bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigation of Dispersion-Relation-Preserving Scheme and Spectral Analysis Methods for Acoustic Waves
Authors: Vanel Florence O. , Baysal Oktay
Published: February 2008

Important characteristics of acoustic wave propagation are encoded in their dispersion relations. Hence, a computational algorithm, which attempts to preserve these relations, was investigated. Considering the linearized, 2-D Euler equations, simulations were performed to validate this scheme and its boundary conditions. The results were found to agree favorably with the exact solutions. The boundary conditions were transparent to the outgoing waves, except when the disturbance source was close to a corner boundary. The time-domain data generated by such computations were often intractable until their spectra was analyzed. For this purpose, the relative merits of three spectral analysis methods were considered. For simple, periodic waves with steep-sloped spectra, the periodogram method produced better estimates than the Blackman-Tukey method, and the Hanning window was more effective when used with the former. For chaotic waves, however, the weighted-overlapped-segment-averaging and Blackman-Tukey methods were better than the periodogram method. Therefore, it was observed that the spectral representation of time-domain data was significantly dependent on the particular method employed.
Frequency Domain Modal Parameter Identification of High Order Systems in a Numerically Stable Way
Authors: Xu K. Q.
Published: February 2008

Frequency domain modal parameter identification methods have several attractive properties as compared with the time domain methods except for the limitation of low-order-and-narrow-band per analysis. As rule of thumb, a limit of less than ten modes has been observed for several popular frequency domain algorithms. However, this paper will show, that with a proper and thorough use of the orthogonal polynomials in the frequency domain, the number of modes per analysis can be increased to as high as 75 in a comparatively wide frequency range of interest while still retaining numerical stability. Both numerical example (75 modes in 5–1000 Hz) and experimental data analysis (56 modes in 50–5000 Hz) are presented to demonstrate the effectiveness of this innovative approach.
The Use of Wave-Absorbing Elements for the Evaluation of Transmission Characteristics of Beam Junctions
Authors: De Langhe K. , Sas P. , Vandepitte D.
Published: February 2008

The following paper addresses the applicability and the advantages of finite elements for the study of transmission and reflection of waves impinging upon beam junctions. It will be shown that it is possible to simulate travelling waves on general beams by using a wave-absorbing element at each end of the beam. The stiffness matrix of the wave-absorbing element is determined by the characteristic stiffness of the beam. A general procedure to identify the characteristic stiffness is given in the appendix. Next, by performing a direct frequency response analysis on the finite element model of the junction (including the wave-absorbing elements at either end), it is possible to calculate the energy absorbed by the wave-absorbing elements. Along with some additional calculations, one can easily deduce the energy transmission characteristics of the junction. The method will be explained in detail in the case of beam junction. The applicability, which is mainly situated in the higher frequency dynamic range, will be highlighted through some relevant examples. One of the main advantages of using finite elements is the possibility of evaluating the transmission characteristics of whatever junction, including all essential geometrical details, in a straightforward way.
Dynamic Loosening and Tightening of a Single-Bolt Assembly
Authors: Hess D. P. , Sudhirkashyap S. V.
Published: February 2008

Previous analyses of threaded fasteners under vibration are based on static equilibrium conditions with supporting data limited to low frequency loading. Such analyses predict only a net loosening action. This paper presents a dynamic model of a single-bolt assembly with moderate pre-load subjected to axial harmonic vibration. Simulations with this model predict that threaded fasteners can, on the average, loosen or tighten in the presence of vibration; and that the applied vibration, as well as other system parameters, can be tuned so that either action occurs. Measurements from a single-bolt assembly apparatus are presented and compared with the simulations.
Nonlinear Fluid-Structure Interaction in Propeller Aircraft Cabins
Authors: Alvelid M.
Published: February 2008

A procedure for studying the acoustic superharmonic response in propeller aircraft cabins subject to stationary single frequency load excitation is proposed. The harmonic balance method is used to solve the nonlinear fluid-structure interaction multi-degree-of-freedom problem at hand. In the problem studied, the structure is nonlinear while the fluid remains linear. In the solution method proposed, generalised coordinates of the assumed series expansion for the displacements are used as unknowns. Two examples, simulating an aircraft structure with a fluid cavity, are examined. The present calculations show that in a lightly damped one-dimensional system with cubic stiffness, the noise levels from the superharmonic resonance may be slightly lower than those resulting from the fundamental frequency. For a typical model of a cross-section of an aircraft cabin, it is shown that nonlinear damping in spacing material will result in a considerable influence of the response in the third tone. For the one-dimensional system, good agreement is obtained with results from parallel nonlinear analyses where the discretized system of inertia equations is solved employing explicit time integration. For the multi-degree-of-freedom system modelling the aircraft cabin, a comparison of results between the harmonic balance method and the explicit time integration of a corresponding FE model indicated a partial agreement of the two. However, several different solutions may exist to a nonlinear equation, which make the comparison uncertain.
Nonlinear Piezothermoelasticity and Multi-Field Actuations, Part 1: Nonlinear Anisotropic Piezothermoelastic Shell Laminates
Authors: Tzou H. S. , Bao Y.
Published: February 2008

