20th Biennial Conference on Mechanical Vibration and Noise

2005;():7-12. doi:10.1115/DETC2005-84151.

This paper presents a finite element approach to analyze the “boom” noise for a compact tractor cabin. The tractor cabin is initially designed to have a structure made up of steel beams and aluminum panels, as well as PMAA panels in windshield, backlight and windows. Cavity acoustic modes of the cab are evaluated and the acoustic resonant frequencies are identified. The study on the structural-borne noise from the cabin structural vibration generated by the engine of the vehicle is performed. A coupled-field finite element model, counting the interactions between the air fluid inside the cabin compartment and the cabin exterior structure, is presented for investigating the structural-borne noise in a low frequency range of 20 Hz to 80 Hz. This range has shown strong boom effects. The interior noise level at driver’s right ear position is investigated. The peak noise levels at the position are determined. The effects of additional stiffeners and damping layers on the boom noise are also investigated.

Commentary by Dr. Valentin Fuster
2005;():13-19. doi:10.1115/DETC2005-84363.

Cavitation is a common fault in centrifugal pumps. The detection and diagnosis of the onset and severity of the cavitation provide the means for preventing harmful effects such as deterioration of the hydraulic performance, damage to pump components, vibration and noise pollution. This paper presents a new approach for monitoring cavitation based on the noise measurement spectrum and analysis. Noise is measured using a microphone and a P.C. equipped with soundcard and Matlab6.1 uses Fast Fourier Transform to change the domain from time to frequency. It has been found that the sound pressure level at some frequencies can be used as a primary monitoring feature to detect the onset of the cavitation and to quantify the severity of the cavitation. One of these frequencies is related to the number of blades. Other detection features are defined in other frequencies, as well. Flow rate increase was used to have stronger cavitation effect.

Commentary by Dr. Valentin Fuster
2005;():21-31. doi:10.1115/DETC2005-84428.

The paper describes a homogenization technique for periodic lattice structures. The analysis is performed by considering the irreducible unit cell as a building block that defines the periodic pattern. In particular, the continuum equivalent representation for the discrete structure is sought with the objective of retaining information regarding the local properties of the lattice, while condensing its global behavior into a set of differential equations. These equations can then be solved either analytically or numerically, thus providing a model which involves a significantly lower number of variables than those required for the detailed model of the assembly. The methodology is first tested by comparing the dispersion relations obtained through homogenization with those corresponding to the detailed model of the unit cells and then extended to the comparison of exact and approximate harmonic responses. This comparison is carried out for both one-dimensional and two-dimensional assemblies. The application to three-dimensional structures is not attempted in this work and will be approached in the future without the need for substantial conceptual changes in the theoretical procedure. Hence the presented technique is expected to be applicable to a wide range of periodic structures, with applications ranging from the design of structural elements of mechanical and aerospace interest to the optimization of smart materials with attractive mechanical, thermal or electrical properties.

Commentary by Dr. Valentin Fuster
2005;():33-38. doi:10.1115/DETC2005-84931.

A normal-mode representation of waveguide behavior is recapitulated in terms of inner and outer responses in order to enhance the analogy with quasi-static beam solutions. This setting is employed to assist in the extension of the classical Saint-Venant’s principle to dynamic problems. The surface load parameters which determine the inner solution in a waveguide with free surfaces, are identified as the frequency and the average power of the load, provided the frequency is low enough and for purely symmetric (or purely antisymmetric) loads. A quantitative estimate of the extension of end effects is given. The one to one correspondence between the equivalent loads and the inner solution is used to reformulate the dynamic analogue of Saint-Venant’s principle.

Topics: Waveguides
Commentary by Dr. Valentin Fuster
2005;():39-43. doi:10.1115/DETC2005-85080.

Since its conception in 1980, nearfield acoustic holography (NAH) has become an accepted analysis tool with a number of commercial packages now available. One limitation of NAH is that the acoustic field is reconstructed through a spatial sampling. Therefore, this technique becomes less efficient at higher frequencies where microphone array spacing must be reduced. Analytical models have indicated that an NAH method relying on energy-based measurements will provide the same reconstruction resolution of current NAH methods with significantly fewer measurement locations. This would lead to a considerable savings in data acquisition time for scanning array systems and reduce the inefficiency at high frequencies. The energy-based reconstruction method will be introduced. Experimental results will be presented for a planar test case and the resulting reconstruction accuracy will be compared to the analytical prediction model.

Commentary by Dr. Valentin Fuster
2005;():45-50. doi:10.1115/DETC2005-85601.

This research is to investigate the behavior of elastic waves in porous media consisting of fluid and solid. A new methodology for describing the wave motion of a fluid-saturated porous medium is developed with the establishment of a mathematical wave model. Dynamic equations in the form of displacements of the fluid and solid are derived for analyzing the elastic waves propagating in homogeneous and isotropic porous media, which are subjected to excitations of multiple energy sources. Solutions of the wave equation are developed on the basis of the moving-coordinate method. Numerical simulations of the waves propagating in the porous media with multiple energy sources are also performed for demonstrating the application of the mathematical model developed.

Commentary by Dr. Valentin Fuster
2005;():51-58. doi:10.1115/DETC2005-85636.

Sound quality analysis is an invaluable tool for the product designer. This tool is designed to help determine customer preferences, which can help the designer improve product quality, or the consumers’ perception of the product’s quality. Many industries desire to know how the consuming public perceives their product as this affects the product life and viability. This paper will present which of two brands of sewing machines ranging in market segments from entry-level, thru mid-level machines, to high-end computer controlled units, is the most acoustically pleasant. Results across market segments independent of brand will be evaluated and compared, as well. The methods used to determine the sound quality of these machines will be presented. These methods are both jury based listening tests and quantitative sound quality metrics.

Commentary by Dr. Valentin Fuster
2005;():59-64. doi:10.1115/DETC2005-85695.

In this paper, dynamic stress concentrations are studied in an infinite piezoelectric medium with a non-circular cavity under time harmonic incident anti-plane shear wave and inplane electric field. Based on complex variable and conformal mapping method, the dynamic stress concentration factors and the electric field concentration factors at the boundary of the non-circular cavity are obtained by applying the orthogonal function expansion technique. Numerical examples about an infinite piezoelectric medium with an elliptic cavity are provided with different elliptic axial length ratios, different wave numbers and different piezoelectric characteristic parameters. The calculating results show that dynamic analyses are very important to an infinite piezoelectric medium with a non-circular cavity at lower frequencies and larger piezoelectric characteristic parameters.

Topics: Cavities
Commentary by Dr. Valentin Fuster
2005;():65-68. doi:10.1115/DETC2005-85706.

