bluuebunny/crossref_metadata_2025 huggingface dataset:
Automotive Occupant Dynamics Optimization
Authors: Bennett J.A. , Park G.J.
Published: January 2014

One of the more difficult optimal design tasks occurs when the data describing the system to be optimized is either highly nonlinear or noisy or both. This situation arises when trying to design restraint systems for automotive crashworthiness using the traditional lumped parameter analysis methods. The nonlinearities in the response can come from either abrupt changes in the occupants interaction with the interior or from relatively minor fluctuation in the response due to the interactions of two restraint systems such as belts and airbags. In addition the calculated response measures are usually highly nonlinear functions of the accelerations. Two approaches using an approximate problem formulation strategy are proposed. One approach uses a first-order approximation based on finite difference derivatives with a nonlocal step size. The second and more effective approach uses a second-order curve fitting strategy. Successful example problems of up to 16 design variables are demonstrated. A conservative design strategy using a derivative-based constraint padding is also discussed. The approach proves effective because analytical expressions are available for the second-order terms.
Motions of a Powered Top with a Spherical Tip on a Curved Surface
Authors: Meeker David C. , Townsend Miles A.
Published: January 2014

The purpose of this article is to model the dynamics of a top with a finite radius tip on a curved basin in a gravitational field without (and with) energy addition and dissipation. This is an extension of a very general and classical problem and requires development of a method for treating the dynamical interactions between the two curved surfaces. The full nonlinear equations of motion are indicated; however, these equations are complex and do not show the dominant mechanisms that define the system motions. A novel method of “partial linearization” is employed that reduces the equations of motion to a relevant and tractable form in which these mechanisms are clearly exposed. The model and related results are compared with relevant examples from the literature. The movement of the top is simulated by an integration of the fully nonlinear equations of motion and compared with the partially linearized results.
Differential Quadrature Analysis of Free Vibration of Symmetric Cross-Ply Laminates with Shear Deformation and Rotatory Inertia
Authors: Malik Moinuddin , Bert Charles W.
Published: January 2014

In the present work, laminates having two opposite edges simply supported are considered. The boundary conditions at the other two opposite edges may be general, and between these two edges, the thickness of the plate may be nonuniform. The theory used for the vibration analysis of such laminates includes shear deformation and rotatory inertia. The solution approach of the problem is semianalytical. By using the trigonometric functions describing the mode shapes between the simply supported edges, the governing plate equations are reduced to ordinary differential equations. The solution of the reduced equations is then sought by the differential quadrature method. The results reported in this article serve two objectives of the present investigations. One, it is demonstrated that the proposed semianalytical quadrature method offers a numerically accurate and computationally efficient technique for the title problem. Two, the relative effects of shear deformation and rotatory inertia are analyzed in a quantitative manner.
Selection of a Suitable Wall Pressure Spectrum Model for Estimating Flow-Induced Noise in Sonar Applications
Authors: Rao V. Bhujanga
Published: January 2014

Flow-induced structural noise of a sonar dome in which the sonar transducer is housed, constitutes a major source of self-noise above a certain speed of the vessel. Excitation of the sonar dome structure by random pressure fluctuations in turbulent boundary layer flow leads to acoustic radiation into the interior of the dome. This acoustic radiation is termed flow-induced structural noise. Such noise contributes significantly to sonar self-noise of submerged vessels cruising at high speed and plays an important role in surface ships, torpedos, and towed sonars as well. Various turbulent boundary layer wall pressure models published were analyzed and the most suitable analytical model for the sonar dome application selected while taking into account high frequency, fluid loading, low wave number contribution, and pressure gradient effects. These investigations included type of coupling that exists between turbulent boundary layer pressure fluctuations and dome wall structure of a typical sonar dome. Comparison of theoretical data with measured data onboard a ship are also reported.
Application of Choi—Williams Reduced Interference Time Frequency Distribution to Machinery Diagnostics
Authors: Gaberson Howard A.
Published: January 2014

This article discusses time frequency analysis of machinery diagnostic vibration signals. The short time Fourier transform, the Wigner, and the Choi–Williams distributions are explained and illustrated with test cases. Examples of Choi—Williams analyses of machinery vibration signals are presented. The analyses detect discontinuities in the signals and their timing, amplitude and frequency modulation, and the presence of different components in a vibration signal.
Abating Earthquake Effects on Buildings by Active Slip Brace Devices
Authors: Akbay Zekai , Aktan Haluk M.
Published: January 2014

A hybrid control system for reducing building vibration under a spectrum of earthquake load amplitudes is presented. The hybrid control is accomplished by an energy dissipation device called the active slip brace device (ASBD). The hybrid control system uses the ASBD to regulate the energy dissipation characteristics of the building during its response to earthquakes by utilizing active control principles. The ASBD consists of a Coulomb friction interface with a clamping mechanism on the interface. The clamping force on the friction interface is altered at short time intervals during building vibration. Computer simulations of building response with and without ASBD are compared.
Continuous Sliding Mode Control of Flow-Induced Vibrations
Authors: Baz A.
Published: January 2014

