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ASME Conference Presenter Attendance Policy and Archival Proceedings

2017;():V008T00A001. doi:10.1115/DETC2017-NS8.
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This online compilation of papers from the ASME 2017 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference (IDETC/CIE2017) represents the archival version of the Conference Proceedings. According to ASME’s conference presenter attendance policy, if a paper is not presented at the Conference by an author of the paper, the paper will not be published in the official archival Proceedings, which are registered with the Library of Congress and are submitted for abstracting and indexing. The paper also will not be published in The ASME Digital Collection and may not be cited as a published paper.

Commentary by Dr. Valentin Fuster

29th Conference on Mechanical Vibration and Noise: Dynamics and Control of Biomechanical Systems

2017;():V008T12A001. doi:10.1115/DETC2017-67614.

This work investigates the human leg joint contact characteristics during a drop-landing exercise. The contact characteristics consist of tibio-femoral contact forces and contact point, and hip contact forces. An inverse dynamics 2-D model of human leg is used on this ballistic task in order to simplify computation. Experimental data used show a maximum of 100 degrees of flexion angle and ground reaction forces up to 4 times the body weight. All contact forces show a pattern in which they reach large magnitudes at the beginning of landing, decreasing as the subject end the exercise with a standing position.

Commentary by Dr. Valentin Fuster

29th Conference on Mechanical Vibration and Noise: Dynamics of Mechanical and Acoustic Metamaterials

2017;():V008T12A002. doi:10.1115/DETC2017-67552.

This research investigates the sound insulation properties — sound absorption coefficient and transmission loss — of a double porosity metamaterial and the functional dependence of such properties on the selection of underlying poroelastic material. The internal metamaterial geometry enables a global rotation phenomenon when the system is under a static compression. Using the finite element method, the influence of such compression upon the acoustic properties is quantified for its role in enhancing and tailoring sound insulation characteristics, while the additional influence of embedded rigid inclusions is examined. By applying these concepts to metamaterials composed from different poroelastic media, it is found that the acoustic properties can be tuned over strategic frequency ranges of relevance for sound insulation. In particular, the results demonstrate that for certain metamaterial compositions the absorption coefficient can be increased by about 100% and the transmission loss enhanced by 20% across a broad range of low frequencies by the introduction of the inclusions, while the compression constraint can increase the properties by 10 to 20% across narrow frequency bands. The outcomes suggest new possibilities for greatly enhancing the acoustic insulation properties of poroelastic materials in applications where space is limited and/or where added mass is not a concern.

Commentary by Dr. Valentin Fuster

29th Conference on Mechanical Vibration and Noise: Dynamics of MEMS and NEMS (VIB/MNS/MSNDC)

2017;():V008T12A003. doi:10.1115/DETC2017-68277.

Cantilevered configurations of thin beams are used in numerous conventional and emerging applications of mechanical, aerospace, and civil engineering, as well as material science. In many resonant scenarios, nonlinearities are inevitably pronounced under moderate to large intensity excitations. Other than dissipative nonlinearities due to internal and external damping mechanisms, and in the absence of material nonlinearities such as those of piezoelectricity, two types of nonlinearities are pronounced for large amplitude dynamics of Euler-Bernoulli cantilevers in the first bending mode: stiffness hardening due to nonlinear curvature and inertial softening. While these two counteracting nonlinearities are both of cubic order, it can be shown theoretically that the geometric hardening always dominates inertial softening for the response of the first bending mode, and therefore one does not expect softening in the resulting dynamics. Most of the existing experiments in conventional structures are aligned with this theoretical expectation. Recent efforts in NEMS cantilevers resulted in experimental data with a softening nonlinearity instead of the classical overall hardening for the first bending mode. The perplexing results made some authors suggest that the Euler-Bernoulli theory was not sufficient to capture the resulting dynamics, and that a new theory would be required. In the present work, we hypothesize that the observed softening effect in the fundamental resonance may be a result of the asymmetric boundary condition of the NEMS cantilever (due to its fabrication) at the clamped end such that the cantilever experiences two different boundary conditions in the two halves of the oscillation cycle. We show both theoretically and experimentally that such uneven boundary conditions indeed result in softening behavior in the first bending mode, while the evenly clamped case yields the expected hardening.

Commentary by Dr. Valentin Fuster
2017;():V008T12A004. doi:10.1115/DETC2017-68317.

Chaotic behavior of an embedded carbon nanotube subjected to an external excitation and the combinational static-dynamic axial loads is investigated. Mathematical formulation has been developed based on the non-local theory in order to reflect the small-scale effects. The tube is supported by the Kelvin-Voigt viscoelastic foundation and the Galerkin method is utilized to solve the governing nonlinear differential equations. The vibration behavior of the system for the parameters of a real model is studied and different vibration responses of the nanotube such as the periodic, quasi-periodic and the chaotic behaviors are detected. The bifurcation diagrams for several critical parameters, including the amplitude of external excitation and the axial applied load are presented. The time history diagram, phase-plane trajectories, and the Poincaré map are presented as the three appropriate techniques for diagnosing the system behavior under various conditions.

Commentary by Dr. Valentin Fuster

29th Conference on Mechanical Vibration and Noise: Emerging Systems and Applications

2017;():V008T12A005. doi:10.1115/DETC2017-67774.

Rotating and vibro-impact Nonlinear Energy Sinks (NESs) have been employed for rapid and passive Targeted Energy Transfer (TET). Both have been proven to be efficient, shown high energy dissipation and have been tested experimentally. A novel type of NES that combines the two principles of nonlinear TET, rotating inertial coupling and vibro-impact, is numerically investigated on a 2 degree of freedom physical system. Two configurations of the new promising NES are considered via changing the location of the impacts. The optimized parameters of both configurations proved that high amounts of energy can be transferred from the primary system to the new promising type of NESs passively and rapidly.

Commentary by Dr. Valentin Fuster
2017;():V008T12A006. doi:10.1115/DETC2017-67787.

The piston impacts against the cylinder liner are the most significant sources of mechanical noise in internal combustion engines. Conventionally, the severity of impacts is reduced through the modification of physical and geometrical characteristics of components in the piston assembly. These methods effectively reduce power losses at certain engine operating conditions. Moreover, the conditions leading to the reduction in power losses inversely increase the engine noise due to piston impacts. An alternative control method that is robust to fluctuations in engine operating conditions is anticipated to improve the engine’s NVH performance whilst exacerbation in power loss remains within the limits of the conventional methods. The concept of Targeted Energy Transfer (TET) through the use of Nonlinear Energy Sinks (NES) has not been applied yet in automotive powertrains. Numerical studies have shown a potential in reducing the severity of impact dynamics by controlling piston’s secondary motion. The power loss of a piston equipped with a nonlinear energy sink is investigated in this study.

Commentary by Dr. Valentin Fuster

29th Conference on Mechanical Vibration and Noise: Industrial Applications of Dynamics, Vibration, and Acoustics (VIB/MSNDC 11)

2017;():V008T12A007. doi:10.1115/DETC2017-67365.

The focus of this investigation was to computationally determine the vibrational characteristics of a rear fuselage mounted aircraft engine support frame. A pseudo-orthogonality check was performed to compare the computational results with experimental data. This produced a matrix with 8 modes with diagonal terms >0.9. Structural modifications were made to the computational model of the frame in order to decrease the modal density near the blade pass frequency of the engine at cruise conditions. Two independent modifications to the frame decreased the modal density within 1% of the critical engine frequency from seven to five and four respectively. It was shown that the modifications produced non-intuitive results, as each modification had a different significance in terms of how it affected each mode of the system. It is recommended that computational analysis be performed on similar structures before such modifications are put in place, as there is low predictability of how different modifications will affect the modal properties of the system.

Commentary by Dr. Valentin Fuster
2017;():V008T12A008. doi:10.1115/DETC2017-67389.

Experimental modal testing using an impact hammer is a commonly used method for obtaining the modal parameters of any structure for which the vibrational behavior is of interest. Natural frequencies and associated mode shapes of the structure can be extracted directly from measured FRFs (Frequency Response Functions) through various curve fitting procedures. This paper provides an overview of the modal testing conducted on an aerospace component. Testing set-up, experimental equipment and the methodology employed are all described in detail. Further validation of the testing procedure was done by ensuring that the experimental results satisfy the requirements of repeatability, reciprocity and linearity. The relevant ISO standard has been referenced and important concepts to modal analysis are expanded upon. Recorded natural frequencies, coherence and a description of the observed mode shapes are presented along with notable trends.

Commentary by Dr. Valentin Fuster
2017;():V008T12A009. doi:10.1115/DETC2017-67450.

