Design Engineering

2002;():3-10. doi:10.1115/IMECE2002-32860.

Analytical target cascading (ATC) is a methodology that can be used during the early development stages of large and complex systems for propagating desirable overall product targets to appropriate individual specifications for the various subsystems and components. The ATC process is applied to the design of an advanced technology heavy truck. A series hybrid-electric propulsion system, in-hub motors, and variable height suspensions are introduced with the intent to improve both commercial and military design attributes according to a dual-use design philosophy. Emphasis is given to fuel economy, ride, and mobility characteristics. These vehicle responses are predicted by appropriately developed analytical and simulation models. This article is an extension to previous work: the engine is now included at the bottom level, several battery types are considered to study their effect on fuel economy, and a more demanding driving schedule is used to assess regenerative braking benefits and ride quality. Results are presented for target values associated with a 100% improvement on fuel economy while maintaining performance attributes relative to existing designs.

Topics: Design , Trucks
Commentary by Dr. Valentin Fuster
2002;():12-20. doi:10.1115/IMECE2002-32908.

Topology optimization of a structure is generally considered as a problem of optimum material distribution (OMD) within a given structural domain, subject to a given amount of material and to boundary conditions and loading conditions applied to the structure. The effective design of a complex engineering structure, however, may require controllability over how the material should be distributed among the various subdomains of the structure, as well as even the use of different materials for the different subdomains. A multi-domain topology optimization technique is therefore proposed in this paper, which is based upon the homogenization method, and which employs a generalized Sequential Approximation Optimization (GSAO) algorithm. This algorithm enhances the capabilities of current topology optimization methods by using advanced updating rules and providing additional flexibility in the optimization process, thus resulting in improved convergence and higher computational efficiency. A Component Mode Synthesis method is also employed, which can significantly reduce the number of degrees of freedom associated with the subdomains whose designs are fixed at the current stage. Several example design problems are considered, including a “structure-fixture simultaneous design” problem, a “functionally graded material design” problem, a “crush energy management” problem, and a “truck frame design” problem that illustrates how the technique developed can be applied to real vehicle substructure design problems.

Commentary by Dr. Valentin Fuster
2002;():21-31. doi:10.1115/IMECE2002-32911.

The paper presents a method to optimise the synchroniser of a road vehicle gearbox in order to improve shiftability and driver comfort. A multi-body physical model of the synchroniser has been developed and validated experimentally. The optimisation method is based on a Multi-objective Programming approach, and it allows to tune the thirty-two parameters of the synchroniser in order to achieve the desired dynamic behaviour of the system during a reference shift action, defined by seven performance indices. A Global Approximation procedure has been followed to solve numerically the optimisation problem. A special study has been performed and implemented in order to explore all of the feasible design solutions within the design variables domain. A global sensitivity method has been applied in order to analyse the relationships among the thirty-two design variables and the seven performance indices. Pareto-optimal design solutions have been computed in a very short time. These Pareto-optimal solutions have been checked for robustness by applying the minimum sensitivity method. The optimisation method has been applied with successful results. A number of optimised synchronisers have been defined, all of them featuring relevant improvements in the dynamic behaviour (shiftability) with respect to the reference synchroniser, aleady effective and under production.

Commentary by Dr. Valentin Fuster
2002;():33-41. doi:10.1115/IMECE2002-32957.

Probability analysis is the key to extracting the maximum information from the evidence surrounding a motor vehicle accident. Moreover, it gives essential perspective to the answers drawn from the evidence, by conveying the uncertainty about the answers. In this paper, probability methods are used to analyze a typical intersection type collision between two vehicles. It is a situation in which one of the vehicles pulls out from a stop sign into the path of the other vehicle, which had the right of way. The vehicle that pulls out into the path of the oncoming vehicle precipitates the accident, but the driver of the oncoming vehicle may have contributed to the accident by traveling at excessive speed and or by being inattentive.

Commentary by Dr. Valentin Fuster
2002;():43-50. doi:10.1115/IMECE2002-32962.

The US Army vision, announced in October of 1999, encompasses people, readiness, and transformation. The goal of the Army vision is to transition the entire Army into a force that is strategically responsive and dominant at every point of the spectrum of operations. The transformation component will be accomplished in three ways: the Objective Force, the Legacy (current) Force, and the Interim Force. The objective force is not platform driven, but rather the focus is on achieving capabilities that will operate as a “system of systems.” As part of the Interim Force, the US Army plans to begin production of the Interim Armored Vehicle (IAV) in FY02 and field the first unit by May 2002 and complete first unit fielding by 2003 to address the current force’s operational shortfall. The intent is to get forces on the ground quickly with enough combat power to influence a potential situation, so the Army is converting six to eight combat brigades into Interim Brigade Combat Teams (IBCTs). These teams will be a rapidly deployable combat brigade task force that will be centered around the IAV (figure 1), which was recently selected during a source selection. The IAV program is a family of medium armored vehicles intended to equip the Army’s IBCTs.

Commentary by Dr. Valentin Fuster
2002;():51-57. doi:10.1115/IMECE2002-32964.

The Pennsylvania Truck Driving Simulator (PTDS) has been implemented in several different studies. The effectiveness of utilizing the simulator for training heavy truck operators was investigated through a study with the Pennsylvania Department of Transportation (PENNDOT). Thirty-four highway equipment operator trainees from PENNDOT completed a series of driving tasks in the simulator. The driving tasks were developed as five independent driving scenarios within the simulator each requiring different skills. Measures of driver performance included ratings from professional driving instructors and numerical records from the simulator’s recording capability. These were analyzed to determine if a) students improved their driving through completing the driving scenarios, and b) the two sets of data agreed in the assessment of driver performance. This paper presents the results of this study, which showed that students’ driving skill did improve as they completed the driving tasks. The vehicle dynamics response measurement data also largely agreed with the instructors’ evaluation.

Topics: Trucks
Commentary by Dr. Valentin Fuster
2002;():59-73. doi:10.1115/IMECE2002-33184.

This paper presents a rigid body modeling approach using ADAMS™ for an overturning stability analysis of a vehicle stopped at an arbitrary heading angle on a steep grade. The vehicle is modeled as a six-degree-of-freedom rigid body with multiple contact forces acting on the ground. A gravity vector bounded by sets of spherical coordinates is applied to the vehicle to represent the physics of a vehicle stopped on a grade with any arbitrary combination of pitch and roll angles. A design of experiments study is performed to locate the overturning stability boundaries within given levels of design parameters. Results are output using two effective graphical means of depicting the stability regions and magnitude of contact forces.

Topics: Stability , Vehicles
Commentary by Dr. Valentin Fuster
2002;():73-79. doi:10.1115/IMECE2002-33186.

Traffic congestion in major cities is a major problem which is growing steadily every year. It is clear that something must be done to curb this trend. Several different concepts are being investigated which can be used to minimize congestion and improve the traffic flow. Automation of the bus system represents one of those methods, and is the focus of this paper. Currently, public opinion of the quality of bus services is generally not perceived as adequate. Buses generally travel about 60% of the speed of other vehicles, and more often than not adherence to schedule is difficult to achieve. The consequence is that people choose to take personal transportation instead, causing increased congestion. Automation seeks to address this issue by offering decreased travel times, increased schedule adherence, and greater overall convenience compared to the current bus systems. The concept of automation is based on expanding upon the ideas of Bus Rapid Transit (BRT) and making the system as efficient as possible.

Commentary by Dr. Valentin Fuster
2002;():81-86. doi:10.1115/IMECE2002-33192.

A backhoe is a tractor-like vehicle that has a hydraulically actuated bucket loader at the front and a hydraulically actuated backhoe shovel at the rear. The operator sits inside a canopy or cab that is mounted to the tractor chassis, and operates the hydraulic controls. The cab is typically isolated somewhat from the chassis using cab mounts. There are instances when the bucket is raised or lowered or wrapped that an instability of the entire machine is excited. In this mode, a frequency oscillation of the vehicle occurs and the operator is unable to keep his hands on the controls. This instability is investigated here and demonstrated through simulation. The instability described here is due to an interaction between the mechanical dynamics and hydraulic dynamics of the machine. All instabilities require an energy source, and, in this case, the energy comes from the fuel. It turns out that the hydro-mechanical interaction has positive feedback components and produces an instability. In order to expose the fundamental cause of the instability, a model is needed that allows the interaction of mechanical and hydraulic components. Bond graphs are a logical choice for development of the model. Bond graphs are a concise pictorial representation of the interactive dynamics of all types of energetic systems. They allow the model to be developed in pieces and then put together into an overall computational model. This procedure is demonstrated for the system here. The end result is a reasonably low order model that exposes the fundamental cause of the instability in backhoes. It also allows assessment of cures for the problem, some requiring redesign of components, and some requiring an automatic stabilization control system.

Commentary by Dr. Valentin Fuster
2002;():87-92. doi:10.1115/IMECE2002-33196.

A generalized nonlinear model is formulated for dynamic analysis of suspension seats with passive, semi-active and active dampers. The model incorporates coulomb friction due to suspension linkages and bushings, forces arising from interactions with the elastic limit stops, a linear suspension spring and nonlinear damping force on the basis of passive, semi-active and active dampers, while the contribution due to biodynamics of the human operator is considered to be negligible. The semi-active and active dampers are charcterized by force generators in accordance with the control laws based upon suspension mass velocity. Two different suspension seats are experimentally assessed in the laboratory under sinusoidal and random excitations arising from an urban bus, and the measured data is used to demonstrate the validity of the proposed generalized model. The results showed reasonably good agreement between the model results and the measured data. Optimal model parameters are selected using the sequential unconstrained minimization technique with an objective to minimize the acceleration due to vibration transmitted to the occupant mass. The comfort and safety performance characteristics of the optimal suspension seat with semi-active and active dampers are evaluated under both the sinusoidal and random excitations on the basis of the guidelines provided in ISO-2631. From the results it is concluded that the comfort performance of a suspension seat with semi-active and active dampers can be considerably enhanced, in the 20% to 30% range.

Topics: Safety
Commentary by Dr. Valentin Fuster
2002;():93-101. doi:10.1115/IMECE2002-33200.

A full nonlinear finite element P185/70R14 passenger car radial-ply tire model was developed and run on a 1.7-meter-diameter spinning test drum. The virtual tire/drum/cleat finite element model was constructed and tested using the nonlinear finite element analysis software, PAM-SHOCK. The tire model was constructed in extreme detail with three-dimensional solid, layered membrane, and beam finite elements, incorporating over 18,000 nodes and 24 different types of materials. In addition to the tire model itself, the rim was also included and rotated with the tire, with proper mass and rotational inertial effects. The FFT algorithm was applied to examine the transient response information in the frequency domain. The result showed that this P185/70R14 tire has clear peaks of 84 and 45 Hz transmissibility in the vertical and longitudinal directions. Also the paper presents the prediction of tire standing waves phenomenon, and computer animations of the standing waves phenomenon were carried out for the first time. The effects of different tire inflation pressures and tire axle loadings were investigated with respect to their influences on the formation of standing waves. The parameters adopted in this FEA tire model were validated against experimental work and showed excellent agreement.