Vortex-induced vibrations of flexible circular cylinders and galloping oscillations of square prisms are controlled using a robust continuous sliding mode (CSM) controller. The ability of the CSM controller in rejecting the flow-induced disturbances and accommodating parameter uncertainties is numerically demonstrated. In the present study, emphasis is placed on the development of theoretical models that describe the interaction between the flexible structures, the flow-induced excitation, and the CSM controller. In our development, the vortex-induced vibrations are based on the lift-oscillator model of Hartlen and Currie and the galloping phenomenon is described using Parkinson and Smith's model. The effectiveness of the CSM controller in suppressing the flow-induced vibrations of cylinders and square prisms is evaluated at various flow conditions and levels of structural uncertainties. The effect of the design parameters of the CSM controller on its performance is also investigated. The results obtained in the study suggest the potential of the robust control strategy presented as an important tool for rejecting undesirable and unmeasurable disturbances acting on critical structures that have considerably large parameter uncertainties.
Free Vibration of Partially Supported Cylindrical Shells
Authors: Mirza S. , Alizadeh Y.
Published: January 2014

The effects of detached base length on the natural frequencies and modal shapes of cylindrical shell structures were investigated in this work. Some of the important applications for this type of problem can be found in the cracked fan and rotor blades that can be idealized as partially supported shells with varying unsupported lengths. A finite element model based on small deflection linear theory was developed to obtain numerical solutions for this class of problems. The numerical results were generated for shallow shells and some of the degenerate cases are compared with other results available in the literature. The computations presented here involve a wide range of variables: material properties, aspect ratios, support conditions, and radius to base ratio.
Modeling and Fuzzy Logic Control of an Active Reaction Compensating Platform System
Authors: Lin Y.J. , Lu Y. , Lee T. , Choi B.
Published: January 2014

This article presents the application of the fuzzy logic (FL) concept to the active control of a multiple degree of freedom reaction compensating platform system that is designed and used for isolating vibratory disturbances of space-based devices. The physical model used is a scaled down two-plate platform system. In this work, simulation is performed and presented. According to the desired performance specifications, a full range of investigation regarding the development of an FL stabilization controller for the system is conducted. Specifically, the study includes four stages: comprehensive dynamic modeling of the reaction compensating system; analysis of the dynamic responses of the platform system when it is subjected to various disturbances; design of an FL controller capable of filtering the vibratory disturbances transmitted to the bottom plate of the platform system; performance evaluation of the developed FL controller through computer simulations. To simplify the simulation work, the system model is linearized and the system component parameter variations are not considered. The performance of the FL controller is tested by exciting the system with an impulsive force applied at an arbitrarily chosen point on the top plate. It is shown that the proposed FL controller is robust in that the resultant active system is well stabilized when subjected to a random external disturbance. The comparative study of the performances of the FL controlled active reaction and passive reaction compensating systems also reveals that the FL controlled system achieves significant improvements in reducing vibratory accelerations over passive systems.
Impact of Thin-Walled Projectiles with Concrete Targets
Authors: Moxley Rayment E. , Adley Mark D. , Rohani Bob
Published: January 2014

An experimental program to determine the response of thin-walled steel projectiles to the impact with concrete targets was recently conducted. The projectiles were fired against 41-MPa concrete targets at an impact velocity of 290 m/s. This article contains an outline of the experimental program, an examination of the results of a typical test, and predictions of projectile deformation by classical shell theory and computational simulation. Classical shell analysis of the projectile indicated that the predicted impact loads would result in circumferential buckling. A computational simulation of a test was conducted with an impact/penetration model created by linking a rigid-body penetration trajectory code with a general-purpose finite element code. Scientific visualization of the resulting data revealed that circumferential buckling was induced by the impact conditions considered.
Seismic Passive Control of Cable-Stayed Bridges
Authors: Ali Hosam-Eddin M. , Abdel-Ghaffar Ahmed M.
Published: January 2014

A three-dimensional modeling procedure is proposed for cable-stayed bridges with rubber, steel, and lead energy dissipation devices. The passive control technique is investigated by considering the response of bridge models with and without energy dissipation devices. The impact of various design parameters on the seismic response of current and future bridge designs is studied. Appropriate locations and properties of the passive devices can achieve better performance for cable-stayed bridges by balancing the significant reduction in earthquake-induced forces against tolerable displacements. Proper design of passive systems can help provide solutions for retro-fitting some existing bridges.
High Resolution Order Tracking at Extreme Slew Rates Using Kalman Tracking Filters
Authors: Vold Håvard , Leuridan Jan
Published: January 2014

