentin Fuster
2005;():713-716. doi:10.1115/IMECE2005-79723.

In the classical design of thick cylinders, if the internal fluid pressure approaches the safe working stress limit of the material, the thickness of the cylinder approaches infinite value. To overcome this difficulty, compound cylinders are used, where another cylinder is shrinkfitted on the inner cylinder. Designing a shrink fit assembly is tricky because the stress developed in the cylinders is a function of internal fluid pressure, shrinkage pressure and the dimensions of the cylinders. Also the shrinkage pressure is a function of the amount of interference and dimensions of the cylinders. That is, unless the shrinkage pressure is known, stresses developed cannot be computed and to compute shrinkage pressure, dimensions of both the cylinders must be known. Hence a cumbersome trial and error method is to be used. In the optimum design of compound cylinders, the thickness of both the cylinders should be just sufficient to withstand the hoop stresses developed. That means the maximum hoop stress produced in both cylinders should be equal. In this, shrinkage (contact) pressure plays an important role. The shrinkage pressure can be such that the limiting compressive stress is produced in inner cylinder. But when subjected to internal pressure, causes unequal stresses in both cylinders. That is, in one of the cylinders, the stress level can be maximum allowable and in other, less than maximum allowable. This paper describes the method of determining the optimum dimensions of both the cylinders made of specified material and to withstand a specified internal pressure so that the volume (and weight) is minimum. The results obtained are verified by using COSMOS and ANSYS finite element analysis packages.

Topics: Fluids , Design , Cylinders
Commentary by Dr. Valentin Fuster
2005;():717-720. doi:10.1115/IMECE2005-79879.

The stress concentration factor in an infinite thin plate with single circular hole, loaded axially is approximately 3. The reason of this high stress is explained through stress flow lines, similar to stream lines in a ideal fluid flow around a circular obstacle. Various methods for stress mitigation have been reported in literature. In the case considered it can also be reduced by removing material from the vicinity. In the present work the removal of the material, introduction of two smaller relief holes, is proposed in such a way that the stress flow lines will follow an elliptical path and thus reducing the stress concentration effect. The size of the relief holes and center distance between the holes are formulated for minimizing the stress concentration effect. The problem is analyzed using FEA software ANSYS. The result is encouraging in a way that for a particular circular singularity the size of the relief hole and center distance is formulated for minimizing the stress concentration factor.

Commentary by Dr. Valentin Fuster
2005;():721-732. doi:10.1115/IMECE2005-79907.

Component selection can be a difficult task for designers, and the components they choose can have a large impact on the robustness of the design. Using previous methods to predict and identify potential failure modes, known as the function-failure design method (FFDM), the impact on failure of selecting a particular component over another can be explored based on failure results from previous design endeavors using the same component. This assists designers in selecting the component that is best suited for the application. Since the predicted distribution of failure modes changes depending on the selected component, failure reduction is possible through component selection. Through this method of component selection, risk can be decreases and potential failures can be eliminated. Experiments based on undergraduate student competition design projects are presented to illustrate this method’s ability to predict failure modes. Initial results indicate that the predictions are accurate and meaningful to designers. The experiment also serves as initial validation previous work in the area of failure prediction.

Commentary by Dr. Valentin Fuster
2005;():733-740. doi:10.1115/IMECE2005-80243.

A large body of literature exists on investigations carried out earlier on the effects of holes in a continuum in the elastic regime of material behavior like for instance the case of the elastic analysis of tube sheets. Mathematical and finite element methods have been presented in detail for the solution of these design problems by a large number of authors in the sixties and seventies. However, it is observed that there is a paucity of reported research investigations on the creep behavior of equipment containing periodic holes such as boiler headers, heat exchangers etc. Material creep effects near holes in a continuum appear to have been investigated only during the past fifteen years and that too restricted to a limited number of configurations. Moreover, a large number of investigations seem to have been focused on the uni-axial behavior while the state of stress in most of the equipment utilized by industry is predominantly biaxial in nature. Creep behavior of substantial number of equipment subject to biaxial loading which is commonplace in industry remains to be relatively not understood fully. In view of the important applications of these mechanical equipment in thermal power stations and in chemical plants, it is essential to address the problem of creep behavior at single, multiple and periodic holes in the material continuum subjected to biaxial loading [1,2]. In order to obtain tractable solutions to the complex problems, it is felt appropriate to carry out detailed finite element analyses aimed at obtaining the strain and stress distribution near holes in the creep regime in certain generalized configurations so that the same can be applied in equipment where an array of holes is present.

Topics: Creep
Commentary by Dr. Valentin Fuster
2005;():741-747. doi:10.1115/IMECE2005-80362.

This paper deals with a two-dimensional stress analysis of adhesive butt joints under static tensile loading and bending moments in order to contribute to an establishment of the fracture criteria of joints. Similar adherends and an adhesive bond are replaced with finite strips in the analyses. Stress distributions in adhesive joints are analyzed strictly by using the two-dimensional theory of elasticity. The effects of stiffness and thickness of adhesive bonds on the stress distributions at the interfaces are shown by numerical computations. It is found that the stress singularity occurs at the ends of the interfaces. For verification, experiments to measure the strains and the strength were carried out. The analytical results are in fairly good agreement with the experimental ones. In addition, the analytical result is also compared with the result obtained by F.E.M in order to verify the stress distributions at the interfaces. It is shown that are in a fairly good agreement.

Commentary by Dr. Valentin Fuster
2005;():749-755. doi:10.1115/IMECE2005-80418.

This paper presents a new analysis scheme and the procedure used to calculate the internal forces and the stresses in the sugar cane mill shafts. One of the contributions of this research is to consider the top roller as a beam on elastic foundation. The reaction of the bagasse layer on the top roller was determined considering it as a beam on elastic foundation. A fracture mechanics based method is presented for determining the residual life of large sugar mill shafts with semi elliptical cracks. Due to the multi axial stress field, an equivalent strain energy release rate stress intensity solution is used in the Paris law to predict crack growth. Ultrasonic inspection intervals for the shafts are established. The crack zone evaluated is located in the shoulder of the bearing nearest to the square box coupling where about 85% of the service failure these types of shafts are observed [1, 2, 3].

Commentary by Dr. Valentin Fuster
2005;():757-762. doi:10.1115/IMECE2005-80419.

In this paper, a new scheme of analysis is used for the stress calculation in the throat area of the weld in lap joints with fillet welds transversely and longitudinally loaded. New calculation expressions are obtained that belong together better than the classic expressions with relationship to the values obtained by the Finite Elements Analysis.

Commentary by Dr. Valentin Fuster
2005;():763-774. doi:10.1115/IMECE2005-80421.

