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Showing 5 results for Time-Domain

H. Alielahi, M. Kamalian, J. Asgari Marnani, M. K. Jafari, M. Panji,
Volume 11, Issue 1 (5-2013)
Abstract

In this paper, an advanced formulation of a time-domain two-dimensional boundary element method (BEM) is presented and

applied to calculate the response of a buried, unlined, and infinitely long cylindrical cavity with a circular cross-section subjected

to SV and P waves. The applicability and efficiency of the algorithm are verified with frequency-domain BEM examples of the

effect of cylindrical cavities on the site response analysis. The analysis results show that acceptable agreements exist between

results of this research and presented examples. For a shallow cavity, the numerical results demonstrate that vertically incident

SV wave reduces the horizontal components of the motion on the ground surface above the cavity, while it significantly increases

the vertical component for a dimensionless frequency (&eta) of 0.5 and h/a=1.5. The maximum values of normalized displacements

in vertical component of P waves are larger than horizontal component of SV waves for &eta=1.0. For a deeply embedded cavity,

the effect of the cavity on the surface ground motion is negligible for incident SV wave, but it increases the vertical component of

the displacement for incident P wave. Additionally, far and near distances from the center of the cavity show different amplitude

patterns of response due to the cavity effect. Increasing the distance from the center of the cavity, the amplitude of displacement

and the effect of the cavity attenuates significantly.


M. Afzalirad, M. Kamalian, M. K. Jafari, A. Sohrabi-Bidar,
Volume 12, Issue 1 (1-2014)
Abstract

In this paper, an advanced formulation of time-domain, two-dimensional Boundary Element Method (BEM) with material damping is presented. Full space two-dimensional visco-elastodynamic time-convoluted kernels are proposed in order to incorporate proportional damping. This approach is applied to carry out site response analysis of viscoelastic topographic structures subjected to SV and P incident waves. Seismic responses of horizontally layered site, semi-circular canyons, slope topography and ridge sections subjected to these incident waves are analyzed in order to demonstrate the accuracy of the kernels and the applicability of the presented viscoelastic boundary element algorithm. The results show an excellent agreement with recent published results obtained in frequency domain. Also, the effects of different material damping ratios on site response are investigated.
Me. Panji, M. Kamalian, J. Asgari Marnani, M. K. Jafari,
Volume 12, Issue 2 (4-2014)
Abstract

In this paper, normalized displacement amplitude of the ground surface was presented in the presence of the semi-sine shaped valley above the truncated circular cavity embedded in a homogenous isotopic linear elastic half-plane, subjected to obliquely propagating incident SH waves as Ricker wavelet type. The proposed direct time-domain half-plane boundary element formulation was used and extended to analyze the combined multi-boundary topographic problems. While using it, only boundary of the valley and the surrounding cavity should be discretized. The effect of four geometric parameters including shape ratio of the valley, depth ratio, horizontal location ratio and truncation thickness of the cavity and incident wave angle was investigated on the responses at a single dimensionless frequency. The studies showed that surface behavior was completely different due to complex topographic features, compared with the presence of either valley or cavity alone. In addition, the cavity existence below the surface could play a seismic isolation role in the case of vertical incident waves and vice versa for oblique waves.
Jafar Najafizadeh, Mohsen Kamalian, Mohammad Kazem Jafari, Naser Khaji,
Volume 12, Issue 3 (7-2014)
Abstract

In this paper, an advanced formulation of the spectral finite element method (SFEM) is presented and applied in order to carry out site response analysis of 2D topographic structures subjected to vertically propagating incident in-plane waves in time-domain. The accuracy, efficiency and applicability of the formulation are demonstrated by solving some wave scattering examples. A numerical parametric study has been carried out to study the seismic response of rectangular alluvial valleys subjected to vertically propagating incident SV waves. It is shown that the amplification pattern of the valley and its frequency characteristics depend strongly on its shape ratio. The natural frequency of the rectangular alluvial valley decreases as the shape ratio of the valley decreases. The maximum amplification ratio along the ground surface occurs at the center of the valley. A simple formula has been proposed for making initial estimation of the natural period of the valley in site effect microzonation studies.
Hamid Alielahi, Mohammad Adampira,
Volume 14, Issue 4 (6-2016)
Abstract

Investigating the seismic amplification of incident waves induced by subsurface cavities and characterizing its patterns for the ground surface are important in seismology, geophysics and earthquake engineering both in theory and practical application. Nowadays, it has been established that the seismic ground response above subsurface structures can be different from the free-field motion during earthquakes. In this regard, this research studied preliminary results of a numerical parametric study on the seismic response of the ground surface above subsurface cavity. Basically, this study is applied to get new idea to move a step forward in site response analysis which can be used in the seismic microzonation of areas located above underground spaces. For analysis purposes, a numerical time-domain analysis is performed by utilizing a robust numerical algorithm working based on the boundary element method. It is observed that the amplification of the ground surface underlain by a shallow elliptical cavity is increased in long periods. Some preliminary simple relationships and tables are presented which could be used while introducing simple preliminary ideas for modification of the standard design spectra in building codes and seismic microzonation studies.



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