Nonlinear characteristics, either material or geometrical nonlinearity, and temperature variations can significantly influence the performance and reliability of piezoelectric sensors, actuators, structures, and systems. This paper is intended to examine the nonlinear piezothermoelastic characteristics and temperature effects of piezoelectric laminated systems, and it is divided into two parts. Part 1 is concerned with a mathematical modeling of nonlinear anisotropic piezothermoelastic shell laminates and Part 2 is a study of static and dynamic control of a nonlinear piezoelectric laminated circular plate subjected to mechanical, electric, and temperature excitations. Geometric nonlinearity induced by large deformations is considered in both parts. A generic nonlinear piezothermoelastic shell lamination theory is proposed and its nonlinear thermo-electromechanical equations are derived based on Hamilton’s principle. Thermo-electromechanical couplings among the elastic, electric, and temperature fields are discussed, and nonlinear components identified. Applications of the nonlinear theory to other materials, continua, sensors, actuators, and linear systems are discussed.
Analysis of a Polarization-Maintaining Optical Fiber Interferometer for Simultaneous Measurement of Acoustic Pressure and Temperature
Authors: Chiu B. , Hastings M. C.
Published: February 2008

An all polarization-maintaining fiber Mach-Zehnder interferometer for simultaneous measurement of acoustic pressure and temperature is examined. Measurements by Farahi et al. (1990) indicate that the cross-sensitivity between temperature and axial strain may be significant for a polarization-maintaining fiber Fabry-Perot interferometer; however, no one has examined the significance of cross-sensitivity for the Mach-Zehnder case. Sensitivities to acoustic pressure and temperature, and the cross-sensitivity generated by simultaneous disturbances are determined both analytically and numerically. The fiber’s relatively high temperature sensitivity compared with its acoustic pressure sensitivity suggests that a short length of sensing fiber is sufficient for use as a temperature sensor with little or no interference from acoustic pressure. To measure acoustic pressure, however, a straight length of the fiber examined in this study is not sufficient. In practice, this sensing fiber could be coiled around a compliant cylinder or into a small diameter sensing element to enhance longitudinal strain and thus sensitivity. Results show that in either case, the cross-sensitivity is extremely small and can be ignored.
Natural Frequencies and Stability of a Spinning Disk Under Follower Edge Tractions
Authors: Chen Jen-San
Published: February 2008

The vibration and stability of a spinning disk under follower edge tractions are studied both numerically and analytically. The edge traction is circumferentially stationary in the space. When the compressive traction is uniform, natural frequencies of most of the non-reflected waves decrease, except some of the zero-nodal-circle modes with small number of nodal diameters in the low frequency range. When the spinning disk is under nonuniform traction in the form of cos kθ, where k is a nonzero integer, it is found that the eigenvalue only changes slightly under the edge traction if the natural frequency of interest is well separated from others. When two modes are almost degenerate, however, modal interaction (frequency loci veering or merging) occurs when the difference between the number of nodal diameters of these two modes is equal to ±k. Types of modal interaction vary as the radius ratio of the circular disk changes. Analytical methods for predicting how the eigenvalue changes and what type of modal interaction will occur are proposed and verified.
Flexural Wave Propagation in a Fluid-Loaded Elastic Plate With Periodically Varying Rigidity
Authors: Hawwa M. A. , Nayfeh A. H.
Published: February 2008

The method of multiple scales is utilized to analyze the propagation of flexural waves in a fluid-loaded elastic plate with periodically varying rigidity. Subsonic modes are coupled under a Bragg condition imposed by the parametric periodicity, leading to a strong stopband interaction. This interaction is analytically described by two coupled-mode equations. The results might be utilized to avoid the undesirable acoustic radiation occurring when subsonic waves encounter a discontinuity.
Identification of Structural Parameters in Mistuned Bladed Disks
Authors: Mignolet Marc P. , Lin Chung-Chih
Published: February 2008

The present investigation focused on the estimation of the parameters of a structural model to represent “at best” a set of measurements of the steady state response of a mistuned bladed disk. The applicability of the least squares and maximum likelihood approaches to the identification of the bladed disk model from this data is first investigated. The advantages and drawbacks of these techniques motivate the introduction of a new mixed least squares-maximum likelihood formulation which is shown to recover well the true model parameters from noisy simulated response data.
A Reduced Order Modeling Technique for Mistuned Bladed
Disks
Authors: Castanier M. P. , Óttarsson G. , Pierre C.
Published: February 2008