In this paper, the model of wave finite element is founded by analyzing the issue of the foundation containing channels excited by transient SH-wave in FEM. The method’s rationality and the simulation infinite territory issue are discussed. The establishment artificial boundary to satisfy the unlimited extent the request, as well as the unit division and the time integral length of stride selection problem are researched. The numerical value of the displacement of the cavity is obtained by calculating the dynamic responds of the underground U-shaped structure with ANSYS. Examples are provided to support the discussion.

Commentary by Dr. Valentin Fuster
2005;():69-73. doi:10.1115/DETC2005-85713.

The utility of the Haar function wavelet has long been dismissed due to its inability to transpose between the time domain and the frequency domain. However, the Haar function possesses attributes that make it an ideal wavelet for certain applications. In this paper, we explore the use of the Haar function as a means to expose aspects of musical tone that are not available through other sound analysis techniques. Specifically, the method presented here was used to identify the differences in the tone of the French Horn created by different acoustically reflective surfaces placed in the near field of the horn bell. The fundamentals of the Haar function wavelet are described and its use as a signal analyzer is explained. Results are shown that demonstrate the effect of two different kinds of sound reflectors constructed for a major North American concert hall.

Topics: Wavelets
Commentary by Dr. Valentin Fuster
2005;():75-82. doi:10.1115/DETC2005-85718.

The nonlinear governing equations of motion for the cracked rotor system with unsymmetrical viscoelastic supported condition are derived and the nonlinear vibrations of the system are analyzed. The effects of the cracked depth, the cracked position and the disc position on the response curves of the rotational speed-the nonlinear vibration amplitude and the response curve of the nonlinear amplitude-frequency are discussed in detail. The results can be used for the on-line crack monitor of the rotor system.

Commentary by Dr. Valentin Fuster
2005;():83-88. doi:10.1115/DETC2005-85775.

The free vibration of clamped elliptical plate, when temperature and stress fields are coupled, is analyzed based on the fundamental equations of nonlinear thermo-elastic vibrations. A system of nonlinear differential equations of time is obtained with utilization of Galerkin’s method. The vibration states are compared with respect to different coefficients. The effects of thermo-elastic coupling on the amplitude and frequency are also presented.

Commentary by Dr. Valentin Fuster
2005;():89-96. doi:10.1115/DETC2005-84294.

A smart fin for a subsonic projectile should be able to produce maneuvering force and moment that can control its rotation during flight. Piezoelectric actuator is an attractive alternative to usual hydraulic actuators due to its simplicity. The cantilever-shaped actuator can also be fully enclosed within the hollow fin. It has an end fixed to the rotation axle of the fin while the other end is pinned at the tip of the fin. A dynamic model of the system, including external moment due to aerodynamic effects, is obtained using the finite element approach. This paper presents a novel approach for automatically creating fuzzy logic controllers for the fin. This approach uses the inverse dynamics of the smart fin system to determine the ranges of the variables of the controllers. Simulation results show that the proposed controller can successfully drive smart fin under various operating conditions.

Commentary by Dr. Valentin Fuster
2005;():97-106. doi:10.1115/DETC2005-84433.

Magnetic bearings are an exciting and innovative technology that has seen considerable advances in recent years. Such systems require active control, and most often, linear techniques are used very successfully. However, there are applications where such methods have limited effectiveness and other control strategies must be considered. Fuzzy logic control performs very well in nonlinear control situations where the plant parameters are either partially or mostly unidentified. Its effectiveness for nonlinear systems also offers advantages to magnetic bearing systems. Little research has been done on non-singleton fuzzy logic systems and their application to noise rejection on magnetic bearings or rotating machinery. Non-singleton fuzzy set inputs allow one to account for input measurement uncertainty. The fuzzy logic controller’s task in this work is two-fold; provide control for stable levitation of the shaft and perform noise filtering to reduce the effects of the disturbance. The current work consist of model development, controller design, simulation and experimental validation. The basic simulation model consist of a horizontal shaft supported by a radial magnetic bearing. The magnetic bearing is modeled as a nonlinear element. The controller designs are implemented and tested using a bench-top rotor rig equipped with a radial magnetic bearing. Some representative results are presented and discussed.

Topics: Fuzzy logic
Commentary by Dr. Valentin Fuster
2005;():107-115. doi:10.1115/DETC2005-84522.

In this paper an investigation is carried out to classify the steady state responses of asymmetric piecewise linear vibration isolators as double hitting, single hitting, and no hitting. In each class, the analysis has been carried out using a set of coupled nonlinear algebraic equations following Natsiavas and Gonzalez [1]. Applying perturbation technique, a closed form analytic expression of the frequency response is also derived for symmetric conditions. The exact frequency response is utilized to validate the analytic results obtained by perturbation techniques. Direct comparison indicates the results obtained by averaging method are mathematically and practically close to the exact solution.

Commentary by Dr. Valentin Fuster
2005;():117-127. doi:10.1115/DETC2005-84580.

This paper deals with development and simulation of the nonlinear model of an elastic ship-mounted crane equipped with the Maryland Rigging. The model contains three inputs to control the planar vibrations due to the planar base excitation; the luff angle is proposed to control the elastic vibration in the boom, and the length of the upper cable in conjunction with the position of its lower suspension point are proposed to control the pendulation of the payload. It is observed, through static and dynamic testing of the derived model, that moving the lower suspension point of the upper cable provides strong controllability of the horizontal displacement of the payload, while changing the length of the cable can be employed to compensate for the vertical displacement. Simulation results show that within a considerable range of pendulation displacements of the payload, the nonlinear model and the linearized one reflect nearly equivalent responses. Hence, with the property of strong controllability, the linear model can be used efficiently to design the control system, which will be discussed later in another paper.

Commentary by Dr. Valentin Fuster
2005;():129-136. doi:10.1115/DETC2005-84822.

The atomic force microscope (AFM) system has evolved into a useful tool for direct measurements of intermolecular forces with atomic-resolution characterization that can be employed in a broad spectrum of applications. In this paper, the nonlinear dynamical behavior of the AFM is studied. This is achieved by modeling the microcantilever as a single mode approximation (lumped-parameters model) and considering the interaction between the sample and cantilever in the form of van der Waals potential. The resultant nonlinear system is then analyzed using Melnikov method, which predicts the regions in which only periodic and quasi-periodic motions exist, and also predicts the regions that chaotic motion is possible. Numerical simulations are used to verify the presence of such chaotic invariant sets determined by Melnikov theory. Finally, the amplitude of vibration in which chaos is appeared is investigated and such irregular motion is proven by several methods including Poincare maps, Fourier transform, autocorrelation function and Lyapunov exponents.