In this paper, a theoretical research is made on the influence of the friction force, the correction coefficient of the tooth and the radial component of the normal force in the Form Factor applicable to the stress on spur gears’ teeth. The Industrial Standards AGMA, ISO and DIN use the Lewis factor as the Form Factor but it doesn’t consider the above mentioned effects. The Standard GOST uses a Form Factor that considers the effect of the correction coefficient of the tooth and the radial component of the normal strength, but it doesn’t include the effect of the friction force. In this paper, a Mathematical Model is developed that incorporates all those effects. The obtained values of the form factors were represented graphically in function of the number of teeth, the correction coefficient and the friction coefficient. A graph is drawn for the driver gear and the driven gear, in which a remarkable influence of the simultaneous action of friction and correction coefficients is appreciated. In this new approach, it is found that the correction coefficients needed to optimize the resistance to the stress fracture of the teeth, in dependence of the values of the friction coefficient, should be greater that those used in the traditional approach. On the other hand, it has always been considered that gears with small number of teeth are the weakest with respect to stress fracture; however, in multiplying transmissions it is possible for driver gears with high number of teeth to be the weakest gear, given the favourable effect of the friction force on Form Factor in the driven gear and unfavourable in the driver gear. For the validation of the obtained results the Program of Finite Elements Analysis COSMOS Design Start 4.0 was used, obtaining very good results. Using FEA and Multiple Lineal Regression, a new expression for the calculation of the stress concentration coefficient in the feet of the tooth, in function of the number of teeth and of the correction coefficient, was found:

kσMEF = 1.497 + 0.126 −0.003933Z

Commentary by Dr. Valentin Fuster
2005;():775-779. doi:10.1115/IMECE2005-80549.

Layered silicate nanolayers can be used as alternative inorganic components for the construction of nanostructured hybrid composites. The clay silicate nanolayers possess stable Si-O bonds and high particle aspect ratios comparable to conventional fibers. Their interlayer surface is easily modified by ion-exchange reaction, and the gallery can be intercalated by organic polymer precursors for the formation of organic-inorganic nanocomposites. Exfoliated clay composites contain single, 1 nm thick layers of clay dispersed in the polymer matrix. Owing to the platy morphology of the silicate layers, exfoliated clay nanocomposites can exhibit dramatically improved properties such as barrier and mechanical properties that are not available for conventional composite materials. Since the clay particles scavenge water, the nanocomposite samples initially absorb slightly higher amounts of water in comparison to the no-clay samples, with the water molecules congregating around the clay particles. On the other hand, the presence of these clay particles still hinders diffusion of water through the sample, thus protecting the structural interfaces. In this work, low viscosity liquid aromatic diglycidyl ether of bisphenol A (DGEBA) epoxy resin Epon 815C was mixed with nanoclay at 60°C for 6 hours. The epoxy-clay mixture was then mixed with curing agent DETA (Diethylenetriamine) at 80°C for 4 minutes and cured at 120°C for 3 hours to produce exfoliated clay — epoxy resin system. These samples were used to first optimize the percent clay level for lowest water uptake, and subsequently immersed in water in stressed condition (flexural stress) to assess the effect of stress on nanocomposite epoxy system for its water uptake behavior. The results revealed up to 33% reduction in water uptake for the stressed samples.

Commentary by Dr. Valentin Fuster
2005;():781-785. doi:10.1115/IMECE2005-80576.

The electrospinning technique was utilized to prepare non-woven fabric carbon nanofibers (CNFs) via polyacrylonitrile (PAN) precursor nanofibers. The volume resistivity (ρv ) of non-woven mat CNFs containing the small size of beads and fiber diameters was lower than the ones possessing large beads and fiber diameters owing to the high specific surface area of the former. The ρv values of CNF mats prepared from 6.5 (fiber dia. ~120–250 nm) and 8.0 (fiber dia. ~250–600) wt% PAN solutions and carbonized at 950 °C were 0.32 and 1.33 Ω.cm, respectively. Additionally, the ρv value of CNF fabrics was improved by silver (Ag) modifications. The CNF mats containing Ag nanoparticles by in-situ preparing Ag nanoparticles in PAN solution prior to electrospinning and carbonization and Ag coating of CNF mats exhibited ρv values more or less 0.15 and 0.24 Ω.cm, respectively, even though the nanofiber diameter obtained from the former method was slightly larger than that of the latter. Effects of the fiber aspect ratio (L/D ratio) and the interconnecting network due to non-woven mat like fibers on the ρv were demonstrated by comparing the ρv of epoxy nanocomposites containing different forms of CNFs, non-woven fabric and short nanofibers. It was found that the ρv value of non-woven mat CNF/epoxy nanocomposite was much lower than that of short CNF/epoxy nanocomposite at 10 phr filler loading. Interestingly, the ρv values of non-woven mat CNF/epoxy nanocomposites dropped rapidly from 1010.5 Ω.cm at 0 phr filler content to 1.05 Ω.cm at about 10 phr filler content. Furthermore, the ρv values of non-woven mat CNF/epoxy nanocomposites leveled off to that of the filler itself or even lower at the filler dosage about 15 phr or higher, because the thickness of CNF mats impregnated in the epoxy composite was increased at high filler loading, thus yielding highly connected network inside the composite.

Commentary by Dr. Valentin Fuster
2005;():787-793. doi:10.1115/IMECE2005-80621.

This study deals with the stress analysis and the estimation of sealing performance of the pipe flange connections with an adhesive under an internal pressure and an external bending moment are analyzed by using the 3-dimensional elastic finite element method (FEM). The experiment of the leakage test of the connections with an adhesive was carried out by applying the above loads to the connections. From the FEM analysis, the following results were obtained; (1) when an internal pressure is applied to the flange connections, the compressive stress at the interface between a flange and an adhesive increases proportionally from the inner side of the interface to outside, and (2) when an internal pressure and a bending moment apply to the flange connections, the stress distribution at the half part of the interface increases as the external bending moments increase and also Young’s modulus of the adhesive increases. From the experiments, the following results were obtained: (1) sealing performance of the pipe flange connections with an adhesive under an internal pressure and an external bending moment increases as the flange thickness and an initial clamping force of bolts increases and (2) the sealing performances were not found between the connections with an adhesive and that with a gasket combining an adhesive. Furthermore, the numerical results are in fairly good agreement with the experimental results.

Commentary by Dr. Valentin Fuster
2005;():795-801. doi:10.1115/IMECE2005-80659.

In practice, PTFE tape is being used for sealing of a pipe fitting. However, the efficiency, the decrease in work time, and the sealing performance can be improved by using adhesive instead of the tape. When such a pipe fitting is under an internal pressure and external bending moment by an internal fluid and others, however, an influence in the sealing performance is taken by how to use an adhesion. This study deals with the stress analysis and the evaluation of the sealing performance of the pipe fitting with an adhesive under an internal pressure and an external bending moment analyzed by using the 3-dimensional elastic finite element method. Furthermore, the experiment of the leakage test of the pipe fitting with an adhesive was carried out when the above loads were applied to the pipe fitting. From 3-D FEM analysis, the following results were obtained: (1) the stress distribution at the interface between thread and adhesive on the side of the internal pressure is tensile stress, and stress on the opposite side is compressive, (2) the stresses at the area of the clearance between the valley of the screw and the mountain increase as the numbers of turns of the thread in fittings increase, and (3) the compressive stress at the side of the tensile part in the fittings decrease as the external bending moments increase. However, the sealing performance will not change when the bending moment is not so great because the compressive stress at the side of the compressive part in the fitting increases. From the leakage tests, the following results of the sealing performance were obtained: (1) the sealing performance of a fittings with adhesive under an internal pressure and a bending moment didn’t decrease when bending moment was not so great, and (2) when it exceeds fixed pressure, rapid leakage from the fitting with adhesive occurred by the exfoliation of the adhesive. Furthermore, the numerical results are in fairly good agreement with the experimental results.

