bluuebunny/crossref_metadata_2025 huggingface dataset:
Procedures to Compute Maximum Structural Responses from Predictions or Measurements at Selected Points
Authors: Piersol Allan G.
Published: January 2014

It is common to establish shock and vibration design and/or test criteria for equipment mounted on a structure by computing a conservative upper bound for the spectrum of the dynamic load induced response of the structure based upon predicted or measured spectra at various points. This task is usually accomplished by one of five procedures, namely, the computation from the available spectra of a simple envelope, a normal tolerance limit, a distribution-free tolerance limit, an empirical tolerance limit, or a normal prediction limit. These five procedures are reviewed and illustrated using the power spectra computed from vibration signals measured during the lift-off of a large launch vehicle at 12 locations in a structural region where equipment will be mounted. The results are compared and the merits and liabilities of the various procedures are discussed.
Frequency and Spatial Shaping of Inputs for Multiaxis Shaker Testing
Authors: Smith Craig C. , Staffanson Forrest L.
Published: January 2014

Controlled amplitude and phase relationships between multiaxial shaker inputs (i.e., spatial shaping) provides for more realistic simulation of a service environment than does conventional frequency shaping alone. Spatial shaping is described in terms of a basic mathematical model relating test article response (absolute and relative motions) to excitation by the shaker. Advantages and objectives are viewed through spectral relationships. The objective of simulating dynamic responses as in service is shown to be the duplication of the resultant cross-modal response for all important modes, even if the sources of excitation in service are unknown.
Identification of Acoustic-Vibratory System by Acoustic Measurement
Authors: Iwatsubo Takuzo , Kawamura Shozo , Kamada Masahito
Published: January 2014

A new method for reducing ill-conditioning in a class of identification problems is proposed. The key point of the method is that the identified vibration of the sound source is expressed as a superposition of vibration modes. The mathematical property of the coefficient matrix, the practical error expanding ratio, and the stochastic error expanding ratio are investigated in a numerical example. The mode-superposition method is shown to be an effective tool for acoustic-vibratory inverse analysis.
Calibrated Noncontact Exciters for Optical Modal Analysis
Authors: Saldner Henrik O.
Published: January 2014

Two types of exciters were investigated experimentally One of the exciters uses a small permanent magnet fastened on the object. The force is introduced by the change in the electromagnetic field from a coil via an air gap. The second exciter is an eddy-current electromagnet one. The amplitude of the forces from these exciters are calibrated by using dynamic reciprocity in conjunction with electronic holography. These forces strongly depend upon the distance between the exciter and the object.
Accelerated Solutions for Transcendental Stiffness Matrix Eigenproblems
Authors: Williams F.W. , Kennedy D.
Published: January 2014

This article outlines many existing and forthcoming methods that can be used alone, or in various combinations, to accelerate the solutions of the transcendental stiffness matrix eigenproblems that arise when the stiffness matrix is assembled from exact member stiffnesses, which are obtained by solving the member differential equations exactly. Thus distributed member mass and/or the flexural effect of axial loading are incorporated exactly, and the solutions are the natural frequencies for vibration problems or the critical load factors for buckling problems.
Environmental Effects on Flutter Characteristics of Laminated Composite Rectangular and Skew Panels
Authors: Chowdary T.V.R. , Sinha P.K. , Parthan S.
Published: January 2014

A finite element method is presented for predicting the flutter response of laminated composite panels subjected to moisture concentration and temperature. The analysis accounts for material properties at elevated temperature and moisture concentration. The analysis is based on the first-order approximation to the linear piston theory and laminated plate theory that includes shear deformation. Both rectangular and skew panels are considered. Stability boundaries at moisture concentrations and temperatures for various lamination schemes and boundary conditions are discussed.
Experimental and Analytical Power Flow in Beams Using a Scanning Laser Doppler Vibrometer
Authors: Blotter Jonathan D. , West Robert L.
Published: January 2014

An experimental spatial power-flow (ESPF) method is presented. This method provides a spatially continuous model of the power-flow vector field derived from experimental measurements. The power-flow vector field clearly indicates locations of energy sources and sinks as well as paths of energy transmission. In the ESPF approach, a scanning laser Doppler vibrometer acquires spatially dense measurements of the vibrating test structure. These measurements are used in solving for a spatially continuous 3-dimensional complex-valued model of the steady-state dynamic response. From this experimentally derived dynamics model, a spatial representation of the power flow is computed.
Matrix Methods for Estimating the Coherence Functions from Estimates of the Cross-Spectral Density Matrix
Authors: Smallwood D.O.
Published: January 2014

