Scattering of seismic waves by three-dimensional large-scale hill topography simulated by a fast parallel IBEM

To solve seismic wave scattering by a large-scale three-dimensional(3-D) hill topography, a fast parallel indirect boundary element method(IBEM) is developed by proposing a new construction method for the wave field, modifying the generalized minimum residual(GMRES) algorithm and constructing an Open MP plus MPI parallel model. The validations of accuracy and efficiency show that this method can solve 3-D seismic response of a large-scale hill topography for broadband waves, and overcome the weakness of large storage and low efficiency of the traditional IBEM. Based on this new algorithm architecture, taking the broadband scattering of plane SV waves by a large-scale Gaussian-shaped hill of thousands-meters height as an example, the influence of several important parameters is investigated, including the incident frequency, the incident angle and the height-width and length-width ratio of the hill. The numerical results illustrate that the amplification effect on the ground motion by a near-hemispherical hill is more significant than the narrow hill. For low-frequency waves, the scattering effect of the higher hill is more pronounced, and there is only a single peak near the top of the hill. However, for high-frequency waves, rapid spatial variation of displacement amplitude appears on the hill surface.

层状地基中隔振沟对移动列车荷载隔振研究-2.5维IBEM方法

建立层状地基-轨道-隔振沟耦合动力系统,采用2.5维间接边界元方法 (IBEM)研究了层状地基中隔振沟对移动列车荷载下地基振动的隔振问题。采用子结构方法,将系统分解为含隔振沟的层状地基和轨道子结构,采用2.5维IBEM方法求得含隔振沟层状地基在移动均布荷载作用下的层状地基柔度,然后通过地基表面轨道中心点的竖向位移与轨道竖向位移相等将轨道和层状地基耦合。通过与已有结果的比较验证了方法的正确性,并对不同地基、隔振沟参数下的模型进行了算例分析。研究表明:不同地基模型下隔振沟有不同的隔振效果,且隔振沟深度及其与轨道距离均对隔振效果有不同程度的影响。通过对瑞典X2000高速列车在实际软土地基上的隔振计算发现,隔振沟的隔振效果随着沟深的增加而增大,且相对低频区域而言,隔振沟对高频区域的隔振效果更好。

P波入射下山体-隔震层-隧道的整体响应分析

采用高精度间接边界元方法(IBEM)开展了山体-隔震层-隧道的整体响应分析,研究了P波入射下柔性隔震层对高斯形山体内双线隧道地震动响应的减弱作用。在隔震层与围岩之间考虑了碎土的错动滑移,以模拟不完美交界面,并系统讨论了隔震层弹性模量、厚度、P波入射频率等因素对隧道地震动响应的影响。数值模拟结果表明:适当增加隔震层厚度可以显著降低隧道应力,有效提升隔震效果,应力降低幅度约达50%以上,且使得结构受力更为均匀;随着隔震层材料的弹性模量减小,隧道动应力数值明显减小,有效减少了其应力放大区的面积,从而有效避免因地震而导致的衬砌裂缝。

平面SV波入射下地上建筑群-地铁隧道群动力相互作用研究

该研究采用一种高精度间接边界元方法(indirect boundary element method, IBEM),研究了平面SV波入射下地上建筑群-地铁隧道群的动力相互作用问题。研究表明:“建筑群-隧道群”系统存在显著的动力相互作用,其规律与入射波性质、建筑物和隧道数量排布等因素密切相关。通过对比不同建筑物数量对隧道动力响应的影响,能够发现:低频波作用下,建筑物对下穿隧道的动力响应有放大作用,而高频波作用下则会削弱隧道的动力响应,最多可以降低37.5%左右。从频域分析中可以看出:隧道对地震波有较强的屏蔽作用,从而降低了其上建筑群的地震响应。建筑群的存在降低了各个单体建筑的动力响应,但在高频波作用时位于建筑群来波一侧的建筑会产生较大的动力响应。该研究成果可为城市建筑群-地铁隧道群的动力相互作用分析以及地上建筑和地铁隧道的抗震设计提供理论依据。