The analysis of the response statistics of mistuned turbomachinery rotors requires an expensive Monte Carlo simulation approach. Simple lumped parameter models capture basic localization effects but do not represent well actual engineering structures without a difficult parameter identification. Current component mode analysis techniques generally require a minimum number of degrees of freedom which is too large for running Monte Carlo simulations at a reasonable cost. In the present work, an order reduction method is introduced which is capable of generating reasonably accurate, very low order models of tuned or mistuned bladed disks. This technique is based on component modes of vibration found from a finite element analysis of a single disk-blade sector. It is shown that the phenomenon of mode localization is well captured by the reduced order modeling technique.
Effect of Void Fraction on Vibrational Behavior of Tubes in Tube Bundle Under Two-Phase Cross Flow
Authors: Lian H. Y. , Noghrehkar G. , Chan A. M. C. , Kawaji M.
Published: February 2008

The effects of local two-phase flow parameters on the vibrational behavior of tubes have been studied in an in-line 5 × 20 tube bundle subjected to air-water cross-flow. One of the tubes was flexibly mounted and instrumented for vibration measurement and the others were rigid. Parameters obtained include local void fraction fluctuations, RMS amplitude of void fraction fluctuations, void fraction distributions across the tube bundle, flow regimes based on probability density function of void fraction signals, damping ratio, and tube vibration response as a function of mass flux, void fraction and dynamic pressure. Damping and tube vibration amplitude in two-phase flow have been found to be closely related to the RMS amplitudes of the local void fraction fluctuations and dynamic pressure fluctuations, respectively.
Vibration of a Simply Supported L-Shaped Plate
Authors: Solecki R.
Published: February 2008

Recently Solecki (1996) has shown that a differential equation for vibration of a rectangular plate with a cutout can be reduced to boundary integral equations. This was accomplished by filling the cutout with a “patch” made of the same material as the rest of the plate and separated from it by an infinitesimal gap. Thanks to this procedure it was possible to apply finite Fourier transformation of discontinuous functions in a rectangular domain. Subsequent application of the available boundary conditions led to a system of boundary integral equations. A plate simply supported along the perimeter, and fixed along the cutout (an L-shaped plate), was analyzed as an example. The general solution obtained by Solecki (1996) serves here to determine the frequencies of natural vibration of a L-shaped plate simply supported all around its perimeter. This problem is, however, more complicated than the previous example: to satisfy the boundary conditions an infinite series depending on discontinuous functions must be differentiated. The theoretical development is illustrated by numerical values of the frequencies of the natural vibrations of a square plate with a square cutout. The results are compared with the results obtained using finite elements method.
Chaotic Vibration of a Simple Model of the Machine Tool-Cutting Process System
Authors: Wiercigroch M.
Published: February 2008

A study on a simple model of the machine tool—cutting process system is presented. As the system is non-linear and discontinuous, and exhibits intermittent cutting, non-linear dynamics techniques such as constructing bifurcation diagrams and Poincare´ maps were employed to ascertain a quality of motion. Untypical routes to chaos and unusual topology of Poincare´ sections were observed. New phenomena such as unidirectional bifurcation and births and deaths of periodic solutions were detected. It was also found out that the dynamic responses of the analysed system can be most effectively controlled by a magnitude of the cutting force.
Flexural Vibration of Cylindrical Shells Partially Coupled With External and Internal Fluids
Authors: Amabili M.
Published: February 2008

In this paper, the free flexural vibrations of a partially fluid-loaded simply supported circular cylindrical shell are studied; the fluid is assumed to be inviscid and to present a free-surface parallel to the shell axis. The presence of external and internal fluids are both studied and the problem for incompressible and compressible fluid are both discussed by using the added virtual mass approach. Circumferential dependence of displacement is extended in a Fourier series. The maximum potential energy of the cylinder is evaluated using a sum of reference kinetic energies of the shell vibrating in vacuum; this fact allows the proposed method to be independent from the theory of shells used. Then, the Rayleigh quotient for fluid-shell coupled vibration is formulated and minimized to obtain the Galerkin equation whose solution gives the natural frequencies and mode shapes. Numerical computations are performed to obtain the modal characteristics as functions of the level of water in contact with the shell in the range of good accuracy of the theory, that is around the half-wet shell level. Results for both a shell partially surrounded and filled with water are obtained and compared.
Existence of Periodic Solution for Beams With Harmonically Variable Length
Authors: Esmailzadeh E. , Nakhaie-Jazar G. , Mehri B.
Published: February 2008

The transverse oscillatory motion of a simple beam with one end fixed while driven harmonically at the other end along its longitudinal axis is investigated. For a special case of zero value for the rigidity of beam, the problem reduces to that of a vibrating string with its corresponding equation of motion. The sufficient condition for the periodic solution of the beam was determined using the Green’s function and Schauder’s fixed point theorem. The criterion for the stability of the system is well defined and the condition for which the performance of the beam behaves as a nonlinear function is stated.
Complex Time Series Modeling and Analysis for Rotor Dynamics Identification
Authors: Lee Chong-Won , Park Jong-Po , Kim Kwang-Joon
Published: February 2008