Commentary by Dr. Valentin Fuster
2002;():103-110. doi:10.1115/IMECE2002-33205.

While methods for vehicle modeling are well established for simulation of handling behavior, there is still a lack of driver models, which are important for the realization of closed-loop maneuvers in a virtual environment. This paper will present preliminary considerations for the development of such a driver model. First, trajectory planning strategies have to be generated and evaluated. To achieve this, a method will be deduced, which calculates the maximum velocity at each point of an arbitrary trajectory, taking into account simplified vehicle characteristics in terms of maximum longitudinal and lateral accelerations and considering the frictional ellipse. Thus, the minimum necessary time for each trajectory can be calculated, this being a possible parameter to rate the quality of a trajectory for a given course. The feasibility of the method is demonstrated with the Nuerburgring race track.

Commentary by Dr. Valentin Fuster
2002;():111-119. doi:10.1115/IMECE2002-33209.

The vehicle control system described in this paper consists of a discrete controller that computes the control parameters in two major steps: Geometric dynamic planning and plan-to-action mapping. Geometric dynamic planning computes a nominal motion, or ‘gd-plan’ of the vehicle for one control interval. Plan-to-action mapping computes the control parameters so that the gd-plan is performed. This control structure allows the independent modeling of two essential control concepts: motivation and knowledge. Motivation is modeled by computing a desired geometric-dynamic plan. Knowledge is represented through plan-to-action mapping as an approximation of the plant’s inverse system function. This paper describes the development of an extremely precise plan-to-action mapper for use in a vehicle control system that is based on empirical data. This approach is majorm step towards the development of a control structure that is indeed able to adapt to any given plant, or specifically any given vehicle. The paper first describes the development of a suiteable database capturing the vehicle’s input/output behavior. This database can then be used by a curve fitting process to find a formula for the relationship between the vehicle’s; geometric-dynamic behavior and the vehicle’s control inputs. Finally, a number of simulation runs are done to demonstrate the effectiveness of the approach.

Topics: Vehicles
Commentary by Dr. Valentin Fuster
2002;():121-127. doi:10.1115/IMECE2002-33216.

Automotive steering system research has traditionally focused on improving vehicle handling and safety, as well as investigating lateral dynamic issues. The emergence of hybrid vehicles provides a motivation for steer-by-wire technology in terms of power source availability and improved performance. From a design perspective, steering systems are difficult to accurately model due to the inherent nonlinearities present in the steering assembly, chassis, wheels, and tire/road interface. One modeling strategy that merits further attention is the Fourier Series Neural Network (FSNN) which has been proven effective for the characterization of dynamic systems. A neural network can approximate nonlinear functions to a high degree of accuracy, given an adequate network structure and sufficient training. In this paper, a Fourier Series activation function neural network will be studied to identify a steer-by-wire system. A behavioral model has been developed for the driver interface and directional control assembly of the rack and pinion steer-by-wire system. Representative numerical results are presented to demonstrate the FSNN’s ability to predict the system’s overall transfer function. This engineering tool may provide an attractive alternative to rigorous system modeling, and inherently captures the response characteristics due to the nonlinear behavior.

Commentary by Dr. Valentin Fuster
2002;():131-140. doi:10.1115/IMECE2002-39139.

We investigate slow passage through the 2:1 resonance tongue in Mathieu’s equation. Using numerical integration, we find that amplification or de-amplification can occur. The amount of amplification (or de-amplification) depends on the speed travelling through the tongue and the initial conditions. We use the method of multiple scales to obtain a slow flow approximation. The WKB method is then applied to the slow flow equations to get an analytic approximation.

Topics: Resonance , Equations
Commentary by Dr. Valentin Fuster
2002;():141-146. doi:10.1115/IMECE2002-39142.

In modeling of dynamical systems, differential equations, either ordinary or partial, are a common outcome of the modeling process. The basic problem becomes the existence of solution of these deferential equations. In the early days of the solution of deferential equations at the beginning of the eighteenth century the methods for determining the existence of nontrivial solution were so limited and developed very much on an ad hoc basis. Most of the efforts on dynamical system are related to the second order systems, derived by applying Newton equation of motion to dynamical systems. But, behavior of some dynamical systems is governed by equations falling down in the general nonlinear third order differential equation x″′+f(t,x,x′,x″)=0, sometimes as a result of combination of a first and a second order system. It is shown in this paper that these equations could have nontrivial solutions, if x, x′, x″, and f(t,x,x′,x″) are bounded. Furthermore, it is shown that the third order differential equation has a τ-periodic solution if f(t,x,x′,x″) is an even function with respect to x′. For this purpose, the concept of Green’s function and the Schauder’s fixed-point theorem has been used.

Commentary by Dr. Valentin Fuster
2002;():147-153. doi:10.1115/IMECE2002-39143.

In this paper, a nonlinear mathematical model has been constructed by deriving the equations of motion of a Rail Vehicle carbody using Newton’s law. The nonlinear formula is used to evaluate the wheel rail contact forces. The nonlinear profile of wheel and rail are taken into account. Also the lateral stiffness of the track is taken into consideration. The equations of motion are derived for (a) Carbody with conventional wheelset (b) Carbody with unconventional wheelset (independently rotating wheels). For lateral vibration, 17 degrees of freedom are considered. The degrees of freedom represent lateral and yaw movements of 4 wheelsets and lateral, yaw and roll movements of the bogie and carbody. These equations of motion are transformed into a form suitable for numerical differential equation by Runge Kutta method. In the interest of computing economy, certain approximations have been introduced for calculating the creep forces. Sample results are given for a model of a typical railway vehicle used by the Indian Railways. The lateral dynamic response of the railway vehicle carbody for both conventional and unconventional wheelset has been analysed.

Commentary by Dr. Valentin Fuster
2002;():155-163. doi:10.1115/IMECE2002-39204.

This research deals with nonlinear dynamics of a permanent magnet freely levitated above a high-Tc superconductor excited in the vertical direction, focusing on generation of spin torque acting on the magnet. Equations of 6 d.o.f motion, nonlinearly coupled by magnetic force and torque, were described on the assumption that a magnet has an eccentricity between the center of gravity and the magnetic center. Force and torque were evaluated analytically by the flux frozen method. Dynamic behavior of the magnet was examined numerically for different frequencies of excitation. A simplified 2 d.o.f. system with only essential terms was introduced in order to discuss the mechanism of nonlinear coupling which generates spinning from vertical oscillation. Spinning motion of the magnet was examined in detail analytically by the method of harmonic balance. Experiments of vertical excitation were also carried out. Experimental results were compared with numerical ones.

Commentary by Dr. Valentin Fuster
2002;():165-176. doi:10.1115/IMECE2002-32362.

The effects of bending stiffness and boundary conditions on the lateral vibration of the stationary and moving hoist cables are investigated. The role of the trial functions in the approximate methods is examined. The optimal stiffness and damping coefficient of the suspension of the car against its guide rails are identified for the moving cable.

Commentary by Dr. Valentin Fuster
2002;():177-189. doi:10.1115/IMECE2002-32368.

An efficient method for calculating the eigensolutions and dynamic response of a serpentine belt drive is presented. The model is a hybrid discrete-continuous one where the motions consist of rotations of the pulleys, rotation of the tensioner arm, and transverse vibrations of the continuum belt spans adjacent to the tensioner. The speed of solution results from discretization of the belt spans where the unusual feature is the use of Lagrange multipliers to enforce the geometric boundary conditions at the belt-tensioner interface. The method reduces the computational effort by several orders of magnitude compared to published methods using the same model. Also, it is not susceptible to numerical problems that binder the published methods. The sensitivities of the belt drive natural frequencies to system parameters are also studied. The model parameters under consideration include belt longitudinal stiffness, tensioner spring stiffiness, span tensions, belt transport speed, belt density, and pulley moments of inertia. Exact solutions for the eigensensitivities to these parameters are obtained using perturbation methods. The exact formulae are reduced to simple expressions related to the modal strain and kinetic energies. The eigensensitivities are readily determined, quantitatively and qualitatively, by inspection of the modal energy distributions. An example is presented to demonstrate the capabilities of the methods.

Commentary by Dr. Valentin Fuster
2002;():191-197. doi:10.1115/IMECE2002-32379.

Considering the workpiece elastic deflection in a turning process, a simulation model that accounts for the radial and tangential vibrations and their abatement using active control is developed. The model is simulated using Simulink in a Matlab environment to assess the possibility of using an active actuator to reduce vibrations in two directions. The results demonstrate the significance of the workpiece elastic deformation and its compensation using active actuators. Actuators that can compensate for the piece deflection and the vibrations due to the surface roughness are speculated on.

Topics: Deflection
Commentary by Dr. Valentin Fuster
2002;():199-208. doi:10.1115/IMECE2002-32381.

Dynamic responses of adhesively bonded tubular joints subjected to a harmonic axial and torsional load are investigated. Adherents are assumed elastic and the adhesive is taken to be a linear viscoelastic material. The effects of adherents and adhesive properties on the joint response as well as on the shear stress amplitude distribution along the overlap are investigated for each case of harmonic loading. Furthermore, the effects of defects such as an annular void in the bond area on the axial and torsional dynamic responses and shear stress amplitude distributions in the bond area are studied. The results indicate that for tubular joint geometries and properties investigated the axial and torsional resonant frequencies of the joint are little affected with the adhesive loss factor. These resonant frequencies initially increase rapidly with increasing adhesive shear modulus. However, the resonant frequencies asymptotically approach a constant value with further increase in adhesive shear modulus. The results further show that the resonant frequencies of the joint may not get affected with the presence of a central void in the bond area. The distribution of shear stress amplitude in the joint area is obtained. The maximum shear stress is confined to the edge of the overlap for all applied loading frequencies. For the adhesive and adherents’ properties and geometries investigated, the maximum shear stress amplitude in the joint area is little affected by the presence of a central annular void covering up to 40% of the overlap length. However, a central void larger than 40% of the overlap length may be detrimental or beneficial to the joint strength. This depends on the applied loading frequency. A central void reduces the system axial and torsional resonant frequencies. This may depart the system further away from the applied loading frequency or may bring it closer. A system excited closer or further from to its resonant frequency will develop higher or lower shear stress amplitude in the bond area.

Commentary by Dr. Valentin Fuster
2002;():209-214. doi:10.1115/IMECE2002-32383.

In the study of free vibration of solid cylinders a linear viscoelastic cylinder of an infinite length models the medium. The analytical modeling is based on three dimensional wave propagation utilizing constant complex moduli. The solution is achieved by determining the displacement and stress on the surface, and by complying with requirements at the boundary. Analysis was conducted to express displacement stresses at any point of the solid cylinder to boundary stress. Dimensionless natural frequencies and mode shapes for different circumferential and axial wave numbers are determined.