Many times, nonlinearities are seen as a burden in the design process as they can result in unpredictable and extremely sensitive response. As such, engineers make design changes to effectively minimize or completely eliminate the nonlinear behavior. In this paper, the periodic response of a buckled beams under piezo-excitation is considered. An optimization approach, as first demonstrated in [1], is utilized that achieves maximum amplitude, periodic, and stable responses of the beam systems. Case studies are presented that demonstrate the utility of this optimization approach to exploit the nonlinear dynamics to achieve desired responses.

Commentary by Dr. Valentin Fuster
2017;():V008T12A010. doi:10.1115/DETC2017-67460.

Gear condition indicators are one of the most important gear transmission fault detection and diagnosis techniques. Various kinds of condition indicators for different kinds of gear fault types (e.g. tooth crack, wear, eccentricity, etc.) have been proposed in the past several decades. However, their relative effectiveness, especially in light of some newly proposed indicators, on gear fault detection or diagnosis has not been fully evaluated. Performance assessment of gear fault condition indicators is not only helpful in designing new advanced indicators but also important for the development of a reliable Condition Based Maintenance (CBM) system. The objective of this paper is to verify and compare the relative performances of twenty-one selected gear condition indicators as applied to a progressive gear tooth crack under constant load and speed working conditions. The main goals are to identify which indicators are sensitive to the fault or have the capability to detect the initial tooth crack and therefore to recommend the most effective gear condition indicators. Dynamic simulations were used to generate the vibration signals which reflect the real underlying vibration behavior of the transmission system. Based on the simulated results, the performances of the selected indicators under noise-free as well as various signal to noise ratio conditions were evaluated and compared. Results indicate that many of the selected indicators are effective for the detection of the progressive tooth crack only under noise-free conditions, and the indicators that only consider time or frequency domain features, such as RMS, Kurtosis, energy ratio, sideband index, are generally less able to detect a tooth crack at an early stage compared to the methods based on reconstructed signals, such as the NA4, FM4, M6A, M8A.

Commentary by Dr. Valentin Fuster
2017;():V008T12A011. doi:10.1115/DETC2017-67548.

This paper develops recursive least-squares (RLS) and extended Kalman filtering (EKF) approaches for estimating uncertain engine friction (and other) parameters necessary for successful implementation of a two-scale command shaping (TSCS) engine restart strategy. The TSCS strategy has been developed for mitigating vibrations in conventional and hybrid electric vehicle (HEV) powertrains during internal combustion engine (ICE) restart. Implementing the TSCS strategy increases the drivability of a HEV by reducing noise, vibration, and harshness (NVH) issues associated with ICE restart during a powertrain mode transition. This is accomplished primarily, by modifying the electric machine (EM) torque profile with linear and time-varying components over multiple time scales. For full implementation, the TSCS strategy requires input parameters characterizing the ICE which may be a) difficult to quantify, and/or b) uncertain due to their dependence on engine operating temperature and other environmental considerations. RLS and EKF algorithms tailored to TSCS are presented herein for estimating these parameters. It is shown that both the RLS and EKF algorithms can be used to estimate the necessary ICE parameters and increase effectiveness of the TSCS strategy. The EKF algorithm, in particular, estimates uncertain ICE parameters with minimal measurement requirements, giving it an advantage over the presented RLS algorithm.

Commentary by Dr. Valentin Fuster
2017;():V008T12A012. doi:10.1115/DETC2017-68130.

Aeolian vibrations are the major cause for the failure of conductor cables. Using a Stockbridge damper reduces these vibrations and increases the life span of the conductor cable. Designing an efficient Stockbridge damper that suits the conductor cable requires a robust mathematical model with minimum assumptions. However it is not easy to analytically model the complex geometry of the messenger. Since, the messenger is a bunch of thin helical wires with nonlinear contact conditions. Therefore an equivalent stiffness must be determined so that it can be used in the analytical model. This paper examines the bending stiffness of the cable and discusses the effect of this stiffness on the natural frequencies. The obtained equivalent stiffness compensates for the assumption of modeling the messenger as a rod. The results from the free vibration analysis of the analytical model with the equivalent stiffness is validated using the full scale finite element model of the Stockbridge damper.

Commentary by Dr. Valentin Fuster

29th Conference on Mechanical Vibration and Noise: Jointed Structures, Contact, Friction, and Damping (VIB/MSNDC 10-5)

2017;():V008T12A013. doi:10.1115/DETC2017-67007.

Two key properties of a vibrating structure are the frequencies at which it resonates and its ability to absorb energy. For a linear structure, these properties are characterised by the natural frequencies and the damping ratios. For nonlinear systems, such properties may not exist and equivalents must be sought. A method of measuring equivalent properties has been developed for nonlinear systems by examining the decaying vibration time history following excitation of the system.

In a first stage, the time history is filtered to separate out a frequency range of interest. In the second stage, which is the main concern of this paper, instantaneous values of natural frequencies and damping ratios are extracted from the decaying time history by means of a curve fitting process. The curve fitting involves finding four parameters two of which are the instantaneous natural frequency and damping ratio and two more which account for the amplitude and phase. The curve fitting is a minimisation process which is divided into two stages. For each minimisation step, the amplitude and phase are extracted first. It is shown that this may be done in a one-step process. Next the frequency and damping are determined. This is found to be a straightforward although more difficult process. The key to simplifying the problem is to recast the model in a favourable form that reduces the curve fitting process from one of finding four parameters to finding just two. The procedure is found to be robust and capable of detailed investigation.

Topics: Damping
Commentary by Dr. Valentin Fuster
2017;():V008T12A014. doi:10.1115/DETC2017-67008.

The dynamics of structures built-up from components connected by bolted joints are not well understood. Experiments were conducted with bolted joints in a shear configuration in which instantaneous vibration frequencies and damping could be measured. A system with bolted joints was excited and the free vibration decay measured. As the vibration decays, the damping decreases and the frequencies increase.

This suggests a new interpretation for the contact patch in a bolted joint, involving bound, slipping and alternating regions. The changing size of the bound region controls the instantaneous frequencies and the relative displacement inside the slipping region and the alternating region controls the damping behaviour.

Shims of different lengths enabled the behaviour of the contact patch to be investigated. A clear trend exists between the length of the shims and the non-linear dynamic behaviour. The introduction of multiple shims did not increase the damping or alter the dynamic nonlinear behaviour. The introduction of grease into the bolted joint increased the damping but oil did not. The vibration measurements enable the size of the contact patch to be estimated.

Topics: Bolted joints
Commentary by Dr. Valentin Fuster
2017;():V008T12A015. doi:10.1115/DETC2017-67379.

Analysis of the influence of cracks on the dynamics of structures is critical for design, failure prognosis, and structural health monitoring. Predicting the dynamics of complex cracked structures is computationally challenging for two reasons: (1) the model size is generally large, and (2) the piecewise-linear nonlinearity caused by contact eliminates the use of linear analysis tools. Recently, a technique referred to as X-Xr approach was developed to efficiently reduce the model size of cracked structures. The method employs relative coordinates to describe the motion of crack surfaces such that an effective model reduction can be achieved using Craig-Bampton component mode synthesis. More recently, a method referred to as the generalized bilinear amplitude approximation (generalized BAA) was developed to approximate the amplitude and frequency of piecewise-linear nonlinear systems. This paper modifies the generalized BAA method and combines it with the X-Xr approach to efficiently predict the dynamics of complex cracked structures. The combined method is able to estimate the amplitude and frequency of cracked systems with a reduced computational effort. The proposed approach is demonstrated on a three degree of freedom spring-mass system and a cracked cantilever beam.

Commentary by Dr. Valentin Fuster
2017;():V008T12A016. doi:10.1115/DETC2017-67524.

High cycle fatigue damage caused by resonance can significantly affect the reliability and life of rotor blades in turbomachinery. Dry friction damper is widely used in vibration reduction design of joint components because of its excellent performance. To predict the vibration response of rotor blades with friction damper, it’s necessary to analyze the pressure distribution of contact area and determine the contact state of each point. Most researchers focused on the construction and improvement of friction models, and assumed that only the normal pressure distribution decides where slip and stick areas are, but the shear traction also play a role.

In this paper, a novel method is proposed to quantitatively conduct the slip-stick area analysis of contact surface by means of theoretical derivation and numerical simulation. Both the non-dimensional normal pressure and shear traction distribution are obtained for different contact conditions. It is found that both the normal pressure and shear traction of each point dominate its contact state. Moreover, the area at contact edges always begins slipping firstly, even if the normal pressure there is much larger than contact center. The developed method will also help to establish more accurate partial-slip model for various jointed structures with friction damping.

Topics: Friction , Dampers , Rotors , Blades
Commentary by Dr. Valentin Fuster
2017;():V008T12A017. doi:10.1115/DETC2017-67553.