A new time series method, directional ARMAX (dARMAX) model-based approach, is proposed for rotor dynamics identification. The dARMAX processes complex-valued signals, utilizing the complex modal testing theory which enables the separation of the backward and forward modes in the two-sided frequency domain and makes effective modal parameter identification possible, to account for the dynamic characteristics inherent in rotating machinery. The dARMAX is superior in nature to the conventional ARMAX particularly in the estimation of the modal parameters for isotropic and weakly anisotropic rotors. Numerical simulations are performed to demonstrate effectiveness of the dARMAX.
Unbalance Response and Stability Analysis of Horizontal Rotor Systems Mounted on Nonlinear Rolling Element Bearings With Viscoelastic Supports
Authors: Bhattacharyya K. , Dutt J. K.
Published: February 2008

Unbalance response and stability analysis of a rotor shaft system, with the rotor mounted in the middle of a massless shaft, having linear elasticity and internal damping, with bearings having nonlinear restoring force characteristics at the ends mounted on viscoelastic support, has been carried out, taking the effect of gravity into account. The restoring force characteristics of the bearing has been linearized, by the method of effective linearization, thereby enabling an approximate stability analysis using simple techniques. It is found that, unlike the case with a bearing having linearly varying restoring force characteristics, gravity not only affects the unbalance response but also causes a decrease in the stability limits when the restoring force characteristics are nonlinear.
On the Control of Chaos in Extended Structures
Authors: Barratt C.
Published: February 2008

A mechanism is proposed for synchronizing the chaotic vibrations of an externally forced array of oscillators with nearest-neighbor viscoelastic coupling. The proposed mechanism involves the application of small time-dependent perturbations to the individual oscillators. The perturbations required to preserve the coherence are of the order of magnitude of any noise present. The mechanism works with any form of external forcing. A modification of the mechanism is used to control the forced chaotic vibrations of a single Duffing oscillator allowed to vibrate out of the vertical plane.
A Finite Element Geometrically Nonlinear Dynamic Formulation of Flexible Multibody Systems Using a New Displacements Representation
Authors: Mayo J. , Domi´nguez J.
Published: February 2008

In previous work (Mayo, 1993), the authors developed two geometrically nonlinear formulations of beams inflexible multibody systems. One, like most related methods, includes geometric elastic nonlinearity in the motion equations via the stiffness terms (Mayo and Domi´nguez, 1995), but preserving terms, in the expression for the strain energy, of a higher-order than most available formulations. The other formulation relies on distinguishing the contribution of the foreshortening effect from that of strain in modelling the displacement of a point. While including exactly the same nonlinear terms in the expression for the strain energy, the stiffness terms in the motion equations generated by this formulation are exclusively limited to the constant stiffness matrix for the linear analysis because the terms arising from geometric elastic nonlinearity are moved from elastic forces to inertial, reactive and external forces, which are originally nonlinear. This formulation was reported in a previous paper (Mayo et al, 1995) and used in conjunction with the assumed-modes method. The aim of the present work is to implement this second formulation on the basis of the finite-element method. If, in addition, the component mode synthesis method is applied to reduce the number of degrees of freedom, the proposed formulation takes account of the effect of geometric elastic nonlinearity on the transverse displacements occurring during bending without the need to include any axial vibration modes. This makes the formulation particularly efficient in computational terms and numerically more stable than alternative geometrically nonlinear formulations based on lower-order terms.
A New Class of Distributed Sensors
Authors: Baz A. , Poh S.
Published: February 2008

A new class of distributed sensors is presented which can measure both the linear and angular deflections of composite beams. The sensor relies in its operation on a set of wires which are embedded off the neutral axes of the composite beams. The wires are arranged in a special manner which allows continuous monitoring of the deflection curve of the beam. The output signals of the wires are processed to determine the linear and angular displacements at critical discrete points along the beam axis. The theoretical and experimental performance of the sensor is presented in both the time and frequency domains. Comparisons are given between the experimental performance of the distributed sensor and that of conventional laser sensors in order to demonstrate the accuracy and merits of the distributed sensor. The results obtained suggest the potential of this new class of sensors as a viable means for monitoring the static and dynamic deflections of flexible composite SMART beams and plates.
Rotational Compliance Measurements of a Flexible Plane Structure Using an Attached Beam-like Tip, Part 2: Experimental Study
Authors: Qu Y. C. , Cheng L. , Rancourt D.
Published: February 2008