It is shown that the usual method for estimating the coherence functions (ordinary, partial, and multiple) for a general multiple-input! multiple-output problem can be expressed as a modified form of Cholesky decomposition of the cross-spectral density matrix of the input and output records. The results can be equivalently obtained using singular value decomposition (SVD) of the cross-spectral density matrix. Using SVD suggests a new form of fractional coherence. The formulation as a SVD problem also suggests a way to order the inputs when a natural physical order of the inputs is absent.
Parametric Nonlinear Finite Element Analysis of Strain Ratcheting in Pressurized Elbows Based on Random Vibration
Authors: Zhao Yong , Stevenson John D. , Tang H.T.
Published: January 2014

The large strain ratcheting in cyclic plasticity of a typical pressurized pipe elbow in a realistic nuclear piping system was investigated in a more quantitative manner than previously. The elbow was modeled using a fine mesh of shell elements that can provide the completed information of detailed time varying strain distributions in the whole elbow area. The nonlinear time history stress analyses performed were based on a pseudostatic concept using the vector-valued stochastic displacement response time series loaded at the elbow ends. The response time series were synthesized using a simulation approach based on the random vibration analyses of the piping system and its supporting building. After a finite element mesh convergence study, parametric analyses were conducted that included the effects due to the magnitude changes in excitation level, internal pressure, material yield stress, and material strain hardening.
Modeling and Simulation of Underwater Shock Problems Using a Coupled Lagrangian—Eulerian Analysis Approach
Authors: Shin Young S. , Chisum James E.
Published: January 2014

The application of coupled Lagrangian—Eulerian analysis to various types of underwater shock problems was investigated, with the verification and validation of this analysis approach in mind. Analyses were conducted for a simple TNT detonation problem and for the classical problems of an infinite cylindrical shell and a spherical shell loaded by a plane acoustic step wave. The advantages, disadvantages, and limitations of this approach are identified and discussed.
Thermodynamic Damping in Porous Materials with Spherical Cavities
Authors: Panteliou Sofia D. , Dimarogonas Andrew D.
Published: January 2014

When a material is subjected to an alternating stress field, there are temperature fluctuations throughout its volume due to the thermoelastic effect. The resulting irreversible heat conduction leads to entropy production that in turn is the cause of thermoelastic damping. An analytical investigation of the entropy produced during a vibration cycle due to the reciprocity of temperature rise and strain yielded the change of the material damping factor as a function of the porosity of the material. A homogeneous, isotropic, elastic bar of cylindrical shape is considered with uniformly distributed spherical cavities under alternating uniform axial stress. The analytical calculation of the dynamic characteristics of the porous structure yielded the damping factor of the bar and the material damping factor. Exsperimental results on porous metals are in good correlation with an analysis.
Substructuring and Component Mode Synthesis
Authors: Seshu P.
Published: January 2014

Substructuring and component mode synthesis (CMS), is a very popular method of model reduction for large structural dynamics problems. Starting from the pioneering works on this technique in the early 1960s, many researchers have studied and used this technique in a variety of applications. Besides model reduction, CMS offers several other crucial advantages. The present work aims to provide a review of the available literature on this important technique.
Investigations into the Uncertainties of Interferometric Measurements of Linear and Circular Vibrations
Authors: von Martens Hans-Jürgen
Published: January 2014

A uniform description is given of a method of measurement using a Michelson interferometer for measuring the linear motion quantities acceleration, velocity and displacement, and a diffraction grating interferometer for measuring the circular motion quantities angular acceleration, angular velocity and rotation angle. The paper focusses on an analysis of the dynamic behaviour of an interferometric measurement system based on the counting technique with regard to the measurement errors due to deterministic and stochastic disturbing quantities. The error analysis and description presented are aimed at giving some rules, mathematical expressions and graphical presentations that have proved to be helpful in recognizing the errors in interferometric measurements of motion quantities, optimizing the measurement conditions (e.g., filter settings), obtaining corrections and estimating the uncertainty of measurement.
Behavior of Uniform Anisotropic Beams of Rectangular Section under Transverse Impact of a Mass
Authors: Chun Lu , Lam K. Y.
Published: January 2014

A numerical method is presented to investigate the dynamic response of uniform orthotropic beams subjected to an impact of a mass. Higher order shear deformation and rotary inertia are included in the analysis of the beams. The impactor and laminated composite beam are treated as a system. The nonlinear differential governing equations of motion are then derived based on the Lagrange principle and modified nonlinear contact law, and solved numerically. The solution procedure is applicable to arbitrary boundary conditions. Numerical results are compared with those available in the literature to demonstrate the validity of the method, and very good agreement is achieved. The effects of boundary conditions on the contact force, contact duration, stress distributions, and beam deflection are discussed.
Basic Mechanical Interactions in Shaker Testing
Authors: Smith Craig C. , Staffanson Forrest L.
Published: January 2014