The analysis of the periodic components in noise and vibration signals measured on rotating equipment such as car power trains, must be done more and more under rapid changes of an axle, or reference RPM. Normal tracking filters (analog or digital implementations) have limited resolution in such situations; wavelet methods, even when applied after resampling the data to be proportional to an axle RPM, must compromise between time and frequency resolution. The authors propose the application of nonstationary Kalman filters for the tracking of periodic components in such noise and vibration signals. These filters are designed to accurately track signals with a known structure among noise and signal components of different, “unknown,” structure. The tracking characteristics of these filters, i.e., the predicted signal amplitude versus time values versus exact signal amplitude versus time values, can be tailored to accurate tracking of harmonics buried in other signal components and noise, even at high rates of change of the reference RPM. A key to the successful construction is the precise knowledge of the structure of the signal to be tracked. For signals that vary with an axle RPM, an accurate estimate of the instantaneous RPM is essential, and procedures to this end will also be presented.
Transient Interaction of a Spherical Shell with an Underwater Explosion Shock Wave and Subsequent Pulsating Bubble
Authors: Huang H. , Kiddy K.C.
Published: January 2014

The nonlinear interaction problem is analyzed by simultaneously solving the mass, momentum, and energy conservation equations together .with appropriate material constitutive equations governing the fluid dynamics of the explosion gaseous product and the water and the structural dynamics of the compliant shell. A finite difference technique in a coupled Eulerian–Lagrangian scheme is used. The computer program PISCES 2DELK is employed to carry out the numerical computations. The results demonstrate that to rigorously analyze the response of a submerged structure to a nearby explosion, the interactions among the explosion shock wave, the structure, its surrounding media, and the explosion bubble need to be considered.
Motions of a Constrained Spherical Pendulum in an Arbitrarily Moving Reference Frame: The Automobile Seatbelt Inertial Sensor
Authors: Allan A. Peter , Townsend Miles A.
Published: January 2014

A common automatic seatbelt inertial sensor design, comprised of a constrained spherical pendulum, is modeled to study its motions and possible unintentional release during vehicle emergency maneuvers. The kinematics are derived for the system with the most general inputs: arbitrary pivot motions. The influence of forces due to gravity and constraint torque functions is developed. The equations of motion are then derived using Kane's method. The equations of motion are used in a numerical simulation with both actual and hypothetical automobile crash data.
A Toeplitz Jacobian Matrix/Fast Fourier Transformation Method for Steady-State Analysis of Discontinuous Oscillators
Authors: Ge T. , Leung A. Y. T.
Published: January 2014

A semianalytical algorithm is proposed for the solutions and their stability of a piecewise nonlinear system. The conventional harmonic balance method is modified by the introduction of Toeplitz Jacobian matrices (TJM) and by the alternative applications of fast Fourier transformation (FFT) and its inverse. The TJM/FFT method substantially reduces the amount of computation and circumvents the necessary numerical differentiation for the Jacobian. An arc-length algorithm and a branch switching procedure are incorporated so that the secondary branches can be independently traced. Oscillators with piecewise nonlinear characteristics are taken as illustrative examples. Flip, fold, and Hopf bifurcations are of interest.
Vibration Analysis of Structures with Rotation and Reflection Symmetry
Authors: Li Baojian , Zheng Xiaozhong , Zhao Jie
Published: January 2014

The article applies group representation theory to the vibration analysis of structures with Cnvsymmetry, and presents a new structural vibration analysis method. The eigenvalue problem of the whole structure is divided into much smaller subproblems by forming the mass and stiffness matrices of one substructure and than modifying them to form mass and stiffness matrices in each irreducible subspace, resulting in the saving of computer time and memory. The modal characteristics of structures with Cnvsymmetry are derived from theoretical analysis. Computation and modal testing are used to verify the validity of the theoretical deductions.
Dynamic Force Identification for Beamlike Structures Using an Improved Dynamic Stiffness Method
Authors: Chen S.L. , Géradin M.
Published: January 2014

In this study a procedure of dynamic force identification for beamlike structures is developed based on an improved dynamic stiffness method. In this procedure, the entire structure is first divided into substructures according to the excitation locations and the measured response sites. Each substructure is then represented by an equivalent element. The resulting model only retains the degree of freedom (DOF) associated with the excitations and the measured responses and the DOF corresponding to the boundaries of the structures. Because the technique partly bypasses the processes of modal parameter extraction, global matrix inversion, and model reduction, it can eliminate many of the approximations and errors that may be introduced during these processes. The principle of the method is described in detail and its efficiency is demonstrated via numerical simulations of three different structures. The sensitivity of the estimated force to random noise is discussed and the limitation of the technique is pointed out.
Mapping Nonsquare and Unevenly Spaced 2-D SLDV Data of an Aircraft Fuselage by Using Spatial DFT-IDFT Techniques
Authors: Li William Xinzuo , Mitchell Larry D. , Lu Min-Fu , Neumann Michael L.
Published: January 2014