Commentary by Dr. Valentin Fuster
2005;():137-144. doi:10.1115/DETC2005-84826.

This paper discusses the effects of substrate motions on the performance of microgyroscopes modeled as suspended beams with a tip mass. The substrate movements can be motions along as well as rotations around the three axes. Using Extended Hamiltonian Principle and Galerkin approximation, the equations of the motion of the beam are analytically derived. In these equations, the effects of beam distributed mass, tip mass, angular accelerations, centripetal and coriolis accelerations are clearly apparent. The effect of electrostatic forces inducing the excitation vibrations are considered as linear functions of beam displacement. The response of the system to different inputs is studied and the system sensitivity to input parameter changes are examined. Finally, the sources of error in the measurement of rotation rate input are recognized. The study demonstrated the importance of errors caused by cross axes inputs on the gyroscope output measurements and overall performance.

Commentary by Dr. Valentin Fuster
2005;():145-151. doi:10.1115/DETC2005-84830.

This paper presents the modeling steps towards development of frequency equations for a cantilever beam with a tip mass under general base excitations. More specifically, the beam is considered to vibrate in all the three directions, while subjected to a base rotational motion around its longitudinal direction. This is a common configuration utilized in many vibrating beam gyroscopes and well drilling systems. The governing equations are derived using Extended Hamilton’s Principle with general 6-DOF base motion. The natural frequency equations are then extracted in closed-form for the case where the base undergoes longitudinal rotation. For validation purposes, the resulting natural frequencies are compared with two example case studies; one with a beam on a stationary base and the other one with a rotor having flexible shaft.

Commentary by Dr. Valentin Fuster
2005;():153-158. doi:10.1115/DETC2005-84940.

Vibration suppression of elastically supported beams subjected to moving loads is investigated in this work. For a Timoshenko beam with an arbitrary number of elastic supports, subjected to a constant axial compressive force, and having a tuned mass damper (TMD) installed at the mid-span, the equations of motion are derived and using the Galerkin approach the solution is sought. The optimum values of the frequency and damping ratio are determined both analytically and numerically and presented as some design curves directly applicable in the TMD design for bridge structures. To show the efficiency of the designed TMD, computer simulation for two real bridges, subjected to a S.K.S Japanese high-speed train, is carried out and the results obtained are compared for before and after the installation of the TMD system.

Commentary by Dr. Valentin Fuster
2005;():159-165. doi:10.1115/DETC2005-84948.

The vibration of a simply-supported beam with rotary springs at either ends is studied. The governing equations of motion are investigated considering the nonlinear effect of stretching. These equations are made non-dimensional and solved to the first-order approximation using the two known methods, namely, the multiple scales and the mode summation. The first five natural frequencies of the beam for different pairs of the boundary condition parameters are evaluated. A multilayer feed-forward back-propagation artificial neural network is trained using these natural frequencies. The artificial neural network used in this study shows high degree of accuracy for the natural frequency of the beam with general pairs of the boundary condition parameters.

Commentary by Dr. Valentin Fuster
2005;():167-177. doi:10.1115/DETC2005-85153.

Sensing and control are essential to achieving the high performance and high precision of modern aerospace structures and systems. Typical off-the-shelf sensors placed at discrete locations usually add additional weights and thus often influence dynamic responses of precision systems. Unlike the conventional discrete add-on sensors, thin lightweight piezoelectric layers can be spatially spread and distributed over the surfaces of precision structures. The purpose of this study is to investigate microscopic neural signal generations from infinitesimal piezoelectric neurons over a cylindrical shell panel of various curvature angles and to determine dominating signal components resulting from longitudinal or circumferential membrane strains or longitudinal or circumferential bending strains. Dynamic equations of cylindrical shells are defined first, followed by free-vibration analysis. Then, mode shape functions and modal spatial strain distributions are used to determine the signal generation of distributed neuron sensors laminated on a linear cylindrical shell panel. The microscopic signal generations of infinitesimal piezoelectric sensors or neurons are investigated for three different curvature angles, i.e., β* = 30°, 90°, and 150°, of a simply-supported cylindrical shell panel. Evaluating these three cases suggests that as the curvature increases from 0° to 360°, the neural signals from the membrane strain dominate for lower natural modes before the neural signals from the bending strain become dominating as the mode increases.

Topics: Pipes , Signals
Commentary by Dr. Valentin Fuster
2005;():179-188. doi:10.1115/DETC2005-85220.

This paper addresses active vibration control of adaptive structures using piezoelectric active structural elements with built-in sensing and actuation function. Optimal placement and feedback gain of these active members are important issues, which are discussed in this study. An efficient optimal placement strategy has been developed using minimum control energy dissipating over infinite time interval. Optimal location of active members has been found through minimization of total control energy dissipating over infinite time interval using Simulated Annealing (SA) algorithm. Moreover, the effect of structural randomness and random load in optimal feedback gain has been investigated. To accomplish this, a mathematical model with reliability constraints on the stress and displacement is developed and the optimal velocity feedback gain of active members, using probabilistic optimization technique, is obtained. Illustrative examples are presented to demonstrate the effectiveness of this methodology. It is shown that deterministic approach can not provide reliable optimum design values.

Commentary by Dr. Valentin Fuster
2005;():189-193. doi:10.1115/DETC2005-84088.

We investigate typical mixing and fractal properties of chaotic scattering of passive particles in open hydrodynamic flows taking as an example a model two-dimensional incompressible flow composed of a fixed point vortex and a background current with a periodic component, the model inspired by the phenomenon of topographic eddies over mountains in the ocean and atmosphere. We have found, described and visualized a non-attracting invariant chaotic set defining chaotic scattering, fractality, and trapping of incoming particles. Geometry and topology of chaotic scattering have been studied and visualized. Scattering functions in the mixing zone have been found to have a fractal structure with a complicated hierarchy that has been described in terms of strophes and epistrophes. Mixing, trapping, and fractal properties of passive particles have been studied under the influence of a white noise with different amplitudes and frequency ranges. A new effect of clustering the particles in a noised flow has been demonstrated in numerical experiments.

Topics: Fluids , Fractals
Commentary by Dr. Valentin Fuster
2005;():195-200. doi:10.1115/DETC2005-84090.