Simple models representing a shaker and a test object are used to illustrate changes in test object response due to shaker dynamics and differences between the test and service environment. The degree of coupling is quantified in terms of ratios of the natural frequencies and the masses. Regions of overstress can depend on reproducing absolute rather than relative motion in a test. Shaker tests reprodusing output spectra observed in service, when shakerlji.xture impedance is higher than the impedance in service, is shown to cause overtest at frequencies below natural frequencies of the service environment.
Analytical Prediction of Hole Diameter in Thin Plates Due to Hypervelocity Impact of Spherical Projectiles
Authors: Jolly William H. , Schonberg William P.
Published: January 2014

A first-principles-based model is presented for calculating the hole diameter resulting from the normal hypervelocity impact of a spherical aluminum projectile on a thin aluminum plate. One-dimensional shock theory is used to predict the creation and attenuation of Hugoniot pressures along the plate surface. Pressures are translated into the plate thickness by calculating intersecting positions of advancing shock fronts and centered-fan rarefaction waves. The radial position at which the shock pressure equals a predetermined value is defined to be the hole diameter. The model was calibrated by determining this critical value for aluminum-an-aluminum impacts using several hundred data points. A residuals analysis indicated some inherent problems with the model. Two empirical factors were added to account for thin plate and two-dimensional shock dissipation effects. The predictions of the adjusted model are shown to compare well with predictions of several empirical hole diameter models.
Synthesis of Optimal Isolation Systems of Hand-Transmitted Vibration
Authors: Książek Marek
Published: January 2014

In this article a procedure is presented for the analytical synthesis of optimal vibration isolation for a hand-arm system subjected to stochastic excitation. A general approach is discussed for a selected vibration isolation criterion. The general procedure is illustrated by analytical examples for different hand-arm systems described by their driving-point impedances. The influence of particular forms of excitation and the structure of the vibroisolated hand-arm systems on the resultant vibration isolation is then discussed. Some numerical examples illustrating the procedure have also been included.
Angular Rate Sensor Joint Kinematics Applications
Authors: Hall Gregory W. , Crandall Jeff R. , Klopp Gregory S. , Pilkey Walter D.
Published: January 2014

High speed rotary motion of complex joints were quantified with triaxial angular rate sensors. Angular rate sensors were mounted to rigid links on either side of a joint to measure angular velocities about three orthogonal sensor axes. After collecting the data, the angular velocity vector of each sensor was transformed to local link axes and integrated to obtain the incremental change in angular position for each time step. Using the angular position time histories, a transformation matrix between the reference frame of each link was calculated. Incremental Eulerian rotations from the transformation matrix were calculated using an axis system defined for the joint. Summation of the incremental Eulerian rotations produced the angular position of the joint in terms of the standard axes. This procedure is illustrated by applying it to joint motion of the ankle, the spine, and the neck of crash dummies during impact tests. The methodology exhibited an accuracy of less than 5% error, improved flexibility over photographic techniques, and the ability to examine 3-dimensional motion.
Force-State Characterization of Struts Using Pinned Joints
Authors: Ferney Brook D. , Folkman Steven L.
Published: January 2014

As part of a research effort to study the microgravity dynamics of a truss with pinned joints, a single strut with a single clevis-tang pinned joint was characterized. Experimental data was collected using a force-state mapping technique. The strut was subjected to axial dynamic loads and the response of the strut was measured. The force-state map aids visualization of the strut dynamics. Finite element modeling of the response was explored. An example is presented that uses a method of manual determination of the finite element model parameters. The finite element model results correspond well with the measured strut response.
Use of Directional Spectra for Detection of Engine Cylinder Power Fault
Authors: Lee Chong-Won , Han Yun-Sik , Park Jong-Po
Published: January 2014

A diagnostic method, which uses the two-sided directional power spectra of complex-valued engine vibration signals, is presented and tested with four-cylinder compression and spark ignition engines for the diagnosis of cylinder power faults. As spectral estimators, the maximum likelihood and FFT methods are compared, and the multi-layer neural network is employed for pattern recognition. Experimental results show that the success rate for identifying the misfired cylinder is much higher with the use of two-sided directional power spectra than conventional one-sided power spectra.
Study on Synchronization of Two Eccentric Rotors Driven by Hydraulic Motors in One Vibrating System
Authors: Zhang Tianxia , Wen Bangchun , Fan Jian
Published: January 2014

In this article the synchronization of two eccentric rotors driven by hydraulic motors (TERDHM) in one vibrating system is studied. The differential equations of TERDHM motion are derived, and the synchronous and stable rotating conditions of TERDHM are established. It is found from the analysis and simulation that the angular velocities of TERDHM act on each other and both vary in a small range approaching their mean value. The synchronous rotation speed is equal to the average angular velocity of TERDHM, and the phase difference between them depends on the difference of the flow rates of the two hydraulic motors.
Toeplitz Jacobian Method for Nonlinear Double-Periodic Excitations
Authors: Ge T. , Leung A.Y.T.
Published: January 2014