The scanning laser Doppler vibrometry (SLDV) technique provides velocities of a structure at 2-dimensional (2-D) angularly evenly spaced (in the laser scanning sense) data points. This causes an unevenly spaced data point distribution on the surface of the test structure. In many cases evenly spaced data point distribution with square or rectangular grids is highly desirable. In this study the SLDV velocity data of a partial surface area of an aircraft fuselage were mapped to truly spatial evenly spaced coordinates by using the spatial DFT-IDFT technique with minimum distortion. This 2-D data mapping technique certainly is not limited to the fuselage, hut can he very useful for many other 3-D structures.
Dissipation of Hysteretic Energy in Base Isolated Structure
Authors: Jangid R.S. , Datta T.K.
Published: January 2014

Dissipation of hysteretic energy in the isolator of the base isolated structure under seismic excitation is investigated. The hysteretic force-deformation characteristics of the base isolator is specified by a nonlinear differential equation. The parameters of the equation can be adjusted to obtain various types of hysteretic models of the isolator including the elastoplastic type. The variation of hysteretic energy dissipated in the isolators is obtained for both harmonic and El-Centro 1940 earthquake ground motion for a set of important parameters. They include time period of superstructure, ratio of superstructure mass to base mass, level of yield strength of the isolator, post- to preyielding stiffness ratio, and the ratio of harmonic excitation frequency to base isolation frequency. It is shown that the dissipation of hysteretic energy in the isolator is significantly influenced by the above parameters.
A Modified Lindstedt–Poincaré Method for a Strongly Nonlinear System with Quadratic and Cubic Nonlinearities
Authors: Chen S.H. , Cheung Y. K.
Published: January 2014

A modified Lindstedt–Poincaré method is presented for extending the range of the validity of perturbation expansion to strongly nonlinear oscillations of a system with quadratic and cubic nonlinearities. Different parameter transformations are introduced to deal with equations with different nonlinear characteristics. All examples show that the efficiency and accuracy of the present method are very good.
Digital Double-Pulse Holographic Interferometry for Vibration Analysis
Authors: Tiziani H.J. , Pedrini G.
Published: January 2014

Different arrangements for double-pulsed holographic and speckle interferometry for vibration analysis will be described. Experimental results obtained with films (classical holographic interferometry) and CCD cameras (digital holographic interferometry) as storage materials are presented. In digital holography, two separate holograms of an object under test are recorded within a few microseconds using a CCD camera and are stored in a frame grabber. The phases of the two reconstructed wave fields are calculated from the complex amplitudes. The deformation is obtained from the phase difference. In the case of electronic speckle pattern interferometry (or image plane hologram), the phase can be calculated by using the sinusoid-fitting method. In the case of digital holographic interferometry, the phase is obtained by digital reconstruction of the complex amplitudes of the wave fronts. Using three directions of illumination and one direction of observation, all the information necessary for the reconstruction of the 3-dimensional deformation vector can be recorded at the same time. Applications of the method for measuring rotating objects are discussed where a derotator needs to be used.
Grazing Orbits and Related Local Bifurcations of an Oscillator with Continuous and Piecewise-Linear Restoring Force
Authors: Hu Haiyan
Published: January 2014

One critical case for the motion of a periodically excited oscillator with continuous and piecewise-linear restoring force is that the motion happens to graze a switching plane between two linear regions of the restoring force. This article presents a numerical scheme for locating the periodic grazing orbit first. Then, through a brief analysis, the article shows that the grazing phenomenon turns the stability trend of the periodic orbit so abruptly that it may be impossible to predict an incident local bifurcation with the variation of a control parameter from the concept of smooth dynamic systems. The numerical simulation in the article well supports the scheme and the analysis, and shows an abundance of grazing phenomena in an engineering range of the excitation frequency.
Dynamic Design Analysis Method DDAM
Authors: Remmers Gene M. , O’Hara George J. , Cunniff Patrick F.
Published: January 2014

This article describes the evolution of the dynamic design analysis method (DDAM) by assimilating information from references spanning more than three decades. This evolution began with attempts to use earthquake engineering practice, circa 1950, in dealing with hostile environments created by modern weaponry. It became necessary to develop new theories that went beyond the then current status. This led to research programs that went back to basic physics and engineering principles that resulted in a sound technique for naval applications. The elements of the technique were theoretically based and confirmed by laboratory and large scale field testing. One important example is the structural interaction effects between a vehicle and large equipment structures by means of a newly defined quantity called modal effective mass. Another example led to the discovery that attaching a vibration generator to a structure in an effort to find the frequencies useful for foundation motion response analysis was guaranteed to produce failure. DDAM continues to be used after its introduction 36 years ago. Although familiar in US and international naval circles, it is not well known by persons other than naval engineers. Many myths and misconceptions have grown during this period, so some of the major ones are addressed.
Free Vibration of a Fluid-Filled Circular Cylindrical Shell with Lumped Masses Attached, Using the Receptance Method
Authors: Amabili Marco
Published: January 2014