Structural dynamics models with localized nonlinearities can be reduced using Hurty/Craig-Bampton component mode synthesis methods. The interior degrees-of-freedom of the linear subcomponents are reduced with a set of dynamic fixed-interface modes while the static constraint modes preserve the physical coordinates at which the nonlinear restoring forces are applied. For finite element models with a highly refined mesh at the boundary, a secondary modal analysis can be performed to reduce the interface down to a truncated set of local-level characteristic constraint modes. In this research, the cost savings and accuracy of the interface reduction technique are evaluated on a simple example problem involving two elastic blocks coming into contact.

Commentary by Dr. Valentin Fuster
2017;():V008T12A018. doi:10.1115/DETC2017-67712.

A method is proposed for fitting the so-called contact stiffnesses (CSs) of interface elements for a nonlinear dynamic model (NDM) of a bladed disk with integral contact couplings. The method is based on comparison between frequencies of the resonant response of NDM and known natural frequencies in limiting linear cases. For this purpose, an effective approach for calculation of the resonant response NDM is presented allowing CSs to be picked individually. The method is demonstrated for the case of steam turbine bladed disk equipped with 48 inch blades.

Topics: Steam turbines
Commentary by Dr. Valentin Fuster
2017;():V008T12A019. doi:10.1115/DETC2017-67859.

Bolted joints are common in assembled structures and are a large contributor to the damping in these assemblies. The joints can cause the structure to behave nonlinearly, and introduce uncertainty because the effective stiffness and damping at the joint are typically unknown. Consequently, improved modeling methods are desired that will address the nonlinearity of the jointed structured while also providing reasonable predictions of the effective stiffness and damping of the joint as a function of loading.

A method proposed by Festjens, Chevallier and Dion addresses this by using a sort of nonlinear modal analysis based on the response of the structure to quasi-static loading. This was further developed by Allen and Lacayo and thoroughly demonstrated for structures with discrete Iwan joints. This work explores the efficacy of quasi-static modal analysis for 2D and 3D finite element models in which the geometry, contact pressure and friction in the joint are modeled in detail. The mesh density, contact laws, and other solver settings are explored to understand what is needed to obtain convergence for this type of problem. For the 2D case study, the effect of bolt preload and coefficient of friction are explored and shown to produce reasonable trends. Three dimensional models prove far more challenging and significant effort was required to obtain convergence and then to obtain results that are physically realistic; these efforts are reported as well as the lessons learned.

Commentary by Dr. Valentin Fuster
2017;():V008T12A020. doi:10.1115/DETC2017-68069.

The resonance frequency, stiffness, and damping of a structure with screws, bolts, or rivets is strongly influenced by the nonlinear interaction of connected faying surfaces. During the design phase of built-up systems, those system properties and their uncertainty must be understood to meet vibroacoustic design criteria. However, the frictional interaction of fastened joints is poorly understood, and hypotheses are still being made in an attempt to explain the causes of damping in fastened joints. Friction models that do exist either require onerous methods or are overly simplistic. To provide measured data to support future model development, this research uses experimental modal analysis and a time-domain approach to track damping via the ringdown of a pair of plates with a fastened joint with varying applied torques. Amplitude-dependent plots of the loss factor for several modes are provided, which represent the system better than their single-value counterparts. Frequency decrements due to increased fastener torque were less than one-half of a percent in the presented modes. Counterintuitively, increasing fastener torque in the experiment increased the loss factor and slightly reduced the resonance frequencies of the presented modes. Loss factors vary by 67–96%; in the case of the second mode, loss factor depends heavily on vibration amplitude.

Commentary by Dr. Valentin Fuster

29th Conference on Mechanical Vibration and Noise: Nonlinear Systems and Phenomena (VIB/MSNDC 10-6)

2017;():V008T12A021. doi:10.1115/DETC2017-67189.

This research presents the mathematical modeling for the nonlinear oscillations analysis of a pre-stretched hyperelastic annular membrane with varying density under finite deformations. The membrane material is assumed to be homogeneous, isotropic, and neo-Hookean and the variation of the membrane density in the radial direction is investigated. The membrane is first subjected to a uniform radial traction along its outer circumference and the stretched membrane is fixed along the outer boundary. Then the equations of motion of the pre-stretched membrane are derived. From the linearized equations of motion, the natural frequencies and mode shapes of the membrane are obtained analytically. The vibration modes are described by hypergeometric functions, which are used to approximate the nonlinear deformation field using the Galerkin method. The results are compared with the results evaluated for the same membrane using a nonlinear finite element formulation. The results show the influence of the stretching ratio and varying density on the linear and nonlinear oscillations of the membrane.

Commentary by Dr. Valentin Fuster
2017;():V008T12A022. doi:10.1115/DETC2017-67780.

Recently, the bistable attachment has been employed as a nonlinear energy sink (NES) for passive targeted energy transfer (TET) from linear structures. The bistable NES (BNES) has been coupled with a linear oscillator (LO) where the resulting LO-BNES system has been studied for passive TET. The nonlinear coupling force between the BNES and the associated LO comprises both negative and nonnegative linear and nonlinear stiffness components. Here, the dynamic behavior of the LO-BNES system on the frequency-energy plot is analyzed. The related FEP plot is obtained via numerical simulation techniques where the wavelet transform is imposed into the FEP for variety of initial conditions and damping content. It is found that the FEP has backbone branches at low energy levels associated with the oscillation of the bistable attachments about one of its stable equilibrium positions where passage through the unstable equilibrium position does not occur.

Commentary by Dr. Valentin Fuster
2017;():V008T12A023. doi:10.1115/DETC2017-67965.

Acoustic reciprocity is a property of linear, time invariant systems in which the locations of the source of a forcing and the received signal can be interchanged with no change in the measured response. This work investigates the breaking of acoustic reciprocity using a hierarchical structure consisting of internally-scaled masses coupled with cubically nonlinear springs. Using both direct results and variable transformations of numerical simulations, energy transmission is shown to occur in the direction of decreasing scale but not vice versa, constituting the breaking of acoustic reciprocity locally. When a linear spring connects the smallest scale of such a structure to the largest scale of another identical structure, an asymmetrical lattice is formed. Because of the scale mixing and transient resonance capture that occurs within each unit cell, it is demonstrated through further numerical experiments that energy transmission occurs primarily in the direction associated with the nonlinear coupling from the large to the small scale, thus signifying the breaking of reciprocity globally. This nonlinear hierarchical structure exhibits strong amplitude-dependency in which reciprocity-breaking is associated with specific ranges of excitation amplitudes for both impulse and harmonic forcing.

Commentary by Dr. Valentin Fuster
2017;():V008T12A024. doi:10.1115/DETC2017-68181.

Flexible links undergoing a slewing motion are widely found in aerospace structures such as satellites and robotic manipulators. In this kind of systems, the lighter the structure the better is its performance and more cost effective is the system. However, the positioning control of flexible structures is challenging because the flexibility may lead the system to vibrate in larger amplitudes, which makes the need of using actuators to control and reduce vibrations. An alternative for those actuators is the use of smart materials, as SMA (Shape Memory Alloys) to control vibrations of such structures. This work will present the angular positioning and vibration control of a flexible link. The angular position control is a torque driven by a DC motor controlled through a sliding modes control method. The system is considered as non-ideal, it means that the vibration of the flexible link accomplishes to the DC motor shaft. SMA actuators are coupled to the flexible link with the objective to reduce the vibration amplitudes and reducing so the settling time of the system. The SMA actuators are controlled through an electric voltage applied to its terminals by applying the Sliding modes control method. The dynamical equations of motion for the system are developed considering a dead zone nonlinearity of the DC motor and a phenomenological model for the SMA. The flexible link is modeled as a continuous structure and just the first vibration mode is analyzed. Numerical simulations results are presented to demonstrate the effectiveness of the sliding modes strategy for the positioning control of the DC motor and for the vibration suppression of the flexible link by using SMA actuators.

Commentary by Dr. Valentin Fuster
2017;():V008T12A025. doi:10.1115/DETC2017-68331.

Nonlinear free undamped vibrations are investigated for ultra-precision manufacturing (UPM) machines with quadratic stiffness. The modes of the system are linearly coupled. The non-resonant case and the bounded internal resonance case are considered. The results of the non-resonant case indicate that the behavior of the system is the same as the linear behavior. However, for the internal resonance case, the results show that the amplitudes are coupled. The results also indicate that the nonlinear frequencies and amplitudes depend not only on the initial conditions, but also on the location of the isolators with respect to the center of gravity of the UPM.

Commentary by Dr. Valentin Fuster

29th Conference on Mechanical Vibration and Noise: Rotating Systems and Rotor Dynamics (VIB/MSNDC 10-8)

2017;():V008T12A026. doi:10.1115/DETC2017-67005.

