Showing papers on "Random vibration published in 1990"

Random vibration and statistical linearization

Abstract: Interest in the study of random vibration problems using the concepts of stochastic process theory has grown rapidly due to the need to design structures and machinery which can operate reliably when subjected to random loads, for example winds and earthquakes. This is the first comprehensive account of statistical linearization - powerful and versatile methods with related techniques allowing the solution of a very wide variety of practical non-linear random vibration problems. The principal value of these methods is that unlike other analytical methods, they are readily generalized to deal with complex mechanical and structural systems and complex types of excitation such as earthquakes.

The Generalized Cell Mapping Method in Nonlinear Random Vibration Based Upon Short-Time Gaussian Approximation

Abstract: This scheme provides a very efficient and accurate way of computing the one-step transition probability matrix of the previously developed generalized cell mapping (GCM) method in nonlinear random vibration

Response of indeterminate two-span beam to spatially varying seismic excitation

Abstract: In order to examine the effect of the spatial variation of ground motion on the response of an indeterminate structure, the stochastic responses of a two-span beam to spatially varying support excitations are analysed. A space-time earthquake ground motion model that accounts for both coherency decay and seismic wave propagation is used to specify the support motions, and the results are compared with those for various simplified excitations that are commonly used in practice. The response is computed through a linear random vibration approach with the structure being modelled by finite elements. The results of the study indicate that, even for moderate lengths, the effect of the spatial variation of ground motion can be significant. The assumption of fully coherent support motions (same excitations at all supports or delayed excitations allowing only for wave propagation) may be overconservative for some beams and unconservative for others.

Structural response to non‐stationary multiple‐support random excitation

Abstract: The seismic behaviour of large-size structures subjected to multiple-support excitation is studied by means of a random vibration approach. Ground motion is modelled as a non-stationary stochastic process having an evolutionary spectral density. To describe the spatial variability of the input motion a model is adopted which accounts for finite propagation velocity and for loss of correlation as a function of distance and frequency. Structural analysis is entirely performed in the frequency domain and full advantage is taken of FFT properties and capabilities. An example is given regarding the behaviour of a 800 m long viaduct. Results are shown in terms of response evolutionary spectral density, variance and reliability with respect to a fixed threshold.

Non‐stationary structural response with evolutionary spectra using seismological input model

Abstract: A recently developed seismological model of ground motion is incorporated into the non-stationary random vibration theory making use of Priestley's evolutionary power spectral density. A general method of computing the input power spectrum is proposed and shown to reduce to the classical method when the input and the output are taken as stationary. Based on the concepts of Yang's non-stationary envelopes and first-passage reliability estimates via extreme point process, a statistical response spectrum for the pseudo-velocity is developed. Comparisons made among the results of non-stationary analysis with different modulating functions, and that of the stationary approximation, on SDOF linear structures with 5 per cent damping show that the type ofmodulating function chosen has little effect on the magnitudes of mean pseudo-velocities, provided the input power spectrum is properly scaled, and that the stationary approximation produces conservative results for structures with natural periods greater than 0.5 sec.

Random Vibration of Hysteretic Systems

Abstract: An approximation procedure is used to compute probability densities for the response variables of a hysteretic system under Gaussian white noise excitations. The excitations can be both additive and multiplicative. Accuracy of the procedure is substantiated by comparison with simulation results.

Multiply Supported Pipeline under Seismic Wave Excitations

Abstract: This paper develops a theory to compute the statistical properties for the response of a surface-mounted pipeline to seismic excitations. Making the assumptions that the pipeline behaves like an infinitely long Euler-Bernoulli beam on evenly spaced supports, that the seismic motion is statistically stationary in time but nonhomogeneous in space, and that the seismic inputs are fed into the pipeline system through the supports, solutions are obtained for the spectral densities of the structural response. The theory developed is aplicable to any spectral distributions.

Dynamic Response of Tall Buildings to Stochastic Wind Load

Abstract: A random vibration‐based procedure is used to estimate the dynamic responses of symmetric tall buildings (coincident centers of mass, rigidity, and geometry) subjected to the effects of wind. The along‐wind, across‐wind, and torsional components of wind force were obtained from a time‐series analysis of surface pressures measured during a wind‐tunnel test of a rigid model. The structural response analysis takes the statistical correlation among these three components of aerodynamic force into account. The contributions of the first and second translational and torsional modes to the response are investigated. The across‐wind and torsional accelerations are the major contributors to building acceleration. A simple approach is developed for evaluating the response statistics that are important for building serviceability. This approach can be used in the preliminary design stage to assess the possibility of unserviceability and the need for more detailed and expensive wind‐tunnel model tests.