The receptance method is applied to the analytical study of the free vibrations of a simply supported circular cylindrical shell that is either empty or filled with an in viscid, incompressible fluid and with lumped masses attached at arbitrary positions. The receptance of the fluid-filled shell is obtained using the added virtual mass approach to model the fluid–structure interaction. The starting data for the computations is the modal properties of the cylinder that can be obtained using any theory of shells. Numerical results are obtained as roots of the frequency equation and also by considering the trivial solution. They are compared to data obtained by experimental modal analysis performed on a stainless steel tank, empty, or filled with water, with a lead mass attached.
Largest Lyapunov Exponents and Bifurcations of Stochastic Nonlinear Systems
Authors: To C.W.S. , Li D.M.
Published: January 2014

Two commonly adopted expressions for the largest Lyapunov exponents of linearized stochastic systems are reviewed. Their features are discussed in light of bifurcation analysis and one expression is selected for evaluating the largest Lyapunov exponent of a linearized system. An independent method, developed earlier by the authors, is also applied to determine the bifurcation points of a van der Pol oscillator under parametric random excitation. It is shown that the bifurcation points obtained by the independent technique agree qualitatively and quantitatively with those evaluated by using the largest Lyapunov exponent of the linearized oscillator.
Vibroacoustic Modeling of Mechanically Coupled Structures: Artificial Spring Technique Applied to Light and Heavy Mediums
Authors: Cheng L.
Published: January 2014

This article deals with the modeling of vibrating structures immersed in both light and heavy fluids, and possible applications to noise control problems and industrial vessels containing fluids. A theoretical approach, using artificial spring systems to characterize the mechanical coupling between substructures, is extended to include fluid loading. A structure consisting of a plate-ended cylindrical shell and its enclosed acoustic cavity is analyzed. After a brief description of the proposed technique, a number of numerical results are presented. The analysis addresses the following specific issues: the coupling between the plate and the shell; the coupling between the structure and the enclosure; the possibilities and difficulties regarding internal soundproofing through modifications of the joint connections; and the effects of fluid loading on the vibration of the structure.
Wavelet Transform in Vibration Analysis for Mechanical Fault Diagnosis
Authors: Wang W.J.
Published: January 2014

The wavelet transform is introduced to indicate short-time fault effects in associated vibration signals. The time-frequency and time-scale representations are unified in a general form of a three-dimensional wavelet transform, from which two-dimensional transforms with different advantages are treated as special cases derived by fixing either the scale or frequency variable. The Gaussian enveloped oscillating wavelet is recommended to extract different sizes of features from the signal. It is shown that the time-frequency and time-scale distributions generated by the wavelet transform are effective in identifying mechanical faults.
Stress Waves in Composite Laminates Excited by Transverse Plane Shock Waves
Authors: Liu G.R. , Lam K.Y. , Chan E.S.
Published: January 2014

A simple 1-dimensional model is presented to investigate elastic stress waves in composite laminates excited by underwater explosion shocks. The focus is on the elastic dynamic stress fields in the composite laminate immediately after the action of the shock wave. In this model, the interaction between the laminate and the water is taken into account, and the effects of the laminate-water interaction on the stress wave fields in the laminate are investigated. In the formulation of the model, wave fields in the laminate and the water are the first obtained in the frequency domain and then transferred into the time domain using the Fourier transform techniques. A quadrature technique is used to deal with the Fourier transform integrals in which the integrands have very sharp peaks on the integral axis. Numerical examples for stress waves in a steel plate and a glass reinforced plastic sandwich laminate are presented. The technique and the results presented in this article may be used in the design of ship hull structures subjected to underwater explosions.
Neoclassical Solution of Transient Interaction of Plane Acoustic Waves with a Spherical Elastic Shell
Authors: Huang Hanson , Mair Hans U.
Published: January 2014

A detailed solution to the transient interaction of plane acoustic waves with a spherical elastic shell was obtained more than a quarter of a century ago based on the classical separation of variables, series expansion, and Laplace transform techniques. An eight-term summation of the time history series was sufficient for the convergence of the shell deflection and strain, and to a lesser degree, the shell velocity. Since then, the results have been used routinely for validation of solution techniques and computer methods for the evaluation of underwater explosion response of submerged structures. By utilizing modern algorithms and exploiting recent advances of computer capacities and floating point mathematics, sufficient terms of the inverse Laplace transform series solution can now be accurately computed. Together with the application of the Cesaro summation using up to 70 terms of the series, two primary deficiencies of the previous solution are now remedied: meaningful time histories of higher time derivative data such as acceleration and pressure are now generated using a sufficient number of terms in the series; and uniform convergence around the discontinuous step wave front is now obtained, completely eradicating spurious oscillations due to the Gibbs' phenomenon. New results of time histories of response items of interest are presented.
A Space-Frequency Data Compression Method for Spatially Dense Laser Doppler Vibrometer Measurements
Authors: Arruda José Roberto de França , Vianna do Rio Sérgio Augusto , Bernardes Santos Luiz Antonio Silva
Published: January 2014