Drivetrains for turbomachinery used in plant operations generally consist of a centrifugal compressor driven by turbines or electric motors, and may include intermediate speed reducing gearboxes. Each of these drivetrain components require accurate torsional modelling to ensure safe operation. Shaft modelling assumptions for these component sections can significantly alter the location of predicted torsional criticals and responses. One essential modelling assumption is the calculation of effective torsional stiffness in stepped shafts. Industry accepted methods include shaft penetration, the 45 degree rule and FEA approaches. A comparison of the three methods and the torsional impacts on a case study are presented.

Topics: Compressors
Commentary by Dr. Valentin Fuster
2017;():V008T12A027. doi:10.1115/DETC2017-67027.

Vibrations of roller bearings will be affected when a surface crack is caused in the bearing system. Thus, it is very helpful to study relationships between the sizes of the surface crack and vibrations of the bearings for detecting and diagnosing the surface crack in the bearing systems. In this study, a dynamic finite element model for a roller bearing with a vertical or slant surface crack on its outer race is presented using an explicit dynamic finite element software package. All components of the roller bearing are formulated as elastic bodies in the finite element model, which can consider the elastic deformations in the bearing system. Effects of the depth and slope angle of the surface crack on the contact forces between the roller and races of the bearing are studied, as well as the vibrations of the bearing. The simulation results show that the explicit dynamic finite element analysis method can be applied for studying the vibration characteristics produced by a vertical or slant surface crack in roller bearings.

Commentary by Dr. Valentin Fuster
2017;():V008T12A028. doi:10.1115/DETC2017-67044.

The presence of transversal cracks in rotating shafts can lead to catastrophic failures, which imply economic losses and security issues. In the last years, an important attention has been devoted to this subject, leading to the development of several vibration-based structural health monitoring approaches. In this paper, a fault detection technique based on the so-called modal state observer is applied to detect transversal cracks in rotating machines. The Luenberger state observer is described in modal domain to determine the most affected vibration modes due to the crack presence. A cracked rotor composed by a flexible horizontal shaft, two rigid discs, and two self-aligning ball bearings is used for illustration purposes. The additional flexibility introduced by the crack is calculated by using the linear fracture mechanics theory. The breathing behavior of the crack is simulated according to the Mayes’ model, in which the crack transition from fully open to fully closed is described by a cosine function. The obtained results lead to the conclusion that the modal state observer is a potential technique to detect cracks in rotating machines.

Commentary by Dr. Valentin Fuster
2017;():V008T12A029. doi:10.1115/DETC2017-67118.

This contribution deals with a design of bladed wheel model with tie-boss couplings for numerical and experimental dynamic analysis. Besides modal analysis of the linearized wheel model a non-linear dynamical response of the three blade bundle with friction couplings in the tie-bosses were computed for description of a friction damping. Three-dimensional FE model with friction contacts was developed in the program ANSYS 15.0. The Augmented Lagrangian method was used to compute contact normal pressures and friction stresses. The friction coupling was modeled by the Isotropic Coulomb’s law. For a description of the friction coefficient, its dependence on relative velocity was considered. The damping ratio of the friction damping was evaluated from the envelope of free vibration attenuations after short harmonic excitation. The first experimental results for validation of the numerical model are discussed at the end.

Commentary by Dr. Valentin Fuster
2017;():V008T12A030. doi:10.1115/DETC2017-67216.

Flexible multistage rotor systems have a variety of engineering applications. Vibration optimization is important to the improvement of performance and reliability for this type of rotor systems. Filling a technical gap in the literature, this paper presents a virtual bearing method for optimal bearing placement that minimizes the vibration amplitude of a flexible rotor system with a minimum number of bearings. In the development, a distributed transfer function formulation is used to define the optimization problem. Solution of the optimization problem by a real-coded genetic algorithm yields the locations and dynamic coefficients of bearings, by which the prescribed operational requirements for the rotor system are satisfied. A numerical example shows that the proposed optimization method is efficient and accurate, and is useful in preliminary design of a new rotor system with the number of bearings unforeknown.

Topics: Bearings , Rotors
Commentary by Dr. Valentin Fuster
2017;():V008T12A031. doi:10.1115/DETC2017-67320.

The dynamic model and control strategy of a rotating cantilever beam are investigated in the paper. The magnetostrictive layer is applied as the actuator and the nonlinear constitutive relation is analyzed. The kinetic energy and potential energy of the beam are obtained. The Hamilton method and Galerkin approach are adopted to obtain and disperse the dynamic equations, respectively. The negative feedback control methodology is used in the control system, which is performed by the solenoid coils. Numerical results show that the magnetostrictive control method is effective and plays the role of damping in the dynamic equations. The nonlinear constrictive characteristics of the magnetostrictive material can affect the control results deeply and should be paid enough attention. The magnetostrictive control performances are influenced by many parameters such as the bias magnetic field, control gain and pre-stress etc.

Commentary by Dr. Valentin Fuster
2017;():V008T12A032. doi:10.1115/DETC2017-67433.

Unbalance of rotating parts is the main source of excitation of lateral oscillations of rotors, of increase of time varying forces transmitted to the rotor stationary part, and of energy losses generated in the support elements. The technological solution, which makes it possible to reduce these undesirable effects, consists in adding damping devices to the rotor supports. A simple dynamical analysis shows that to achieve their optimum performance their damping effect must be adaptable to the current operating speed. This is enabled by magnetorheological squeeze film dampers, the damping effect of which is controlled by the change of magnetic flux passing through the lubricating layer. The developed mathematical model of the magnetorheological squeeze film damper is based on assumptions of the classical theory of lubrication and on representing the magnetorheological oil by a bilinear material. The results of the carried out computational simulations show that the appropriate control of the damping force makes it possible to minimize the energy losses in a wide range of operating speeds. The development of a new mathematical model of the magnetorheological squeeze film damper, the extension of computational procedures, in which this model has been implemented, the confirmation that the magnetorheological dampers make it possible to reduce energy losses in the rotor supports, and learning more on influence of controllable dampers on behavior of rotor systems are the principal contributions of the presented paper. The carried out research highlights the possibility of reducing the energy losses by means of employing magnetorheological squeeze film dampers, which represents a new field of their prospective application.

Commentary by Dr. Valentin Fuster
2017;():V008T12A033. doi:10.1115/DETC2017-67687.

Understanding vibration of the wind turbine blades is of fundamental importance. This paper regards the effect of blade mistuning on the coupled blade-hub dynamics. Unavoidably, at any stage of the wind turbine, the set of blades will not be precisely identical due to the inhomogeneous material, manufacturer tolerances, etc.

This paper is based on blade-hub dynamics of a horizontal-axis wind turbine with mistuned blade. The equations of motion are derived for the wind turbine blades and hub exposed to centrifugal effects and gravitational and cyclic aerodynamic forces. The equations are coupled. To decoupled them, the independent variable is changed from time to rotor angle. The resulting blade equations include parametric and direct excitation terms. The method of multiple scales is applied to examine response of the system. This analysis shows that superharmonic and primary resonances exist and are influenced by the mistuning. Resonance cases and the relations between response amplitude and frequency are studied.

Commentary by Dr. Valentin Fuster
2017;():V008T12A034. doi:10.1115/DETC2017-67750.

The active magnetic bearings (AMBs) are often the preferred bearing solution in high speed rotating machines. Even though AMBs have numerous advantages in comparison to normal bearings they are sensitive to the power shutdowns. In the absence of electromagnetic field, the rotor collides with touchdown bearing. The high contact forces occurring between the rotor and touchdown bearing might lead to a contact surface failure in the touchdown bearings. In this study, the simulation model has been used to study the stresses of the touchdown bearing with an artificial crack. Flexibility of the rotor is modelled using the finite element method and frictional contacts are defined between the rotor and touchdown bearing. Hertzian contact theory is used to model all internal contacts in the ball bearing type touchdown bearings. This makes it possible to obtain the Hertzian contact stresses in each ball of the touchdown bearing and evaluate the stress intensity factors for a crack propagation analysis. The results show that increase in the dynamic friction coefficient between the rotor and bearing as well as increase in the air gap leads to a higher maximum Hertzian stress. As a result of the higher contact stress the stress intensity factor will increase.

Commentary by Dr. Valentin Fuster
2017;():V008T12A035. doi:10.1115/DETC2017-68375.

This study investigates the use of the mapped density of time response using orthogonal functions to detect single and multiple faults in rolling element bearings. The method is based on constructing the density of a single time response of the system by using orthogonal functions. The coefficients of the orthogonal functions create the feature vector in order to discriminate between different rolling element bearing faults. The method does not require preprocessing of the data, noise reduction, or feature selection. This method has been applied to vibration data of different bearing conditions at rotational speeds ranging from 300 rpm to 3000 rpm. These conditions include a healthy bearing, and bearings with defects in inner race, outer race, combination of inner race and outer race and rolling element. The results have shown remarkable detection efficiency in the case of a single and two bearing fault configurations. In general, for all bearing configurations, the approach has high performance in detecting defective conditions. These results indicate that using the mapped density to characterize the system under different conditions has considerable potential in bearing diagnostics.