The Toeplitz Jacobian matrix method is an efficient algorithm for computing the steady state solutions of nonlinear periodic vibration. In this paper, the method is generalized by using multiple time scales to double-periodic solutions in a multi-frequency excited system. The method is combined with a standard multi-dimensional FFT algorithm to accurately simulate the nonlinear oscillators with widely separated frequencies. The continuation technique can also be incorporated with the Newton–Raphson iteration to further increase its efficiency, and to achieve the complete frequency response characteristics.
Fluid Surface Damping: A Technique for Vibration Suppression of Beams
Authors: Ghoneim Hany
Published: January 2014

A fluid surface damping (FSD) technique for vibration suppression of beamlikestructures is proposed. The technique is a modification of the surface layer damping method. Two viscoelastic surface layers containing fluid-filled cavities are attached symmetrically to the opposite surfaces of the beam. The cavities on one side are attached to the corresponding cavities on the other side via connection passages. As the beam vibrates, the fluid is pumped back and forth through the connecting passages. Therefore, in addition to the viscoelastic damping provided by the surface layers, the technique offers viscous damping due to the fluid flow through the passage. A mathematical model for the proposed technique is developed, normalized, and solved in the frequency domain to investigate the effect of various parameters on the vibration suppression of a cantilever beam. The steady-state frequency response for a base white-noise excitation is calculated at the beam's free tip and over a frequency range containing the first five resonant frequencies. The parameters investigated are the flow-through passage viscous resistance, the length and location of the layers, the hydraulic capacitance of the fluid-filled cavities, and inertia of the moving fluid (hydraulic inertance). Results indicate that the proposed technique has promising potential in the field of vibration suppression of beamlike structures. With two FSD elements, all peak vibration amplitudes can be well suppressed over the entire frequency spectrum studied.
Shock Protection of Portable Electronic Products: Shock Response Spectrum, Damage Boundary Approach, and Beyond
Authors: Goyal Suresh , Papadopoulos Jim M. , Sullivan Paul A.
Published: January 2014

The pervasive shock response spectrum (SRS) and damage boundary methods for evaluating product fragility and designing external cushioning for shock protection are described in detail with references to the best available literature. Underlying assumptions are carefully reviewed and the central message of the SRS is highlighted, particularly as it relates to standardized drop testing. Shortcomings of these methods are discussed, and the results are extended to apply to more general systems. Finally some general packaging and shock-mounting strategies are discussed in the context of protecting a fragile disk drive in a notebook computer, although the conclusions apply to other products as well. For example, exterior only cushioning (with low restitution to reduce subsequent impacts) will provide a slenderer form factor than the next best strategy: interior cushioning with a “dead” hard outer shell.
Reflected-Afterflow Virtual-Source Model Compared to Exact Calculations for Elastic Cylinders Attacked by Planar Waves
Authors: Waldo George V.
Published: January 2014

A recently developed theoretical approximation, the reflected-afterflow virtual-source (RAVS) model, is applied to the case of a planar shock wave attacking an elastic cylindrical shell. Calculations are shown to be in good agreement with the exact calculations that were published by Huang for all locations and times. It is concluded that the RAVS model gives a good approximation for the loading and response of an elastic cylindrical shell attacked by planar waves. The RAVS model is shown to be even better for spherical waves that are of much more practical interest.
Eigenvalue Sensitivity Analysis for a Combined Beam Structure with Varying Constraints
Authors: Won Kwang-Min , Park Youn-sik
Published: January 2014

An eigenvalue sensitivity formula for a combined beam structure due to the variation of its shape or joint coordinates is proposed based on the Lagrange multiplier technique for a free vibration equation of the structure. The shape variation is decomposed into the length and the orientation variation of each beam to obtain individual effects on the total sensitivity. The sensitivity equations due to the length and the orientation variations are expressed as an energy density form and the cross product of joint forces and displacements respectively. Several numerical examples are also presented to validate the proposed formulation and to show how to implement the idea.
Numerical Study on Identification of Time Varying Parameters of Vibration Systems
Authors: Liang Yanchun , Zhen Qiang , Wang Zaishen
Published: January 2014

An on-line least squares algorithm has previously been successfully applied to linear vibration systems in order to identify time varying parameters. In this article the limitations of the approach and the factors affecting the identification are further examined. The existence of the nonlinear term is determined by means of the time varying characteristics of the estimated linear parameters using the linear model and the data from a time invariant nonlinear system. The identification of the time varying linear parameters is also examined in accordance with the linear model by using the data with nonlinear elements.
Finite Element Modeling and Analysis of Nonlinear Impact and Frictional Motion Responses Including Fluid—Structure Coupling Effects
Authors: Zhao Yong
Published: January 2014