考虑土体非线性山-谷耦合复杂场地空间相关多点地震动模拟

采用考虑局部场地非线性地震波散射效应的空间相关多点地震动模拟方法,对山-谷耦合场地的地震动进行定量模拟分析。非线性地震波散射效应基于有限元-间接边界元耦合法和等效线性土体模型进行计算。结果表明,山体的存在会增大沉积内的地震动反应,对短周期的地震波的放大效应更为显著,增幅可达50%。相较于单一沉积谷地地形的沉积谷地外部,山-谷耦合场地中山体地震响应有所减小。相比线性模型,考虑土体非线性时,沉积谷地地震动强度较线性时的结果有所降低,反应谱峰值位置也会发生改变,但山体影响更为显著。不同山体形状对谷地影响不同,对于谷地内部分点位影响的差别可达40%。该研究为山-谷耦合场地工程结构抗震设防提供了部分理论依据和计算方法。

Vibration and acoustic radiation of bogie area under random excitation in high-speed trains

Based on the experiments on a platform with real vehicle structure and finite element simulation, the vibration and interior acoustic radiation under random excitations of high-speed trains’ bogie area were studied. Firstly, combined with line tests, a vehicle body with a length of 7 m was used as the research object. By comparing the results of experiment and simulation, the accuracy of the finite element model was verified. Secondly, the power spectral density curves at typical measuring points in bogie area were obtained by processing and calculating the line test data, which was measured when the vehicle ran at high speeds, and the standard vibration spectrum of the bogie area was obtained by the extreme envelope method. Furthermore, the random vibration test and simulation prediction analysis of the real vehicle structure were carried out to further verify the accuracy of the noise and vibration prediction model. Finally, according to the vibration and acoustic radiation theory, the indirect boundary element method was adopted to predict the acoustic response of the real vehicle. The analysis shows that the simulated power spectral density curves of acceleration and sound pressure level are highly consistent with the experimental ones, and the error between the simulated prediction and the experimental result is within the allowable range of 3 dB.

Comparison of indirect boundary element and finite element methods A case study:Shiraz-Esfahan railway tunnel in Iran

Because of the high importance of transportation tunnels,most precise analyses of stress concentration and displacement around them are essential to provide safety of them as much as possible.Recently,various numerical methods such as finite element method(FEM),discrete element method(DEM),finite difference method(FDM)and boundary element method(BEM)have been used extremely in geosciences problems,but among these numerical methods,BEM has been used less than others because the computational algorithm is not so straightforward.This paper suggests the implementation of the indirect boundary element method(IBEM)as a formulation of BEM to analyze displacement around Shiraz-Esfahan railway tunnel in Zagros Mountains southwest of Iran.For this purpose,this tunnel has been modeled numerically using two-dimensional fictitious stress method(TWOFS)algorithm.To validate the results,they were compared with FEM results as a commonly used numerical method.Results of current theoretical study have shown that the presented approach using IBEM is reasonably accurate and can be used for analysis of displacement in geosciences problems.In rock mechanics,for problems with a low ratio of boundary surface to volume,FEM is not very well suited and may be cumbersome,but use of such a proposed IBEM approach can be particularly attractive.

利用FEM/IBEM计算流体介质中的壳体的结构声耦合问题

利用有限元和间接边界元的声振耦合方程同时计算结构表面的振动和相应的辐射声场 ,将结构的物理坐标转化成模态基本量来表示 ,对完全耦合的结构动力学方程及声场方程进行解耦。对浸没于两种流体介质中的椭圆球壳体的数值计算结果表明 ,流体介质改变了结构的共振特性及声辐射特性。

基于修正随机有限断层法的沉积盆地地震动模拟

基于随机有限断层法理论框架,采用间接边界元方法求解沉积盆地地震动放大效应,以此修正场地放大因子,发展了一种可考虑盆地效应的修正随机有限断层法。基于该方法,模拟了2021年2月13日日本M_(W)7.1海域地震中日本关东盆地地震反应,并与常规随机有限断层法及实测地震记录进行了对比。结果表明:与常规随机有限断层法相比,采用修正随机有限断层法模拟盆地地震动表现出更显著的空间变异性,盆地边缘地震动峰值加速度较常规方法放大了6.24倍,与实测地震记录吻合度更高;区域地震动峰值加速度空间分布整体特征与实测地震记录基本一致;相较于不考虑场地影响下的结果盆地内部分台站长周期下的谱加速度值扩大了近5倍,表明深厚沉积盆地在长周期范围内的场地放大更加明显。