Random response analysis of frictional base isolation system

Abstract: In this work, the response analysis of a randomly excited nonlinear system is considered. The system resembles a frictional base isolation system under random earthquake excitation. The equivalent ...

Finite element, large-deflection random response of thermally buckled beams

Abstract: The effects of temperature and acoustic loading are included in a theoretical finite element, large-deflection formulation for the random response of thin, isotropic beams. Thermal loads are applied as steady state temperature distributions, and acoustic loads are taken to be ergodic and gaussian with zero mean and uniform magnitude and phase along the length of the beam.

Recursive Modeling of Dynamic Systems

Abstract: The dynamic response analysis of structural systems to a variety of random excitations using recursive models is presented. The methodology permits analysis of stationary, nonstationary, or transient response of structures under stochastic loads, e.g., correlated multi-input loading due to fluctuations in wind or wave surface profile, or seismic excitation. For the nonstationary, or transient, excitation, the analysis involves a direct computation of the output covariance from a given nonstationary correlation structure of the input. The accuracy and stability of the simulated time histories is assessed. A detailed example is presented to illustrate the proposed recursive model. The concept of an ARMA (auto-recursive moving average) system is presented in which the ARMA representation of the response is obtained in terms of the ARMA description of the stationary excitation. The usefulness of the recursive approach for nonlinear systems is demonstrated by means of an example involving an elasto-plastic beam subjected to a suddenly applied load.

Dynamic Analysis and Failure Modes of Simple Structures

Abstract: Mechanical Loads and Failure Modes. Natural Frequency of Simple Components. Natural Frequency of Simple Structures. Random Vibration. Shock. Isolation. Fatigue. Fracture. Elastic Instability. Structural Analysis of Mounted Housings. Venting. Thermal Analysis. References. Appendices. Index.

Effects of whole-body vibration waveform and display collimation on the performance of a complex manual control task

Abstract: An experiment is described in which two independent groups of eight subjects each performed a combined continuous and discrete tracking task during exposure to vertical whole-body vibration. Both groups received sinusoidal and random vibration at preferred third-octave centre frequencies of 0.5-10 Hz. One group performed the task with the display collimated by a convex lens. Without the collimation, performance was disrupted by both types of vibration at all vibration frequencies; collimation removed the disruption at frequencies above 1.6 Hz. There were differences in the effects of random and sinusoidal vibration at 2.0 and 2.5 Hz, suggesting that compensatory eye movements were assisting performance during exposure to the predictable sinusoidal motion. The results show that continuous control performance was disrupted by visual interference at frequencies above 1.6 Hz; closed-loop system transfer functions showed that visual interference increased the phase lags which impaired control performance. Possible mechanisms explaining the disruption in performance at lower frequencies are discussed. Language: en

Probabilistic analysis of bladed turbine disks and the effect of mistuning

Abstract: Probabilistic assessment of the maximum blade response on a mistuned rotor disk is performed using the computer code NESSUS The uncertainties in natural frequency, excitation frequency, amplitude of excitation and damping have been included to obtain the cumulative distribution function (CDF) of blade responses Advanced mean value first order analysis is used to compute CDF The sensitivities of different random variables are identified Effect of the number of blades on a rotor on mistuning is evaluated It is shown that the uncertainties associated with the forcing function parameters have significant effect on the response distribution of the bladed rotor

Friction Damping of Random Vibration in Gas Turbine Engine Airfoils

Abstract: The optimal value of slip load is calculated for a frictionally damped turbine blade subjected to random excitation. The nature of excitation is assumed to be Gaussian white noise and the statistics of response are obtained using equivalent linearization approach. The results from this technique are compared with those from numerical simulations.Copyright © 1987 by ASME