Commentary by Dr. Valentin Fuster
2005;():803-811. doi:10.1115/IMECE2005-80746.

In designing a bolted joint, it is important to examine the interface stress distribution (clamping effect) and to estimate the load factor, that is the ratio of an additional axial bolt force to a load. In order to improve the clamping effect raised faces of the interface have been used. But these interfaces in bolted joints have been designed empirically and the theoretical grounds are not made clear. In the present paper, in the case of T-shaped flanges with raised faces the clamping effect is analyzed by a two-dimensional theory of elasticity and the point matching method. Then, the load factor is analyzed. Moreover, with the application of the load a bending moment is occurred in bolts and the stress is added due to this bending moment. The bending moment in the bolt is also analyzed. In order to verify these analyses experiments to measure the load factor and the maximum bolt stress were carried out. The values of the load factor and the load when interface start to separate are compared with those of the joints with flat-faces. The analytical results are in fairly good agreements with the experimental ones.

Commentary by Dr. Valentin Fuster
2005;():813-818. doi:10.1115/IMECE2005-80784.

The stress variations and stress distributions in scarf and stepped-lap adhesive joints of similar adherends under static and impact tensile loadings were analyzed in elastic range using three-dimensional finite element method. The impact loadings were applied to the lower adherend by dropping a weight. The stress distributions in scarf adhesive joints of similar adherends under static tensile loadings were also analyzed using FEM. The effects of Young’s modulus of the adherends, the adhesive thickness, and the angle of the adherends on the stress distributions at the interfaces between the adherends and the adhesive were examined under static loadings. The maximum value of σ1 decreased as young’s modulus of the adhesive increased in the stepped-lap adhesive joints under static loadings. However, the result of the scarf adhesive joints under static loadings was opposite to the above result. The value of σ1 became minimum when the scarf angle was 52°in the scarf adhesive joint. In addition, the experiments to measure the strain response and strain of joints subjected to impact and static tensile loadings were carried out using strain gauges. Fairly good agreements ware found between the numerical and the measured results.

Commentary by Dr. Valentin Fuster
2005;():819-825. doi:10.1115/IMECE2005-80804.

The stress variations and stress distributions in stepped-lap adhesive joints of dissimilar adherends under impact tensile loadings were analyzed in elastic range using three-dimensional finite element method. The impact loadings were applied to the lower adherend by dropping a weight. The stress distributions in stepped-lap adhesive joints of dissimilar adherends under static tensile loadings were also analyzed using FEM. The effects of Young’s modulus of the adherends, the adhesive thickness and the number of butted steps of adherents ware examined under both impact and static loadings. As the results, The maximum value of stress σ1 increased as Young’s modulus of the adherends increased for the impact loadings. The maximum value of stress σ1 increased as the numbers of steps in the adherends increased for the static loadings. In addition, the experiments to measure the strain response of joints subjected to impact tensile loadings were carried out using strain gauges. A fairly good agreement was found between the numerical and the measured results concerning the strain responses.

Commentary by Dr. Valentin Fuster
2005;():827-836. doi:10.1115/IMECE2005-80965.

Probabilistic design optimization addresses the presence of uncertainty in design problems. Extensive studies on Reliability-Based Design Optimization (RBDO), i.e., problems with random variables and probabilistic constraints, have focused on improving computational efficiency of estimating values for the probabilistic functions. In the presence of many probabilistic inequality constraints, computational costs can be reduced if probabilistic values are computed only for constraints that are known to be active or likely active. This article presents an extension of monotonicity analysis concepts from deterministic problems to probabilistic ones, based on the fact that several probability metrics are monotonic transformations. These concepts can be used to construct active set strategies that reduce the computational cost associated with handling inequality constraints, similarly to the deterministic case. Such a strategy is presented as part of a sequential linear programming algorithm along with a numerical example.

Topics: Design , Optimization
Commentary by Dr. Valentin Fuster
2005;():837-844. doi:10.1115/IMECE2005-81120.

NASA’s Ames Research center is currently designing a testbed to validate and compare potential Integrated System Health Management (ISHM) technologies. The proposed testbed represents a typical power system for a spacecraft and includes components such as a fuel cell, solar cells and redundant batteries. To fulfill design requirements, the testbed must be capable of hosting a wide variety of ISHM technologies including those developed by NASA as well as those developed in the aerospace industry abroad. An internal fault injection subsystem must be built into the system to provide a common interface for evaluating these different ISHM technologies. Additionally, to ensure robust operation of the testbed, the capability to detect and manage external faults must also be present. In order to develop a set of requirements for the internal fault injection subsystems as well as predict external faults, a comprehensive set of potential failures must be identified for all of the components of the testbed. To best aid the development of the testbed, these failures needed to be identified as early as the conceptual design phase, where little is known about the actual components that would comprise the finished system. This paper demonstrates the use a function-based failure mode identification method to identify the potential failures of the testbed during the conceptual design phase. Using this approach, designers can explore the potential failure modes at the functional design stage, before a form or solution has been determined. A function-failure database is used to associate the failures of components from previous design efforts to the testbed based on common functionality. The result is a list of potential failure modes and associated failure rates, which are used to improve the design of the testbed as well as provide a framework for the fault injection subsystem.

Commentary by Dr. Valentin Fuster
2005;():845-851. doi:10.1115/IMECE2005-82560.

Boards made of composites are susceptible of structural failure or irreversible damage under thermally raised stresses. A thermal/structural finite element model is integrated in this study to enable the predictions of the temperature and stress distribution of vertically clamped parallel circuit boards that include series of symmetrically mounted heated electronic modules (chips). The board is modeled as a thin plate containing four heated flush rectangular areas that represent the electronic modules. The finite element model should be to able to accept the convection heat transfer on the board surface, heat generation in the modules, and directional conduction inside the board. A detailed 3-D CFD model is incorporated to predict the conjugate heat transfer coefficients that strongly affect the temperature distribution in the board and modules. Structural analyses are performed by a FE model that uses the heat transfer coefficients mentioned above, and structural elements capable of handling orthotropic material properties. The stress fields are obtained and studied for the models possessing two and there laminates with different fiber orientations, and inter-fiber angles. Appreciable differences in values of max stress intensity were observed as the fiber orientation and inter-fiber angle changed. The angular parameters in this study were guided by experimental design (DOE) concepts leading to a metamodel of the stress intensity in the board. The optimum design variables found by the equations of the metamodel.