Topics: Cylinders
Commentary by Dr. Valentin Fuster
2002;():215-219. doi:10.1115/IMECE2002-32385.

The identification of model damping is a key for response analysis. A method is presented for updating damping of the computational model of substructure based on frequency response experiment. The proposed method directly identifies mass, stiffness and damping matrices by using the substructure error coefficient and frequency response experiment, then computational model damping is updated, finally the effectiveness of the method with simulated data gauging is studied in this paper.

Commentary by Dr. Valentin Fuster
2002;():221-230. doi:10.1115/IMECE2002-33570.

Spherical shell-type structures and components appear in many engineering systems, such as radar domes, pressure vessels, storage tanks, etc. This study is to evaluate the micro-control actions and distributed control effectiveness of segmented actuator patches laminated on hemispheric shells. Mathematical models and governing equations of the hemispheric shells laminated with distributed actuator patches are presented first, followed by formulations of distributed control forces and micro-control actions including meridional/circumferential membrane and bending control components. Due to difficulties in analytical solution procedures, assumed mode shape functions based on the bending approximation theory are used in the modal control force expressions and analyses. Spatially distributed electromechanical actuation characteristics resulting from various meridional and circumferential actions are evaluated. Distributed control forces, patch sizes, actuator locations, micro-control actions, and normalized control authorities of a free-floating hemispheric shell are analyzed in a case study. Parametric analysis indicates that 1) the control forces and membrane/bending components are mode and location dependent and 2) the meridional/circumferential membrane control actions dominate the overall control effect.

Topics: Actuators , Shells
Commentary by Dr. Valentin Fuster
2002;():231-239. doi:10.1115/IMECE2002-33571.

Dynamic response of single lap joints, subjected to a harmonic peeling load is studied theoretically and experimentally. In the theoretical part, dynamic response of a single lap joint clamped at one end and subjected to a harmonic peeling load at the other end is investigated. Adherents are modeled as Euler-Bernouli beams joined in the lap area by a viscoelastic adhesive layer. Both axial and transverse deformations of adherents are considered in deriving the equations of motion. The effects of adhesive layer thickness, mechanical properties and its loss factor on the dynamic response of the joint are investigated. Furthermore, effects of defects such as a void in the lap area on the dynamic response of the joints are studied. The results showed that frequencies where peak amplitudes occurred were little dependent on the adhesive loss factor. However, peak amplitudes reduced for joints with a higher adhesive loss factor. Furthermore, the results indicated that for the joint geometries and properties investigated the system resonant frequencies were not affected by the presence of a central void covering up to 80% of the overlap length. In the experimental part, single lap joints were fabricated using 6061-T6 Aluminum. Adherents were joined together using Hysol EA 9689 adhesive film. Joints with various central voids were manufacture by removing adhesive film from the desired area of lap joints prior to bonding adherents. Dynamic responses of the joints were investigated using the hammer test technique. The system response was measured using both an accelerometer and a non-contact laser vibrometer. The natural frequencies of the joints obtained by using the laser vibrometer were very close to those obtained theoretically. However, natural frequencies obtained by using an accelerometer depended on the accelerometer location in the system, which was attributed to its mass contribution to the over all system mass. A central void covering less than 80% of the overlap length had little effect on the system resonance frequencies. This was in agreement with the theoretical results. In contrast, total system-damping ratios were a function of the void size. Joints without a void exhibited higher damping.

Commentary by Dr. Valentin Fuster
2002;():241-246. doi:10.1115/IMECE2002-33574.

Based on classical laminated plate theory and Navier solutions, the control of the piezoelastic laminated cylindrical shell’s dynamic response under hydrostatic pressure is discussed in this paper. Considering the direct and inverse piezoelectric effects of piezoelectric materials and from Hamilton’s principle, the nonlinear dynamic equations of the piezoelastic laminated cylindrical shell are derived first. Using close circuit method, the charge enclosed in the piezoelectric sensor layer can be measured. Furthermore, the voltage applied on the actuator layer can be obtained based on the closed-circuit charge signal of the sensor and velocity negative feedback control algorithm. An active dynamic response control model of simply supported laminated cylindrical shells with piezoelectric sensor/actuator under various dynamic loads is established in this paper at last. Three types of loading conditions, namely sinusoidal distributed load, line load and moving point load, are considered in numerical examples to investigate the performance of the control model. The numerical results show that the active control model presented in this paper can suppress the vibration of the structure under dynamic loading effectively.

Commentary by Dr. Valentin Fuster
2002;():247-256. doi:10.1115/IMECE2002-33580.

Toroidal shell structure has been proposed for components of inflatable space structures and telescope etc. Thus, distributed control of toroidal shells becomes a critical issue in precision maneuver, operation, and reliability. The converse effect of piezoelectric materials has made it one of the best candidates for distributed control actuators. The resultant control forces and micro-control actions induced by the distributed actuators depend on applied voltages, geometrical (e.g., spatial segmentation and shape) and material (i.e., various actuator materials) properties of the actuators. The purpose of this analysis is to study the location effects of actuator placement and to evaluate the micro-control actions imposed upon toroidal shell structures. Mathematical models and governing equations of the toroidal shells laminated with distributed actuator patches are presented first, followed by formulations of distributed control forces and micro-control actions including meridional/circumferential membrane and bending control components. Spatially distributed electromechanical microscopic actuation characteristics and control effects resulting from various meridional and circumferential actions are evaluated.

Topics: Actuators , Shells
Commentary by Dr. Valentin Fuster
2002;():257-265. doi:10.1115/IMECE2002-33582.

Sub-surface cracks in pipelines with internal pressure may severely affect their dynamic response. The extreme cases of these cracks are when these cracks go through the thickness of the pipes. Dynamic responses of cracked and un-cracked pipes with fixed ends and under various internal pressures were evaluated experimentally and theoretically. In the experimental part, the effects of pipe internal pressure on the resonant frequencies and damping of the pipe were evaluated. In the theoretical part, finite element analyses were performed to find dynamic response of pipes with various crack length and orientation respect to the axis of the pipe. The experimental results showed resonant frequencies of the pipe are little sensitive to the pipe internal pressure. Similar results were obtained from the theoretical investigations. An axial crack had little effect on the pipe resonant frequencies. In contrast, cracks oriented at an angle to the axis of the pipe had a pronounced effect on some of the resonant frequencies of the pipe. This depended on the crack location in a particular mode shapes. For frequencies where the nodal point of the mode shape was located on the crack region, the frequencies were not significantly affected by the presence of the crack in the pipe. Furthermore, it was observed that the pipe internal pressure had little effect on the resonant frequencies of the cracked pipes.

Commentary by Dr. Valentin Fuster
2002;():267-276. doi:10.1115/IMECE2002-39148.

A finite-element model of a vehicle rear suspension is developed and experimentally evaluated for predicting the vibration response of the rear suspension to 300 Hz. The suspension model is developed from ten major component finite-element models that were individually correlated to 300 Hz prior to assembly. The bushing and isolator connections between the components are represented using measured dynamic stiffness and damping rates, and a modal tire model is used to represent the tire-wheel assembly. Shaker excitation tests were conducted with the rear suspension supported in a specially designed test fixture to obtain the measured vibration response of the suspension. Comparisons are made of the predicted and measured frequency response functions (FRFs) and modes to experimentally assess the accuracy of the suspension model to 300 Hz. The accuracy of a traditional rigid-link rear suspension model is also assessed.

Topics: Vehicles , Vibration
Commentary by Dr. Valentin Fuster
2002;():277-284. doi:10.1115/IMECE2002-39149.

In this paper, an accurate computational model for analyzing tire-soil interaction is presented. In the traditional approach, Bekker equation is written in a global form and a quasi-static analysis is done to iteratively model the interaction of the tire and soil. This is due to the nonlinear relationship between soil sinkage and pressure and the unknown loading and unloading status of soil as they are dependent on past loading histories. In this work, an incremental form of Bekker model is proposed. The resulting tire-soil interaction problem is described by a set of nonlinear complementarity equations, which are easier to solve compared to the iterative approach required in the traditional Bekker model. Two numerical examples are presented to demonstrate the effectiveness of the algorithm presented in this work.

Topics: Modeling , Equations , Soil , Tires
Commentary by Dr. Valentin Fuster
2002;():285-289. doi:10.1115/IMECE2002-39154.

Torsional vibration of a two-stage gear train system is investigated, considering backlash and crack. Two criteria are used to detect backlash and crack for the purpose of vibration monitoring. A discretized model is considered which consists of a servomotor, a two-stage gearbox and a brake. It is shown that second moment of acceleration increases, increasing backlash. Kurtosis number diagnoses the tooth crack. Abrupt change in Kurtosis number shows that crack has been developed.

Commentary by Dr. Valentin Fuster
2002;():291-295. doi:10.1115/IMECE2002-39155.

The Kinematics and dynamics is the important properties of a mechanical system or a mechanical product. In this paper, a describing method by the symbol sets, motion equations auto-building method and auto-solving method are discussed, a software system MSKDSP (Mechanical System Kinematics and Dynamics Simulation Program) is developed, and an example is given.

Commentary by Dr. Valentin Fuster
2002;():297-301. doi:10.1115/IMECE2002-39156.

In this paper a lumped mass model was used to simulate the behavior of the human body during vertical vibration. Force method has been used to obtain the differential equations of the model, which were solved using simulink toolbox of Matlab software the appropriate damping and stiffness coefficients of shoes were chosen by comparing the results with the experimental data. The model has been used to produce a useful package, which has various abilities. We obtained the kinematics characteristics for each links of the model, in response of sine wave stimulation. This package has also the ability of comparing results by changing the damping and stiffness coefficients for the contact point (shoe) of the model. One of the important specifications of this package is its flexibility. With a little change in the codes of the program we can obtain the curves in response of other kinds of stimulations like noises and pulses.

Topics: Vibration
Commentary by Dr. Valentin Fuster
2002;():303-309. doi:10.1115/IMECE2002-39202.

A passive TVA is only effective when it is tuned properly; otherwise, it can magnify the vibration levels. Often, inevitable off-tuning of a TVA occurs due to changes in the primary structure mass and stiffness for force-excited structural systems such as a floor. The main purpose of this study is to evaluate the robustness of semi-active groundhook TVAs to structure mass and stiffness off-tuning. In the case of floor systems, adding external mass to an existing floor, such as people and furniture, will increase the floor mass, and reduce the mass ratio. Theses changes result in off-tuning of the frequency ratio, which is defined by the ratio of the natural frequency of the TVA to the primary structure natural frequency. In order to study the effect of off-tuning, a force-excited equivalent model of a groundhook TVA is developed and its closed-form solutions are obtained for dynamic analysis of such systems. Moreover, the optimal design parameters of both passive and groundhook equivalent semiactive TVA models are obtained based on minimization of peak transmissibility. The two optimally tuned models are compared as the primary mass and primary structure stiffness changes. The results indicate that the peak transmissibility of the groundhook TVA is lower than that of passive, implying that the groundhook TVA is more effective in reducing vibration levels. The results further indicate that the groundhook TVA is more robust to changes in primary structure mass and stiffness.