This paper presents an experimental assessment of the Tip Excitation Technique (TET) introduced in a companion paper. The aim of the technique is to measure the rotational compliance of attached plane structures. Following the guidelines established on the basis of a numerical study in the companion paper, experimental measurements were performed on a rectangular plate and results were compared with numerical simulations. The investigation focuses on the general performance of the technique, on the different types of excitation used and on other factors necessary to ensure accurate results. In addition, an error analysis is conducted to demonstrate the sensitivity of the results to biased measurement quantities. It is concluded that the proposed technique can be used in the low to middle frequency range, where relatively strong modal behavior is involved.
Optimal Design of Active Suspensions Using Damping Control
Authors: Lieh Junghsen
Published: February 2008

This paper studies the effect of optimal damping control suspensions on vehicle ride performance. The gain matrix is developed from second-order equations with the road roughness represented by a stochastic process. With only velocities as the feedback signal, the number of unknowns and measurements is reduced leading to more efficiency in data processing. The control is implemented on a quarter-car model which includes the tire damping effect. The spectral density is compared with those for passive and fully active systems.
A Computationally Efficient Objective Function for the Evaluation of the Natural Frequency in Structural Modification and Optimization Problems
Authors: Chang Tien-Sheng , Magrab E. B.
Published: February 2008

A highly computationally efficient objective function for measuring the change in the natural frequency when a structure is modified is introduced. When the optimization of an orthotropic plate is studied, a decrease in CPU time by at least a factor of 40 is obtained when the new objective function is compared to that derived from the minor structural modification technique. The greater the number of finite elements affected by the design changes the higher the factor of improvement will be. This new objective function has the additional advantage that it can be used for substantial modifications to the original design.
Time Domain Simulation of Jack-up Dynamics With the Extremes of a Gaussian Process
Authors: Taylor P. H. , Jonathan P. , Harland L. A.
Published: February 2008

Random simulations are often used to simulate the statistics of storm-driven waves. Work on Gaussian linear random signals has lead to a method for embedding a large wave into a random sequence in such a way that the composite signal is virtually indistinguishable (in a rigorous statistical limit) from a purely random occurrence of a large wave. We demonstrate that this idea can be used to estimate the extreme response of a jack-up in a severe sea-state in a robust and efficient manner. Results are in good agreement with those obtained from a full random time-domain simulation.
Free Vibration of Buckled Laminated Plates by Finite Element Method
Authors: Shiau Le-Chung , Wu Teng-Yuan
Published: February 2008

Free vibration behavior of buckled composite plates are studied by using a high precision triangular plate element. This element is developed based on a simplified high order plate theory and von Ka´rma´n large deformation assumptions. The nonlinear governing equations of motion for the plates is linearized into two sets of equations by assuming small amplitude vibration of the laminates about its buckled static equilibrium profile. Results show that, in the postbuckling regime, the fundamental mode may be shifted from the first mode to the second due to squeezing effect of the in-plane force on the plate. For plate with certain boundary conditions, the natural frequency may have a sudden jump due to buckle pattern change of the plate in the postbuckling regime.
Simulations of an Internal Model-Based Active Noise Control System for Suppressing Periodic Disturbances
Authors: Bai Mingsian R. , Wu Tenyau
Published: February 2008

This study proposes an active noise control algorithm using the internal model principle. The structure of the noise is built in the transfer function of the controller in the unity feedback configuration. This method is particularly effective in suppressing periodic disturbance in spite of its simplicity. Perfect disturbance rejection at selected frequencies is achieved by the infinite loop gain of the system. A simulation was performed to investigate the internal model-based algorithm. The guidelines of choosing the control parameters with reference to a robust stabilization theory are summarized.
Vibration Control of Structures With Closely Spaced Frequencies by a Single Actuator
Authors: Abe´ M.
Published: February 2008

A variable gain direct velocity feedback is proposed to control vibrations in structures with two closely spaced natural frequencies using a single actuator. First, limitation of the conventional constant gain velocity feedback is discussed based on perturbation analysis of the free response of structures with two vibration modes and a single actuator. Then, a variable gain feedback is constructed from the physical intuitions obtained from these solutions. The variable feedback gain is derived in terms of the state of the system while the feedback loop remains direct velocity feedback. Numerical studies confirm the efficiency of the proposed method.
Vibration Localization in Rotating Shafts, Part 1: Theory
Authors: Ulsoy A. Galip , Pierre Christophe , Choi Suhyun
Published: February 2008

This paper presents a theoretical study of vibration localization in single-span, flexible, rotating shafts. A noncircular cross-section of the rotating shaft, leading to dissimilar lateral moments of inertia, can introduce disorder. Internal coupling between the principal directions of vibration is provided by the rotational speed through the gyroscopic moments. It is shown, both analytically and numerically, that directional vibration localization can occur for certain appropriate combinations of disorder and coupling.
Vibration Localization in Rotating Shafts, Part 2: Experiment
Authors: Ulsoy A. Galip , Pierre Christophe , Choi Suhyun
Published: February 2008