Commentary by Dr. Valentin Fuster
2005;():853-859. doi:10.1115/IMECE2005-82622.

The fillet welds are conventionally calculated to shear stress in the weakest section: the throat area of the weld. This consideration is a simplification for any fillet weld. Nevertheless, this procedure is internationally accepted as a justified procedure, mainly, for the simplification that makes the calculation of the welded joints of an engineering construction an easy procedure. This premise has motivated that different authors try to obtain calculation expressions for different cases that are presented in the practice, looking to facilitate the work of the industry technicians and engineers in charge of carrying out the calculation of these unions, however, in this pawn they don’t always use the most appropriate methods settled down by the Mechanics of the Materials introducing inaccuracies in these expressions. The Fracture Mechanics has outlined a new necessity: the development of methods of predicting defects that could exist in the welding cords. In order to do that, it is required to determine the stresses that arise in the welding with a superior accuracy. In this paper, the Theory of the Torsion of Thin Walls Profiles is applied to the calculation of the torsion shear stresses of the fillet weld joints. New calculation expressions are obtained that belong together better than the classic expressions with relationship to the values obtained by the Finite Elements Method.

Commentary by Dr. Valentin Fuster
2005;():861-867. doi:10.1115/IMECE2005-79048.

The first part of the paper are analyzed the components of the torque of the forces of inertia that act upon the frame of the frontal–sinusoidal transmission with balls. Analyzing at turn the expressions of the main vector and of the momentum of the forces of inertia one realizes that these are null, which shows that the transmission is balanced. In the second part they determine the way in which the geometrical parameters of the running channels of the balls influence the energy dissipation in the frontal sinusoidal transmission with balls.

Commentary by Dr. Valentin Fuster
2005;():869-874. doi:10.1115/IMECE2005-79142.

Determining the vibration characteristics of a realistic branched biological network, such as the respiratory system, faces many hurdles, which includes using the appropriate theory, specifying suitable boundary conditions and selecting accurate physical properties. Further, dichotomized or bifurcated structures beyond a simple circular cylindrical shell induce problems and difficulties in boundary matching between generations. This paper determines the natural frequencies using the Donnell-Mushtari formulation, membrane-shell approximation, a simplified limiting ring formula and the finite element method using COSMOS/Works™ for circular cylindrical shells with classical boundary conditions. Some experimental data are used for comparison and validation. Comparative study between the various methods sets the pros, cons, limitations of each method and the boundaries for the resonant frequencies of each individual generation of this system.

Topics: Vibration , Networks
Commentary by Dr. Valentin Fuster
2005;():875-880. doi:10.1115/IMECE2005-79434.

The BEI Systron Donner’s quartz rate sensor (QRS) uses double-ended quartz tuning fork to sense angular rate. The drive fork, acting as a Coriolis sensor, is coupled to a similar fork as a pickup to produce the rate output signal. In this paper, the theoretical analysis of the quartz fork model is presented. Following that, FEA analysis results are discussed. The consideration to optimize fork design is detailed. Experiments from mechanical testing and electrical testing are presented to show the improvement of the fork design.

Topics: Sensors , Design , Quartz
Commentary by Dr. Valentin Fuster
2005;():881-889. doi:10.1115/IMECE2005-79865.

The aim of this work is the improvement of the cam design for automotive valve trains. A constrained optimization problem is defined, using the control points of the cam profile, which is represented by harmonic splines, as design variables. Additionally to the optimization problem the advantages of the calculation of sensitivity information using direct or adjoint methods are determined. The valve train model is defined by a multi body system containing discontinuities due to the loss of contact between two consecutive components of the valve train. The objective function is to maximize the area below the valve lift, which has a great influence on the gas flow. Constraints for dynamic force, the valve opening and closing phase and the valve lift based on the engine’s thermodynamics considerations are taken into account. Furthermore some constraints for the geometric coordinates of the control points of the cam profile must be imposed.

Commentary by Dr. Valentin Fuster
2005;():891-901. doi:10.1115/IMECE2005-80016.

This paper investigates the forced response dynamics of a clamped-clamped beam to which a rigid body is attached, and in the presence of periodic or non-periodic impacts between the body and a comparatively compliant base structure. The assembly is subjected to base excitation at specified frequency and acceleration, and the potentially complex responses that occur are examined analytically. The two sets of natural frequencies and vibration modes of the beam-rigid body structure (in its in- contact state, and in its not-in-contact state), are used to treat the forced response problem through a series of algebraic mappings among those states. A modal analysis based on extended operators for the (continuous) beam and (discrete) rigid body establishes a piecewise linear state-to-state mapping for transition between the in-contact and not-in-contact conditions. The contact force, impulse, and displacement each exhibit complex response characteristics as a function of the excitation frequency. Periodic responses occurring at the excitation frequency, period-doubling bifurcations, grazing impacts, sub-harmonic regions, fractional harmonic resonances, and apparently chaotic responses each occur at various combinations of damping, excitation frequency, and contact stiffness. Parameter studies are discussed for structural asymmetry and eccentricity of contact point’s location.

Commentary by Dr. Valentin Fuster
2005;():903-911. doi:10.1115/IMECE2005-80018.

Repetitive collision occurring between structural and machine components is a topic of practical and scientific importance. Some types of machinery are inherently susceptible to impacts because of the small clearances present between adjacent components, thermal expansion, and relative motion as in gear trains. One can observe repetitive impacts in milling machines, shakers and off-shore structures. Energy transfer between components that are subjected to repetitive impacts is a complex phenomenon that often exhibits deceptive and non-intuitive behavior. Even in seemingly simple structures, period-doubling bifurcations, sub-harmonic resonances, and chaotic responses occur. This paper presents detailed experimental data obtained from an impact vibration test stand that was instrumented for displacement, velocity, and impact force measurements. In addition, the apparatus was fabricated in such a way to allow for precise positioning of the impact point, and varying of the gap distance between impacting components. The paper includes companion simulation results obtained from a model for the repetitive impact dynamics of otherwise linear single or multiple degree of freedom discrete structures. Simulation results are presented for the effect of natural frequency placement, model dimension, and gap clearance on the qualitative and quantitative character of the response. Of particular interest is the transition of behavior as the system’s model is augmented from having one to several degrees of freedom.

Commentary by Dr. Valentin Fuster
2005;():913-924. doi:10.1115/IMECE2005-80076.

The grazing bifurcation and periodic motion switching of the harmonically forced, piecewise linear system with impacting are investigated. The generic mappings based on the discontinuous boundaries are introduced. Furthermore, the mapping structures are developed for the analytical prediction of periodic motions in such a system. The local stability and bifurcation conditions for specified periodic motions are obtained. The regular and grazing, periodic motions are illustrated. The grazing is the origin of the periodic motion switching for this system. Such a grazing bifurcation cannot be estimated through the local stability analysis. This model is applicable to prediction of periodic motions in nonlinear dynamics of gear transmission systems.