Commentary by Dr. Valentin Fuster
2002;():311-321. doi:10.1115/IMECE2002-32389.

The mathematical models representing machine tool chatter dynamics have been cast as differential equations with delay. The suppression of regenerative chatter by spindle speed variation is attracting increasing attention. In this paper, we study nonlinear delay differential equations with periodic delays which models the machine tool chatter with continuously modulated spindle speed. The explicit time-dependent delay terms, due to spindle speed modulation, are replaced by state dependent delay terms by augmenting the original equations. The augmented system of equations is autonomous and has two pairs of pure imaginary eigenvalues without resonance. We make use of Lyapunov-Schmidt Reduction method to determine the periodic solutions and analyze the tool motion. Analytical results show both modest increase of stability and existence of periodic solutions close to the new stability boundary.

Commentary by Dr. Valentin Fuster
2002;():323-332. doi:10.1115/IMECE2002-32392.

Dynamic rolling instability known as fifth-octave chatter is studied using a nonlinear model developed to describe the responses of work rolls subjected to the exertion of sheet forces of various spectral characteristics. The model enables the dynamic instability of sheet rolling to be correlated with work roll stiffiness, rolling speed, inter-stand tension, roll-bite entry and exit thickness, and the sheet force resulted from the interactive action of the work roll with the plastic deformation of the rolled strip. It is found that roll-bit elastic-plastic deformation sheet force is nonlinearly coupled with the rollstack stiffness and also plays a dominant role in affecting rolling instability. In addition, whenever the frequency spectrum of the normal sheet forces containing spectral components that match the fundamental modes of the roll stand, resonance-like beating would occur. This highly linear physical phenomenon, which is accompanied by large vibration amplitudes in the active work rolls, is recognized as chatter. Although many different dynamic modes of instability including mode excitation and beating are induced in response to sheet forces of nonlinear and non-stationary in nature, however, the rolling system never responds chaotically.

Topics: Chatter
Commentary by Dr. Valentin Fuster
2002;():333-340. doi:10.1115/IMECE2002-32397.

An explicit general formula is proposed for controlling Hopf bifurcation using state feedback. This method can be used to either delay (or even eliminate) an existing Hopf bifurcation or change a subcritical Hopf bifurcation to supercritical. The Lorenz system is used to illustrate the application of the formula.

Topics: Bifurcation
Commentary by Dr. Valentin Fuster
2002;():341-352. doi:10.1115/IMECE2002-32400.

Friction-induced vibration of a two-degrees-of-freedom mass-spring system interacting with a decelerating rigid strip is considered. The friction law is approximated by an analytic function to facilitate the numerical integration, whereas the truncated Taylor expansion of this function gives good qualitative results. It was shown that after a quasi-harmonic transient period, accompanied by viscous energy dissipation, a relatively short period of intensive stick-slip vibration occurs, with its out-of-phase component generating a series of micro-impacts on the strip. It was further shown that, because of the impulsive character of such kind of loading, its Fourier spectrum is sufficiently rich. Based on the simplified ‘normal form’ equations, it was shown that the out-of-phase vibration mode of the block system absorbs more energy from the decelerating strip if the corresponding natural frequencies satisfy the resonance condition. The out-of-phase stick-slip vibration of the blocks creates an impulsive bending moment applied to the strip, and therefore can be considered as a possible source of flexural vibration. In particular, the results are applied to explanation of squeal generation in automotive disc brakes, although the technique can be extended on other ‘squealing systems’ including geophysical fault (earthquake) models.

Commentary by Dr. Valentin Fuster
2002;():353-359. doi:10.1115/IMECE2002-32401.

This study makes use of energy dissipation to identify damping from mechanical vibration systems. Both the viscous damping and dry friction are assumed to coexist in vibration systems. By balancing the energy loss as registered in the force-displacement relationship of the real system against that of a theoretical model, consisting of viscous damping and dry friction components, the identification algorithms are developed and the equivalent viscous-damping and dry-friction parameters are estimated. We apply the estimation equations to both numerical and experimental systems to show the effectiveness and reliability of the new identification method.

Commentary by Dr. Valentin Fuster
2002;():361-367. doi:10.1115/IMECE2002-32402.

We present a new regularization for Coulomb’s law of friction for single point contacts. This modification permits a straightforward application of friction within existing numerical simulations. Similar to existing regularizations, the proposed modification to Coulomb frictions leads to continuous representation of friction and does not require the separate identification of transitions between slip and stick. However, unlike more common regularizations, the current reformulation maintains an equilibrium structure identical to the classical, discontinuous form of Coulomb friction. The implementation and performance of this regularization is illustrated by a simple one degree-of-freedom system in which stick-slip motion induced by sliding friction is of primary importance. The simulations illustrate the existence of non-trivial equilibrium states and the ability of the current regularization toprovide a computationally efficient scheme for simulating the dissipation arising from sliding friction.

Topics: Friction , Coulombs
Commentary by Dr. Valentin Fuster
2002;():369-376. doi:10.1115/IMECE2002-32414.

We recently developed a symbolic-numerical formulation for the nonlinear planar motion of rotors under fluid confinement, based on a spectral/Galerkin approach, for gap geometries of about δ = H/R ≈ 0.1 — where H is the average annular gap and R is the rotor radius. Results showed a quite good agreement between the class of approximate models generated, the corresponding analytical exact planar model and experiments. This methodology can be almost entirely automated on a symbolic computing environment. In the present paper this symbolic-numerical spectral/Galerkin procedure is extended in order to deal with nonlinear orbital motions — X (t) and Y (t) taking place in orthogonal directions. Numerical simulations performed over a centered rotor configuration maintained by non-isotropic supports (Ky st /Kx st = 0.4, where kx st and ky st stand for the structural stiffnesses), which exhibit an interesting dynamics, show a quite good agreement between this type of approximate models and the corresponding analytical exact (but quite involved) model, developed in the past by the authors. With the proposed symbolic-numerical approach one can obtain accurate nonlinear dynamical formulations enabling the study, understanding and prediction of nonlinear orbital rotor-dynamics.

Topics: Motion , Rotors
Commentary by Dr. Valentin Fuster
2002;():377-385. doi:10.1115/IMECE2002-32415.

It is still a challenge to properly simulate the complex stick-slip behavior of multi-degree-of-freedom systems. In the present paper we investigate the self-excited nonlinear responses of bowed bars, using a time-domain modal approach, coupled with an explicit model for the frictional forces, which is able to emulate stick-slip behavior. This computational approach can provide very detailed simulations and is well suited to deal with systems presenting a dispersive behavior. The effects of the bar supporting fixture are included in the model, as well as a velocity-dependent friction coefficient. We present the results of numerical simulations, for representative ranges of the bowing velocity and normal force. Computations have been performed for constant-section aluminum bars, as well as for real vibraphone bars, which display a central undercutting, intended to help tuning the first modes. Our results show limiting values for the normal force FN and bowing velocity ẏbow , for which the “musical” self-sustained solutions exist. Beyond this “playability space”, double period and even chaotic regimes were found for specific ranges of the input parameters FN and ẏbow . As also displayed by bowed strings, the vibration amplitudes of bowed bars also increase with the bow velocity. However, in contrast to string instruments, bowed bars “slip” during most of the motion cycle. Another important difference is that, in bowed bars, the self-excited motions are dominated by the system first mode. Our numerical results are qualitatively supported by preliminary experimental results.

Commentary by Dr. Valentin Fuster
2002;():387-395. doi:10.1115/IMECE2002-32419.

The purpose of this study is to investigate the nonlinear effect of gravity on the free vibration of a cable against a straight obstacle. The cable model is expressed in terms of nonlinearly coupled transverse and axial displacements. The penalty method is used to simulate the obstacle, which is equivalent to inserting a stiff elastic foundation. The first symmetric frequencies are obtained when the depth of the obstacle is 1/2 and 1/3 of the initial transverse displacement. The effects of varying amplitude and equilibrium curvature are investigated.

Commentary by Dr. Valentin Fuster
2002;():397-403. doi:10.1115/IMECE2002-32420.

This paper presents a methodology for modeling very flexible structures. A theory for the dynamics of traveling, arbitrarily sagged, elastic cables is developed for demonstration of this methodology. In this theory, the cable motion is modeled through the rigid-body motion and elastic deformation, and the rigid-body motion of cable configuration is modeled as an inextensible cable model. The dynamic, rigid-body configuration of a cable is a referenced base to describe its elastic deformation motion for any instantaneous moment. In this paper, the analytical solution for the rigid-body motion of the cable under a certain loading is developed as Part I of this investigation. From the dynamical configuration of the rigid-body motion of cable, an elastic motion of nonlinear cables is further investigated in sequel as the part II. This theory can be applied any cable structures and the methodology is useful for the perfectly flexible structures such as membranes.

Topics: Motion , Cables
Commentary by Dr. Valentin Fuster
2002;():405-411. doi:10.1115/IMECE2002-33605.

The nonlinear dynamic behavior of a rotor-bearing system is analyzed based on a continuum model. The finite element method is adopted in the analysis. Emphasis is given on the so called “Oil-Whirl phenomena” which might lead to the failure of the rotor system. The dynamic response of the system in unbalanced condition is approached by direct integration method and mode superposition method, it is found that a typical “Oil-Whirl phenomenon” is successfully produced. Furthermore, the bifurcation behavior of the Oil-Whirl phenomenon that is much concerned in recent nonlinear dynamics research is analyzed. The rotor-bearing system is also examined by the simple discrete model. Significant differences are found between these two models. It is suggested that a careful examination should be made in modeling such nonlinear dynamic behavior of the rotor system.

Topics: Bearings , Rotors
Commentary by Dr. Valentin Fuster
2002;():413-423. doi:10.1115/IMECE2002-39384.

The purpose of this work is to develop a unified approach to study the dynamics of single degree of freedom systems excited by both periodic and random perturbations. The near resonant motion of such systems is not well understood. We will study this problem in depth with the aim of discovering a common geometric structure in the phase space, and to determine the effects of noisy perturbations on the passage of trajectories through the resonance zone. We consider the noisy, periodically driven Duffing equation as a prototypical single degree of freedom system and achieve a model-reduction through stochastic averaging. Depending on the strength of the noise, reduced Markov process takes its values on a line or on graph with certain gluing conditions at the vertex of the graph. The reduced model will provide a framework for computing standard statistical measures of dynamics and stability, namely, mean exit times, probability density functions, and stochastic bifurcations. This work will also explain a counter-intuitive phenomena of stochastic resonance, in which a weak periodic force in a nonlinear system can be enhanced by the addition of external noise.