A nonlinear three dimensional (3D) single rack model and a nonlinear 3D whole pool multi-rack model are developed for the spent fuel storage racks of a nuclear power plant (NPP) to determine impacts and frictional motion responses when subjected to 3D excitations from the supporting building floor. The submerged free standing rack system and surrounding water are coupled due to hydrodynamic fluid-structure interaction (FSI) using potential theory. The models developed have features that allow consideration of geometric and material nonlinearities including (1) the impacts of fuel assemblies to rack cells, a rack to adjacent racks or pool walls, and rack support legs to the pool floor; (2) the hydrodynamic coupling of fuel assemblies with their storing racks, and of a rack with adjacent racks, pool walls, and the pool floor; and (3) the dynamic motion behavior of rocking, twisting, and frictional sliding of rack modules. Using these models 3D nonlinear time history dynamic analyses are performed per the U.S. Nuclear Regulatory Commission (USNRC) criteria. Since few such modeling, analyses, and results using both the 3D single and whole pool multiple rack models are available in the literature, this paper emphasizes description of modeling and analysis techniques using the SOLVIA general purpose nonlinear finite element code. Typical response results with different Coulomb friction coefficients are presented and discussed.
Analysis of Cylindrical Shells Using Generalized Differential Quadrature
Authors: Loy C.T. , Lam K.Y. , Shu C.
Published: January 2014

The analysis of cylindrical shells using an improved version of the differential quadrature method is presented. The generalized differential quadrature (GDQ) method has computational advantages over the existing differential quadrature method. The GDQ method has been applied in solutions to fluid dynamics and plate problems and has shown superb accuracy, efficiency, convenience, and great potential in solving differential equations. The present article attempts to apply the method to the solutions of cylindrical shell problems. To illustrate the implementation of the GDQ method, the frequencies and fundamental frequencies for simply supported-simply supported, clamped-clamped, and clamped-simply supported boundary conditions are determined. Results obtained are validated by comparing them with those in the literature.
Statistically Generated Weighted Curve Fit of Residual Functions for Modal Analysis of Structures
Authors: Bookout Paul Stanley
Published: January 2014

A statistically generated weighting function for a second-order polynomial curve fit of residual functions has been developed. The residual flexibility test method, from which a residual function is generated, is a procedure to modal test large structures in a free-free environment to measure the effects of higher order modes and stiffness at distinct degree of freedom interfaces. Due to the present damping estimate limitations in the modal parameter evaluation (natural frequencies and mode shapes) of test data, the residual function has regions of irregular data, which should be a smooth curve in a second-order polynomial form. A weighting function of the data is generated by examining the variances between neighboring data points. From a weighted second-order polynomial curve fit, an accurate residual flexibility value can be obtained. The residual flexibility value and free-free modes from testing are used to improve a mathematical model of the structure, which is used to predict constrained mode shapes.
Explosion Gas Bubbles Near Simple Boundaries
Authors: Chisum James E. , Shin Young S.
Published: January 2014

Finite element analyses of explosion gas bubbles show that including the compressibility of the surrounding media leads to appreciable differences in key areas of the bubble’s behavior. In order to more fully understand the behavior of bubbles created by detonations near simple boundaries, analyses incorporating fluid compressibility were conducted at various stand-off distances from simple rigid and constant pressure surface boundaries. The results from these analyses serve to characterize the behavior of the bubbles for the charge type, charge weight, and hydrostatic pressure used in the analyses.
Laser Doppler Vibrometer: Application of DOE/Taguchi Methodologies to Pyroshock Response Spectra
Authors: Litz C. J.
Published: January 2014

Statistical methodologies were employed for measuring and analyzing the explosively induced transient responses of a flat steel plate excited with shock. The application of design of experiment methodology was made to structure and test a Taguchi L9(32) full factorial experimental matrix (which uses nine tests to study two factors, with each factor examined at three levels) in which a helium-neon laser Doppler vibrometer and two piezocrystal accelerometers were used to monitor explosively induced vibrations ranging from 10 to 105Hz on a 96 × 48 × 0.25 in. flat steel plate. Resulting conclusions were drawn indicating how these techniques aid in understanding the pyroshock phenomenon with respect to the effects and interrelationships of explosive-charge weight and location on the laser Doppler and contract accelerometer recording systems.
Comparison of Force Reconstruction Methods for a Lumped Mass Beam
Authors: Bateman Vesta I. , Mayes Randall L. , Carne Thomas G.
Published: January 2014

Two extensions of the force reconstruction method, the sum of weighted accelerations technique (SWAT), are presented in this article. SWAT requires the use of the structure’s elastic mode shapes for reconstruction of the applied force. Although based on the same theory, the two new techniques do not rely on mode shapes to reconstruct the applied force and may be applied to structures whose mode shapes are not available. One technique uses the measured force and acceleration responses with the rigid body mode shapes to calculate the scalar weighting vector, so the technique is called SWAT-CAL (SWAT using a calibrated force input). The second technique uses the free-decay time response of the structure with the rigid body mode shapes to calculate the scalar weighting vector and is called SWAT-TEEM (SWAT using time eliminated elastic modes). All three methods are used to reconstruct forces for a simple structure.
Measurement of Strong Shock Pressure
Authors: Takada Hajime , Fujimaki Daisuke , Tsuboi Takao
Published: January 2014