This paper presents an experimental study of vibration localization in single-span, flexible, rotating shafts. It was shown in a companion paper (Part I) that a noncircular cross-section of the rotating shaft, leading to dissimilar lateral moments of inertia, can introduce disorder. Internal coupling between the principal directions of vibration is provided by the rotational speed through the gyroscopic moments. It is experimentally demonstrated here that directional vibration localization can occur for appropriate combinations of disorder and coupling. The steady state response, due to mass unbalance, of a simply supported rotating shaft is considered. It is shown that disorder and gyroscopic coupling lead to directional vibration localization; i.e., larger vibration amplitudes in one of the two orthogonal principal directions of the shaft cross section.
A General Approach on the Mechanical Analysis of Nonuniform Beams With Nonhomogeneous Elastic Boundary Conditions
Authors: Lee Sen Yung , Wang Wen Rong , Chen Terry Yuan-Fang
Published: February 2008

The dynamic and static response of a nonuniform beam with nonhomogeneous elastic boundary conditions is studied by generalizing the method of Mindlin-Goodman and utilizing the exact solutions of general elastically restrained non-uniform beams given by Lee and Kuo. A general form of change of dependent variable is introduced and the shifting functions expressed in terms of the four fundamental solutions of the system, instead of the fifth degree polynomials taken by Mindlin-Goodman, are selected. The physical meanings of these shifting polynomial functions are explored. Finally, the limiting cases are discussed and examples are given to illustrate the analysis.
Multiple Harmonic Balance Method for Aperiodic Vibration of a Piecewise-Linear System
Authors: Kim Y. B.
Published: February 2008

A multiple harmonic balance method is presented in this paper for obtaining the aperiodic steady-state solution of a piecewise-linear system. As the method utilizes general and systematic computational procedures, it can be applied to analyze the multi-tone or combination-tone responses for the higher dimensional nonlinear systems such as rotors. Moreover, it is capable of informing the stability of the obtained solution using Floquet theory. To demonstrate the systematic approach of the new method, the almost periodic forced vibration of an articulated loading platform (ALP) with a piecewise-linear stiffness is computed as an example.
Three-Dimensional Analysis for the Free Vibration of Finite-Length Orthotropic Piezoelectric Circular Cylindrical Shells
Authors: Chen Chang-Qing , Shen Ya-Peng
Published: February 2008

An exact elasticity study of the free vibration of a simply-supported cross-ply cylindrical shell containing a piezoelectric layer is presented. The solution of the derived governing differential equations is obtained through the power series expansion method. Both the direct and inverse piezoelectric effects are investigated. Results presented here provide an understand of the behavior of piezoelectric materials when acted as smart materials and can be used to assess various numerical results obtained from approximate shell theories.
A Practical Method for Noise Reduction in a Vehicle Passenger Compartment
Authors: Kim Seock Hyun , Lee Jang Moo
Published: February 2008

The structural-acoustic response of a vehicle passenger compartment is explicitly described in terms of the structural-acoustic modal coupling coefficients and modal parameters of the system. Based on the concept of the coupling coefficients and the contribution of the surrounding panels, a practical method for noise reduction is proposed. A computer program package was developed for the noise reduction and design modification and applied to a half scale simplified model for the vehicle compartment. The experimental results supported the effectiveness of the proposed method.
An Experimental Investigation into the Semi-Active and Active Control of Longitudinal Vibrations in a Large Tie-Rod Structure
Authors: Brennan M. J. , Day M. J. , Randall R. J.
Published: February 2008

An experimental study into the use of one semi-active and two active control devices employed to attenuate the transmission of longitudinal vibrations on a large tie-rod structure is described. A tie-rod structure similar to that found in marine machinery installations was assembled in the laboratory. This type of structure was chosen because it is difficilt to apply standard passive techniques due to the static stiffness requirement. A tunable pneumatic vibration absorber was used as the semi-active device, and an inertial electrodynamic exciter and a magnetostrictive actuator were used as the active devices. The way in which these devices couple into and modify the dynamic behaviour of the tie-rod structure is discussed, and experimental results are presented showing the effectiveness of the control measures in attenuating longitudinal vibrations. Significant reductions in transmitted vibrations were achieved by all the devices and the merits of each method are discussed.
Development and Verification of Transfer Matrix Unbalance Response Procedure for Three-Level Rotor-Foundation Systems
Authors: Rieger N. F. , Zhou Shixiang
Published: February 2008

Details are presented of an analysis and computer code for the calculation of complex multi-span rotor-bearing-pedestal-foundation systems. This multi-level system analysis is based on the Prohl-Myklestad transfer matrix method. The rotor model used is similar to that given by Lund and Orcutt [1]. Eight-coefficient bearings are also used, to permit elliptical orbit rotor motions. The bearings are mounted in massive, damped flexible pedestals, which are themselves mounted upon a foundation structure with distributed mass and stiffness properties. The foundation in turn, is supported on a number of flexible-damped supports. Different foundation properties in the horizontal and vertical directions are included. The analysis is described in detail, along with the computer code, and the results obtained with it are compared with data published previously by other investigators. It is shown that transfer matrix methods can be successfully used for multi-level systems, and that the additional computational ejfort involved is moderate. Three applications of the code are described which validate various aspects of the analysis and the computer program.
Extraction of Impulse Response Data via Wavelet Transform for Structural System Identification
Authors: Robertson A. N. , Park K. C. , Alvin K. F.
Published: February 2008