Nonlinear dynamics in the fundamental interaction between a two-level atom with recoil and a quantized radiation field in a high-quality microcavity is studied. We consider the strongly coupled atom-field system as a quantum-classical hybrid with dynamically coupled quantum and classical egrees of freedom. We show that, even in the absence of any other interaction with environment, the coupling of quantum and classical degrees of freedom provides the emergence of classical dynamical chaos from quantum electrodynamics. It manifest itself in the atomic external degree of freedom as a random walking of an atom inside a cavity with a prominent fractal-like behavior and in the quantum atom-filed degrees of freedom as a sensitive dependence of atomic inversion on small variations in initial conditions. It is shown that dependences of variance of quantum entanglement and of the maximum Lyapunov exponent on the detuning of the atom-field resonance correlate strongly. This result provides a quantum-classical correspondence in a closed physical system.

Topics: Atoms , Photons , Chaos , Fractals
Commentary by Dr. Valentin Fuster
2005;():201-205. doi:10.1115/DETC2005-84203.

After analyzing the inefficiency of the conventional Cell Mapping Methods in global analysis for high-dimensional nonlinear systems, several principles should be followed for these methods’ implementations in high-dimensional systems are proposed in this paper. Those are: appropriate selection of investigating plane, reduction of data size, and projection of attractors to the investigating plane. According to these, the idea of dynamic array is introduced to the method of Point Mapping Under Cell Reference (PMUCR) to improve computing efficiency. The comparison of the CPU time between the applications of this modified method to a 2-dimensional system and to a 4-dimensional one is carried out, and the results confirm this modified method can be utilized to analyze high-dimensional systems effectively. Finally, as examples, the periodic and chaotic motions of a coupled Duffing system are investigated through this method and some diagrams of global characteristics are presented.

Commentary by Dr. Valentin Fuster
2005;():207-212. doi:10.1115/DETC2005-84469.

An impact of integration over the paths of the Lévy flights on the quantum mechanical kernel has been studied. Analytical expression for a free particle kernel has been obtained in terms of the Fox H-function. A new equation for the kernel of a partical in the box has been found.

Topics: Flight
Commentary by Dr. Valentin Fuster
2005;():213-217. doi:10.1115/DETC2005-84636.

The paper mathematically proves that a pendulum with oscillatory forcing makes chaotic motions for certain parameters. The method is more intuitive than using the Poincare’ map. It provides more information about when the chaos occurs.

Topics: Motion , Pendulums
Commentary by Dr. Valentin Fuster
2005;():219-229. doi:10.1115/DETC2005-84754.

The numerical prediction of chaos and quasi-periodic motion on the homoclinic surface of a 2-DOF nonlinear Hamiltonian system is presented through the energy spectrum method. For weak interactions, the analytical conditions for chaotic motion in such a Hamiltonian system are presented through the energy incremental energy approach. The Poincare mapping surfaces of chaotic motions for such nonlinear Hamiltonian systems are illustrated. The chaotic and quasiperiodic motions on the phase planes, displacement subspace (or potential domains), and the velocity subspace (or kinetic energy domains) are illustrated for a better understanding of motion behaviors on the homoclinic surface. Through this investigation, it is observed that the chaotic and quasi-periodic motions almost fill on the homoclinic surface of the 2-DOF nonlinear Hamiltonian systems. The resonant-periodic motions are theoretically countable but numerically inaccessible. Such conclusions are similar to the ones in the KAM theorem even though the KAM theorem is based on the small perturbation.

Commentary by Dr. Valentin Fuster
2005;():231-235. doi:10.1115/DETC2005-84944.

A viscoelastic nonlinear beam with cubic nonlinearities is considered. In order to obtain the equations of nonlinear motion of the beam for large deformation vibrations, the Lagrangian dynamics and Hamilton principle is used. It is considered that the beam vibrates in two directions, one in longitudinal direction and the other in the transverse direction. Large amplitude vibrations cause the nonlinearities in inertia and geometry terms. Also, due to viscoelastic property of the beam, a nonlinear damping term is appeared in the equations of motion. Using the condition of inextensible beams, the equation of motion and boundary conditions of bending vibration of a Kelvin-Voigt viscoelastic beam has been obtained. Finally, if one considers the damping coefficient to be equal to zero in the obtained equation of motion of viscoelastic system then, an equation of motion for the elastic beam will be obtained.

Topics: Motion , Equations
Commentary by Dr. Valentin Fuster
2005;():237-241. doi:10.1115/DETC2005-84970.

An analytical study on the chaos control of Duffing oscillator both in amplitude domain and in frequency domain is made in this paper. By means of the combined action of harmonically parametrical perturbation and forcing perturbation and suitably adjusting the parameters of perturbations, the chaotic motion of Duffing oscillator can be effectively controlled in a small region in the parametric space. We find that, in the amplitude domain, the chaotic motion exists only in the region where the ratio of the amplitudes of the perturbations is large than critical ratio, and, in the frequency domain, the chaotic motion exists only in a limited region where the frequency of perturbation is lower than superior frequency limit and larger than inferior frequency limit. The inferior frequency limit and superior frequency limit of chaotic region are discovered and determined firstly. An analytical expression of the critical ration of the amplitudes of forcing and parametrical perturbations is established.

Topics: Chaos
Commentary by Dr. Valentin Fuster
2005;():243-247. doi:10.1115/DETC2005-85170.

The generalized form of the non-homogeneous Mathieu differential equation is analyzed in this paper. This type of differential equation arises from dynamic behavior of a pendulum subjected to the butterfly support motion. The Lindstedt-Poincare’s technique is considered in order to obtain the analytical solutions. The transition curves in some special cases are presented and their related periodic solutions with periods of 2π and 4π are obtained. Numerical simulation is carried out for some typical points in ε-δ plane.

Commentary by Dr. Valentin Fuster
2005;():249-253. doi:10.1115/DETC2005-85710.

A numerical model is established in the present research on the basis of a theoretical analysis, for describing and analyzing the electric field of High Voltage Direct Current (HVDC) wall bushing that demonstrates highly nonlinear characteristics. The relationship between the electric field intensity and the resistance of the insulators of the wall bushing is highly nonlinear and the wall bushing is subjected high voltage with nonlinear electric field. A numerical iteration technique is developed with the Parameter Design Language (PDL) of a Finite Element Analysis software package for carrying out the numerical calculations. The nonlinear characteristics of the HVDC wall bushing are investigated with the model and the iteration technique established. The methodology presented in the research provides a new approach for designing and manufacturing the HVDC wall bushing.

Commentary by Dr. Valentin Fuster
2005;():255-258. doi:10.1115/DETC2005-85726.

Current statistical model needs to pre-define the value of maximum accelerations of maneuvering targets. So it may be difficult to meet all maneuvering conditions. In this paper a novel adaptive algorithm for tracking maneuvering targets is proposed. The algorithm is implemented with fuzzy-controlled current statistic model adaptive filtering and unscented transformation. The Monte Carlo simulation results show that this method outperforms the conventional tracking algorithm based on current statistical model.