Commentary by Dr. Valentin Fuster
2002;():425-433. doi:10.1115/IMECE2002-32406.

We investigate the effect of nonlinearites on a parametrically excited ordinary differential equation whose linearization exhibits the phenomena of coexistence. The differential equation studied governs the stability mode of vibration in an unforced conservative two degree of freedom system used to model the free vibrations of a thin elastica. Using perturbation methods, we show that at parameter values corresponding to coexistence, nonlinear terms can cause the origin to become nonlinearly unstable, even though linear stability analysis predicts the origin to be stable. We also investigate the bifurcations associated with this instability.

Commentary by Dr. Valentin Fuster
2002;():435-443. doi:10.1115/IMECE2002-32410.

In a previous paper [6], the authors investigated the dynamics of the equation:

d2xdt2 + (δ + ε cos t)x
  + εAx3 + Bx2dxdt + Cxdxdt2 + Ddxdt3 = 0
. We used the method of averaging in the neighborhood of the 2:1 resonance in the limit of small forcing and small nonlinearity. We found that a degenerate bifurcation point occurs in the resulting slow flow and some of the bifurcations near this point were looked at. In this work we present additional results concerning the bifurcations around this point using analytic techniques and AUTO. An analytic approximation for a heteroclinic bifurcation curve is obtained. Additional results on the bifurcations of periodic orbits in the slow flow are also presented.

Commentary by Dr. Valentin Fuster
2002;():445-456. doi:10.1115/IMECE2002-32412.

A numerical method for constructing nonlinear normal modes for systems with internal resonances is presented based on the invariant manifold approach. In order to parameterize the nonlinear normal modes, multiple pairs of system state variables involved in the internal resonance are kept as ‘seeds’ for the construction of the multi-mode invariant manifold. All the remaining degrees of freedom are constrained to these ‘seed’ variables, resulting in a system of nonlinear partial differential equations governing the constraint relationships, which must be solved numerically. The solution procedure uses a combination of finite difference schemes and Galerkin-based expansion approaches. It is illustrated using two examples, both of which focus on the construction of two-mode models. The first example is based on the analysis of a simple three-degree-of-freedom example system, and is used to demonstrate the approach. An invariant manifold that captures two nonlinear normal modes is constructed, resulting in a reduced-order model that accurately captures the system dynamics. The methodology is then applied to a more large system, namely an 18-degree-of-freedom rotating beam model that features a three-to-one internal resonance between the first two flapping modes. The accuracy of the nonlinear two-mode reduced-order model is verified by time-domain simulations.

Commentary by Dr. Valentin Fuster
2002;():457-463. doi:10.1115/IMECE2002-32416.

The (M:1)-resonant bands in the left and right potential wells are skew-symmetric, and the (2M:1)-resonant bands of the large orbit motion are symmetric. The analytical conditions for the onset and destruction of a resonant band are developed through the incremental energy approach. The numerical predictions of such the onset and destruction are also completed by the energy increment spectrum method. The sub-resonance interaction occurs for strong excitations, which needs to be further investigated. These results are applicable to the small orbit and large orbit motions of post-buckled structure under a parametric excitation.

Commentary by Dr. Valentin Fuster
2002;():465-470. doi:10.1115/IMECE2002-32417.

The human-body in a vehicle traveling on the rough terrain is modeled through the lumped mass approach and its periodic impact motions and stability are investigated through a linear model of vehicle and passenger systems. The linear model assumes the motion response of vehicle is very small compared to passenger’s rotational motion since the vehicle chassis has a very large mass and moment of inertia. The period-1 impact motion for two impacts respectively on two walls for a specific number of periods is predicted analytically and numerically. The stability and bifurcation of such a period-1 impact motion are developed analytically. The phase planes of the periodic impact motions are illustrated for a better understanding of the human-body impacting motion in the vehicle.

Commentary by Dr. Valentin Fuster
2002;():471-479. doi:10.1115/IMECE2002-32811.

Friction-induced vibration is a phenomenon that has received extensive study by the dynamics community. This is because of the important industrial relevance and the evere-volving development of new friction models. In this paper, we report the result of bifurcation study of a single-degree-of-freedom mechanical oscillator sliding over a surface. The friction model we use is that developed by Canudas de Wit et al, a model that is receiving increasing acceptance from the mechanics community. Using this model, we find a stable limit cycle at intermediate sliding speed for a single-degree-of-freedom mechanical oscillator. Moreover, the mechanical oscillator can exhibit chaotic motions. For certain parameters, numerical simulation suggests the existence of a Silnikov homoclinic orbit. This is not expected in a single-degree-of-freedom system. The occurrence of chaos becomes possible because the friction model contains one internal variable. This demonstrates a unique characteristic of the friction model. Unlike most friction models, the present model is capable of simultaneously modeling self-excitation and predicting stick-slip at very low sliding speed as well.

Commentary by Dr. Valentin Fuster
2002;():481-492. doi:10.1115/IMECE2002-32404.

This paper presents a control study of the Lorenz system by using feedback linearization. The effects of the state transformation on the dynamics of the Lorenz system are studied first. Then, composite controllers are developed for both stabilization and tracking of the system. The controls are designed to overcome the barrier in controllability imposed by the state transformation. The transition through the manifold defined by such a singularity is achieved by inducing the chaotic response within a boundary layer that contains the singularity. Outside this region, a conventional feedback nonlinear control is applied. In this fashion, the authority of the control is enlarged to the whole state space and the need for high control efforts is substantially mitigated. Tracking problems that involve single and cooperative objectives are studied by using the differential flatness property of the system. A good understanding of the system dynamics proves to be invaluable in the design of better controls. In all numerical examples, the proposed approach led to excellent control performances.

Commentary by Dr. Valentin Fuster
2002;():493-499. doi:10.1115/IMECE2002-32407.

This paper is Part I of a preliminary study to simultaneously control vibration and static shape deformation in flexible payloads. In Part I, the dynamics of a flexible payload grasped by an actuated gripper, which is attached to a rigid link robotic manipulator, is investigated using the component mode synthesis (CMS) method. Robot and actuator dynamics are also added to the system dynamic model to fully define the rigid body motion and elastic motion of the flexible payload. The CMS method is employed to explicitly model the coupling between the payload and actuators, and to reduce the system order. With the addition of fixed-interface quasi-static modes to fixed-interface vibration normal modes and actuator constraint modes an improved component mode representation is defined. Here, it is found that the inclusion of quasi-static modes in the CMS formulation results in increased ac curacy for simulation of dynamic behaviour of flexible payloads subject to both gravity and robot motion induced forces. Numerical examples are presented to demonstrate the effectiveness of the new component mode representation for the given robotics problem. In Part II [9], the two-time scale modeling (TSM) technique is used taking advantage of two-time scale behavior between the quasi-static modes and vibration modes in the dynamic model.

Commentary by Dr. Valentin Fuster
2002;():501-507. doi:10.1115/IMECE2002-32408.

Part I of this work models the dynamics of a flexible payload grasped by an actuated gripper undergoing large rigid body motion by a robotic manipulator. In Part II, the controllability and observability conditions of the system are discussed. In Part I, the dynamic model of the actuated flexible payload is derived using the component mode synthesis (CMS) method with addition of actuator constraint, fixed-interface vibration and quasi-static modes. Here, the two-time scale modeling (TSM) technique is employed taking advantage of the two-time scale behavior between the quasi-static modes and vibration modes in the dynamic model. Due to the complexity of the resulting system, the controllability and observability conditions are not trivial. Hence, the controllability and observability study addressed herein becomes essential in showing the advantages of using the CMS and TSM techniques in control system design for the problem. A simulation example demonstrates that simultaneous vibration and quasi-static deformation control is achievable by proper selection of each type of modes.

Topics: Motion , Grippers
Commentary by Dr. Valentin Fuster
2002;():509-514. doi:10.1115/IMECE2002-32409.

Multiple maneuvering target tracking in a dense clutter environment is investigated. An effective parallel processing algorithm based on state fusion and fast joint probabilistic data association (FJPDA) is proposed. State fusion and feedback of all state information are used to fit different movements of targets. The FJPDA combining cluster matrix decomposition with fast data association algorithm is built for tracking multiple targets. Two examples are simulated to prove the validity and reliability of the proposed new algorithm.

Topics: Algorithms
Commentary by Dr. Valentin Fuster
2002;():515-518. doi:10.1115/IMECE2002-32411.

A method for adaptive beamforming based on model transformation is presented to overcome beam distortion with colored noise in this paper. The colored noise field is changed into the white one through the instrumental variable, further, the conventional method can be used. The proposed method is feasible for adaptive beamforming in colored noise, and numerical simulations are carried out.

Topics: Noise (Sound)
Commentary by Dr. Valentin Fuster
2002;():519-528. doi:10.1115/IMECE2002-32475.

A technique is developed to predict the dynamic contact forces arising after passing road surface irregularities by a vehicle modeled as an undamped multiple-degrees-of-freedom (MDOF) system. An MDOF system moving along an uneven profile is decomposed into an aggregate of independent oscillators in the modal space, such that the response of each oscillator can be calculated independently. The technique developed is applied to the calculation of the coefficients of the harmonic components of the contact forces arising after the passage of a “cosine” pothole. The application of the technique to other problems is also discussed. One interesting phenomenon reported in the DIVINE project [1], regarding the replacement of a steel suspension by an air suspension resulted in increase of the maximum response of short-span bridges is explained by applying the technique suggested. The discussion is amply illustrated by examples of the application of the technique to the calculation of the tire forces due to a pothole for two simple—quarter-car and half-car—vehicle models.

Commentary by Dr. Valentin Fuster
2002;():531-546. doi:10.1115/IMECE2002-33416.

The stress interference effects adhesively bonded scarf and butt joints were investigated when an additional adhesive layer was incorporated in overall joint design. Finite element models were developed and analyzed to compare interfacial stress states and peak stresses on the double adhesive layer joints with those on the single adhesive layer joints with respect to the scarf angle, adhesive layer separation (ALS) and adhesive modulus. This comparison was done in terms of stress ratio calculated as a ratio of interfacial peak stress on double adhesive layer joint to that an single adhesive layer joint. The tensile task results were correlated with the finite element analysis (FEA) results in terms of load ratio calculated as a ratio of failure load on single adhesive layer joint to that on double adhesive layer joint. Six scarf angles (15°, 30°, 45°, 60°, 75° and 90°), three ALS and adhesives were analyzed for this study.

Topics: Adhesives , Stress
Commentary by Dr. Valentin Fuster
2002;():547-552. doi:10.1115/IMECE2002-33418.