This paper deals with measurement of a strong shock pressure like an imploding detonation of over 1 GPa which cannot be measured directly with currently available commercial pressure transducers. After the transfer functions of three kinds of materials were measured using a shock tube, Teflon was selected as a shock absorber. As an example of pressure beyond the limit of the pressure transducer, we tried to measure pressure at the center of an imploding detonation. From this measurement, we could estimate the pressure peak of about 1.7 GPa.
Generation of Stationary Non-Gaussian Time Histories with a Specified Cross-spectral Density
Authors: Smallwood David O.
Published: January 2014

The paper reviews several methods for the generation of stationary realizations of sampled time histories with non-Gaussian distributions and introduces a new method which can be used to control the cross-spectral density matrix and the probability density functions (pdfs) of the multiple input problem. Discussed first are two methods for the specialized case of matching the auto (power) spectrum, the skewness, and kurtosis using generalized shot noise and using polynomial functions. It is then shown that the skewness and kurtosis can also be controlled by the phase of a complex frequency domain description of the random process. The general case of matching a target probability density function using a zero memory nonlinear (ZMNL) function is then covered. Next methods for generating vectors of random variables with a specified covariance matrix for a class of spherically invariant random vectors (SIRV) are discussed. Finally the general case of matching the cross-spectral density matrix of a vector of inputs with non-Gaussian marginal distributions is presented.
Torsional Vibrations at Guide-Vane Shaft of Pump–Turbine Model
Authors: Predin Andrej
Published: January 2014

This article focuses on the problem of guide-vane vibrations of reversible pump–turbines, especially, in the pump mode. These vibrations are transmitted to the guide-vane shaft torque. The guide-vane vibrations are caused by the impeller exit flow, which has a turbulent and partly nondeterministic property. Experimentally determined flow velocities at the impeller exit are given. The mathematical models for theoretical torsional vibration prediction formulated using linear and nonlinear differential equations are presented. The results of theoretical calculations are compared with measurement results. The possibility of transferring the parameters from the model to the prototype is discussed.
Iterated Dynamic Condensation Technique and Its Applications in Modal Testing
Authors: Hou Zhikun , Chen Shiyu
Published: January 2014

This article addresses an application of the dynamic condensation in modal testing, which requires measurements of natural frequencies and a limited number of components of modal shapes only. The measured frequencies can be employed as the initial estimates in the iterated dynamic condensation to effectively find an exact solution for the original eigenvalue problem and determine the transformation matrix between the testing and nontesting coordinates. Complete modal shapes including the nontesting coordinates can then be estimated based on the limited measurements. Numerical results are presented to illustrate the feasibility and efficiency of the iterated dynamic condensation. A comparison with the experimental results of a multiple disk system is also provided.
Finite Element Model Optimization Using Diagonal Mass Matrix
Authors: Wang B.P. , Chu F.H.
Published: January 2014

By adjusting the analytic mass matrix or stiffness parameters, the correlation between measured and computed modal data can be improved. This article proposes a simple method for model optimization. Numerical examples will be included to illustrate the proposed approach.
Dynamic Response of Wall Backfill Retaining System
Authors: Alampalli Sreenivas , Elgamal Ahmed-W.
Published: January 2014

An in situ full-scale test is conducted to measure the dynamic response of a long cantilever wall that retains backfill soil. The recorded modal parameters of this retaining wall exhibited significant similarity to those of a clamped cantilever plate (rather than those of a cantilever beam or plane-strain analysis). Such a three-dimensional (3-D) response pattern is not accounted for by current analysis procedures. A simple 3-D finite element model is employed to further analyze the observed resonant configurations. The results indicate that such configurations play an important role in the seismic response of wall backfill soil systems of variable height, such as wing walls supporting highway approach ramps.
Sensitivity of Parameter Changes in Structural Damage Detection
Authors: Jenkins C. H. , Kjerengtroen L. , Oestensen H.
Published: January 2014

Structural damage detection by nondestructive methods is highly desirable. Changes in modal parameters such as frequency, damping, and mode shape are particularly inviting. Evidence is presented here that reveals that static deflection can, in many cases, be a more sensitive predictor of structural damage than frequency. The reasons for this are illuminated within, and hinge on very fundamental issues about the very nature of structural response. Furthermore, static deflection measurements are often easier to make, with higher levels of accuracy than dynamic measurements. Comparisons are made between theoretical models and experimental results for simple structures, with extensions given to more complex structures.
Bulging Modes of Circular Bottom Plates in Rigid Cylindrical Containers Filled with a Liquid
Authors: Amabili Marco
Published: January 2014

