Crack growth tests and analyses of CCT specimens made of LY12CZ Al-uminium alloy and 30CrMnSiA high strength steel materials are carried out. The speci-mens are subjected to transport flight-by-flight random spectra o...Crack growth tests and analyses of CCT specimens made of LY12CZ Al-uminium alloy and 30CrMnSiA high strength steel materials are carried out. The speci-mens are subjected to transport flight-by-flight random spectra of high loads encoun-tered 10 times per 1000 flights. The crack growth life is predicted with an equivalentmodel. Comparing the spectra based on 100 flights with those based on 1000 flights, theformer requires only 10 per cent data for cycles. Experiment results show that the differ-ences between two spectra are less than 10% for crack growth life. A more simply con-densed spectrum is derived, retaining groundtoair cycle during every flight and ar-ranging some constant amplitude cycles according to equivalent damage rule. The dataof this spectrum is 10 per cent less than that based on 100 flights, but the differences oftwo spectra whether the predicted or tested results for crack growth life are less than 15per cent. Accordingly, a complex random spectrum may arbitranly be changed to acondensed spectrum with equivalent damage rule, reducing calculation and test work.展开更多
The goal of this study is to provide a stochastic method to investigate the eff ects of the randomness of soil properties due to their natural spatial variability on the response spectra spatial variation at sites wit...The goal of this study is to provide a stochastic method to investigate the eff ects of the randomness of soil properties due to their natural spatial variability on the response spectra spatial variation at sites with varying conditions. For this purpose, Monte Carlo Simulations are used to include the variability of both incident ground motion and soil parameters in the response spectra by mean of an appropriate coherency loss function and a site-dependent transfer function, respectively. The approach is built on the assumption of vertical propagation of SH type waves in soil strata with uncertain parameters. The response spectra are obtained by numerical integration of the governing equation of a single-degree-of-freedom (SDOF) system under non-stationary site-dependent and spatially varying ground motion accelerations simulated with non-uniform spectral densities and coherency loss functions. Numerical examples showed that randomness of soil properties signifi cantly aff ects the amplitudes of the response spectra, indicating that as the heterogeneity induced by the randomness of the parameters of the medium increases, the spectral ordinates attenuate.展开更多
This work presents a new approach for simulating the random waves in viscous fluids and the associated bottom shear stresses. By generating the incident random waves in a numerical wave flume and solving the unsteady ...This work presents a new approach for simulating the random waves in viscous fluids and the associated bottom shear stresses. By generating the incident random waves in a numerical wave flume and solving the unsteady two-dimensional Navier-Stokes equations and the fully nonlinear free surface boundaiy conditions for the fluid flows in the flume, the viscous flows and laminar bottom shear stresses induced by random waves axe determined. The deterministic spectral amplitude method implemented by use of the fast Fourier transform algorithm was adopted to generate the incident random waves. The accuracy of the numerical scheme is confirmed by comparing the predicted wave spectrum with the target spectrum and by comparing the nanlerical transfer function between the shear stress and the surface elevation with the theoretical transfer function. The maximum bottom shear stress caused by random waves, computed by this wave model, is compared with that obtained by Myrhaug＇ s model （1995）. The transfer function method is also employed to determine the maximum shear stress, and is proved accurate.展开更多
文摘Crack growth tests and analyses of CCT specimens made of LY12CZ Al-uminium alloy and 30CrMnSiA high strength steel materials are carried out. The speci-mens are subjected to transport flight-by-flight random spectra of high loads encoun-tered 10 times per 1000 flights. The crack growth life is predicted with an equivalentmodel. Comparing the spectra based on 100 flights with those based on 1000 flights, theformer requires only 10 per cent data for cycles. Experiment results show that the differ-ences between two spectra are less than 10% for crack growth life. A more simply con-densed spectrum is derived, retaining groundtoair cycle during every flight and ar-ranging some constant amplitude cycles according to equivalent damage rule. The dataof this spectrum is 10 per cent less than that based on 100 flights, but the differences oftwo spectra whether the predicted or tested results for crack growth life are less than 15per cent. Accordingly, a complex random spectrum may arbitranly be changed to acondensed spectrum with equivalent damage rule, reducing calculation and test work.
文摘The goal of this study is to provide a stochastic method to investigate the eff ects of the randomness of soil properties due to their natural spatial variability on the response spectra spatial variation at sites with varying conditions. For this purpose, Monte Carlo Simulations are used to include the variability of both incident ground motion and soil parameters in the response spectra by mean of an appropriate coherency loss function and a site-dependent transfer function, respectively. The approach is built on the assumption of vertical propagation of SH type waves in soil strata with uncertain parameters. The response spectra are obtained by numerical integration of the governing equation of a single-degree-of-freedom (SDOF) system under non-stationary site-dependent and spatially varying ground motion accelerations simulated with non-uniform spectral densities and coherency loss functions. Numerical examples showed that randomness of soil properties signifi cantly aff ects the amplitudes of the response spectra, indicating that as the heterogeneity induced by the randomness of the parameters of the medium increases, the spectral ordinates attenuate.
基金the Science Council (Grant No. NSC95-2221-E-006-474)
文摘This work presents a new approach for simulating the random waves in viscous fluids and the associated bottom shear stresses. By generating the incident random waves in a numerical wave flume and solving the unsteady two-dimensional Navier-Stokes equations and the fully nonlinear free surface boundaiy conditions for the fluid flows in the flume, the viscous flows and laminar bottom shear stresses induced by random waves axe determined. The deterministic spectral amplitude method implemented by use of the fast Fourier transform algorithm was adopted to generate the incident random waves. The accuracy of the numerical scheme is confirmed by comparing the predicted wave spectrum with the target spectrum and by comparing the nanlerical transfer function between the shear stress and the surface elevation with the theoretical transfer function. The maximum bottom shear stress caused by random waves, computed by this wave model, is compared with that obtained by Myrhaug＇ s model （1995）. The transfer function method is also employed to determine the maximum shear stress, and is proved accurate.