Topics: Motion , Bifurcation
Commentary by Dr. Valentin Fuster
2005;():925-937. doi:10.1115/IMECE2005-80099.

In this paper, periodic motion in an oscillator moving on a periodically vibrating belt with dry-friction is investigated. The conditions of stick and non-stick motions for such an oscillator are obtained in the relative motion frame, and the grazing and stick (or sliding) bifurcations are presented as well. The periodic motions are predicted analytically and numerically, and the analytical prediction is based on the appropriate mapping structures. The eigenvalue analysis of such periodic motions is carried out. The periodic motions are illustrated through the displacement, velocity and force responses in the absolute and relative frames. This investigation provides an efficient method to predict periodic motions of such an oscillator involving dry-friction. The significance of this investigation lies in controlling motion of such friction-induced oscillator in industry.

Commentary by Dr. Valentin Fuster
2005;():939-950. doi:10.1115/IMECE2005-80108.

This paper presented a methodology to determine the analytical dynamics of the periodically forced friction oscillator. The friction force is modeled by a piecewise linear, kinetic friction model with the static force. The input and output force concepts in the vicinity of the discontinuous friction force boundary are introduced. The force criteria for the onset and vanishing of stick and non-stick motions are presented through the input and output forces. The periodic motion of such an oscillator is determined through the corresponding mapping structure. The local stability of the periodic motions is presented. Illustrations of the periodic motions in such a piecewise friction model are given for better understanding the stick motion with static friction. The force responses are presented, which agreed very well with the force criteria.

Commentary by Dr. Valentin Fuster
2005;():951-956. doi:10.1115/IMECE2005-80117.

The scattering field of SH-wave in a half-space with a semi-cylindrical hill and a subsurface horizontal hole is studied in the present research by utilizing a complex function and the moving-coordinate method. Based on the concept of ‘conjunction,’ the domain considered is divided into two subdomains. The first subdomain is a cylindrical one which includes the surface of the hill, while the rest is the second subdomain. In the cylindrical subdomain, a standing wave function is constructed which automatically satisfies the zero-stress condition at the hill surface and arbitrary-stress condition at the other part of the circular subdomain. For the second subdomain, which contains a semi-cylindrical canyon and a subsurface hole, a scattering wave function is assumed, which satisfies the zero-stress condition on the horizontal surface. By employing the moving-coordinate method, the solutions of the mathematical model established for the SH-wave can be obtained with the satisfaction of the continuous conditions of stress and displacement across the junction interface together with the zero-stress condition at the surface of the tunnel. The solutions such obtained consist of a series of infinite linear algebraic equations, which can be solved numerically with consideration of the first finite terms corresponding to the frequencies of the wave. For demonstrating the application of the model developed, the displacements of the horizontal and semi-cylindrical hill surfaces are quantified with different properties of wave and geometry parameters.

Commentary by Dr. Valentin Fuster
2005;():957-962. doi:10.1115/IMECE2005-80161.

In this paper, a NNI (Neural Network Identifier) is presented to learn model for an articulated multiple DOF (Degrees of Freedom) pneumatic robot position system. It can adjust the weights and biases of NNC (Neural Network Controller) on line. This controller can effectively solve the difficult problems of single rod cylinders, which are mainly caused by asymmetric structures and different friction characteristics in two directions. On these bases an articulated four DOF pneumatic robot is designed and its work space is analyzed. Experimental results prove that, the dynamic performance of the system can be much improved. The system using NN (Neural Network) has strong self-adaptability and robustness. It obtains desired percentage overshoot and repeatability in steady-state responses.

Commentary by Dr. Valentin Fuster
2005;():963-967. doi:10.1115/IMECE2005-80246.

A fusion approach is proposed to refine the resolution of multi-spectral images using the corresponding high-resolution panchromatic images. The technique is based on intensity modulation and non-separable wavelet frame. The high-resolution panchromatic image is decomposed by the non-separable wavelet frame. Then the wavelet coefficients are used as the factor of modulating to modulate the multi-spectral image. Experimental results indicate that, comparing with the traditional methods, the proposed method can efficiently preserve the spectral information while improving the spatial resolution of remote sensing images.

Commentary by Dr. Valentin Fuster
2005;():969-973. doi:10.1115/IMECE2005-80290.

A new method for systems stability analysis is presented. This method is called weight functions method and it replaces the problem of Liapunov function finding with a problem of finding a number of functions (weight functions) equal to the number of first order differential equations describing the system. It is known that there are not general methods for finding Liapunov functions. The weight functions method is simpler than the classical method since one function at a time has to found. This method’s conditions of solution stability for linear and nonlinear systems are presented. Applications such as Lurie-Postnikov problem and controlled systems stability are presented as well.

Commentary by Dr. Valentin Fuster
2005;():975-981. doi:10.1115/IMECE2005-80307.

This papers deals with nonlinear vibrations of non-uniform beams with geometrical nonlinearities such as moderately large curvatures, and inertia nonlinearities such as longitudinal and rotary inertia forces. The nonlinear fourth-order partial-differential equation describing the above nonlinear effects is presented. Using the method of multiple scales, each effect is found by reducing the nonlinear partial-differential equation of motion to two simpler linear partial-differential equations, homogeneous and nonhomogeneous. These equations along with given boundary conditions are analytically solved obtaining so-called zero-and first-order approximations of the beam’s nonlinear frequencies. Since the effect of mid-plane stretching is ignored, any boundary conditions could be considered as long as the supports are not fixed a constant distance apart. Analytical expressions showing the influence of these three nonlinearities on beam’s frequencies are presented up to some constant coefficients. These coefficients depend on the geometry of the beam. This paper can be used to study these influences on frequencies of different classes of beams. However, numerical results are presented for uniform beams. These results show that as beam slenderness increases the effect of these nonlinearities decreases. Also, they show that the most important nonlinear effect is due to moderately large curvature for slender beams.

Commentary by Dr. Valentin Fuster
2005;():983-991. doi:10.1115/IMECE2005-80341.

The variation of dynamic instability in a high speed drilling process was investigated in this article. A pre-twisted beam is used to simulate the drill. The time dependent thrust force and drilling depth are considered in the equation of motion. A moving Winkler-Type elastic foundation assumption is employed to the drill tip to approximate the time varying boundary conditions in the drilling process. The Galerkin method is used to formulate the characteristic equation in a discrete form. The variation of instability regions of the drill system is solved and analyzed by employing the multiple scales perturbation method. Numerical results indicate that unstable regions are enlarged and shifted toward a lower frequency suddenly at the moment when the drill attaches the work piece. The effects of spinning speed, pre-twisted angle and thrust force of the drill on the variation of the dynamic instability in a high speed drilling process are also studied.

Topics: Drilling
Commentary by Dr. Valentin Fuster
2005;():993-997. doi:10.1115/IMECE2005-80437.

A nonlinear position controller based on backstepping control technique is proposed for a hybrid stepper motor in micro-step operation. Backstepping control approach is adapted to derive the control scheme, which is robust to parameter uncertainties and external load disturbance. Simulation results clearly show that the proposed controller can track the position reference signal successfully under parameter uncertainties and load torque disturbance rejection.