Topics: Filtration
Commentary by Dr. Valentin Fuster
2005;():259-264. doi:10.1115/DETC2005-84628.

The accurate prediction of the sound power radiated from complicated structures, whose precise models are practically difficult to be made by the finite element method, is performed by an experimental-based approach combining impulse vibration testing and the boundary element method. This approach is applied to a small boat hull comprising of some panels with some longitudinal bending stiffeners and ribs as a basic research work in the series of a research for establishing an integrated analysis and optimization of mechanical systems to be assembled some components such as boat hulls and outer engines by means of using both experimental and theoretical modeling. It is verified that the predicted sound power level radiated from the hull is in a good agreement with an experiment. The parts of the hull radiating the noise dominantly can be identified.

Commentary by Dr. Valentin Fuster
2005;():265-272. doi:10.1115/DETC2005-84629.

This paper presents a new method for identifying the stiffness of engine mounts under the condition of being built in a structural system as in practical use. A conventionally standard method is to use a dynamic stiffness measurement equipment that can deal with only an individual mount. In the new method, the stiffness values of mounts built in a structural system are identified using the modal parameters of the system which are obtained by experimental modal analysis. Vibration testing of the structural system in an operational condition can make it possible to consider preload effect caused by the gravitational and driving force, such as thrust force, applied to the structural system. Additionally, vibration testing using an impact hammer is widely available so that the new method can make it much easier to identify the stiffness of mounts in various situations than the conventional method. In this paper, the validity of the method is demonstrated using both a simulation study using a finite element model and an actual trial for an actual outboard engine. The result shows the dependence of the mount stiffness on the gravitational force and the thrust force at the propeller of the outboard engine.

Topics: Engines , Stiffness
Commentary by Dr. Valentin Fuster
2005;():273-280. doi:10.1115/DETC2005-84630.

A complete experimental approach is here carried out to obtain the dynamic characterization of an automotive brake disc fixed on its grounded knuckle. The operative deflection shapes (ODS) were measured under harmonic excitation in the 1–23 kHz frequency range. Electronic Speckle Pattern Interferometry (ESPI) [1, 2] technology was exploited to measure high spatially defined full field displacement maps at each frequency by means of optical non-contact techniques. The harmonic excitation source was an electrodynamic shaker. The displacement maps acquired depict the dynamic behavior of the brake disc with high accuracy in the whole range, from the global bending modes at low frequency to the arising of small lobes at high frequency, with particular attention paid to the transition over resonance frequencies. Results are reported and discussed in detail.

Commentary by Dr. Valentin Fuster
2005;():281-288. doi:10.1115/DETC2005-84631.

The assessment of structural damage location in composite honeycomb sandwich panels is here pursued by means of a complete experimental non-destructive approach on a pre-damaged sample. In the experiments proposed full field displacement maps were acquired by means of optical non-contact Electronic Speckle Pattern Interferometry (ESPI) technology [1, 2], in order to obtain high spatial definition and locate small defects on the sample, like debondings, material separations, voids, cracks and delaminations. When dealing with holographic/speckle interferometry it is important to find the stressing technique able to produce singularities in the state of the object surface. Four different loading approaches were taken to detect the flaws: acoustic, thermal, static and harmonic excitation. The displacement maps acquired depict with high accuracy the inhomogeneous local behavior of the structure induced by the defects. Results are reported from the different loading approaches and discussed in detail.

Commentary by Dr. Valentin Fuster
2005;():289-298. doi:10.1115/DETC2005-84650.

Output-only methodologies are nowadays well established to extract modal parameters in many areas of engineering, such as civil, mechanical and aeronautical. In the past, civil engineering tests have been mainly developed for road bridges, with the vehicle passage over the bridge deck representing the main source of excitation with some contribution given by the ambient noise. In the road bridge cases, the excitation is considered to be a function of the road surface roughness, the vehicles speed, the weight and suspension vehicles characteristics, and also the random access of the vehicles over the bridge, whilst for the railway case, not all these issues are correctly addressed, and other characteristics rise-up, possibly advantageous for a correct identification process; to demonstrate this statement, we can bear in mind how the random access of the vehicles becomes meaningless for railway bridges, the single train being a quasi deterministic source; furthermore, the influence of the train weight should be considered if compared to usual road vehicles. Since output-only techniques are conceived for random excitation noise, their use in these conditions is considerably stressed and special care, or alternative techniques, has to be considered to avoid errors. In this sense, the bridge reference model becomes more important and some special techniques have to be developed.

Topics: Railroads
Commentary by Dr. Valentin Fuster
2005;():299-304. doi:10.1115/DETC2005-84651.

This paper presents a study of the frequency domain behaviour of a single degree of freedom (SDOF) system with a fractional derivative model, named Fractional Kelvin-Voigt. Frequency response functions (FRFs) as receptance and transmissibility are analytically studied. Then the model is applied to describe the dynamic behaviour of a magneto-mechanic system in the frequency domain, consisting of a body of para or dia-magnetic material vibrating in a field created by a pair of magnets.

Commentary by Dr. Valentin Fuster
2005;():305-313. doi:10.1115/DETC2005-84681.

This paper presents a modelling approach of a high-speed spindle-bearing system based on a finite-element model analysis coupled to an experimental modal identification. Dynamic equations of the rotating entity are obtained using Lagrangian formulation associated with a numerical finite element method based on Timoshenko beam theory. Element kinematics is formulated in a co-rotational coordinate frame. A method for the experimental characterization of the dynamic behavior of a High Speed Machining (HSM) spindle is proposed. The goal of this method is to understand the influence of spindle structure elements on overall dynamic behavior. Each element is individually characterized and is integrated or not into the global model depending on the results. The choice of the finite element type for generating the numeric model is carried out on the basis of modal and harmonic experimental results. High-speed rotational effects including gyroscopic coupling and spin softening effects are investigated. The Campbell diagram indicates the potential critical speed for mass unbalance response and for synchronous excitation representative of the milling forces at tooth impact frequency. Excessive vibration levels at specific node location enable spindle component stress or failure during manufacturing processes to be predicted. The model is a useful tool for qualifying spindles in the manufacturing process and predicting their reliability. The proposed modeling approach can be transferred to other type of spindle.

Commentary by Dr. Valentin Fuster
2005;():315-322. doi:10.1115/DETC2005-84805.

This paper provides two new analytical solutions to the computation of surface location errors, or part geometric errors that arise due to forced vibrations of the cutting tool, during stable milling. The two approaches are based on frequency domain and harmonic balance analyses. Comparisons between the analytical results, time domain simulation, and experiment are included.