Ground vibration measurements with special reference to pile driving

Abstract: There has been increased concern in recent years over the level and nature of the ground vibrations. The importance of such vibration has increased rapidly due to developments in construction in urban areas, where the effects of ground borne vibration on both humans and structures are considerable. Research has been undertaken to improve techniques used in the measurements, analyses and evaluation of ground vibrations caused by rail and road traffic, blasting and in particular those generated from pile driving activities. The amplitude of the vibration caused by the pile driving operation is a function of pile type, hammer type and the ground conditions. In order to investigate the effects of these three variables, a large number of visits were made to different sites which provided a range of different driving conditions. The main requirements in the analysis of the vibrations measured include vibration amplitude and their relevant frequency. The vibration amplitude is usually expressed in term of peak particle acceleration, velocity or displacement. In this work, the ground vibration is measured in terms of peak particle velocity using velocity transducers (geophone). In order to evaluate the true peak particle resultant velocity, the three components of the ground vibration are measured simultaneously by three orthogonally positioned sets of geophone. Recording the vibration data is achieved by employing a portable digital recorder which digitizes the analogue signals recieved from the transducers and stores the captured data on standard floppy disks for further analysis. The results are presented in tables and diagrams and detailed comments are given in the discussion of the recorded data. Some methods of analyses are reviewed and two new methods are proposed. These proposed methods include the application of the hemispherical projection technique in interpreting and displaying the three dimesional vibration information into a two dimensional plane. The other method analysed the attenuation of the ground vibration according to the arrival time of the generated waves from the pile toe and along the ground surface. It is suggested that when the arrival times of these two wave fronts coincide at one particular point, a highest vibration amplitude may be expected at that poinL The effect of ground vibration on building is investigated in large scale test in Aitwick where the dynamic strain of purpose built L-shape walls are recorded during driving steel sheet and H-pile at different stand-off from the walls using a winch-drop-hammer and a vibrodriver.

Optimal active dynamic vibration absorber for multi-degree-of-freedom systems. Feedback and feedforward control using a Kalman filter.

Abstract: This study presents a method of feedforward control design of an active dynamic vibration absorber for multi-degree-of-freedom systems. The feedforward control, obtained by assuming that the shaping filter has the same natural frequency as a primary structure in the frequency range of input disturbance, is effective in the broad frequency range and is robust for input disturbance. Furthermore, to improve reliability, a digital control system consisting of reduced-order feedback control and feedforward control, using a Kalman filter, is synthesized

Analysis of dual control vibration testing

Abstract: Analysis of dual control vibration testing is conducted using a two-degree-of-freedom system to represent the interaction between a vibration mode of a test item and a mode of a mounting structure. The results indicate that exact dual control based on specification of the source free acceleration and blocked force is strictly valid only if phase is taken into account. However, extremal dual control without phase alleviates overtesting without risk of undertesting, when the limit acceleration and force specifications are chosen to envelope the coupled system results. Several approaches to deriving appropriate force specifications are explored. Random vibration parametric results from the literature are used to estimate the limit force between coupled oscillators with different source and load masses.

A note on the fast computation of response spectra estimates

Abstract: An algorithm is presented for fast computation of estimates of response spectra. It is based on the formalism of random vibration theory. Numerical results show that estimates are reliable and useful for practical applications.

The spectral density of the nonlinear damping model: single DOF case

Abstract: An analytical method of computing the frequency response of single degree of freedom (DOF) oscillators with nonlinear damping is described. The author proposes an energy-type nonlinear damping model and the corresponding stationary probability density with white noise input can be obtained explicitly. A theorem is presented which gives an interesting result, in terms of the Krylov-Bogoliubov approximation, concerning the modeling and identification of nonlinear internal damping in flexible structures. This analysis also serves as a contribution to random vibration theory by providing a method of computing the first- and second-order statistics (steady-state probability density, correlation function, and spectral density) of nonlinearity damped oscillators with white noise input. >

Vibrations, Dynamics and Structural Systems

Abstract: Introduction Free vibration of single degree of freedom system Forced vibration of single degree of freedom system Numerical methods in structural analysis: Applied to SDF systems Vibration of two degrees of freedom system Free vibration of multiple degrees of freedom system Free vibration analysis of continuous systems Forced vibration of continuous systems Dynamic direct stiffness method Vibration of ship and aircraft as a beam Finite element method in vibration analysis Finite difference method for the vibration analysis of beams and plates Nonlinear vibration Random vibration Computer program in vibration analysis The stiffness matrix Table of spring stiffness Index.