基于ABAQUS的三维粘弹性边界单元及地震动输入方法研究

Study of 3D Viscoelastic Boundary Elements Based on ABAQUS and Earthquake Input Method

基于大型通用有限元软件ABAQUS,利用FORTRAN语言编写了适用于粘弹性人工边界的外源波动输入子程序SDAB.FOR.该子程序包含粘弹性边界和加载两部分,粘弹性边界通过子程序UEL结合隐式积分算法定义粘弹性边界单元对整个系统的雅克比矩阵贡献来实现;人工边界上的总波场分解为无局部场地效应影响的自由场与局部场地效应引起的散射场,地震波作用于人工边界的自由场荷载可由设计地震动位移时程和速度时程统一表达,利用描述法向荷载和切向荷载的加载子程序DSLOAD、UTRACLOAD实现,从而可方便实现地震动的有效输入,避免了单独求解自由场.将考虑粘弹性边界条件的外源波动输入和内源地震动输入方法分别应用于某高拱坝的动力响应分析,并与常规无质量地基模型计算结果进行了对比,结果表明,考虑地基辐射阻尼的两种地震动输入方法均会显著降低结构的动力响应,其中采用外源波动输入方法的降幅更大.

The external source wave input subroutine SDAB.FOR of viscoelastic artificial boundary is achieved by FORTRAN language based on the commercial FEM code ABAQUS.The subroutine includes two parts,the viscoelastic boundary and the loading.The viscoelastic boundary is carried out by subroutine UEL,in which Jacobian matrix contribution of the boundary is defined in form of implicit integral algorithm.The wave field at artificial boundary is separated into free field without local topography effect and scattering field induced by local topography effect.The free field of earthquake action at the artificial boundary is expressed generally by the design earthquake time histories of displacement and velocity,and is realized by the loading subroutines of DSLOAD and UTRACLOAD which describes the normal loads and tangential loads respectively.Thus the earthquake input is carried out effectively and the free field with solution separately is avoided.The external source wave input and the internal seismic motion input method with viscoelastic boundary conditions are applied to the dynamic analysis of a high arch dam respectively;and compared to the results of the massless foundation model.The results show that the two methods with the radiation damping of the foundation will reduce the structure＇s dynamic response obviously;and the decrease range of the external source wave input is more obvious.