黏弹性人工边界在ABAQUS中的实现及地震动输入方法的比较研究

为了确保大型复杂模型有限元数值计算过程的高效性及其地震反应结果的精度和可靠性,根据波场分离理论,推导与黏弹性人工边界相适应的地震动输入公式,给出一种提取边界节点控制面积的方法,并结合ABAQUS二次开发功能,编写相应的边界条件自动施加和地震动输入程序。在此基础上,选取垂直入射剪切波(SV)作用下的二维土体模型,对12种不同的边界条件与地震动输入方式的组合工况进行对比分析,并基于地震波在不连续分界面上的透射和反射原理,揭示黏弹性边界条件下加速度输入和位移输入不合理的机制。研究结果表明:对于黏弹性人工边界,采用等效节点力输入方法,数值计算结果与理论解基本一致,计算精度高;而采用加速度输入或位移输入的地震动输入方法,均会使黏弹性边界失效,计算结果严重偏离理论解。研究内容可为地下结构抗震分析中黏弹性边界的精确施加和地震动输入方法的合理选择提供参考。

Implementation of viscous-spring boundary in ABAQUS and comparative study on seismic motion input methods

To ensure the computational efficiency of large-scale models using finite element method(FEM) and the accuracy of their seismic response results,a seismic wave input formula adapted to the viscous-spring boundary is deduced according to the wave field separation theory,a method for extracting the control area of boundary nodes is given,and the program for automatic setting of viscous-spring boundary and seismic wave input is realized and verified after the secondary development of ABAQUS. On this basis,a two-dimensional soil model under the action of vertical incident shear wave(SV) is established to compare 12 different combinations of boundary conditions and seismic wave input methods. Based on the principle of transmission and reflection of seismic waves on discontinuous interfaces,the mechanism of interaction between viscous-spring boundary condition and several seismic wave input methods is revealed. The results illustrate that for the viscous-spring boundary,the calculation results using the equivalent nodal load input method are in good agreement with the theoretical solutions with a high calculation accuracy,while the energy absorption capacity of viscous-spring boundary is lost using the acceleration input or the displacement input methods. The research work can provide a reference for the accurate application of viscous-spring boundary and the reasonable selection of seismic wave input methods in seismic analysis of underground structures.