Topics: Engines
Commentary by Dr. Valentin Fuster
2005;():999-1007. doi:10.1115/IMECE2005-80489.

The contact between the drilling bit and formation is known to excite severe torsional and axial vibrations in the drillstring. A dynamic model of the drillstring including both drillpipe and drillcollars is formulated. The equation of motion of the rotating drillstring is derived using Lagrangean approach together with the finite element method. The model accounts for the gyroscopic effect, the torsional/bending inertia coupling, the axial/bending geometric nonlinear coupling, and the stiffening effect due to the gravitational force field. Reduced order modal form of the dynamic equations is obtained using complex modal transformation. The developed model is integrated into a computational scheme to calculate time-response of the drillstring due to torsional excitations.

Topics: Drilling , Vibration
Commentary by Dr. Valentin Fuster
2005;():1009-1012. doi:10.1115/IMECE2005-80903.

This paper presents an approach for finding the solution of partial differential equation describing the motion of transverse vibrations of rectangular plates of unidirectional convex parabolic varying thickness. The partial differential equation consists of three operators: fourth-order spatial-dependent, second-order spatial-dependent, and second-order time-dependent. Using the method of multiple scales, the partial differential equation has been reduced to two simpler partial differential equations which can be analytically solved and which represent two levels of approximation. The first partial differential equation was a homogeneous equation and consisted of two operators, the fourth-order spatial-dependent and second-order time-dependent. Using the factorization method, so-called zero-order approximation of the exact solution has been found. The second partial differential equation was an inhomogeneous equation. Its solution, so-called first-order approximation of the exact solution has been found. This way the first-order approximations of the natural frequencies and mode shapes are found. Various boundary conditions can be considered. The influence of Poisson’s ratio on the natural frequencies and mode shapes could be further studied using the approximations reported here. This approach can be extended to nonlinear, and/or forced vibrations.

Commentary by Dr. Valentin Fuster
2005;():1013-1017. doi:10.1115/IMECE2005-80911.

Control of floor vibration, via damping, using a three-degree-of-freedom (DOF) tuned mass damper (TMD) is explored. Three-DOF TMDs can provide as much effectiveness as traditional one degree-of-freedom TMDs while possessing less internal damping than the traditional TMDs. In this work, the use of such a system as a damping treatment for floor vibration is explored. To evaluate the effectiveness of the proposed damping-enhancement system, a scaled floor with the first resonant frequency of around 9 Hz (typical first resonant frequency of most commercial building floors) is fabricated. A 3-DOF TMD, appended to the center of the floor, is tuned to the first mode of the floor to provide damping at that mode. The comparison of the floor vibration without and with this damping treatment exhibited an average reduction of close to 10 dBs in the magnitude of the targeted mode, signifying the high damping effectiveness of the treatment.

Topics: Damping , Vibration
Commentary by Dr. Valentin Fuster
2005;():1019-1030. doi:10.1115/IMECE2005-81151.

Although piezoelectric actuators have been widely used in active control, the hysteresis nonlinearity and the non-minimum phase characteristic could potentially deteriorate the system performance, especially in high precision control applications under disturbance. In this study, a resistance/inductance circuit is connected to the piezoelectric actuator to form an actuator network. With the actuator dynamics, the system model can be directly cast into the state-space whereas the system nonlinearity appears as explicit functions of the state variables. We then develop an integral continuous sliding mode control scheme to tackle the hysteresis nonlinearity and the disturbance issues. Instead of inverse hysteresis cancellation which might not be reliable due to the measurement noise, a direct piezoelectric hysteresis compensation can be achieved using this control strategy. The newly developed control scheme combines the advantages of both integral control and continuous sliding mode control with cubic state feedback. Not only can the control action react efficiently and effectively for the non-minimum phase response, but also, a zero steady state tracking error is guaranteed. Detailed analysis and case studies demonstrate that this new methodology can lead to improved tracking control precision, enhanced control robustness, and smoother control action.

Commentary by Dr. Valentin Fuster
2005;():1031-1039. doi:10.1115/IMECE2005-81241.

Axially elastic rods are basic machine elements in hydraulic hammers, pilers and percussive drills. The problem to analyze the motion history of such mechanisms is a very complex one, because the rods are simultaneously in large amplitude axial motion superimposed with a small amplitude elastic wave motion. The wave motion experiences division to reflected and transmitted components at each rod-rod interface depending on the current boundary stiffness. The wave motion in each rod can be computed by finite elements or alternatively in space of semidefinite eigenfunctions. The feasibility of these methods in solving wave propagation problems in multi-rod systems with nonlinearly behaving rod-rod interfaces has been investigated and evaluated. The object of the case study is a classical Hopkinson split bar apparatus used in experimental analysis of material response to shock pulses.

Commentary by Dr. Valentin Fuster
2005;():1041-1047. doi:10.1115/IMECE2005-81301.

The longitudinal liquid dynamics in partially filled horizontal cylindrical tanks is studied on the basis of a fully 3D mathematical approach. Governing equations based on the potential flow theory for liquid in tanks are solved to obtain natural frequencies and transient liquid motion. The governing equations are transformed by continuous coordinate mappings to perform the discretization in the computational domain for overcoming the difficulties in dealing with the boundary conditions at the curved walls and the free surface. The natural frequencies of liquid sloshing in partially filled tanks are determined by solving the generalized eigenvalue problem of liquid under different fill levels and for different tank configurations. The efficiency of the method is presented by comparing with the frequency results reported in other publications.

Topics: Fluids , Motion
Commentary by Dr. Valentin Fuster
2005;():1049-1054. doi:10.1115/IMECE2005-81427.

Parametrically excited tuning fork micro gyroscopes have several attractive features. Most of all, the excitation may be externalized, which could simplify the design and fabrication of micro gyroscopes. However, there are no readily applicable tools to guide the design of these gyroscopes since the gyro structures are more complex than those structures whose responses to parametric excitations are known and since finite element analysis tools are not capable of studying parametric excitations. In this work, we adopt a novel approach to obtain a simplified model of the parametrically excited structure. Parameters in the simplified model are obtained using dynamic analysis capability of typical finite element programs and static nonlinear analysis capabilities.

Commentary by Dr. Valentin Fuster
2005;():1055-1060. doi:10.1115/IMECE2005-81491.

An analytical method is adopted to determine natural frequencies for a nonlinear spinning disk. The disk is assumed to be isotropic and rotating under steady state conditions. The effects of amplitude and rotating speed on natural frequencies are determined. The developed procedure is also capable of analyzing natural frequencies of linear free vibration, which is independent of amplitude. Attention is confined to determine natural frequencies for different numbers of nodal diameters. The developed procedure does not consider modes of vibration corresponding to nodal circles. Validity of this procedure is verified by comparing some of the computed results with those established for certain cases.

Commentary by Dr. Valentin Fuster
2005;():1061-1071. doi:10.1115/IMECE2005-81506.