Topics: Density , Bearings
Commentary by Dr. Valentin Fuster

29th Conference on Mechanical Vibration and Noise: Structures and Continuous Systems

2017;():V008T12A036. doi:10.1115/DETC2017-67218.

This paper deals with electrostatically actuated micro- and nano-electromechanical systems (M/NEMS) cantilever resonator under electrostatic actuation. The model includes Casimir effect. Three different methods are used to investigate the primary resonance of the MEMS resonator. The first two methods are based on a Galerkin approach in which the initial value and boundary value problem, given by the partial differential equation (PDE) of motion and the initial and boundary conditions, is transformed into an initial value problem of one ordinary differential equation (ODE) or a system of ODEs depending on how many modes of vibrations are considered in the model. The first method used is the Method of Multiple Scales (MMS) which is an approximate analytical method used to solve the model using one mode of vibration. The second method referred to as Reduced Order Model (ROM) solves the model using two to five modes of vibration using numerical integration. The third method is different than the first two in the sense that the initial value and boundary value problem describing the MEMS resonator is transformed into a boundary value problem (BVP) by using finite differences tor time derivatives. For this Matlab built-in function bvp4c is used to solve the problem. This built-in function is used for two different versions of the same equation. One which involves Taylor expansions of the nonlinear terms, and the other which does not. Results between the methods are in agreement. Thus any of these methods can be used to accurately predict the behavior of the MEMS resonator. For the ROM, two equations are also used, one for Casimir and one for without. The influence of damping, Casimir, and voltage parameter are also shown.

Commentary by Dr. Valentin Fuster
2017;():V008T12A037. doi:10.1115/DETC2017-67289.

In this study, analysis and results of linear and nonlinear aeroelastic of a cantilever beam subjected to the airflow as a model of a high aspect ratio wing are presented. A third-order nonlinear beam model is used as structural model to take into account the effects of geometric structural nonlinearities. In order to model aerodynamic loads, Wagner state-space model has been used. Galerkin method is implemented to solve dynamic perturbation equations about a nonlinear static equilibrium state. The small perturbation flutter boundary is determined by these perturbation equations. The effect of geometric structural nonlinearity of the beam model on the flutter behavior is significant. As it is observed the system’s response to upper speed of flutter goes to limit cycle oscillations and also the oscillations lose periodicity and become chaotic.

Topics: Wings
Commentary by Dr. Valentin Fuster
2017;():V008T12A038. doi:10.1115/DETC2017-67316.

Structural shape reconstruction is a critical issue for real-time structural health monitoring in the fields of engineering application. This paper shows how to implement structural shape reconstruction using a small number of strain data measured by fiber Bragg grating (FBG) sensors. First, the basic theory of structural shape reconstruction is introduced using modal superposition method. A transformation is derived from the measured discrete strain data to global displacement field through modal coordinate, which is the same for strain mode shape superposition and displacement mode shape superposition. Then, optimization of the sensor layout is investigated to achieve the effective reconstruction effect. Finally, structural shape reconstruction algorithm using modal superposition method is applied in experiments. The experiment results show that the reconstructed displacements match well with those measured by a laser displacement sensor and the proposed approach is a promising method for structural shape reconstruction.

Commentary by Dr. Valentin Fuster
2017;():V008T12A039. doi:10.1115/DETC2017-67367.

This paper deals with electrostatically actuated Double Walled Carbon Nanotubes (DWCNT) cantilevered resonators. The governing equations for the motion of the DWCNT are derived through Euler-Bernoulli beam model assumptions that account for inertial and viscoelastic effects. The DWCNT is a specific type of multi-walled carbon nanotube (MWCNT) that is comprised of two coaxially concentric carbon nanotubes. Electrostatic, damping, and intertube van der Waals forces act on the outer tube of the DWCNT, while only intertube van der Waals force acts on the inner tube. A soft AC voltage provides the electrostatic actuation. The nonlinear behavior and phenomena in the system are provided by the electrostatic and intertube van der Waals forces. The DWCNT is subjected to nonlinear parametric dynamics. The Method of Multiple Scales (MMS) is employed to investigate the system under soft excitations and/or weak nonlinearities. The frequency-amplitude response is found in the case of parametric resonance. The resulting nonlinear dynamic behavior is important to improve DWCNT resonator sensitivity in the application of mass sensing.

Commentary by Dr. Valentin Fuster
2017;():V008T12A040. doi:10.1115/DETC2017-67516.

In modal testing, the measured Frequency Response Functions (FRFs) are often affected by transducer mass effects. Especially in Multi-Input-Multi-Output (MIMO) modal test, multiple sensors are employed and the effects of additional masses are more significant. This paper deal with removing masses effects of multiple sensors from the measured FRFs. The proposed method offers some advantages over the available techniques in that extra FRFs measurements with different configurations are not required during the correction process. First, a general correction formulation is derived theoretically. Then, validations of the proposed methods are demonstrated using simulated data. It demonstrates a good performance in numerical simulation. To investigate the performance of the proposed method in practical application, further simulations are presented by employing noise-polluted data. And it is shown that the accuracy of correction results will be affected to some extent by the noise. It is thus suggested that the measured FRFs be preprocessed using the curve-fitting procedure or noise reduction processing before applying the proposed method. Since the FRFs measurements required for corrections refer to different excitation points, it requires moving the exciter to different locations. This is usually easy to achieve in hammer impact testing. However, moving the exciter is usually inconvenient in shaker modal testing. Further work is necessary to extend this proposed method so as to make it also applicable for shaker modal test case.

Topics: Transducers
Commentary by Dr. Valentin Fuster
2017;():V008T12A041. doi:10.1115/DETC2017-67598.

A new locking-free formulation of a three-dimensional shear-deformable beam with large deformations and large rotations is developed. The position of the centroid line of the beam is integrated from its slope that is related to the rotation of a corresponding cross-section and stretch and shear strains. The rotation is parametrized by a rotation vector, which has a clear and intuitive physical meaning. Taylor polynomials are used for certain terms that have zero denominators to avoid singularity in numerical implementation. Governing equations of the beam are obtained using Lagrange’s equations for systems with constraints, and several benchmark problems are simulated to show the performance of the current formulation. Results show that the current formulation do not suffer from shear and Poisson locking problems that the absolute nodal coordinate formulation can have. Results from the current formulation for a planar static case are compared with its exact solutions, and they are in excellent agreement with each other, which verifies accuracy of the current formulation. Results from the current formulation are compared with those from commercial software ABAQUS and RecurDyn, and they are in good agreement with each other; the current formulation uses much fewer numbers of elements to yield converged results.

Commentary by Dr. Valentin Fuster
2017;():V008T12A042. doi:10.1115/DETC2017-68208.

This paper focuses on nonlinear forced vibration analysis of a free-form conveying fluid nanotube. Non-Uniform Rational B-Splines (NURBS) is used to model the free-form curvature of the nanotube, analytically. In order to develop the ordinary differential equations of motion, the Euler-Bernoulli beam theory and Galerkin method are implemented and the frequency response and the primary resonance of the nanotube under a harmonic excitation are studied. The effects of the free-form curvature of the nanotube and its physical characteristic on the nonlinear vibration behavior of the system are discussed as a parametric study.

Commentary by Dr. Valentin Fuster
2017;():V008T12A043. doi:10.1115/DETC2017-68211.

Nonlinear free vibration analysis of stiffened plates is presented in this paper. The von Karman theory is employed to model the rectangular stiffened steel plate. The first two symmetric and asymmetric modes are taken into consideration and the coupled nonlinear differential equations of system are derived using the Galerkin approach. The Variational Iteration Method (VIM) is considered as the solution technique and an integral iterative formulation is presented to obtain the nonlinear natural frequencies. Subsequently a parametric sensitivity study is carried out and the effect of different initial amplitudes on the frequency responses is investigated.

Commentary by Dr. Valentin Fuster
2017;():V008T12A044. doi:10.1115/DETC2017-68297.

A new global spatial discretization method is developed to accurately calculate natural frequencies and dynamic responses of two-dimensional continuous systems such as membranes and Kirchhoff plates. The transverse displacement of a two-dimensional continuous system is separated into a two-dimensional internal term and a two-dimensional boundary-induced term; the latter is interpolated from one-dimensional boundary functions that are further divided into one-dimensional internal terms and one-dimensional boundary-induced terms. The two- and one-dimensional internal terms are chosen to satisfy predetermined boundary conditions, and the two- and one-dimensional boundary-induced terms use additional degrees of freedom at boundaries to ensure satisfaction of all boundary conditions. A general formulation of the method that can achieve uniform convergence is established for a two-dimensional continuous system with an arbitrary domain shape and arbitrary boundary conditions, and it is elaborated in detail for a general rectangular Kirchhoff plate. An example of a rectangular Kirchhoff plate that has three simply-supported boundaries and one free boundary with an attached Euler-Bernoulli beam is investigated using the developed method and results are compared with those from other global and local spatial discretization methods. Natural frequencies and dynamic responses that include the displacement, the velocity, rotational angles, a bending moment, and a transverse shearing force are calculated using both the developed method and the assumed modes method, and compared with results from the finite element method and the finite difference method, respectively. Advantages of the new method over local spatial discretization methods are much fewer degrees of freedom and much less computational effort, and those over the assumed modes method are better numerical property, a faster calculation speed, and much higher accuracy in calculation of the bending moment and the transverse shearing force that are related to high-order spatial derivatives of the displacement of the plate with an edge beam.