有限元/间接边界元法求解浸水板振动特性

针对浸水板结构振动,考虑流体可压缩特性,利用间接边界元法计算附加质量矩阵,包含计算中奇异边界单元的处理。结合结构有限元法求解无限域浸水板的振动特性,通过编制的相应计算机程序,对浸水悬臂矩形平板进行了流体间接边界元与结构有限元耦合数值模拟;并对水下自由板进行了模态识别实验,实验结果验证了数值计算结果的可靠性。典型算例表明了流体介质改变了结构的动力特性,在低频段流体的可压缩性对结构的动力特性影响甚微;推导的流固耦合数值方法对研究浸水结构动力和声辐射研究有很好的参考价值。

局部断层场地对P波的散射影响研究

采用间接边界元法,借助Wolf的土层和半空间精确动力刚度矩阵和斜线荷载格林函数,在频域内求解了局部断层场地对P波的散射,着重分析了破碎带较窄断层两侧围岩动力响应的基本规律,以及场地动力特性对散射的影响。研究表明,破碎带断层对入射P波有着显著的影响,即使破碎带很窄,也可对P波产生很大的放大作用;层状场地动力特性对放大作用有显著的影响。

NUMERICAL SIMULATION OF COUPLED STRUCTURAL- ACOUSTIC PROBLEMS USING FEM/IBEM

The numerical method of a coupled finite element and indirect boundary element equation for computing both the structural vibration and the acoustic radiation was presented. The coupling matrices were discussed and physical degrees of freedom of the structure were treated in terms of its modal basis in vacuum to decouple the computation from the entire coupled structural acoustic equations. The numerical results for the ellipsoidal shell immersed in two different fluids indicate that heavy fluid changes greatly structural and acoustic behavior. This method can be applied to analyze acoustic and vibration for arbitrary complex structures in fluids.

斜入射平面SH波在层状饱和半空间中沉积谷地周围的三维散射

为研究层状饱和场地中沉积谷地对斜入射地震波的三维散射问题,建立了求解问题的2.5维间接边界元方法。通过沿沉积谷地轴线方向的傅里叶变换将三维问题降为二维问题,进而在沉积谷地的截面内进行边界单元的离散和求解,求得沉积谷地截面内的动力响应,然后再将截面内计算结果沿沉积谷地轴线方向进行波数展开即可求得任意位置动力响应。通过与弹性情况的比较验证了方法的正确性,并以均匀饱和半空间和基岩上单一饱和土层中沉积谷地对斜入射平面SH波的三维散射为例进行了数值计算和分析。研究发现沉积谷地对SH波的三维散射与二维散射之间存在显著差异;饱和情况(透水或不透水)与干土情况沉积谷地附近地表位移的差别很大;另外层状饱和半空间中沉积谷地和均匀饱和半空间中沉积谷地对斜入射SH波的放大作用也存在显著差别。

消除声学间接边界元非唯一解的方法的对比研究

间接边界元法在求解外域声学问题时面临着解的非唯一性问题,因此需要引入特定的处理方法以保证数值结果的稳定性。间接边界元法在求解大规模声学问题时还面临着计算规模受限问题,快速多极算法是目前克服此问题的常用方法,然而不同的非唯一解处理方法给快速多极算法的适用性和效率带来了不同影响。首先给出基于常值单元离散推导出的无奇异间接边界积分方程,然后将内部阻抗法、内部刚性面法以及混合势等几种常用的非唯一解处理方法引入快速多极间接边界元法,通过数值结果对比得出这些方法对快速多极间接边界元法求解精度和计算效率的影响规律,为发展更准确高效的快速间接边界元法提供了参考。

Amplification of in-plane seismic ground motion by group cavities in layered half-space (Ⅱ): with saturated poroelastic soil layers

As the continuation study on amplification of in-plane seismic ground motion by underground group cavities in layered half-space, this study extends to the case of poroelastic half-space with dry poroelastic and saturated poroelastic soil layers. The influence of poroelastic layers on the amplification of seismic ground motion is studied both in frequency domain and time domain using indirect boundary element method （IBEM）. It is shown that for the example of a saturated poroelastic site in Tianjin under the excitation of Taft wave and E1 Centro wave, the amplification of seismic ground motion in poroelastic case is slightly smaller than that in the elastic case, and the amplification of PGA （peak ground acceleration） and its PRS （peak response spectrum）.. can be increased up to 38.8% and 64.6%; the predominant period of response spectra in poroelastic case becomes shorter to some extent compared with that in the elastic case. It is suggested that the effect of underground group cavities in poroelastic half-space on design seismic ground motion should be considered.