Research on vibration of soils and foundations has yielded several fundamental methods for formulation of interaction problems. This paper is intended to survey the development of the current state-of-practice for design and analysis of dynamically loaded foundations. Extensive studies in this field utilize various linear mathematical models for interaction between foundations and different soil media. The effective analytical, numerical and experimental techniques and their methodologies which are well established for treating problems in dynamic soil-foundation interaction are outlined. Described techniques are categorized based upon formulation procedures and their applications. Some areas are indicated where further research is needed.

Topics: Vibration , Soil
Commentary by Dr. Valentin Fuster
2005;():1073-1078. doi:10.1115/IMECE2005-81598.

Rotor balancing is a requirement for the smooth operation of high-speed rotating machinery. In field balancing, minimization of the residual vibrations at important locations/speeds under practical constraints is usually a challenging task. In this paper, the generalized minmax coefficient influence method is formulated as an optimization problem with flexible objective functions and constraints. The optimization problem is cast in a Linear Matrix Inequality (LMI) form and a balancing code is developed to solve it. Two balancing examples are run to verify the efficiency and flexibility of the proposed method. Over the existing methods, current method is more flexible for the various requirements encountered in field balancing and can be solved accurate with current mathematical software.

Topics: Rotor balancing
Commentary by Dr. Valentin Fuster
2005;():1079-1092. doi:10.1115/IMECE2005-81770.

When simulating the behavior of a mechanical system, the time evolution of the generalized coordinates used to represent the configuration of the model is computed as the solution of a combined set of ordinary differential and algebraic equations (DAEs). There are several ways in which the numerical solution of the resulting index 3 DAE problem can be approached. The most well-known and time-honored algorithms are the direct discretization approach, and the state-space reduction approach, respectively. In the latter, the problem is reduced to a minimal set of potentially new generalized coordinates in which the problem assumes the form of a pure second order set of Ordinary Differential Equations (ODE). This approach is very accurate, but computationally intensive, especially when dealing with large mechanical systems that contain flexible parts, stiff components, and contact/impact. The direct discretization approach is less but nevertheless sufficiently accurate yet significantly faster, and it is the approach that is considered in this paper. In the context of direct discretization methods, approaches based on the Backward Differentiation Formulas (BDF) have been the traditional choice for more than 20 years. This paper proposes a new approach in which BDF methods are replaced by the Newmark formulas. Local convergence analysis is carried out for the proposed method, and step-size control, error estimation, and nonlinear system solution related issues are discussed in detail. A series of two simple models are used to validate the method. The global convergence analysis and a computational-efficiency comparison with the most widely used numerical integrator available in the MSC.ADAMS commercial simulation package are forthcoming. The new method has been implemented successfully for industrial strength Dynamic Analysis simulations in the 2005 version of the MSC.ADAMS software and used very effectively for the simulation of systems with more than 15,000 differential-algebraic equations.

Commentary by Dr. Valentin Fuster
2005;():1093-1102. doi:10.1115/IMECE2005-81837.

Mathematical modeling of thermal effects on steady state dynamics of microresonators, utilizing an analytical approach is studied. Thermal phenomena has two distinct effects, which in this report are called, thermal damping and temperature relaxation. In this part of a two-part report we investigate the thermal damping and its effects on microresonator dynamics. To do this, first the reduced order mathematical model of the system is introduced as a forced mass-spring-damper system, and then a linearized model of electric actuated microbeam resonator is employed. The effect of thermal damping is modeled as an increase in damping rate, utilizing a Lorentzian function of excitation frequency. The steady state frequency-amplitude dependency of the system will be derived utilizing averaging perturbation method. The developed analytic equation describing the frequency response of the system around resonance can be utilized to explain the dynamics of the system, as well as design of dynamic parameters. However, we have focused on exploration of thermal damping.

Commentary by Dr. Valentin Fuster
2005;():1103-1113. doi:10.1115/IMECE2005-81853.

An adapted averaging method is employed to obtain an implicit function for frequency response of a bilinear vibration isolator system under steady state. This function is examined for jump-avoidance and a condition is derived which when met ensures that the undesirable phenomenon of ‘Jump’ does not occur and the system response is functional and unique. The jump avoidance and sensitivity of the condition are examined and investigated as the dynamic parameters vary. The results of this investigation can be directly employed in design of effective piecewise linear vibration isolators. A linear vibration system is defined as one in which the quantities of mass (or inertia), stiffness, and damping are linear in behavior and do not vary with time [1]. Although mathematical models employing a linear ordinary differential equation with constant coefficients portray a simple and manageable system for analytical scrutiny, in most cases they are an incomplete representation simplified for the sake of study. Most real physical vibration systems are more accurately depicted by non-linear governing equations, in which the non-linearity may stem from structural constraints causing a change in stiffness and damping characteristics, or from inherent non-linear behavior of internal springs and dampers. This paper focuses on a general form of such a non-linear system. This study of piecewise-linear systems will allow hazardous system behavior over operating frequency ranges to be gauged and controlled in order to avoid premature fatigue damage, and prolong the life of the system.

Commentary by Dr. Valentin Fuster
2005;():1115-1123. doi:10.1115/IMECE2005-81856.

Many vibration isolators can be modeled with a discontinuity in the stiffness and damping coefficients. The sudden change in the values of the coefficients can be represented as a piecewise linear or nonlinear function. Soft suspensions are best for isolation; however, a nonlinear hardening suspension is required to minimize relative displacement at high amplitudes. Often, the physical design limits the relative displacement. Taking advantage of nonlinearity in the suspension is not enough in limiting the relative displacement at very high amplitude. Therefore, a secondary suspension must be involved to limit very high relative displacements. In this investigation, the averaging method was applied to the differential equation generated from the model to find the frequency response. A sensitivity analysis was performed to find regions of instability in the frequency response

Commentary by Dr. Valentin Fuster
2005;():1125-1132. doi:10.1115/IMECE2005-81860.

In this paper a new design of the passive hydraulic engine mount is introduced. A means for improved decoupler control is introduced that does not noticeably affect the mechanisms steady state behavior, but improves start up and transient response. In addition, the decoupler mechanism is incorporated into a smaller, lighter, yet more tunable and hence more effective hydraulic mount design. The performance of the new hydraulic mount is discussed by means of a full nonlinear model. The increased design flexibility afforded by the redesigned support structure provides means by which to tune the engine mount to various engine support configurations. In addition, the proposed mount does not rely as heavily on hysteretic damping provided through elastomeric materials, which can be difficult to control, but more so on fluid behavior inside the engine mount; therefore, the damping of the system is much more tunable than previous hydraulic engine mount designs.

Commentary by Dr. Valentin Fuster
2005;():1133-1142. doi:10.1115/IMECE2005-81882.