When spatially dense mobility shapes are measured with scanning laser Doppler vibrometers, it is often impractical to use phase-separation modal parameter estimation methods due to the excessive number of highly coupled modes and to the prohibitive computational cost of processing huge amounts of data. To deal with this problem, a data compression method using Chebychev polynomial approximation in the frequency domain and two-dimensional discrete Fourier series approximation in the spatial domain, is proposed in this article. The proposed space-frequency regressive approach was implemented and verified using a numerical simulation of a free-free-free-free suspended rectangular aluminum plate. To make the simulation more realistic, the mobility shapes were synthesized by modal superposition using mode shapes obtained experimentally with a scanning laser Doppler vibrometer. A reduced and smoothed model, which takes advantage of the sinusoidal spatial pattern of structural mobility shapes and the polynomial frequency-domain pattern of the mobility shapes, is obtained. From the reduced model, smoothed curves with any desired frequency and spatial resolution can he produced whenever necessary. The procedure can he used either to generate nonmodal models or to compress the measured data prior to modal parameter extraction.
A Parameter Study of Localization
Authors: Mester Sandor Stephen , Benaroya Haym
Published: January 2014

Extensive work has been done on the vibration characteristics of perfectly periodic structures. Disorder in the periodic pattern has been found to lead to localization in one-dimensional periodic structures. It is important to understand localization because it causes energy to be concentrated near the disorder and may cause an overestimation of structural damping. A numerical study is conducted to obtain a better understanding of localization. It is found that any mode, even the first, can localize due to the presence of small imperfections.
Spatially Filtered Vibration Control of Cylindrical Shells
Authors: Tzou H.S. , Zhong J.P.
Published: January 2014

Distributed actuators offer spatially distributed actuations and they are usually effective to multiple modes of a continuum. Spatially filtered distributed vibration controls of a laminated cylindrical shell and a piezoelectric shell are investigated, and their control effectivenesses are evaluated in this study. In general, there are two control actions, the in-plane membrane control forces and the counteracting control moments, induced by the distributed actuator in the laminated shell. There is only an in-plane circumferential control force in the piezoelectric shell. Analyses suggest that in either case the control actions are effective in odd natural modes and ineffective in even modes. Spatially filtered control effectiveness and active damping of both shells are studied.
A Learning Method for Neural Networks Based on a Pseudoinverse Technique
Authors: Pal Chinmoy , Hagiwara Ichiro , Kayaba Naoki , Morishita Shin
Published: January 2014

A theoretical formulation of a fast learning method based on a pseudoinverse technique is presented. The efficiency and robustness of the method are verified with the help of an Exclusive OR problem and a dynamic system identification of a linear single degree of freedom mass–spring problem. It is observed that, compared with the conventional backpropagation method, the proposed method has a better convergence rate and a higher degree of learning accuracy with a lower equivalent learning coefficient. It is also found that unlike the steepest descent method, the learning capability of which is dependent on the value of the learning coefficient ν, the proposed pseudoinverse based backpropagation algorithm is comparatively robust with respect to its equivalent variable learning coefficient. A combination of the pseudoinverse method and the steepest descent method is proposed for a faster, more accurate learning capability.
Vibration Isolation Review: II. Shock Excitation
Authors: Nelson F.C.
Published: January 2014

This is the second part of a two part review of shock and vibration isolation. It covers three distinct categories of shock excitation—pulselike shock, velocity shock, and complex shock—and discusses the means that are available in each case to measure the effectiveness of shock mitigation by the imposition of flexible connections between the isolated system and its base.
Sensitivity of Occupant Response Subject to Prescribed Corridors for Impact Testing
Authors: Crandall J.R. , Pilkey W.D. , Kang W. , Bass C.R.
Published: January 2014

A technology to study the sensitivity of impact responses to prescribed test conditions is presented. Motor vehicle impacts are used to illustrate the principles of this sensitivity technology. Impact conditions are regulated by specifying either a corridor for the acceleration time history or other test parameters such as velocity change, static crush distance, and pulse duration. By combining a time domain constrained optimization method and a multirigid body dynamics simulator, the upper and lower bounds of occupant responses subject to the regulated corridors were obtained. It was found that these prescribed corridors may be either so wide as to allow extreme variations in occupant response or so narrow that they are physically unrealizable in the laboratory test environment. A new corridor based on specifications for the test parameters of acceleration, velocity. crush distance, and duration for frontal vehicle impacts is given.
Experimental Motion Analysis of Radially Rotating Beams Using High-Speed Camera and Motion Analyzer
Authors: Low K.H. , Lau Michael W.S. , Low K.K.
Published: January 2014