Commentary by Dr. Valentin Fuster

29th Conference on Mechanical Vibration and Noise: System Identification, Damage Detection and Diagnostics

2017;():V008T12A045. doi:10.1115/DETC2017-67160.

Weak fault detection is crucial to incipient mechanical fault diagnosis. In order to extract weak fault signals, a method named improved Re-scaling Frequency Stochastic Resonance (IRFSR) is proposed in this paper. The method consists of four steps: (i) Frequency Information Exchange (FIE); (ii) Amplitude Coefficient Adjustment; (iii) Re-scaling Frequency Stochastic Resonance (RFSR); and (iv) Frequency Information Recovery. By means of the exchange of frequency information, the high-frequency information of the target signal is accordingly transferred to the low frequency band which can be rescaled to satisfy the small-parameter limits of classical stochastic resonance. Then IRFSR is able to overcome the limitation of RFSR, which is that the sampling frequency of RFSR is at least 50 times greater than the frequency of the target signal. Numerical results are reported to evaluate the effectiveness of IRFSR to detect the target signal with higher frequency at a low sampling frequency as compared with RFSR. And the feasibility of the IRFSR in incipient fault detection is demonstrated using case history data obtained from a sliding bearing test rig.

Topics: Resonance , Signals
Commentary by Dr. Valentin Fuster
2017;():V008T12A046. doi:10.1115/DETC2017-67171.

Bearing fault diagnosis under constant operational condition has been widely investigated. Monitoring the bearing vibration signal in the frequency domain is an effective approach to diagnose a bearing fault since each fault type has a specific Fault Characteristic Frequency (FCF). However, in real applications, bearings are often running under time-varying speed conditions which makes the signal non-stationary and the FCF time-varying. Order tracking is a commonly used method to resample the non-stationary signal to a stationary signal. However, the accuracy of order tracking is affected by many factors such as the precision of the measured shaft rotating speed and the interpolation methods used. Therefore, resampling-free methods are of interest for bearing fault diagnosis under time-varying speed conditions. With the development of Time-Frequency Representation (TFR) techniques, such as the Short-Time Fourier Transform (STFT) and wavelet transform, bearing fault characteristics can be shown in the time-frequency domain. However, for bearing fault diagnosis, instantaneous time-frequency characteristics, i.e. Time-Frequency (T-F) curves, have to be extracted from the TFR. In this paper, an algorithm for multiple T-F curve extraction is proposed based on a path-optimization approach to extract T-F curves from the TFR of the bearing vibration signal. The bearing fault can be diagnosed by matching the curves to the Instantaneous Fault Characteristic Frequency (IFCF) and its harmonics. The effectiveness of the proposed algorithm is validated by experimental data collected from a faulty bearing with an outer race fault and a faulty bearing with an inner race fault, respectively.

Commentary by Dr. Valentin Fuster
2017;():V008T12A047. doi:10.1115/DETC2017-67508.

Structural Health Monitoring (SHM) systems become an integral part of most technical systems in recent years. An integration of SHM in technical systems is closely related to: i) providing the guaranteed service lifetime of a system, ii) scheduled/planned maintenance actions, and iii) optimized system operation. For these purposes, different system variables can be monitored and utilized for an estimation of aging level of the system. Monitored system variables are therefore correlated to stochastically occurring damage, indirectly also to Remaining Useful Lifetime (RUL). Among challenges related to SHM, high attention is given to the reduction of a large amount of measured data and its real-time signal processing. In this contribution, classification of damages in composite materials using measurements of Acoustic Emission (AE) is proposed. Here, Discrete Wavelet Transform (DWT) is applied to AE signal to identify different damages in composites. As AE-signal is found in high frequency bandwidth, the amount of data captured in a short time period is enormous. Consequently, the calculation of DWT of such signal requires processing time quite far from real time and delays the entire classification procedure. Due to this, real-time implementation of DWT is proposed to cope with huge amount of captured data in this case and to reduce the time required for signal processing. Using FPGA-based system, real-time implementation of DWT is shown. Obtained results are compared with the results of offline DWT calculation to prove the efficiency and accuracy of real-time implementation.

Commentary by Dr. Valentin Fuster
2017;():V008T12A048. doi:10.1115/DETC2017-67566.

Localized damages such as spalls, dents and raised metal may develop on bearing raceways and roller bodies in operation for various reasons. They can excite bearings and adjacent mechanical structures into vibration. By measuring machine vibration, it is possible to detect potential bearing damage. However, to do so, it is critical to understand the bearing vibration characteristics that are excited by localized damages.

The vibration of a TRB (tapered roller bearing) excited by a localized damage on a rotating cone (inner ring) raceway was studied using a three-dimensional, non-linear vibration model. Bearing vibration responses were analyzed in three directions. The responses exhibited multiple BPFI (ball passing frequency, inner) harmonics. The spectral envelope is determined by the bearing’s dynamic properties. The vibration characteristics in the axial direction were discovered to be different from those in the radial directions. The reason behind that is revealed in this paper.

Commentary by Dr. Valentin Fuster
2017;():V008T12A049. doi:10.1115/DETC2017-67993.

There is a huge amount of research and study on the quality, parameter manipulation, material selection etc. of welding to develop optimized results for specific applications. To have a profound understanding of the process, and to investigate and verify various parameters which affect the quality of the welding process, experts use analytical, numerical and experimental methods. The major concern regarding the welding procedure is welding defect, which can affect the integrity of the welded structure. Various nondestructive structural health monitoring methods and modal analysis techniques have been employed to study and improve the strength and quality of the welded structure. Modal analysis is one of the most accurate and commercial techniques to track down the damage within the structures. It uses natural frequency, damping factors and modal shapes to observe the structural and material defects in details. There have been noticeable developments in this area and lots of studies have been conducted applying this technique to put welding procedure under rigorous scrutiny to improve its efficiency. While modal analysis is a tool to identify structural integrity of the components, vibration can affect the nature of the metal and change the mechanical properties in some cases. Mechanical vibration and Ultrasonic as low and high frequency oscillations respectively, are able to change the microstructure of the structures so that dislocations move, hence the stress trapped within will redistribute. This redistribution can lead to residual stress reduction up to a level. In this review paper, all remarks above are considered, defined and accurately studied through various cases in order to address different application of vibratory stress relief and recent achievement in this field.

Topics: Welding , Stress , Damage
Commentary by Dr. Valentin Fuster

29th Conference on Mechanical Vibration and Noise: Time-Varying and Time-Delay Systems

2017;():V008T12A050. doi:10.1115/DETC2017-68450.

In this paper, we study the response of a linear differential equation, for which the damping coefficient varies periodically in time. We use Floquet theory combined with the harmonic balance method to find the approximate solution and capture the stability criteria. Based on Floquet theory the approximate solution includes the exponential part having an unknown exponent, and a periodic part, which is expressed using a truncated series of harmonics. After substituting the assumed response in the equation, the harmonic balance method is applied. We use the characteristic equation of the truncated harmonic series to obtain the Floquet exponents. The free response and stability characteristics of the damped system for a set of parameters are shown.

Topics: Damping
Commentary by Dr. Valentin Fuster

29th Conference on Mechanical Vibration and Noise: Vibration and Stability of Mechanical Systems

2017;():V008T12A051. doi:10.1115/DETC2017-67626.

Planetary gear trains (PGTs) are widely used in various machines owing to their many advantages. However, they suffer from problems of noise and vibration due to the structural complexity and giving rise to substantial noise, vibration, and harshness with respect to both structures and human users. In this report, the sound level from PGTs is measured in an anechoic chamber based on human aural characteristic, and basic features of sound are investigated. Gear noise is generated by the vibration force due to varying gear tooth stiffness and the vibration force due to tooth surface error, or transmission error (TE). Dynamic TE is considered to be increased because of internal and external meshing. The vibration force due to tooth surface error can be ignored owing to almost perfect tooth surface. A vibration force due to varying tooth stiffness could be a major factor.

Commentary by Dr. Valentin Fuster
2017;():V008T12A052. doi:10.1115/DETC2017-67792.