In this article the free vibrations of the bottom plate of an otherwise rigid circular cylindrical tank filled with liquid are studied, considering only the bulging modes (when the amplitude of the plate displacement is predominant with respect to that of the free surface). The tank axis is vertical, thus the free liquid surface is orthogonal to the tank axis. The liquid is assumed to be inviscid, and the contribution of the free surface waves to the dynamic pressure on the free liquid surface is neglected. Wet and dry mode shapes of the plate are assumed to be the same, so that the natural frequencies are obtained by using the nondimensionalized added virtual mass incremental (NA VMI) factors and the modal properties of dry plates. This simplifies computations compared to other existing theoretical approaches. NAVMI factors express the nondimensionalized ratio between the reference kinetic energy of the liquid and that of the plate and have the advantage that, due to their nondimensional form, they can be computed once and for all. Numerical results for simply supported and clamped bottom plates, as well as for supported plates with an elastic moment edge constraint are given. For more accurate results, and to exceed the limits of the assumed modes approach, the Rayleigh-Ritz method is applied and results are compared to those obtained by using the NAVMI factors and other existing methods in the literature.
Optimal Vibration Suppression in Modal Space for Flexible Beams Subjected to Moving Loads
Authors: Lin Yih-Hwang
Published: January 2014

Optimal independent modal space control for vibration suppression of beam structures traversed by a moving concentrated force was examined. Two control methodologies, optimal linear quadratic tracking and an optimal linear quadratic regulator, were utilized, with the former approach taking into account the disturbance due to the moving load and the latter one simply ignoring that disturbance. One single actuator placed at the beam center was found to be sufficient to suppress excessive vibration of a beam traversed by the moving load with a reasonable amount of control input. This study shows that excessive vibration of the beam structure induced by the moving load can be more effectively suppressed using the tracking control approach than using the regulator design, even with ±50% variation of the moving load magnitude or speed from that designed for the tracking control system.
Narrow-Band Excitation of Hysteretic Systems
Authors: Zhu W.Q. , Huang C.D. , Soong T.T.
Published: January 2014

The stationary response of smooth and bilinear hysteretic systems to narrow-band random excitations is investigated by using the quasistatic method and digital simulation. It is shown that the response is qualitatively different in different ranges of values of the ratio of the excitation central frequency to the natural frequency of the system. In the resonant zone, the response is essentially non-Gaussian. For bilinear hysteretic systems with strong yielding, stochastic jumps may occur for a range of values of the ratio between nonresonant and resonant zones.
Dynamic Behavior of Tubes Subjected to Internal and External Cross Flows
Authors: Huang Yii-Mei , Hsu Chih-Shan
Published: January 2014

This article presents a method for thoroughly examining the dynamic characteristics of a tube under the influence of either the internal flow or the external cross flow. The tube is modeled as a thin cylindrical shell whose governing equations are derived from an energy method. The effects due to internal flow are introduced into the system through initial stress. Galerkin’s method in conjunction with the method of multiple scales is employed for obtaining the stability of the tube vibration. According to the results, instability can occur under certain conditions of resonance. Regarding the effects of the external cross flow, a numerical approach is initially employed to interpolate the experimental data of the pressure distributions due to the flow. The dynamic characteristics of the tube under steady flows and flows with small time variation are then investigated. Stability of the solution is also discussed.
Measuring the Acceleration of a Rigid Body
Authors: Martin Peter G. , Hall Gregory W. , Crandall Jeff R. , Pilkey Walter D.
Published: January 2014

Two methods to measure the six‐degree‐of‐freedom acceleration of a point on a rigid body are presented. The first, referred to as the periphery scheme, makes use of three clusters of accelerometers mounted orthogonal to each other and coincident with the axes of the point. One of the clusters consists of the three accelerometers attached to a cube‐shaped triaxial angular rate sensor (ARS). The second method, called the compact cube scheme, uses a single 3‐accelerometer/ARS cluster that may be mounted anywhere on the rigid body. During impact tests with an instrumented rigid body, both methods produced measurements that were highly correlated near the time of peak acceleration. Whereas the compact cube scheme was more economical and easier to implement, the periphery scheme produced results that were less disrupted by instrument signal errors and noisy environments.
Statistics of the Von Mises Stress Response For Structures Subjected To Random Excitations
Authors: Chen Mu-Tsang , Harichandran Ronald
Published: January 2014

Finite element‐based random vibration analysis is increasingly used in computer aided engineering software for computing statistics (e.g., root‐mean‐square value) of structural responses such as displacements, stresses and strains. However, these statistics can often be computed only for Cartesian responses. For the design of metal structures, a failure criterion based on an equivalent stress response, commonly known as the von Mises stress, is more appropriate and often used. This paper presents an approach for computing the statistics of the von Mises stress response for structures subjected to random excitations. Random vibration analysis is first performed to compute covariance matrices of Cartesian stress responses. Monte Carlo simulation is then used to perform scatter and failure analyses using the von Mises stress response.
Left Posteroventral Pallidotomy Results in a Deficit in Verbal Memory
Authors: Crowe S. F. , O’Sullivan J. D. , Peppard R. F. , McNeil P. M. , Bardenhagen F. , Bowden S.
Published: January 2014