Topics: Errors , Milling
Commentary by Dr. Valentin Fuster
2005;():323-331. doi:10.1115/DETC2005-84810.

The paper describes the dynamical real-time simulation of the Z axis of a five axis machining center for high speed milling. The axis consists of a mechanical structure: machine head and electro-mandrel, a CNC Control System provided with feed drives and a Pneumatic System to compensate the weight of the entire vertical machine head. These three sub-systems have been studied and modeled by means of: • FEM modeling of the mechanical structure; • an equation set to represent the main functions of the CNC; • an equation set to represent the functioning of the Pneumatic System. These different modeling sub-systems have been integrated to obtain the entire actual dynamical behavior of the Z axis. A particular analysis was developed to represent the friction phenomena by a specific analytical model. Experimental activity was developed to test and validate the different modeling sub-systems, and other experimental tests were performed on the machining center to compare simulation outputs with experimental responses.

Commentary by Dr. Valentin Fuster
2005;():333-341. doi:10.1115/DETC2005-85259.

The paper is concerned with the assessment of dynamic tire forces that arise when a vehicle traverses a road with a harmonic profile. In this case, solutions of all equations are found analytically. The technique developed is not specific to a particular linear vehicle model, which is represented by its mass, stiffness, and damping matrices. A factored representation of the vector of the tire forces as the product of a matrix and a vector, where both the matrix and the vector are functions of only one variable, is derived. The matrix is constructed either by the mathematical model of the vehicle or by results of special tests on the vehicle at several values of speed. The vector is given by an explicit formula and requires knowledge of only the wheelbase distances. An application of the technique discussed to the so-called low-speed testing is discussed. It is shown that, in spite of the wheelbase filtering phenomenon, it is possible to replace testing vehicles at highway speeds by tests at artificially low speeds. The results of the latter tests can then be recalculated into those corresponding to the highway conditions. The discussions are illustrated by numerical examples.

Topics: Force , Testing , Vehicles , Tires
Commentary by Dr. Valentin Fuster
2005;():343-351. doi:10.1115/DETC2005-85524.

An identification procedure for a sample class of mechanical system exhibiting non-linear behavior is presented and validated experimentally. The proposed procedure operates on the free-vibration response of the system and is able not only to extract the time-depended modal parameters, but also to identify the functional relationships between modal frequencies and modal amplitudes of oscillation. These relationships depend just on the mechanical characteristics of the system and thus, they characterize entirely the dynamic behavior. An experimental validation of the procedure performed on a physical laboratory system is presented and discussed. The experimental set-up was designed in order to allow for different configurations and hence for different levels of nonlinearity. The comparison between the identified results and the results of a proper analytical model of the system allows for highlighting the sensibility and effectiveness of the proposed procedure.

Commentary by Dr. Valentin Fuster
2005;():353-361. doi:10.1115/DETC2005-85633.

This paper describes vibro-acoustic direct and indirect measurements for road noise NVH predictions from a complete car. Attention is devoted to the dynamic response of the structure and interior pressure field toward tire patch displacement inputs. The direct measurements exploited the Team Corporation CUBE™ high frequency 6 degree-of-freedom (DOF) shaker recently installed at the KULeuven Vehicle Technologies Laboratory; the input was provided directly at the tire contact patch, while the responses were measured as accelerations and pressures on the structure. In the indirect measurements a low-mid frequency volume velocity source (LMFVVS) was used to acoustically excite the structure in the reverse path direction from the inside of the interior car cavity, while accelerations on the car and forces/torques where acquired by a 6-DOF dynamometer at the tire patch. From both types of excitations Frequency Response Functions (FRF) were calculated in the frequency range [0–500 Hz]. The non-linearity of the full car system was investigated with different direct and indirect measurement tests, in order to assess the feasibility of the reciprocity principle in such a complex structure. Measurement set-ups, results and comparisons are described and discussed in detail.

Commentary by Dr. Valentin Fuster
2005;():363-372. doi:10.1115/DETC2005-85659.

In this work the dynamic contact of hemispherical indenter covered by a thick viscoelastic layer and pressed against a flat rigid surface is modelled. The goal is to investigate the dynamic behavior of robotic fingertips composed by an inner rigid structure covered by a soft layer, mimicking the human biological model. A quasi-linear model, frequently used to describe the behavior of soft and pulpy biological tissues, is adopted in order to achieve a compromise between the simplicity of classical linear models and the difficulty of nonlinear approaches. Two different materials (a polyurethane gel and a silicon rubber) have been experimentally tested in order to find the parameters of the model and to validate it. Finally, the advantage of the use of digital filters method in identification process is exploited, so that the identification becomes suitable for online process.

Commentary by Dr. Valentin Fuster
2005;():373-381. doi:10.1115/DETC2005-85725.

Non integer, fractional order derivative rheological models are known to be very effective in describing the linear viscoelastic dynamic behaviour of mechanical structures made of polymers [1]. The application of fractional calculus to viscoelasticity can be physically consistent [2][3][4] and the resulting non integer order differential stress-strain constitutive relation provides good curve fitting properties, requires only a few parameters and leads to causal behaviour [5]. When using such models the solution of direct problems, i.e. the evaluation of time or frequency response from a known excitation can still be obtained from the equations of motion using standard tools such as modal analysis [6]. But regarding the inverse problem, i.e. the identification from measured input-output vibrations, no general technique has so far been established, since the current methods do not seem to easily work with differential operators of non integer order. In this paper a frequency domain method is proposed for the experimental identification of a linear viscoelastic model, namely the Fractional Zener also known as Fractional Standard Linear Solid [5], to compute the frequency dependent complex stress-strain relationship parameters related to the material. The procedure is first checked with respect to numerically generated frequency response functions for testing its accuracy, and then to experimental inertance data from a free-free homogeneous beam made of High Density Polyethylene (HDPE) in plane flexural and axial vibration.

Commentary by Dr. Valentin Fuster
2005;():383-389. doi:10.1115/DETC2005-84009.

The most widely known nonlinear phenomena in Micro-electro-mechanical systems (MEMS) are probably the contact instabilities. Contact problem is an important topic in the research of micro-motors. While the micro-motor is in operation, the rotor is intended to be in electrical contact with the ground plane, and the rotor and bearing hub form a pair of contact bodies. In the paper, a mathematic model is proposed to describe the contact process and two simplified contact finite element models of the rotor, bearing and ground plane are presented to simulate the contact. The effects on the contact stress, strain and pressure are analyzed in micro-scale. The rotor-to-bearing-hub and the hemispherical-bushing-on-ground-plane configurations finite element models (FEM) are established and the implementation of the contact problem is introduced to provide the numerical solutions acted as a guide to solution of contact problems in a variable capacitance micromotor. The numerical results of the contact stress, strain and pressure and the effects of the coefficient of friction and the surface roughness of the contact pairs on contact characteristics are studied and discussed in detail. It is indicated that the nonlinear effects should not be ignored and these results must be evaluated on a relative scale to compare different design options.