Although strain gauges can be attached to a system for vibration analysis, wires connected to the strain gauges may disturb the system and affect the accuracy of the strain measurement. As an alternative, this work presents the use of a high-speed camera combined with a motion analyzer to study the motion of rotating flexible beams. One end of the beam is rigidly connected to a motor, while the other end is free. White stickers placed on selected points on a given beam are the reference points in a digitization process. The modes of the vibrating beams can be filmed and analyzed. The vibration parameters, such as deflection and frequency, can be obtained by using a film motion analyzer. The results show that the beam does not behave in a clamped-free or a pinned-free fashion, but instead occurs at an intermediate boundary between these two classical conditions.
Optimal Design of Structures under Impact Loading
Authors: Schramm Uwe , Pilkey Walter D.
Published: January 2014

In the design process structural optimization is a useful tool to reach design decisions. The impact behavior of structures is important for many designs, such as for automobiles. This article reviews methodology for the optimization of structures under impact loading. The optimization problem is to minimize the structural mass with constraints on the transient dynamic response of the structure. The structural behavior is nonlinear dynamic. Optimization is performed using the approximation concept. Design sensitivity analysis for transient response is treated.
Rigid-Plastic Approximations for Predicting Plastic Deformation of Cylindrical Shells Subject to Dynamic Loading
Authors: Hoo Fatt Michelle S. , Wierzbicki Tomasz , Moussouros Minos , Koenig John
Published: January 2014

A theoretical approach was developed for predicting the plastic deformation of a cylindrical shell subject to asymmetric dynamic loads. The plastic deformation of the leading generator of the shell is found by solving for the transverse deflections of a rigid-plastic beam/string-on-foundation. The axial bending moment and tensile force in the beam/string are equivalent to the longitudinal bending moments and membrane forces of the shell, while the plastic foundation force is equivalent to the shell circumferential bending moment and membrane resistances. Closed-form solutions for the transient and final deformation profile of an impulsive loaded shell when it is in a “string” state were derived using the eigenfunction expansion method. These results were compared to DYNA 3D predictions. The analytical predictions of the transient shell and final centerline deflections were within 25% of the DYNA 3D results.
Equivalent Modal Damping Ratios of a Composite Tube-Type Tall Building to Dynamic Wind Loading
Authors: Huang B.C. , Lam K.M. , Leung A.Y.T. , Cheung Y.K.
Published: January 2014

This article discusses computing methods of the equivalent modal damping ratio for a composite tube-type tall building. The equivalent damping ratio of a composite structure under wind-induced vibrations encompasses the combined effects from the different values of damping, mass, and stiffness of the external and internal tubes. A detailed method incorporating Rayleigh damping and the transfer matrix method is proposed for the determination of the equivalent modal damping ratio. A simplified method for engineering applications is also proposed. Results for a 40-story building are presented exemplifying the computation and relationships between the properties of the external and internal tubes.
A Modified Eigenstructure Assignment Technique for Finite Element Model Updating
Authors: Ziaei-Rad S. , Imregun M.
Published: January 2014

This article deals with an extended application of the constrained eigenstructure assignment method (CEAM) to finite element model updating. The existing formulation is modified to accommodate larger systems by developing a quadratic linear optimization procedure that is unconditionally stable. Further refinements include the updating of the mass matrix, a hysteretic damping model, and the introduction of elemental correction factors. Six numerical test cases, dealing with effects of damping and measurement noise, mode shape incompleteness, and discretization differences, were conducted in the case of a 3-D frame model with 114 coordinates. The performance of the CEAM was evaluated systematically for both the purpose of error location and the global correction of the initial model. The same cases were also studied using another model updating approach, namely the response function method (RFM). It was found that the CEAM had a number of distinct advantages, such as yielding a noniterative direct solution, requiring much less computing power, and providing acceptable results for cases, that could not he handled using the RFM.
Measurement of Translational and Angular Vibration Using a Scanning Laser Doppler Vibrometer
Authors: Stanbridge A.B. , Ewins D.J.
Published: January 2014

An experimental procedure for obtaining angular and translational vibration in one measurement, using a continuously scanning laser Doppler vibrometer, is described. Sinusoidal scanning, in a straight line, enables one angular vibration component to be measured, but by circular scanning, two principal angular vibrations and their directions can be derived directly from the frequency response sidebands. Examples of measurements on a rigid cube are given. Processes of narrow-band random excitation and modal analysis are illustrated with reference to measurements on a freely suspended beam. Sideband frequency response references are obtained by using multiplied excitation force and mirror-drive signals.
Vibration Analysis of Viscoelastically Damped Sandwich Shells
Authors: He Ji-Fan , Ma Bang-An
Published: January 2014