Whilst pallidotomy is emerging as a popular approach to the treatment to Parkinson’s disease, little is yet known about the cognitive effects of this procedure. This study presents 19 patients (6 right, 13 left) who were assessed both before and after the procedure on a battery of cognitive tests. The results indicate that subjects with left‐sided lesions display significant decline in verbal memory between one and three months following the procedure. The results are consistent with the notion of either a classic amnesic syndrome or a deficit in striato‐frontal working memory.
Nonlinear Response of Cantilever Beams to Combination and Subcombination Resonances
Authors: Nayfeh Ali H. , Arafat Haider N.
Published: January 2014

The nonlinear planar response of cantilever metallic beams to combination parametric and external subcombination resonances is investigated, taking into account the effects of cubic geometric and inertia nonlinearities. The beams considered here are assumed to have large length‐to‐width aspect ratios and thin rectangular cross sections. Hence, the effects of shear deformations and rotatory inertia are neglected. For the case of combination parametric resonance, a two‐mode Galerkin discretization along with Hamilton’s extended principle is used to obtain two second‐order nonlinear ordinary‐differential equations of motion and associated boundary conditions. Then, the method of multiple scales is applied to obtain a set of four first‐order nonlinear ordinary‐differential equations governing the modulation of the amplitudes and phases of the two excited modes. For the case of subcombination resonance, the method of multiple scales is applied directly to the Lagrangian and virtual‐work term. Then using Hamilton’s extended principle, we obtain a set of four first‐order nonlinear ordinary‐differential equations governing the amplitudes and phases of the two excited modes. In both cases, the modulation equations are used to generate frequency‐ and force‐response curves. We found that the trivial solution exhibits a jump as it undergoes a subcritical pitchfork bifurcation. Similarly, the nontrivial solutions also exhibit jumps as they undergo saddle‐node bifurcations.
Cortical Auditory Disorders: A Case of Non‐Verbal Disturbances Assessed with Event‐Related Brain Potentials
Authors: Johannes Sönke , Jöbges Michael E. , Dengler Reinhard , Münte Thomas F.
Published: January 2014

In the auditory modality, there has been a considerable debate about some aspects of cortical disorders, especially about auditory forms of agnosia. Agnosia refers to an impaired comprehension of sensory information in the absence of deficits in primary sensory processes. In the non‐verbal domain, sound agnosia and amusia have been reported but are frequently accompanied by language deficits whereas pure deficits are rare. Absolute pitch and musicians’ musical abilities have been associated with left hemispheric functions. We report the case of a right handed sound engineer with the absolute pitch who developed sound agnosia and amusia in the absence of verbal deficits after a right perisylvian stroke. His disabilities were assessed with the Seashore Test of Musical Functions, the tests of Wertheim and Botez (Wertheim and Botez, Brain 84, 1961, 19–30) and by event‐related potentials (ERP) recorded in a modified ′oddball paradigm’. Auditory ERP revealed a dissociation between the amplitudes of the P3a and P3b subcomponents with the P3b being reduced in amplitude while the P3a was undisturbed. This is interpreted as reflecting disturbances in target detection processes as indexed by the P3b. The findings that contradict some aspects of current knowledge about left/right hemispheric specialization in musical processing are discussed and related to the literature concerning cortical auditory disorders.
Review: Optimal Shock and Vibration Isolation
Authors: Balandin D.V. , Bolotnik N.N. , Pilkey W.D.
Published: January 2014

This is a review of the investigations into the field of optimum shock and vibration isolation, including the mathematical foundations of both optimal open‐loop and optimal feedback isolation systems. This survey covers the literature from the initial studies to the present.
Sound Power Estimation by Laser Doppler Vibration Measurement Techniques
Authors: Revel G.M. , Rossi G. L.
Published: January 2014

The aim of this paper is to propose simple and quick methods for the determination of the sound power emitted by a vibrating surface, by using non‐contact vibration measurement techniques. In order to calculate the acoustic power by vibration data processing, two different approaches are presented. The first is based on the method proposed in the Standard ISO/TR 7849, while the second is based on the superposition theorem. A laser‐Doppler scanning vibrometer has been employed for vibration measurements. Laser techniques open up new possibilities in this field because of their high spatial resolution and their non‐intrusivity. The technique has been applied here to estimate the acoustic power emitted by a loudspeaker diaphragm. Results have been compared with those from a commercial Boundary Element Method (BEM) software and experimentally validated by acoustic intensity measurements. Predicted and experimental results seem to be in agreement (differences lower than 1 dB) thus showing that the proposed techniques can be employed as rapid solutions for many practical and industrial applications. Uncertainty sources are addressed and their effect is discussed.