Thermal phenomena have two distinct effects, which are called, in this report, “thermal damping” and “temperature relaxation”. In this second part of a two-part report we (only) model and investigate the temperature relaxation and its effects on microresonator dynamics. A reduced order mathematical model of the system is introduced as a mass-spring-damper system actuated by a linearized electrostatic force. Temperature relaxation is the thermal stiffness softening and is modeled as a decrease in stiffness rate, utilizing a Lorentzian function of excitation frequency. The steady state frequency-amplitude dependency of the system will be derived utilizing averaging perturbation method. Analytic equation describing the frequency response of the system near resonance which can be utilized to explain the dynamics of the system, as well as design of involved dynamic parameters is developed.

Commentary by Dr. Valentin Fuster
2005;():1143-1147. doi:10.1115/IMECE2005-81951.

This paper will illustrate the application of the Lambert Function, as originally proposed by Asl and Ulsoy, to obtain the stability lobes in orthogonal cutting operations. The Lambert function approach will be compared to the classical approach. It will be shown that the stability lobes obtained with this procedure match with those obtained with the classical approach, under certain system parameter values.

Topics: Chatter , Cutting
Commentary by Dr. Valentin Fuster
2005;():1149-1156. doi:10.1115/IMECE2005-82138.

This paper is an overview of recent spacecraft payload vibration isolation systems for further possible application to reusable launch vehicles sub-orbital missions. A summary of vibro-acoustic environment of Orbital Science and Kistler Aerospace’s small launch vehicles indicated a severe level of random vibrations, shock and acoustics that the payload must endure. The same level of random vibrations has been found for an entire family of sounding rockets: Black Brant, Orion, Nike-Orion, Taurus-Orion and Terrier-Orion. This paper also presents recent flight experiments designed to test either launch isolation or on-orbit isolation systems. While the on-orbit vibration isolation systems were active-passive systems, which lately used smart structures and new control algorithms including adaptive neural network-based, launch isolation systems evolved from passive to active-passive systems which were lately tested during the VALPE-2 experiment. Launch active-passive systems provided a vibration reduction 10 to 1 versus up to 5 to 1 provided by passive systems. Also, on-orbit active-passive systems provided a vibration reduction of about 10 to 1. Suborbital missions became very important due to the growing number of research projects dedicated to remote sensing of high resolution and effects of microgravity. The number of orbital and especially suborbital reusable launch missions is estimated to increase considerably in the near future as vehicles develop. The actual tendency is to reduce payload weight and mission costs, and to improve the payload environment. This requires more efficient vibration isolation systems that will guarantee payload safety and better operational performance for reusable launch vehicles.

Commentary by Dr. Valentin Fuster
2005;():1157-1160. doi:10.1115/IMECE2005-82252.

The paper presents comparatively the measured and estimated natural frequencies and mode shapes of a rectangular orthotropic panel. The experimental tests were performed using a shaker. The plate was fixed in horizontal position directly on the shaker armature using a rigid rod. The experimental modes shapes were visualized using sand particles. The measured natural frequencies and also the modes shapes correspond to the whole system in motion. So, the analytic model of the plate must include the effect of the vibrator connected to the plates. The purpose of this experimental measurements and analytic modeling of such plates is to further developing a methodology to estimate the material properties of the composite panels. At this research stage, an orthotropic plate with unknown material properties was investigated. Using an adequate finite element model, the mechanical properties of the material were estimated. Using these properties it is possible to numerically estimate the dynamic behavior of the plate for additional sets of boundary conditions.

Commentary by Dr. Valentin Fuster
2005;():1161-1167. doi:10.1115/IMECE2005-82254.

The first part of this article presents a dynamic analysis of the fan of a generator connected by rigid coupling to a diesel engine. The purpose of this analysis is to correlate the main components of the fan’s frequency response spectrum with the ones of the excitation source, i.e., the diesel engine. The second part describes a finite element analysis of the fan in order to find the best design solution.

Commentary by Dr. Valentin Fuster
2005;():1169-1175. doi:10.1115/IMECE2005-82354.

In this work, the basic problem of order reduction nonlinear systems subjected to an external periodic excitation is considered. This problem deserves attention because the modes that interact (linearly or nonlinearly) with the external excitation dominate the response. A linear approach like the Guyan reduction does not always guarantee accurate results, particularly when nonlinear interactions are strong. In order to overcome limitations of the linear approach, a nonlinear order reduction methodology through a generalization of the invariant manifold technique is proposed. Traditionally, the invariant manifold techniques for unforced problems are extended to the forced problems by ‘augmenting’ the state space, i.e., forcing is treated as an additional degree of freedom and an invariant manifold is constructed. However, in the approach suggested here a nonlinear time-dependent relationship between the dominant and the non-dominant states is assumed and the dimension of the state space remains the same. This methodology not only yields accurate reduced order models but also explains the consequences of various ‘primary’ and ‘secondary resonances’ present in the system. Following this approach, various ‘reducibility conditions’ are obtained that show interactions among the eigenvalues, the nonlinearities and the external excitation. One can also recover all ‘resonance conditions’ commonly obtained via perturbation or averaging techniques. These methodologies are applied to some typical problems and results for large-scale and reduced order models are compared. It is anticipated that these techniques will provide a useful tool in the analysis and control of large-scale externally excited nonlinear systems.

Commentary by Dr. Valentin Fuster
2005;():1177-1182. doi:10.1115/IMECE2005-82374.

Nonlinear active suspension systems are very popular in the automotive applications. They include nonlinear stiffness and nonlinear damping elements. One of the types of damping element is a magneto-rheological fluid based damper which is receiving increased attention in the applications to the automotive suspension systems. Latest trends in suspension systems also include electronically controlled systems which provide advanced system performance and integration with various processes to improve vehicle ride comfort, handling and stability. A control bifurcation of a nonlinear system typically occurs when its linear approximation loses stabilizability. These control bifurcations are different from the classical bifurcation where qualitative stability of the equilibrium point changes. Any nonlinear control system can also exhibit control bifurcations. In this paper, control bifurcations of the nonlinear active suspension system, modeled as a two degree of freedom system, are analyzed. It is shown that the system looses stability via Hopf bifurcation. Parametric control bifurcation analysis is conducted and results presented to highlight the significance of the design of control system for nonlinear active suspension system. A framework for the design of feedback using the parametric analysis for the control bifurcations is proposed and illustrated for the nonlinear active suspension system.

Commentary by Dr. Valentin Fuster
2005;():1183-1188. doi:10.1115/IMECE2005-82536.

Traditionally a skyhook control, widely applied to vibration control, requires two sensors to measure sprung mass acceleration and relative displacement, respectively. For the implementation, these two measurement signals are converted into velocities and then the damping control signal is decided and sent to controllable HH/SS dampers. In this paper, a one sensor based skyhook control policy is developed. The proposed control policy just needs one measurement signal, sprung mass acceleration, to estimate these two velocities for semiactive control. The new strategy is explained through a typical spring-mass system of a quarter-car model. But the effectiveness of the new control approach for vibration isolation is validated with ride control through simulation study of a 7-DOF full car suspension system with application of magneto-rheological (MR) dampers.

Commentary by Dr. Valentin Fuster