This paper introduces a novel approach to increasing the loading ability of adhesive joints by adding adhesively filled columns. Following procedures are taken for making adhesive joints with adhesively filled columns: At first, holes are drilled at the overlap region of adherends, and then these holes are filled with adhesive or reinforced columns (such as reinforced fiber composite, metal columns, etc.). At the same time, adhesive is also applied on the surfaces of the overlap of adherends. After cured, the reinforced columns and adhesive in the holes form so-called adhesively filled columns. In this study, strengths of single-lap adhesive joints with adhesively filled columns were measured experimentally. Stress and strain distributions at typical positions in adhesive layer were analyzed by using Finite Element Method (FEM). Failure mechanics of the joint were analyzed. It was found that to well-bonded joints, the metal columns make the joint strength increase obviously and the joint strength increases with increasing of adherend thickness. Therefore, using reinforced columns in adhesive joints is an effective approach to generalizing adhesive joints from thin-walled joints to loading sizable bulk ones.

Commentary by Dr. Valentin Fuster
2002;():553-561. doi:10.1115/IMECE2002-33422.

In this paper, some preliminary analysis techniques are presented to help incorporate the effects of the adherend surface topography as a discrete entity in the adhesive joint composite. We believe that topographies obtained on treated surfaces can be approximated by a collection of single and/or multiple scarf, lap, or butt sections, which can be in stepped and/or straight configurations. Consequently, examples of multi-stepped double scarf joints with void, and disbond effects are illustrated to shed more light into the behavior of joints, which are not fully wetted, and contain void and/or disbond sections as a result.

Commentary by Dr. Valentin Fuster
2002;():563-567. doi:10.1115/IMECE2002-33423.

Machine structures assembled by adhesive bonding are expected to possess a high damping capacity because of the high damping capacity of the adhesive. In this study, the damping characteristics of a beam in which two steel strips are faced and joined to small butt straps by an adhesive have been investigated. The primary aim of this study was to clarify the damping characteristics of adhesively bonded structures and to establish an estimation method for the damping capacity. In the analysis, strain energy distributions in the adhesively bonded beam is derived using the strain energies and damping ratios of the two materials, i.e. the steel strips and the adhesive, which were obtained beforehand in independent experiments. The validity of the proposed estimation method for the damping capacity and the effects of the lengths of the butt straps and vibration modes on the damping capacity were confirmed by experiments. The estimated values of the damping capacity of the beam were shown to be consistent with the experimental results.

Commentary by Dr. Valentin Fuster
2002;():569-574. doi:10.1115/IMECE2002-33428.

An estimation of actual axial bolt force ill bolted joints is difficult. In practice, supersonic transducers have been used to measure the axial bolt force. However, the method is complicated and the accuracy for measuring the axial bolt force of bolts with shorter clamping length and the smaller nominal diameter is worse. It is necessary to develop a simple method to estimate the axial bolt force more accurately in practice. The displacement at the bolt head is proportional to the axial bolt force. Thus, when the relationship between the displacement and the axial bolt force is obtained, the bolt force is estimated as an inverse problem by using the bolt head displacement measured by a laser displacement transducer. In order to obtain the relationship between the displacement at the bolt head and the axial bolt force, finite element calculations were carried out. The effects of the friction coefficient between the contact surfaces of the bolt head and the clamped parts and the thickness of the clamped parts (hollow cylinder) are examined on the bolt head displacement by the FEM. As a result, the relationship between tile displacement and the axial bolt force was found to be linear by the FEM calculations. Then, the measurements of the bolt head displacement were carried out and the axial bolt force was measured by strain gauges attached at the bolt shank. By using the measured displacement and the relationship between the displacement and axial bolt force, the axial bolt force was estimated. The estimated values of the axial bolt force were in fairly good agreements with those measured by the strain gauges. It can be concluded that the method is available for measuring the axial bolt forces in bolted joints accurately.

Commentary by Dr. Valentin Fuster
2002;():575-588. doi:10.1115/IMECE2002-33432.

The effect of tapering the ends of the adherend on the joint strength and joint deformation behavior of the single lap joint geometry was studied. First, the joints were geometrically modeled using finite element (FE) techniques involving linear, as well as nonlinear (bilinear) material behavior. Then, the FEA results were compared with the experimental results for different configurations of the single lap joints, and the FEA results were found to be consistent with the experimental results with the normal and shear stresses significantly decreasing in the modified geometries over those in unmodified geometries leading to increased loading capacity in modified joints, especially with small-angle taper (~10°).

Commentary by Dr. Valentin Fuster
2002;():589-595. doi:10.1115/IMECE2002-33435.

The stress distributions in a combination joint of an adhesive with a tap bolt under external tensile loadings are analyzed in elasto-plastic deformation using a finite element method. The FEM code employed is MARC. The effects of the initial clamping force (preload), external loadings and the position of engagement screw thread on the interface stress distributions are analyzed. In addition, the stress distribution in the combination joints of the adhesive with the tap bolt is compared with that in tap bolted joint without an adhesive and the adhesive joints without the tap bolt. As the results, it is found that the stress distribution (compression) in the combination joint is less than that of bolt joints. In addition, the experiments were carried out to measure the strain of the combination joint under external tensile loads using strain gauges. Furthermore, the joint strengths under external loadings were measured. Fairly good agreements are observed between the numerical and the measured results. In addition, the usefulness of the combination joints is demonstrated in comparison with the bolted joints and the adhesive joints.

Commentary by Dr. Valentin Fuster
2002;():597-602. doi:10.1115/IMECE2002-33443.

This study deals with the stress analysis and the estimation of the sealing performance of the pipe flange connections combining a metallic gasket with an adhesive subjected to an internal pressure and a temperature change. Stress distributions at the interface between the adherends and the adhesive in the connections are analyzed by using the finite element method (FEM). From the numerical calculations, the following results are obtained: (1) the stress distributes uniformly at the interface except near the edges, (2) the stress increases as Young’s modulus of an adhesive decreases, (3) the stress becomes singular at the edges of the interfaces. In the experiments, the pipe flange connections consisting of dissimilar circular gaskets with an adhesive were manufactured, and the leakage tests of the connections were carried out by applying an internal pressure and a temperature change to the connections. From the experimental results, the following results were obtained: (1) the sealing performance increased as the width of a gasket decreased and the initial clamping stress increased, and (2) the sealing performance of the pipe flange connections subjected to a temperature change increased under a moderately high temperature.

Commentary by Dr. Valentin Fuster
2002;():603-615. doi:10.1115/IMECE2002-33447.

A mathematical procedure is developed to utilize the complementary energy method, by minimization, in order to obtain an approximate analytical solution to the 3-D stress distributions in bonded interfaces of dissimilar materials. In order to incorporate the effects of surface topography, the interface is expressed as a general surface in Cartesian coordinates, i.e., F(x, y, z) = 0 . In this paper, the parabolic interface problem, i.e., y = x2 surface is considered.

Topics: Stress
Commentary by Dr. Valentin Fuster
2002;():617-624. doi:10.1115/IMECE2002-33455.

The stress variations in butt adhesive joints of dissimilar hollow cylinders under impact tensile loadings are analyzed in elastic and elasto-plastic deformation using a finite element method. The FEM code employed is DYNA3D. The effect of Young’s modulus of the adhesive, adhesive thickness and the inside diameter of the hollow cylinders and Young’s modulus ratio between dissimilar adherends on the stress variations at the interfaces are examined. In addition, a process in rupture at the interface of the joint is analyzed. The stress distributions in the joints under static loadings are also analyzed by an FEM. The characteristics of the stress variations in the joints under impact loadings are compared with those in the joints under the static loadings. Also, the joint strenths under impact loadings are estimated. As the results, it is found that the maximum value of the maximum principal stress σl occurs at the outside of the interface. It is also found that the maximum principal stress σl at the interface decreases as the inside diameter of the hollow cylinders increases. The characteristics of the joints subjected to the impact loadings are found to be opposite to those subjected to the static loadings. In addition, the experiments were carried out to measure the strain response of the butt adhesive joints under impact tensile loads using strain gauges. Furthermore, the joint strengths under impact loadings were measured. Fairly good agreements are observed between the numerical and the measured results.

Commentary by Dr. Valentin Fuster
2002;():625-629. doi:10.1115/IMECE2002-33466.

Considering existing microscopical techniques to study microstructures of materials, one can find that non-destructive information from the internal structure of an object in natural conditions can be obtained by transmission X-ray microscopy. Combination of X-ray transmission technique with tomographical reconstruction allows to get three-dimensional information about the internal microstructure. In this case any internal area can be reconstructed as a set of flat cross sections which can be used to analyse the two- and three-dimensional morphological parameters. For X-ray methods the contrast in the images is a mixed combination of density and compositional information which provides means for non-destructive reconstruction of the internal structure. The paper presents experimental results of crack propagation and fibre bridging glass fibre epoxy samples that were collected in-situ during loading in a X-ray scanner.

Topics: X-rays , Delamination
Commentary by Dr. Valentin Fuster
2002;():631-638. doi:10.1115/IMECE2002-33473.

When designing products, it is crucial to assure failure and risk-free operation in the intended operating environment. Failures are typically studied and eliminated its much as possible during the early stages of design. The few failures that go undetected result in unacceptable damage and losses in high-risk applications where public safety is of concern. Published NASA and NTSB accident reports point to a variety of components identified as sources of failures in the reported cases. In previous work, data from these reports were processed and placed in matrix form for all the system components and failure modes encountered, and then manipulated using matrix methods to determine similarities between the different components and failure modes. In this paper, these matrices are represented in the form of a linear combination of failures modes, mathematically formed using Principal Components Analysis (PCA) decomposition. The PCA decomposition results in a low-dimensionality representation of all failure modes and components of interest, represented in a transformed coordinate system. Such a representation opens the way for efficient pattern analysis and prediction of failure modes with highest potential risks on the final product, rather than making decisions based on the large space of component and failure mode data. The mathematics of the proposed method are explained first using a simple example problem. The method is then applied to component failure data gathered from helicopter accident reports to demonstrate its potential.

Topics: Design , Databases , Failure
Commentary by Dr. Valentin Fuster
2002;():641-649. doi:10.1115/IMECE2002-39413.

This paper presents an introduction to concepts of complexity in support of assembly-oriented design, to guide the designer in creating a product with the most effective balance of manufacturing and assembly difficulty. The goal is to provide the designer with such information throughout the design process so that an efficient design is produced in the first instance. In this paper, the range of definitions and applications of the term ‘complexity’ are reviewed and then definitions appropriate for the situation are selected. The metrics required for comparison of variants of different complexity is discussed. Finally, a research agenda is presented for development of the proposed metrics within the Designers’ Sandpit project.

Topics: Design
Commentary by Dr. Valentin Fuster
2002;():651-655. doi:10.1115/IMECE2002-39415.