This paper presents a wavelet transform-based method of extracting the impulse response characteristics from the measured disturbances and response histories of linear structural dynamic systems. The proposed method is found to be effective in determining the impulse response functions for systems subjected to harmonic (narrow frequency-band) input signals and signals with sharp discontinuities, thus alleviating the Gibbs phenomenon encountered in FFT methods. When the system is subjected to random burst input signals for which the FFT methods are known to perform well, the proposed wavelet method performs equally well with a fewer number of ensembles than FFT-based methods. For completely random input signals, both the wavelet and FFT methods experience difficulties, although the wavelet method appears to perform somewhat better in tracing the fundamental response modes.
Identification of Structural Dynamics Models Using Wavelet-Generated Impulse Response Data
Authors: Robertson A. N. , Park K. C. , Alvin K. F.
Published: February 2008

This paper addresses the use of discrete wavelet transforms for the identification of structural dynamics models. First, the discrete temporal impulse response functions are obtained from vibration records by the discrete wavelet transform (DWT). They are then utilized for system realizations. From the realized state space models, structural modes, mode shapes and damping parameters are extracted. Attention has been focused on a careful comparison of the present DWT system identification approach to the FFT-based approach. Numerical examples demonstrate that the present DWT-based structural system identification procedure is a serious alternative to the FFT-based procedure, and outperforms FFT methods for narrow frequency-band inputs.
Estimation of the Fuzzy Substructure Model Parameters Using the Mean Power Flow Equation of the Fuzzy Structure
Authors: Soize C.
Published: February 2008

This paper presents a theoretical approach for identifying the dimensionless mean coefficient of participating fuzzy mass which is the main unknown parameter of the type I or II fuzzy law previously introduced by the author. This method is based on the use of the associated power flow equation, each power term being identified by using a global statistical energy analysis of the fuzzy structure (master structure with its fuzzy substructures). Identification is then carried out by solving a nonlinear constrained optimization problem. An example is given to illustrate the theoretical results.
Eigenmode Approach for a Periodic Composite Transducer Subject to Fluid Loading
Authors: Varadan V. V. , Jeng Jen Hwa , Chin Liang Chi , Bao Xiao Qi , Varadhan V. K.
Published: February 2008

A hybrid finite element eigenmode—Floquet mode representation is formulated and numerically implemented to study the performance of composite transducers subject to fluid loading. The periodic distribution of the piezoelectric elements in the form of rods in a dielectric host material permits consideration of only one unit cell of the distribution in the finite element solution. Again, due to periodicity, the acoustic field in the infinite fluid is represented as superposition of plane wave Floquet modes. The finite element method is used to solve the eigenmodes of vibration of the transducer and an eigenmode superposition with unknown weighting coefficients is interfaced with the Floquet representation. Continuity at the boundary is used to solve for both sets of unknown coefficients. The effect of rod cross section, concentration, material damping are studied as a function of frequency. Useful transducer parameters such as transmission efficiency and the conductance spectrum as well as reflection and transmission spectrum of the array are simulated numerically.
Edge Buckling of Imperfectly Guided Webs
Authors: Lakshmikumaran A. V. , Wickert J. A.
Published: February 2008

Web handling is germane to a diverse set of industries, including paper, polymer, textile, and sheet metal processing. Angular misalignment of the guides used to position a web in its transport system generates non-uniform in-plane forces that can result in transverse buckling of the web, even for misalignments as small as a fraction of a degree. In this paper, the state of stress, the associated in-plane deformation, out-of-plane vibration, and stability of webs with misaligned guides are investigated experimentally and theoretically. The onset of edge buckling, in which transverse corrugations are present along an entire free edge or are localized near a guide, is governed by the stability of a relatively high mode of the nominally aligned web. Two models of common web transport components—termed “free sliding” and “edge guided” —are developed and discussed in the light of laboratory measurements for predicting and bounding critical buckling angles.
Using Residual Flexibility for Improved Observation of Reaction Forces in Flexible Structures
Authors: Clark W. W. , Kim J. H. , Marangoni R. D.
Published: February 2008