Amplification of in-plane seismic ground motion by group cavities in layered half-space (Ⅰ)

Amplification of in-plane seismic ground motion by underground group cavities in layered half-space is studied both in frequency domain and time domain by using indirect boundary element method （IBEM）, and the effect of cavity interval and spectrum of incident waves on the amplification are studied by numerical examples. It is shown that there may be large interaction between cavities, and group cavities with certain intervals may have significant amplification to seismic ground motion. The amplification of PGA （peak ground acceleration） and its PRS （peak response spectrum） can be increased up to 45.2% and 84.4%, for an example site in Tianjin, under the excitation of Taft wave and E1 Centro wave; and group cavities may also affect the spectra of the seismic ground motion. It is suggested that the effect of underground group cavities on design seismic ground motion should be considered.

3D Diffraction of obliquely incident SH waves by twin infinitely long cylindrical cavities in layered poroelastic half-space

Abstract This paper studies three-dimensional diffraction of obliquely incident plane SH waves by twin infinitely long cylindrical cavities in layered poroelastic half-space using indirect boundary element method. The approach is validated by comparison with the literature, and the effects of cavity interval, incident frequency, and boundary drainage condition on the diffraction are studied through numerical examples. It is shown that, the interaction between two cavities is significant and surface displacement peaks become large when two cavities are close, and the surface displacement may be significantly amplified by twin cavities, and the influence range with large amplification can be as wide as 40 times of the cavity radius. Surface displacements in dry poroelastic case and saturated poroelastic cases with drained and undrained boundaries are evidently different under certain circumstances, and the differences may be much larger than those in the free-field response.

双吸离心泵正反转工况流致振动噪声研究

为深入了解双吸离心泵运行的振动噪声规律,以某一双吸式离心泵为研究对象,基于声学间接边界元法(IBEM),采用LMS Virtual-Lab分析计算平台,进行基于泵壳模态的强迫振动响应计算。然后根据泵壳模态强迫振动响应计算与声学间接边界元的声学波动方程求解耦合方程,得到双吸泵在液力透平工况和泵工况下外辐射声场的声压级指向分布和声压级分布。结果表明:偶极子声源是流体噪声的主要声源;在蜗壳隔舌处非定常脉动力是主要的噪声源;叶频及其倍频是双吸泵外辐射声场噪声的主要诱导频率;泵壳发生了共振,所以声振耦合的作用不可忽略。研究揭示了双吸泵作液力透平及泵工况内部流动诱发的外辐射声场的声振耦合计算规律,为后续减振降噪研究提供了理论基础。

空沟对层状饱和地基中列车移动荷载的隔振性能研究

基于Biot流体饱和多孔介质理论,建立含空沟层状饱和地基–轨道耦合动力系统,研究了空沟对移动列车荷载引起层状饱和地基振动的隔振问题。方法首先将系统分解为含空沟层状饱和地基和轨道两个子结构,然后采用2.5维间接边界元方法(IBEM)求解含空沟层状饱和地基在移动均布竖向线荷载作用下的动力响应,同时求解轨道在移动列车荷载和均布竖向线荷载共同作用下的动力响应,最后通过令轨道竖向位移与层状饱和地基表面轨道中心处竖向位移相等实现两者的耦合。文中通过与已有结果的比较验证了方法的正确性,并以均质饱和地基和饱和基岩上单一饱和土层地基为模型进行了数值计算分析,研究了饱和地基参数和隔振沟参数对隔振效果的影响。数值结果表明,层状饱和地基中空沟的隔振效果优于均质饱和地基中空沟的隔振效果;且饱和地基中空沟的隔振效果优于相应单相弹性地基中空沟的隔振效果;另外,空沟深度、饱和土孔隙率和基岩与饱和土层刚度比等也对空沟的隔振效果有着重要影响。

含断层破碎带场地对平面SH波的放大作用

借助Wolf的土层和半空间精确动力刚度矩阵和斜线荷载格林函数,采用间接边界元法在频域内求解了含断层破碎带场地对SH波的放大作用,着重分析了破碎带较窄断层两侧围岩动力响应的基本规律及场地动力特性对散射的影响.结果表明,断层破碎带对SH波有显著的影响,即使破碎带很窄,也可对SH波产生很大的放大作用;层状场地动力特性对放大作用有显著的影响.