In spite of advances in industrial automation, manual assembly tasks continue to be an important feature of many industrial operations. In heavy part assembly, some pieces of raw material or equipment are too heavy to be safely handled by just one operator. Material handling devices such as Jib cranes or overhead cranes are employed to help operators work safer and, in some cases, faster. However, during full-load productions, access to these devices could become limited due to insufficient resources and hence, delay or extend the cycle times. The authors studied how people perform the assembly and subsequently applied Fitts’ Index of Difficulty to develop a model which indicates factors that increase the task difficulty. This model can also be used as an assembly time predictor. Since improving the efficiency of an overhead crane could significantly reduce the total cycle times and production costs, the authors modified the crane by adding a spring between the hook and the gripper to help support the weight. Two sets of experiments were conducted. The first set was to investigate the effect of spring stiffness on assembly time. The result indicated that using a spring that was too soft could create a parasitic oscillation, which increases the assembly time. The objective of the second set was to compare the assembly time of using the regular crane to that of the modified crane in situations where the part weights and the task difficulty vary. As a result of the modifications, assembly performance tended to increase by approximately 250% from using the modified crane.

Topics: Manufacturing , Design
Commentary by Dr. Valentin Fuster
2002;():657-662. doi:10.1115/IMECE2002-39416.

This paper introduces an effective new Design For Quality tool called the Assembly Reliability Evaluation Method (AREM) that visualizes assembly fault potential. The distinctive features of AREM are: (1) visualization of parts and operations having a high fault probability; (2) evaluation of shop reliability, as well as product reliability and, (3) easy data input by symbol selection as well as simultaneous assemblability evaluation; can be evaluated quantitatively. The method can be integrated with other DFX tools such as the Assemblability Evaluation Method (AEM), and the Recyclability/Disassemblability Evaluation Method (REM/DEM) to realize a comprehensive production design evaluation system.

Commentary by Dr. Valentin Fuster
2002;():663-669. doi:10.1115/IMECE2002-39417.

Assembly error prediction is one of the key problems in quality control. The objective of this paper is to develop the statistical error analysis model for assembling, to derive measures of controlling the geometric variations in assembly with multiple assembly stations, and to provide a statistical tolerance prediction/distribution toolkit integrated with CAD system for responding quickly to market opportunities with reduced manufacturing costs and improved quality. First the homogeneous transformation is used to describe the location and orientation of assembly features, parts and other related surfaces. The desired location and orientation, and the related fixturing configuration (including locator position and orientation) are automatically extracted from CAD models. The location and orientation errors are represented with differential transformations. Then the statistical error prediction model is formulated and the related algorithms are integrated with the CAD system so that the complex geometric information can be directly accessed. In the prediction model, the manufacturing process (joining) error, induced by heat deformation in welding, is taken into account. Finally case studies are presented to verify the prediction algorithms. The proposed model has following characteristics: 1) variety error elements of both design and process aspects are taken into account; 2) assembly error prediction and control can be dealt with for multiple assembly stations and multiple fixtures in each station; and 3) the technical approach is integrated with CAD system.

Commentary by Dr. Valentin Fuster
2002;():671-686. doi:10.1115/IMECE2002-39419.

The successful extraction of 3D features in mechanical parts has always been a challenging task and has yielded mixed results. Extracting features from organic shapes however is even more difficult. This is due to the fact that they are defined by both gradual and abrupt changes in surface curvature. The term curvature is explained in detail in section 4. Learning how to recognize organic shapes may give insights into better ways of performing feature recognition on mechanical parts. Determining the exact values of curvature, based on the underlying parameters can prove to be quite difficult. Curvature can be a good tool to identify features as most of the features are areas of slowly changing curvature bounded by sudden changes in curvature. The benefits of developing a generic algorithm that picks out curvature, and hence the organic features, are quite huge. This paper explains one approach taken to accomplish this task. This paper studies characteristics of the watershed algorithm[1] when applied to the features on bones. This algorithm is used to isolate features based on curvature gradients. This paper uses the knowledge from the field of anthropology and medicine to explore the sensitivity factor analysis of the watershed and its effectiveness in extracting the features on bones. The paper also compares the differences between the anatomists definition of a feature and the algorithm interpretation of the same feature.

Topics: Shapes
Commentary by Dr. Valentin Fuster
2002;():687-696. doi:10.1115/IMECE2002-39420.

Collaborative re-use of design and manufacturing data is one way that global e-commerce could significantly reduce development costs and lead times of new products. However the proliferation of web based catalogues for standard components (e.g. brochure-ware for nuts and washers etc.) only hints at the possible productivity gains if a 3D search engine could be created. Consequently the research reported here is motivated by the belief that shape matching technology is key to enabling a much deeper form of Internet-based collaborative commerce. This paper describes the coarse “shape” filters that support a 3D, Internet-based search engine, known as ShapeSifter, whose ultimate aim is to enable the location of parts already in production that have a shape similar to a desired “newly designed” part. The challenge of the research is to identify the key metrics that produce meaningful characterizations of 3D models for similarity comparison purposes. In this context the work reported focuses on the use of novel indices based on an object’s convex-hull and surface area distribution to carry out a coarse filtering of candidates prior to the application of more detailed analysis (e.g. the construction of multi-dimensional feature vectors). In doing this, the paper describes the crucial role played by a benchmark database of geometrical similar objects.

Topics: Filters , Shapes
Commentary by Dr. Valentin Fuster
2002;():697-705. doi:10.1115/IMECE2002-39422.

Research has shown that nearly 80% of the costs and problems are created in product development and that cost and quality are essentially designed into products in the conceptual stage. Currently failure identification procedures (such as FMEA, FMECA and FTA) and design of experiments are being used for quality control and for the detection of potential failure modes during the detail design stage or post-product launch. Though all of these methods have their own advantages, they do not give information as to what are the predominant failures that a designer should focus on while designing a product. This work uses a functional approach to identify failure modes, which hypothesizes that similarities exist between different failure modes based on the functionality of the product/component. In this paper, a statistical clustering procedure is proposed to retrieve information on the set of predominant failures that a function experiences. The various stages of the methodology are illustrated using a hypothetical design example.

Topics: Failure
Commentary by Dr. Valentin Fuster
2002;():707-715. doi:10.1115/IMECE2002-39425.

A genetic algorithm based welding planner capable of using parametric features to determine the manufacturing cost of welded assemblies has been developed. Parametric weld feature information obtained from a CAD system is translated to a hybrid traveling salesman problem. A genetic algorithm is used to search for a sequence of welds that minimizes the cost of the welded assembly. Emphasis is placed on developing a mechanistic, feature based DFM tool, with the aim of rapidly providing welded assembly cost feedback to the designer in a CAD environment, while maintaining a balance between accuracy and computational speed.

Commentary by Dr. Valentin Fuster
2002;():717-729. doi:10.1115/IMECE2002-39426.

This paper describes an algorithm for automated design of multi-stage molds for manufacturing multi-material objects using multi-shot injection molding process. The algorithm described in this paper is a significant improvement over our previous algorithm [15] that worked on multi-material objects with simple planar interfaces. In the multi-stage molding process, the desired multi-material object is produced by carrying out multiple molding operations in a sequence, adding one material in the target object in each mold-stage. Each mold-stage can add only one type of material. Therefore, we need a sequence of mold-stages such that (1) each mold-stage adds a single-material component either fully or partially, and (2) the molding sequence completely produces the desired object. We expect that our algorithm will provide the necessary foundations for automating the design of multi-stage molds and therefore will help in significantly reducing the mold manufacturing lead-time.

Topics: Algorithms , Design
Commentary by Dr. Valentin Fuster
2002;():731-735. doi:10.1115/IMECE2002-39427.

This paper addresses the kinematics design and analysis of a special class of mechanical presses used for deep drawing and ironing process. The key design objectives are to obtain a longer stroke and a quicker punch return. From the kinematics equations, it is shown that the horizontal quick return mechanism exhibits the preferred characteristics. The behavior of the press is studied based on the placement of the links. The kinematics constraints are observed and the placement of press components to achieve better performance is summarized.

Commentary by Dr. Valentin Fuster
2002;():739-744. doi:10.1115/IMECE2002-39468.

Micro-electro-mechanical systems (MEMS) and nanotechnology are a fast developing technology which combines very small mechanical structures with microelectronics circuits. These devices range in scale from nanometers (10−9 m) to several millimeters, and they are fabricated using the established techniques of microelectronics construction. Due to the increasingly large size and opportunities in these fields, it is becoming necessary to offer course work with small systems for students at the undergraduate and graduate level. A course in MEMS/NEMS small systems was taught at the University of Nevada, Reno in the spring of 2002. The course used the text written by Hsu [1] along with supplementary material. Problems and examples of applying fundamental principles from mechanics, electromagnetism, thermodynamics and optics among others to problems in MEMS design, fabrication and actuation were considered. The course is primarily designed to introduce both engineering undergraduate and graduate students to the possibilities of this exciting new engineering field. Also, current MEMS, NEMS, and microfluidic applications, such as sensors, actuators, heat exchangers, and chemical/biological analysis systems, were discussed. The course introduced a broad spectrum of topics related to small system development including basic engineering science for small system design, engineering mechanics, thermofluid engineering, scaling laws, materials for small systems, fabrication technologies, small system design, advanced nano-materials (molecular motors, nanotubes, polymer nanocomposites), standard characterization techniques: SEM, TEM, AFM, and applications (MEMS, NEMS and microfluidics).

Commentary by Dr. Valentin Fuster
2002;():745-748. doi:10.1115/IMECE2002-39469.

A mechatronics course has been recently introduced as a 4th year elective at the University of Saskatchewan Department of Mechanical Engineering. The necessity and the rational for this training are reviewed. A curriculum for the course is proposed supported by student feedback following its first year of introduction. The curriculum and the structure of the course is such that training in mechatronics may be provided through an elective course. Notwithstanding, the merits of establishing a degree in mechatronics are discussed given the strong industrial demand for this topic.

Commentary by Dr. Valentin Fuster
2002;():749-756. doi:10.1115/IMECE2002-39471.

This paper addresses an approach to improve the quality of engineering education by incorporating research components into the teaching in the form of team projects. By reflecting the author’s experience on teaching an undergraduate junior course – ME106/EE106 Mechatronics, the feasibility and effectiveness of this approach is demonstrated. It is shown that integrating research activities, industry sponsored projects, lab construction, and national student design contests into teaching helps improving the quality of engineering education. Properly integrating research activities into classroom also helps the faculty to maintain the dynamic balance between the teaching and research.

Commentary by Dr. Valentin Fuster
2002;():757-762. doi:10.1115/IMECE2002-32085.

Our group is developing a new project-centered “Freshman Engineering Graphics and Design” course. The project-centered approach emphasizes a desire for individual learning, teamwork, and communication abilities using modern computer graphics tools. The modular graphics and design curriculum emphasizes the development of a 3-D geometric computer model and application of this digital database to design analysis, simulation, prototyping, and documentation. The students work as a team to dissect a common mechanical assembly. They measure the parts, make hand sketches, build computer models, perform various analyses, and make rapid prototypes of their assembly. At the conclusion of this integrated graphics and design project, the team assembles a final report. This paper presents some preliminary results in implementing these new course objectives in the Spring 2002 semester.