Commentary by Dr. Valentin Fuster
2005;():391-396. doi:10.1115/DETC2005-84144.

We present analysis of the global dynamics of electrically actuated microbeams under subharmonic excitation. The microbeams are excited by a DC electrostatic force and an AC harmonic force with a frequency tuned near twice their fundamental natural frequencies. We show that the dynamic pull-in instability can occur in this case for an electric load much lower than that predicted with static analysis and the same order-of-magnitude as that predicted in the case of primary-resonance excitation. We show that, once the subharmonic resonance is activated, all frequency-response curves reach pull-in, regardless of the magnitude of the AC forcing. Our results show a limited influence of the quality factor on the frequency response. This result and the fact that the frequency-response curves have very steep passband-to-stopband transitions make the combination of a DC voltage and a subhormonic of order one-half a promising candidate for designing improved high-sensitive RF MEMS filters.

Topics: Microbeams
Commentary by Dr. Valentin Fuster
2005;():397-404. doi:10.1115/DETC2005-84146.

We present a dynamic analysis and simulation of electrically actuated microelectromechanical systems (MEMS) resonators under primary-resonance excitation. We use a shooting technique, perturbation techniques, and long-time integration of the equation of motion to investigate the global dynamics of the resonators. We study the dynamic pull-in instability and show various scenarios and mechanisms for its occurrence. Our results show that dynamic pull-in can occur through a saddle-node bifurcation, a period-doubling bifurcation, or homoclinic tangling, depending on factors such as the initial conditions of the device and the level of the electrostatic force.

Commentary by Dr. Valentin Fuster
2005;():405-412. doi:10.1115/DETC2005-84190.

In this paper, the derivation of the finite element equations of piezothermoelasticity is presented using the classical and generalized Fourier’s law. Galerkin’s method is used to the spatial discretization of the equations. Based upon these equations, a finite element code is under development.

Commentary by Dr. Valentin Fuster
2005;():413-425. doi:10.1115/DETC2005-84482.

This article presents an efficient explicit dynamic formulation for modeling curved and twisted Carbon Nanotubes (CNT’s) based on a recently-developed intrinsic beam description (i.e. the dynamic state given by curvatures, strains, and velocities only) [Hodges, 2003] together with a finite element discretization incorporating atomistic potentials. This approach offers several advantages primarily related to the model’s computational efficiency: 1) the resulting partial differential equations governing motion are in first-order form (i.e. have first-order time derivatives only), 2) the system nonlinearities appear at low order, 3) the intrinsic description incorporating curvature allows low-order interpolation functions to describe generally curved and twisted nanotube centerlines, 4) inter-element displacements, slopes, and curvatures are matched at the element boundaries, and 5) finite rotational variables are absent, along with their inherit complexities. In addition, the developed model and finite element discretization are able to capture the nanotube’s dynamic response, without the expense of calculating the dynamic response of individual atoms as per Molecular Dynamics models. Simulation results are presented which illustrate the dynamic response of a typical CNT to axial, bending, and torsional loading. Results from the simulations are compared to similar results available in the literature, and close agreement is documented.

Commentary by Dr. Valentin Fuster
2005;():427-432. doi:10.1115/DETC2005-84521.

This paper presents analytic derivation of dynamic behavior of a liniearized micro-electro-mechanical resonator. The parametric oscillation results from a displacement-dependent electrostatic force generated by oscillation of a microbeam. The utilized device is a MEMS with a time-varying capacitor. The stability and steady state dynamic behavior of the MEMS has been analyzed without polarization voltage. The main characteristic of the no-polarization model is effects of parameters in stability of the system. A set of stability charts is provided for prediction of the boundary between the stable and unstable domains for the principal resonance. Applying perturbation method, analytical equations are derived to describe both the steady state and time response of the system.

Commentary by Dr. Valentin Fuster
2005;():433-439. doi:10.1115/DETC2005-84549.

This paper is concerned with the effect of axial load, shear deformation and rotary inertia on wave propagation in double-walled carbon nanotubes (DWCNTs) within terahertz range. Our analysis is based on Timoshenko-beam model and Euler-beam model. The present models predict some terahertz critical frequencies at which the number of wave speeds changes. In these models the amounts of wave speed is unique only when the frequency is below the lowest critical frequency. When the frequency is equal to the lowest critical frequency, there can be one or two (for CNTs of smaller radii) wave speeds. Furthermore, when the frequency is higher than the lowest critical frequency, more than one wave speed exists and waves of given frequency could propagate at various speeds. It can be seen that rotary inertia and shear deformation have a significant effect on both the wave speeds and the critical frequencies. Hence, terahertz wave propagation in CNTs should be better modeled by Timoshenko-beam model, instead of Euler-beam model.

Commentary by Dr. Valentin Fuster
2005;():441-451. doi:10.1115/DETC2005-84591.

This paper presents the nonlinear system identification of model parameters for a capacitive dual-backplate MEMS microphone. System parameters of the microphone are developed by lumped element modeling (LEM) and a governing nonlinear equation is thereafter obtained with coupled mechanical and electrostatic nonlinearities. The approximate solution for a general damped second order system with both quadratic and cubic nonlinearities and a non-zero external step loading is explored by the multiple time scales method. Then nonlinear finite element analysis (FEA) is performed to verify the accuracy of the lumped stiffnesses of the diaphragm. The microphone is characterized and nonlinear least-squares technique is implemented to identify system parameters from experimental data. Finally uncertainty analysis is performed. The experimentally identified natural frequency and nonlinear stiffness parameter fall into their theoretical ranges for a 95% confidence level respectively.

Commentary by Dr. Valentin Fuster
2005;():453-461. doi:10.1115/DETC2005-84603.

Due to the position-dependent nature of electrostatic forces, many microelectromechanical (MEM) oscillators inherently feature parametric excitation. This work considers the nonlinear response of one such oscillator, which is electrostatically actuated via non-interdigitated comb drives. Unlike other parametrically-excited systems, which feature only linear parametric excitation in their equation of motion, the oscillator in question here exhibits parametric excitation in both its linear and nonlinear terms. This complication proves to significantly enrich the system’s dynamics. Amongst the interesting consequences is the fact that the system’s nonlinear response proves to be qualitatively dependent on the system’s excitation amplitude. This paper includes an introduction to the equation of motion of interest, a brief, yet systematic, analysis of the equation’s nonlinear response, and experimental evidence of the predicted behavior as measured from an actual MEM oscillator.