The simplified governing equations and corresponding boundary conditions of vibration of viscoelastically damped unsymmetrical sandwich shells are given. The asymptotic solution to the equations is then discussed. If only the first terms of the asymptotic solution of all variables are taken as an approximate solution, the result is identical with that obtained from the modal strain energy method. By taking more terms of the asymptotic solution with successive calculations and use of the Padé approximants method, accuracy of natural frequencies and modal loss factors of sandwich shells can be improved. The lowest three or four natural frequencies and modal loss factors of simply supported cylindrical sandwich shells are calculated.
Nonlinear Structural Dynamic Finite Element Analysis Using Ritz Vector Reduced Basis Method
Authors: Yao M.S.
Published: January 2014

The large number of unknown variables in a finite element idealization for dynamic structural analysis is represented by a very small number of generalized variables, each associating with a generalized Ritz vector known as a basis vector. The large system of equations of motion is thereby reduced to a very small set by this transformation and computational cost of the analysis can be greatly reduced. In this article nonlinear equations of motion and their transformation are formulated in detail. A convenient way of selection of the generalized basis vector and its limitations are described. Some illustrative examples are given to demonstrate the speed and validity of the method. The method, within its limitations, may be applied to dynamic problems where the response is global in nature with finite amplitude.
Determination of Effective Thoracic Mass
Authors: Marcus Jeffrey H.
Published: January 2014

Effective thoracic mass is an important parameter in specifying mathematical and mechanical models (such as crash dummies) of humans exposed to impact conditions. A method is developed using a numerical optimizer to determine effective thoracic mass (and mass distribution) given a number of acceleration signals and a force signal response. Utilizing previously reported lateral and frontal impact tests with human cadaveric test specimens in a number of different conditions, the effective thoracic mass is computed. The effective thoracic masses are then computed for a variety of crash dummies exposed to identical test conditions.
Comparison of Mechanical Impedance Methods for Vibration Simulation
Authors: Gatscher Jeffrey A. , Kawiecki Grzegorz
Published: January 2014

The work presented here explored the detrimental consequences that resulted when mechanical impedance effects were not considered in relating vibration test requirements with field measurements. The ways in which these effects can be considered were evaluated, and comparison of three impedance methods was accomplished based on a cumulative damage criterion. A test structure was used to simulate an equipment and support foundation system. Detailed finite element analysis was performed to aid in computation of cumulative damage totals. The results indicate that mechanical impedance methods can be effectively used to reproduce the field vibration environment in a laboratory test. The establishment of validated computer models, coupled with laboratory impedance measurements, can eliminate the overtesting problems inherent with constant motion, infinite impedance testing strategies.
Protection for Thorax Injury Severity in 90° Lateral Collision
Authors: Kallieris Dimitrios , Boggasch Frank , Mattern Rainer
Published: January 2014

The thoracic trauma index (TTI) and the viscous criterion (VC) are injury criteria intended for the prediction of torso injury severity. The criteria were assessed in two series of experiments: 90° (lateral) car to car collisions and controlled left trunk impacts against either a rigid or padded wall. Forty-two belt restrained human cadavers in the age range 18–65 years, located in the near-side front passenger seat, were used. The impact velocity was between 40 and 60 km/h. Left and right side impacts were simulated using standard or modified car side structures. With the second series of experiments, the left side of each subject was impacted under one of two different test conditions: 24 km/h rigid wall or 32 km/h padded wall. The thorax deformation was evaluated through the double integration of the accelerated difference at the fourth and eight ribs, near and far side. Deformation maxima of 6–138 mm (mean 69 mm), VC values of 0.3–4.7 m/s (mean 1.6 m/s), and TTI values of 85–252 (mean 63) occurred. Torso abbreviated injury severity (AIS) values were between 0 and 5. Statistical analyses showed a stronger influence of age on injury severity than the injury criteria or biomechanical responses in the two series of experiments. The TTI showed the highest correlation with thoracic AIS and the number of rib fractures, while VC was the better predictor of abdominal AIS. The results are discussed critically and the strength and robustness of the injury criteria analyzed.
Influence of Flexible Foundation on Isolator Wave Effects
Authors: Xiong Ye-Ping , Song Kong-Jie , Ai Xing
Published: January 2014

This article deals with the interaction between wave effects in mounts and resonances of foundations inflexible vibration isolation systems. A new model is proposed that is represented as a rigid mass supported by two linear unidirectional isolators on a flexible foundation beam, whose closed-form solutions for transmissibility and response ratio are then obtained, with which the influence of wave effects coupled with the flexibility of the foundation on the effectiveness of isolation is discussed. The wave effects on flexible isolation systems are analyzed under various parametric conditions and compared with those in rigid systems. In addition, several special cases are presented to show the transition between various limiting cases. Some approaches to control wave effects are also proposed.