Commentary by Dr. Valentin Fuster
2002;():763-769. doi:10.1115/IMECE2002-32086.

Since 1998 the author has been developing and teaching computer aided design and computer aided engineering courses intended for mechanical engineering students using the Pro/ENGINEER and I-DEAS software systems. An outline of one of these courses is given and the experience related to another such course is discussed in detail. Students find these courses challenging and enjoyable. The success rate has regularly been very high. By taking such CAD/CAE courses and learning these widely used industry-standard, high-end software systems the students gain valuable experience directly applicable as they join the workforce. The participating students have regularly rated these courses among the most popular ones. The paper discusses the author’s experiences in developing and teaching courses in CAD and CAE, which utilize high-end software. It is intended to provide two examples of successful blends of theoretical and practical topics that have worked very well.

Commentary by Dr. Valentin Fuster
2002;():771-775. doi:10.1115/IMECE2002-32152.

This paper presents initial planning for the development of a process control breadboard system. The proposed system will be composed of mechatronic, thermal/fluid, and control elements that using simple hand tools can be easily reconfigured by undergraduate students. An approach for integrating the breadboard system throughout the curriculum, enhancing the design education experience beginning with freshmen and continuing through the senior capstone experience, is proposed. This system is expected to significantly enhance the ability of students to work with a thermal/fluid-based process control system, and to provide the opportunity for design/build/test realization for a variety of completely functional systems. A sampling of configurations will be presented to demonstrate how this proposed system might be used to address an open-ended design problem with external constraints. A comparison with existing educational trainer systems commonly found at academic institutions will be presented, along with preparations for a proof-of-concept adaptation to occur during the fall semester of 2002. Support for K-12 outreach activities and EC2000 professional component program criteria will also be discussed.

Commentary by Dr. Valentin Fuster
2002;():777-783. doi:10.1115/IMECE2002-39224.

This paper investigates the identification of mechanisms of disc brake squeal by the application of a recently developed Empirical Mode Decomposition method (EMD). A known strength of the EMD is its adaptive nature in analyzing nonstationary data, with success in its original application to ocean mechanics. The EMD decomposes an original signal into a number of intrinsic mode functions (IMFs), with each IMF often containing distinct physical significance. Several sets of disc brake squeal data were obtained and processed by EMD. A typical set data is presented in this paper for discussion. Employing a sifting process in the EMD, four prominent squeal-related IMFs are identified in this set of data. The Hilbert transform is then used to analyze the frequency and amplitude contents of the four IMFs, and it is shown that the first IMF is dominant. The spectrogram method is applied to analyze the time-evolution of the frequency components of the IMFs in the squeal process. This analysis procedure confirms an important squeal mechanism, i.e., the squeal condition is governed by the coupling of in-plane and out-of-plane vibration modes of the rotor and the coalescence of their natural frequencies. The inverse approach outlined in this paper is shown to be useful for providing new insights and confirming established hypotheses of disc brake squeal.

Commentary by Dr. Valentin Fuster
2002;():785-791. doi:10.1115/IMECE2002-39225.

As the result of vibration emission in air, the mechanical noise signal carries affluent information about the working condition of machinery and it can be used in mechanical fault diagnosis. But in practice, the measured sound signal is usually the mixing of condition signal and other uncorrelated signals. And the signal received is usually of very low SNR. Therefore, to obtain the features of original signals, the mixed signals have to be separated and the uncorrelated signals have to be removed by means of the blind source separation technique. The BSS is a class of signal processing method that can recover the original signals according to the observed mixing signals. In application of BSS algorithms, it is generally supposed that the number of sources is known. But unfortunately, this is not the case in application. Then, before applying the BSS method, the singular-value analysis method is introduced to estimate the number of sound sources at first. On the other hand, to avoid the ill-conditioned problem caused by environment noise and/or measuring noise in applying BSS method, the partial singular-value analysis method is employed to select those signals with maximum information entropy from mixed signals. This method significantly reduces the distortion of separated signals. Afterward, the second order blind identification (SOBI) algorithm, one of the BSS methods, which only relies on the second order statistics of measuring signals, is utilized and it is modified, in this paper, especially for purpose of spectra separation. Finally, the spectra separation results obtained from the mixed signals measured in a semi-anechoic chamber demonstrate the availability of the presented method.

Commentary by Dr. Valentin Fuster
2002;():793-800. doi:10.1115/IMECE2002-39226.

Dynamical instability induced by the initiation and advancement of mechanical faults in rotary elements is detrimental to the reliability and operation safety of the entire system. The inherent nonlinearity associated with bifurcation presents itself as difficulties in identifying and isolating features indicative of the presence and progression of faults that could lead to eventual mechanical deterioration. The perturbed and deteriorated states of a bearing-shaft system subjected to the actions of two types of commonly seen mechanical faults, namely, rotor speed and imbalance, are investigated using the basic notion of instantaneous frequency. The presented approach realizes temporal events of both short and long time scales as instantaneous frequencies in the joint time-frequency domain and thus effectively uncouples the harmonic components resulted from the coupling of multitude faults. Examples are given to demonstrate the feasibility of applying the approach to the characterization of various deteriorating bearing states and the identification of parameters associated with various modes of instability and chaotic response.

Commentary by Dr. Valentin Fuster
2002;():801-806. doi:10.1115/IMECE2002-39227.

Sensitivity analysis is an essential component in the design of structural/acoustic systems. Current structural/acoustic sensitivity algorithms assume deterministic system design parameters and therefore predict changes in the deterministic response of the system. Due to variability associated with manufacturing tolerances most structural/acoustic systems consist of random and deterministic structural design parameters and therefore produce a probabilistic acoustic response. In this work, a structural/acoustic sensitivity algorithm is presented that considers systems comprised of random and deterministic design parameters. The new sensitivity algorithm calculates the change in the probabilistic vibro-acoustic response of a system due to a change in a deterministic design parameter. The new algorithm uses boundary element analysis, finite element analysis, and an advanced mean value method. An elastically supported panel subject to a non-uniform load is used to illustrate the algorithm. Variability is considered in the elastic support while structural sizing parameters are taken to be deterministic. The response of the panel is defined in terms of probabilistic radiated sound power. Probabilistic sound power sensitivity results are calculated and used to predict new sound power values via finite difference analysis. These results are compared successfully to results obtained through re-analysis.

Commentary by Dr. Valentin Fuster
2002;():807-811. doi:10.1115/IMECE2002-39228.

In the current literature, most assessments for speech privacy and speech intelligibility are relying on the subjective measurements utilized with the test materials of English and other Western languages. Effects of different languages and accents in speech privacy and speech intelligibility are usually overseen. This study aims at the speech privacy assessment of closed offices in multicultural environments. Subjective measurements are conducted in this study for closed offices by using English and a tonal language. The evaluation differences in speech privacy between the two languages are evident and significant. It is also found in this study that the existing single word tests used in research and industrial practice for subjectively evaluating speech privacy should be modified when closed spaces are considered. The subjective measurement results of this study are also compared with the objective measurement indices AI.

Commentary by Dr. Valentin Fuster
2002;():813-817. doi:10.1115/IMECE2002-39229.

A finite element model for a generator-bearing system with asymmetrical stiffness is developed for investigation of the double frequency vibration. The modal reduction method is used for reducing the degrees of freedom system to improve computing efficiency, and the Newmark direct integration method is employed to solve the reduced motion equations. The two-modal interaction vibration is induced when the rotation speed is half a critical speed of the system due to asymmetry and gravity force of the generator. Such a phenomena is observed in the practical test.

Commentary by Dr. Valentin Fuster
2002;():819-824. doi:10.1115/IMECE2002-39604.

This paper presents a method for the thermal crack evaluation of railroad wheel materials and the results. The research investigated the basic thermal crack resistance as a low cycle fatigue behavior in terms of Δεt -Ni and da/dN-ΔK. In order to be able to evaluate such material characteristics in service by experimentation, reproducible conditions such as similar stress-strain, temperature rise, and damage morphology are required. The methods proposed in the past for high temperature low cycle fatigue or thermal shock such as Coffin’s and Manson’s methods do not provide the above conditions at the same time for thermal cracks in railroad wheels. The material design to avoid such thermal damages has not yet been established. Therefore, a simple brake tester with a special device for measuring radial deflection converted into strain was designed and manufactured. The relations of Δεt -Ni and da/dN-ΔK, which have not been clarified for thermal crack behavior in railroad wheels, were obtained for wheel materials by experiment using this new device. To predict the life of a wheel, one must know the real service conditions from field measurements. Once the histogram of the initial brake speed, intensity of brake application, and number of brakings from the initial speed is obtained, the histogram can be converted into the relation of strain range and number of cycles. The calculation of cycles for crack origination and propagation is possible based on the experimental results on Δεt -Ni and da/dN-ΔK. From the material data of fracture toughness and possible residual stress value in the field, the critical crack length for wheel fracture can be then estimated, and the life from the cycles to the critical length is estimated. This method will provide the appropriate maintenance schedule to prevent wheel fracture.

Commentary by Dr. Valentin Fuster
2002;():825-833. doi:10.1115/IMECE2002-39605.

This paper is a study of avoiding failures during the assembly of a trunnion-hub-girder (THG) for bascule bridges. The currently used assembly procedure, AP#1, cools the trunnion for a shrink fit into the hub, followed by cooling of the trunnion-hub assembly to shrink fit it into the girder. During assembly, using AP#1, development of cracks on the hub was observed in one THG assembly. Yet, during another assembly, the trunnion got stuck in the hub before it could be fully inserted. A complete analytical, numerical, and experimental study was conducted to understand these failures, and the results were used to develop specifications and recommendations for assembly. The causes of failures include development of high stresses at low temperatures during assembly, while noting that fracture toughness of THG material decreases with temperature. Recommended specifications included following an alternative assembly procedure that doubled allowable crack length, and lower cooling temperatures to avoid trunnions sticking in the hub.

Commentary by Dr. Valentin Fuster
2002;():835. doi:10.1115/IMECE2002-39423.

Realization of successful recycling of end-of-life products greatly depends on, as well as environmentally conscious, whether the recycling process can be made economically feasible. We regard the ease of product recycling as indispensable in order to realize a feasible recycling process. In order to make products easier to recycle, it is necessary to take the ease of disassembly, processing and final treatment into consideration at the design stage. Therefore, an advanced evaluation method that can evaluate a product’s ease of recycling, with minimal prototyping and testing of the product is required at the early design stage. In answer to this, we have developed the Recyclability Evaluation Method (REM). In this paper, the theory of the method, procedure and the structure of the system are presented and a number of application examples are given.

Commentary by Dr. Valentin Fuster

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