The spatial and temporal harmonic balance (STHB) method is used to solve the periodic solution for a nonlinear partial differential equation (PDE) demonstrated by a nonlinear string equation with a linear complex boundary condition, and stablity analysis is conducted for the periodic solutions using Hill’s method. In order to avoid the integration procedure for discretizing the PDE to obtain the ordinary differential equations (ODEs), spatial and temporal harmonic balance procedures are conducted simultaneously, which can be efficiently achieved by the discrete sine transform and the fast Fourier transform. An additional coordinate associated with the generalized coordinates of the trial functions for the spatial discretization is introduced to make the solution satisfy all boundary conditions, and a relationship of the additional coordinate and the generalized coordinates is developed and used in the STHB method so that the test functions can be the same to the trial functions. Jacobian matrix of the harmonic balanced residual is obtained analytically, which can be used in Newton method for solving the periodic response. The STHB method and Jacobian matrix make the calculation of the periodic solution for the nonlinear string with a linear spring boundary condition efficient and easy to be implemented by computer programs. The relationship between the Jacobian matrix and the system matrix of the linearized ODEs are developed, so that one can directly obtain the Toeplitz form of the system matrix, and Hill’s method can be used to analyze the stability with the eigenvalues of the Toeplitz-form system matrix without the derivation of the ODEs. The frequency curve of the periodic solutions is obtained and their stability is indicated by the method in this work.

Commentary by Dr. Valentin Fuster
2017;():V008T12A053. doi:10.1115/DETC2017-67827.

In this contribution, a chatter detection method is investigated for milling operations. The proposed approach can give not only qualitative condition (stable or unstable), but a quantitative measure of stability. For this purpose, it requires an external excitation of stable machining condition. Transient vibration of the perturbation is captured by means of stroboscopic section, and the corresponding monodromy operator is approximated by its projection to the subspace of the dominant modes. The monodromy matrix is determined with the application of homogeneous coordinate representation. Then, the periodic solution and the dominant characteristic multipliers are calculated and their modulus determines the quantitative measure of stability condition.

Topics: Milling
Commentary by Dr. Valentin Fuster
2017;():V008T12A054. doi:10.1115/DETC2017-67900.

In this work the effect of the inhomogeneous material properties are investigated in regenerative turning processes by introducing white noise in the cutting coefficient. The model is a one degree of freedom linear delayed oscillator with stochastic parameters. A full discretization method is used to calculate the time evolution of the second moment to determine the moment stability of the turning process. The resultant stability chart is compared with the deterministic turning model.

Commentary by Dr. Valentin Fuster
2017;():V008T12A055. doi:10.1115/DETC2017-68188.

Drill string and downhole tool failure usually results from failing to control one or more of the vibration mechanisms. The solution starts with the ability to measure different modes and hence identify the different vibration mechanisms. An in house experimental setup was developed to imitate the downhole axial, lateral and torsional vibration modes and mechanisms. Single and coupled vibration modes and mechanisms were created. This paper mainly focused the design and fabrication of the experimental setup. Capability of the setup for creating different vibration modes were examined. Experiments were performed to investigate the effects of rotational speeds and lateral vibration mode on the fatigue life of drill strings. Fatigue life is measured from the number of cycles associated with the amplitude of the stress cycles created due to lateral vibration Results showed that drill string size and lateral vibration stress cycles have significant effects on the fatigue life of the drill string. Investigations also showed that operating on a rotation speed higher than 90% of the drill string critical speed leads to yielding of the drill string. Such setup is essential for oil/gas industries as it can be utilized to investigate and provide solutions for very common problems such as drill string fatigue failure.

Commentary by Dr. Valentin Fuster

29th Conference on Mechanical Vibration and Noise: Vibration Control, Energy Harvesting, and Smart Structures (VIB/MSNDC 10-2)

2017;():V008T12A056. doi:10.1115/DETC2017-67168.

In the study of nonlinear bi-stable piezoelectric cantilever energy harvesting system, the accuracy of magnetic force’s calculation on which the potential function and dynamics of the system depend is essential to predict the output response and energy harvesting effect. In this paper, we built a shape function to calculate the trace of the end of the beam with the integral of the entire cantilever beam’s slope, and the magnetic force is consequently derived from the achieved magnets’ real-time position and posture using the magnetizing currents method. With the comprehensive consideration of axial magnetic force and lateral magnetic force, the change of both resultant magnetic force’s value and direction are achieved. The simulation results demonstrate that when the displacement of the magnet at the end of the beam is large enough, the axial and lateral magnetic forces change turn from repulsion to attraction, which leads to a large veer of the direction of resultant magnetic force across two quadrants. And the relationship between magnetic force and interval between two magnets is also achieved. The calculation results of this work are nicely consistent with experimental data. So, the accuracy of this calculation method has been proved to be much higher than the existing calculation method.

Commentary by Dr. Valentin Fuster
2017;():V008T12A057. doi:10.1115/DETC2017-67442.

Nonlinear energy harvesting has a better performance than linear resonators, because realistic ambient vibrations are spread over a wide frequency spectrum. We present a broadband nonlinear energy harvester with internal resonance induced by two resonators. Each resonator contains a cantilever beam with a magnet tip, and one is partially covered by piezoelectric material. The perturbation method of multiple scales is used to solve coupled partial different equations by applying internal resonance of ratio 2:1. The shooting method validates the analytical solutions of the frequency response and output voltage numerically. Output voltage for different excitation levels and distances are investigated. Simulations show the design, by applying internal resonance and nonlinearity, increases the bandwidth of frequency response.

Commentary by Dr. Valentin Fuster
2017;():V008T12A058. doi:10.1115/DETC2017-67504.

This paper proposes the experimental application of a novel hybrid control technique to perform eigenstructure assignment in vibrating systems. The method takes advantage of the concurrent use of passive modifications of the elastic and inertial parameters, and of state-feedback active control. The system modifications are computed through the solution of a rank minimization problem to shape the space of the allowable eigenvectors that can be achieved through active control. The test consists of a cantilever beam, which is modified and controlled to feature a second vibrational mode whose vibrations are confined to the part of the beam near the free end. The beam is controlled through a piezoelectric actuator and a Kalman filter is adopted to estimate the state vector for state-feedback control. The method proposed is able to overcome the limitations of the use of either passive modifications or active control alone, by significantly enlarging the set of assignable eigenpairs in vibrating systems.

Commentary by Dr. Valentin Fuster
2017;():V008T12A059. doi:10.1115/DETC2017-67522.

In this paper we perform reliability analysis for a piezoelectric energy harvester to power the tire pressure monitoring sensor (TPMS) under various uncertainty. Reliability based design optimization (RBDO) is applied to improve the performance of the system. Wasted vibrational energy in a vehicle’s rotating tire can be exploited to enable a self-powered TPMS. Piezoelectric type energy harvesters (EHs) are frequently used to collect vibrational energy and power such devices. While exposed to a high impact loading condition in a tire, the harvester experiences increasing strains which is under a higher risk of mechanical failure. Therefore, there is a need for a design to enhance the harvester’s fatigue life as well as maintaining the required power generation. Multiple design optimization studies found to consider the design update by traditional deterministic design optimization (DDO) which does not show reliable performance as it is unable to account for various uncertainty factors including manufacturing tolerances, environmental effects, and material properties. In this study, we consider uncertainty issue by using reliability-based design optimization under presence of various source of uncertainties. The RBDO problem is defined to satisfy power requirement and durability concerns as the constraints while considering design limitations such as compactness and weight. The time varying response of the EH such as generated power, dynamic strain, and stresses are measured by a transient analysis. Sequential Quadratic Programming (SQP) algorithm is used for both DDO and RBDO, and the design results are compared. The RBDO results demonstrate that the reliability of EH is increased by 26% with scarifying the objective function for 2.5% compared to DDO.

Commentary by Dr. Valentin Fuster
2017;():V008T12A060. doi:10.1115/DETC2017-67550.

In order to effectively take advantage of stiffness nonlinearities in vibration energy harvesters, the harvesters must be appropriately designed to ensure optimum direct current (DC) power generation. Yet, such optimization has only previously been investigated for alternating current (AC) power generation although most electronics demand DC power for their functioning. Moreover, real world excitations contain stochastic contributions combined with periodic components that challenges conventional approaches of investigation that only give attention to the harmonic excitation parts. To fill in the knowledge gap, this research undertakes comprehensive simulations to begin formulating conclusive understanding on the relationships between rectified power generation and nonlinear energy harvester system characteristics when the platforms are subjected to realistic combinations of harmonic and stochastic excitations. According to the simulation results, the rectified power demonstrates clear dependence on the load resistance in the unique limiting cases of complete or no stochastic excitation. When the excitation vibrations include both harmonic and stochastic components, the optimal resistance to maximize DC power exhibits a smoothly correlated but nonlinear change between the limiting case values of the resistance. The results of this investigation provide direct evidence of the intricate relationships among peak DC power, optimal resistive loads, and the nonlinear energy harvester design, and encourage continued study for direct analytical expressions that define such relationships.