This paper focuses on developing a full-state observer that can be used to obtain unmeasurable reaction forces in a flexible structure. In the context of modal truncation of a distributed parameter system, accurate representation of reaction forces is discussed and is shown to require a more comprehensive model than for displacement representation. This fact, coupled with the difficulty in directly measuring reaction forces in many applications points to the need for accurate estimation of ferees with reduced-order models. The residual flexibility, a term from past literature, is used to recapture some of the lost force information in a truncated model. This paper presents numerical and experimental results of a study where the residual flexibility is used in conjunction with a Kalman filter so that accurate force information may be obtained from a small set of displacement measurements with a reduced-order model. The motivation for this paper is to be able to obtain accurate information about dynamic bearing loads in a rotating machine for diagnostic and control purposes.
Study of the Oscillations of a Nonlinearly Supported String Using Nonsmooth Transformations
Authors: Pilipchuk V. N. , Vakakis A. F.
Published: February 2008

An analytical method for analyzing the oscillations of a linear infinite string supported by a periodic array of nonlinear stiffnesses is developed. The analysis is based on nonsmooth transformations of a spatial variable, which leads to the elimination of singular terms (generalized functions) from the governing partial differential equation of motion. The transformed set of equations of motion are solved by regular perturbation expansions, and the resulting set of modulation equations governing the amplitude of the motion is studied using techniques from the theory of smooth nonlinear dynamical systems. As an application of the general methodology, localized time-periodic oscillations of a string with supporting stiffnesses with cubic nonlinearities are computed, and leading-order discreteness effects in the spatial distribution of the slope of the motion are detected.
Predictive Maintenance Using the Rotordynamic Model of a Hydraulic Turbine-Generator Rotor
Authors: Bettig Bernhard P. , Han Ray P. S.
Published: February 2008

A use of rotordynamic models in predictive maintenance is described in which variables characterizing the state of a deterioration mechanism are determined from online measurements. These variables are trended to determine the rate of deterioration and to perform a simulation to predict either the machine life or the maintenance period. Some useful terms for using models in predictive maintenance are defined and the prediction procedure is described. The procedure is demonstrated with a simple two degree-of-freedom example and the numerical model of an actual hydraulic turbine-generator rotor. Some benefits and problems associated with the implementation of the procedure are then discussed. It is considered that this procedure brings the possibility of a better understanding of deterioration processes and a resulting better life prediction.
A Rapidly Convergent Adaptive Controller Applied to Suppression of Random Noise Transmission
Authors: Koshigoe S. , Teagle A. , Tsay C.-H.
Published: February 2008

In this paper, an efficient rapid convergent control algorithm will be developed and will be compared with other adaptive control algorithms using a plate-cavity system. The plate-cavity system used for these numerical experiments is a test bed of noise suppression technology for expendable launch vehicles. It consists of a flexible plate backed by a rigid cavity. Piezoelectric (PZT) actuators are considered to be bonded on both sides of the plate symmetrically. The plate is bombarded with an amplified random noise signal, and the control system is used to suppress the noise inside the cavity generated by the outside sound source. Other control algorithms included for the comparisons are LMS Widrow’s finite impulse response (FIR) adaptive control algorithm [1], and a modified Godard’s algorithm [2]. Comparisons of the random noise attenuation capability, transient and convergence performance, and computational requirements of each algorithm will he made as the order of the controller and relevant convergence parameters are varied.
Vibration and Noise Control of the Fuselage via Dynamic Absorbers
Authors: Huang Y. M. , Fuller C. R.
Published: February 2008

A closed, elastic cylindrical shell is used as a simple model of the aircraft’s fuselage. For reducing the vibration of the fuselage and the subsequent interior sound pressure due to the propellers, several dynamic absorbers are attached to the shell. In the paper, we analytically derive the vibration and the interior sound pressure of the shell by employing the techniques of subsystem synthesis and modal expansion where the external distributed pressures are chosen according to experimental data of an actual aircraft. The absorbers are successful for attenuating the vibration and the noise. The effects of altering various parameters of the shell, the external pressures, and the absorbers, are also studied and discussed. Finally, some general guidelines of absorber design for vibration and noise control of the fuselage are presented.
Nonlinear Dynamics of a Magnetically Supported Rotor on Safety Auxiliary Bearings
Authors: Wang X. , Noah S.
Published: February 2008

This study concerns the dynamic response of a rotor landed on auxiliary (catcher) bearings in an Active Magnetic Bearing (AMB) supported rotor, following postulated loss of power or overload of the AMB. An analytical model involving a disk, a shaft and auxiliary bearings on damped flexible supports is constructed and appropriate equations of the nonlinear dynamic system are developed. The equations include a switch function to indicate contact/non-contact events and determine the existence of contact normal forces and tangential friction forces between the shaft and the bearings. Steady state solutions are obtained. An analytical method was formulated and used to yield solutions for cases with well balanced rotors, in absence of any side forces. The Fixed Point Algorithm (FPA) is used to obtain steady state periodic solutions of the unbalanced rotor for various parameters. The FPA is used to determine the stability of the periodic solutions and the type of bifurcation involved. Multiple periodic solutions, quasi-periodic and chaotic responses are detected and discussed. A set of preliminary guidelines for selection of the parameters of the catcher bearings is given.