Commentary by Dr. Valentin Fuster
2005;():463-471. doi:10.1115/DETC2005-84620.

The materials used in the field of printed circuit boards are becoming increasingly complex as they are common to make use of numerous combination of metallic and composite plies. The potential for utilization of circuit boards is generally verified through the numerical simulation, especially for the multilayer printed circuit boards with high electronic density. This paper provides a numerical model intended to describe numerically the behavior of multilayer multimaterial circuit boards. Two parts are considered in the developed model: one is elastic-plastic damaging model that is presented to describe the metallic ply in the multilayer circuit boards; another is degenerated bi-phase model that is presented to describe composite ply. With the combination of equivalent laminate (EQLAM) method, the degenerated bi-phase successfully models the woven glass-fiber/epoxy-resin composite ply. These two plies are the basic components of multilayer circuit boards. Meanwhile, with the verification of static tests and dynamic tests, the reliability of presented model is confirmed.

Topics: Lumber , Modeling , Circuits
Commentary by Dr. Valentin Fuster
2005;():473-478. doi:10.1115/DETC2005-84747.

A [10, 10]/[5,5] nanotube-based oscillator is studied using molecular dynamics in this paper. The inner tube can oscillate inside the outer tube with a stable frequency of 55GHz, if this nanomechanical system is insulated. When temperature effects are considered, it is found that the nanooscillator will stop due to the temperature-related interlayer friction between the outer tube and the inner tube. A nanoelectromechanical system (NEMS) is designed by coating electrodes on the top of the outer tube. The electromagnetic forces, induced by the WRITE voltage pulses that are applied on the electrodes, can overcome the interlayer friction. The frequency of the proposed NEMS oscillator depends on the frequency of the WRITE voltage pulses.

Commentary by Dr. Valentin Fuster
2005;():479-487. doi:10.1115/DETC2005-85090.

Instabilities in a vibrating MEMS gyroscope that is subject to periodic fluctuations in input angular rates are investigated. For the purpose of acquiring stability conditions, when the angular rate input is subject to small intensity periodic fluctuations, dynamic behavior of periodically perturbed linear gyroscopic systems is studied in detail. An asymptotic approach based on the method of averaging has been employed for this purpose, and closed-form conditions for the onset of instability due to parametric resonances have been obtained. A numerical approach based on the Floquet-Lyapunov theory is employed for validating the analytical stability predictions. Furthermore, for characterizing the effect due to change in angular rate input, an in-depth natural frequency analysis has been performed. Stability predictions have been illustrated via stability diagrams in the excitation amplitude-frequency space.

Commentary by Dr. Valentin Fuster
2005;():489-494. doi:10.1115/DETC2005-85225.

Future optical micro systems such as Micro Electro Mechanical Systems (MEMS) scanners and micro-mirrors will extend the resolution and sensitivity offered by their predecessors. These systems face the challenge of achieving nanometer precision subjected to various disturbances. Predicting the performance of such systems early in the design process can significantly impact the design cost and also improve the quality of the design. Our approach aims to predict the performance of such systems under various disturbance sources and develop a generalized design approach for MEMS structures. In this study, we used ANSYS for modeling and analysis of a torsional MEMS scanner mirror. ANSYS modal analysis results, which are eigenvalues (natural frequencies) and eigenvectors (modeshapes), are used to obtain the state space representation of the mirror. The state space model of the scanner mirror was reduced using various reduction techniques to eliminate the states that are insignificant for the transfer functions of interest. The results of these techniques were compared to obtain the best approach to obtain a lower order model that still contains all of the relevant dynamics of the original model. After the model size is reduced significantly, a disturbance analysis is performed using Lyapunov approach to obtain root-mean-square (RMS) values of the mirror rotation angle under the effect of a disturbance torque. The Lyapunov approach results were validated using a time domain analysis.

Commentary by Dr. Valentin Fuster
2005;():495-500. doi:10.1115/DETC2005-85330.

Next generation optical Micro Electro Mechanical Systems (MEMS) such as micro mirrors and micro scanners will extend the resolution and sensitivity offered by their predecessors. It is advantageous to predict the performance of such systems early in the design stage. In this study, we developed a sensitivity analysis framework to investigate the effect of the modal and physical parameters on the performance of a torsional MEMS scanner. The sensitivity framework described in this paper is related to the disturbance analysis framework which was introduced in the first part of this study. Disturbance analysis framework uses the Lyapunov Approach to obtain root-mean-square (RMS) values of the mirror rotation angle under the effect of a disturbance torque. Analytical formulas were derived for the calculation of the modal parameter sensitivities and the results were verified by the finite difference method. The analytical formulas for the calculation of physical parameter sensitivities were described but they were found to be very inefficient due to the complexity and computational expense in calculating the eigenvalue and eigenvector derivatives included in these equations. Instead, the finite difference method was used to calculate the physical parameter sensitivities for the torsional MEMS scanner.

Commentary by Dr. Valentin Fuster
2005;():501-507. doi:10.1115/DETC2005-85742.

We study the nonlinear multi-mode dynamics of a microbeam for noncontact atomic force microscopy in ultra-high vacuum. A boundary-value problem that includes a coupled linear thermo- and viscoelastic field with a localized nonlinear atomic interaction force, augmented by the linearized heat equation, is reduced to a modal dynamical system via Galerkin’s method. An equivalent linear thermoelastic quality factor is obtained and compared with a closed form solution. A numerically obtained escape curve defines valid operating parameters for low damping conditions. Primary, secondary and coupled internal resonances of a three-mode system are examined to reveal a rich bifurcation structure.

Commentary by Dr. Valentin Fuster
2005;():509-515. doi:10.1115/DETC2005-84095.

This paper introduces a model for multiple degradation features of an individual component. The maximum likelihood approach is employed to estimate the model parameters. Afterwards, a proportional hazards model is presented, which considers hard failures and multiple degradation features simultaneously. The integrated model enables us to predict the mean remaining useful life of a component based on on-line degradation information. An example for bearing prognostic is provided to demonstrate the proposed models in practical use.

Commentary by Dr. Valentin Fuster
2005;():517-524. doi:10.1115/DETC2005-84178.

A Blind Source Separation (BSS) based new method for multi-fault diagnosis of rotors is presented. The statistic variable based decorrelation approach is employed to a