Commentary by Dr. Valentin Fuster
2017;():V008T12A061. doi:10.1115/DETC2017-67559.

This paper proposed multi-resonant electromagnetic (EM) shunt dampers and investigated the optimal designs and performances of shunt circuits for a single DOF primary system. The circuits are arranged in parallel or series based on the analogy of multiple tuned mass dampers (TMDs). The objective is to minimize the root-mean-square (RMS) vibration of the primary system subjected to random base excitations. For single resonant EM shunt damper, closed-form solutions of optimal system parameters are obtained. For multi-resonant EM shunt dampers, the system parameters are numerically optimized. The vibration suppression performance of multi-resonant EM shunt dampers are compared with double-mass TMDs under the same 5% total stiffness ratio. It shows that the parallel shunt damper can achieve slightly better performance than parallel TMDs while the series shunt damper behaves differently from series TMDs. The optimal result of the series shunt damper will be the same as the single resonant shunt damper. It is also found that the multi-resonant EM shunt damper is much more sensitive to the capacitance than the resistance in the shunt circuits.

Commentary by Dr. Valentin Fuster
2017;():V008T12A062. doi:10.1115/DETC2017-67567.

Harvesting of acoustoelastic wave energy in thin plates and other structures is a promising new research direction for scavenging energy to power small sensors and devices. In particular, metamaterial-inspired harvesting concepts have shown strong potential for enhancing harvesting of acoustoelastic wave energy. In support of continued development of these metamaterial-based concepts, this paper presents a fully-coupled T-matrix formulation for assessing scattering of incident wave energy from a piezoelectric patch attached to a thin plate. The T-matrix serves as an input-output relationship between incident and reflected waves, and is developed herein for a piezoelectric patch connected to an external circuit. The utility of the T-matrix is evident in problems with multiple piezoelectric harvesters, where it can be used with other T-matrices (such as those previously formulated for rigid, void, and elastic inclusions) in a multiple scattering context. This has the potential for many uses in predicting the dynamic response of smart and active structures, but may be particularly useful in accurately assessing metamaterial-based energy harvesting enhancement strategies. Following development of the requisite T-matrix, harvesting in an example Gradient-Index (GRIN) metamaterial structure is predicted using the multiple scattering approach.

Commentary by Dr. Valentin Fuster
2017;():V008T12A063. doi:10.1115/DETC2017-67667.

A new LaSMP smart material exhibits shape memory behaviors and stiffness variation via UV light exposures. This dynamic stiffness provides a new noncontact actuation mechanism for engineering structures. Isogeometric analysis utilizes high order and high continuity NURBS as basis functions which naturally fulfills C1-continuity requirement of Euler-Bernoulli beam and Kirchhoff plate theories. The UV light-activated frequency control of LaSMP laminated beam and plate structures based on the isogeometric analysis is presented in this study. The accuracy and efficiency of the proposed isogeometric approach are demonstrated via several numerical examples in frequency control. The results show that, with LaSMPs, broadband frequency control of beam and plate structures can be realized. Furthermore, the length of LaSMP patches on beams is varied, which further broadens its frequency variation ranges. Studies suggest that 1) the newly developed IGA is an effective numerical tool and 2) the maximum frequency change ratio of beam and plate structures respectively reach 24.30% and 6.37%, which demonstrates the feasibility of LaSMPs induced vibration control of structures.

Commentary by Dr. Valentin Fuster
2017;():V008T12A064. doi:10.1115/DETC2017-67693.

The frequency control of LaSMP laminated shell structures in the framework of isogeometric analysis is presented. LaSMP is a novel smart material which realizes shape memory function and stiffness variation via light exposures. This dynamic properties of stiffness provides a natural way for the noncontact actuation of shell structures. Isogeometric analysis utilizes high order and high continuity NURBS as basis functions which is an ideal candidate for the analysis of shell structures where curved geometries can be captured exactly. A variationally consistent Nitsche’s method is proposed for the coupling between Kirchhoff-Love shell patches to prevent hinge-like motion. The accuracy and efficiency of the proposed isogeometric approach are demonstrated via several numerical examples. The results show that, with LaSMPs, broadband frequency control of shell structures can be realized which further opens a door for the dynamic control of engineering-related LaSMP shell structures.

Commentary by Dr. Valentin Fuster
2017;():V008T12A065. doi:10.1115/DETC2017-67709.

In this paper an electro-Acoustic Nonlinear Absorber (ANLA) is described. It is composed of a baffled nonlinear membrane with its front face coupled to an acoustic cavity and the other one enclosed. The enclosure includes a feedback loop composed of a microphone and a loudspeaker that control the acoustic pressure seen by the rear face of the membrane. Due to the nonlinear geometrical properties of the membrane, the ANLA can synchronize it resonance with one of the resonances of the cavity. It allows to bring out the energy transfer toward the ANLA and thus to reduce pressure in the cavity. The feedback loop tunes the resonance frequency of the ANLA at low level, wich is a key factor for the triggering threshold of the targeted energy transfer. An numerical study of the efficiency of the ANLA to reduce noise in a cavity is presented including the influence of the feedback loop parameters.

Commentary by Dr. Valentin Fuster
2017;():V008T12A066. doi:10.1115/DETC2017-67960.

Many industrial applications incorporate rotating shafts with fluctuating speeds around a desired mean value. This often harmonic component of the shaft speed is generally undesirable, since it can excite parts of the system and can lead to large oscillations (potentially durability issues), as well as to excessive noise generation. On the other hand, the addition of sensors on rotating shafts for system monitoring or control poses challenges due to the need to supply power to the sensor and extract data from the rotating application. In order to tackle the requirement of powering sensors for structure health monitoring or control applications, this work proposes a nonlinear vibration energy harvester design intended for use on rotating shafts with harmonic speed fluctuations. The essential nonlinearity of the harvester allows for increased operating bandwidth, potentially across the whole range of shaft’s operating conditions.

Commentary by Dr. Valentin Fuster
2017;():V008T12A067. doi:10.1115/DETC2017-68029.

A novel vibration-based energy harvester which consists of a monostable Duffing oscillator connected to an electromagnetic generator with a mechanical motion rectifier (MMR-Duffing) is studied. The mechanical motion rectifier converts the bi-directional vibratory motion from ambient environments into uni-directional rotation to the generator and causes the harvester to periodically switch between a larger- and small-inertia system, resulting in nonlinearity in inertia. By means of the method of averaging, it is analytically shown that the proposed Duffing-MMR harvester outperforms traditional monostable Duffing oscillator energy harvesters in twofold. First of all, it increases the bandwidth of energy harvesting, given identical nonlinear stiffness. Second of all, it mitigates the jump phenomenon due to nonlinear stiffness and thus exploits more potential bandwidth of energy harvesting without inducing any jump phenomenon. Finally, the analytical analyses are verified via numerical simulations of a prototype of the proposed Duffing-MMR harvester.

Topics: Vibration
Commentary by Dr. Valentin Fuster
2017;():V008T12A068. doi:10.1115/DETC2017-68056.

It has been shown theoretically that by prescribing the mass and stiffness distributions of a subordinate oscillator array (SOA) that is attached to a host structure, significant vibration attenuation of a host can be obtained over a finite frequency range. This case stands in stark contrast to classical vibration isolator designs for two degree of freedom systems that achieve exact vibration cancellation at a single isolated frequency. Despite the attractiveness of SOAs for the design of broader band vibration suppression, the theoretically desired result can deteriorate rapidly due to small fabrication imperfections in the SOA. This paper introduces and compares variational thermodynamic formulations of composite piezoelectric SOA that are designed to be adjustable in real-time to ameliorate the effects of disorder due to fabrication in a SOA.

Commentary by Dr. Valentin Fuster
2017;():V008T12A069. doi:10.1115/DETC2017-68283.

We demonstrate numerically an efficient vibrational energy harvester based on a triboelectric mechanism. The energy harvester consists of a clamped-clamped beam with center mass to enable the impact between the triboelectric layers subjected to external vibrations. The lower electrode is aluminum covered with a polydimethylsiloxane (PDMS) layer and the top electrode is an aluminum foil. Upon contact, electric charges are generated and alternative current flows between the upper and lower electrodes. We report the frequency bandwidth gets wider with a hardening behavior introduced by the impact nonlinearity in the structure. We then investigate the effect of the surface charge density on the output voltage, current, and power. The output voltage and power are as large as 1.73 V, 3 μW, respectively with 0.4 g vibrational amplitude and 30 μC/m2 surface charge density. The frequency bandwidth ranged between 5–18 Hz.

Topics: Modeling , Vibration
Commentary by Dr. Valentin Fuster

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