基于UPFs的珊瑚岛礁场地地震反应分析方法研究

A method for seismic response analysis of coral island sites based on UPFS

合理且高效地模拟珊瑚砂非线性动力特性、远场无限地基辐射阻尼以及海域岛礁动水压力的影响是进行珊瑚岛礁抗震安全分析的关键技术问题。以通用有限元软件ANSYS为研究工具,基于UPFs二次开发灵活性的特点,建立了适用于珊瑚砂地基条件下的岛礁场地地震反应分析时域计算模型。通过创建一种新的珊瑚砂等价线性单元描述岛礁场地的非线性动力特性,推导并开发了黏性人工边界单元用于考虑截断外边界的能量耗散及外源地震动的输入,基于Westergaard附加质量公式以mass21单元模拟航道的动水压力,建立FORTRAN接口程序实现自由场响应与交界面作用力求解的交互。通过典型珊瑚岛礁场地的自由场分析验证了所开发时域分析模型的合理有效性。以国内某实际珊瑚岛礁场地为例,从地表峰值加速度和反应谱等方面探讨了珊瑚岛礁场地非线性地震反应规律;结合ANSYS良好的前处理及大规模求解分析能力,可开展各类复杂岛礁场地的动力响应分析。

The key technical problem for seismic safety analysis of coral islands is to reasonably and efficiently simulate the nonlinear dynamic characteristics of coral sand,the radiation damping of far-field infinite foundation,and the influence of hydrodynamic pressure of sea islands.Based on the characteristics of UPFs,a time-domain calculation model for analyzing the seismic response of island sites with coral sand foundation was established by using the general finite element software ANSYS.A new equivalent linear element of coral sand was created to describe the nonlinear dynamic characteristics of coral island sites,and a viscous artificial boundary element was derived and developed.Based on Westergaard's added mass formula,the hydrodynamic pressure of the channel was simulated with mass21 element,and the FORTRAN interface program was established to realize the free-field response.Furthermore,the rationality and effectiveness of the proposed model were verified by the free-field analysis of a typical coral island site.Finally,an actual coral island site in China was taken as an example,and the nonlinear seismic response of coral island sites was discussed from the aspects of surface peak acceleration and response spectrum.Thus,the dynamic response analysis of various complex island sites can be carried out by using the large-scale solution and analysis ability of ANSYS.