考虑流固耦合的桥墩地震反应方法

Dynamic Response Method of Bridge Piers under Earthquake Excitation Considering Fluid-structure Interaction

跨海桥梁地震反应中,作用于桥墩上的动水压力具有明显的流固耦合特征。依据张量理论,推导时变区域散度变换关系及微分形式的几何守恒律;基于任意拉格朗日-欧拉描述,从采用欧拉描述的流体运动Navier-Stokes方程出发,推导时变区域的流体运动控制方程;给出流固耦合问题中的结构计算模型、耦合面接触条件、耦合场计算方法以及流场网格运动控制方法。以某跨海大桥为例说明桥墩地震反应方法,重点突出地震动输入、流场初始条件模拟等问题。计算结果表明:流固耦合理论能够模拟桥梁墩台地震反应中的流场和结构特性;流场初始条件的正确模拟可保证计算稳定性,并减少运算量;横向地震动激励下,桥墩基底剪力较大,纵向地震动激励下,结构运动剧烈;流固耦合系统中的线弹性结构在地震反应中具有明显的非线性特征。

In seismic response of a sea-spanning bridge, dynamic pressure of fluid on bridge piers shows clear fluid-structure interaction. Based on the tensor theory, divergence transform relation in time dependent domain and spatial conversation principle in differential form are set up. With the arbitrary Lagrange- Euler description, governing equations of fluid motion in time dependent domain are built up from Navier- Stokes equations in Euler description which govern the fluid motion. Structural computing model, contact condition in fluid-structure interface, computing method of coupling field and controlling of fluid domain mesh motion are carefully presented in this paper. Then a sea-spanning bridge is taken as an example for dynamic analysis of its piers. In the analysis, the input ground motion and the initial conditions in fluid do- main are explained in detail. Simulation results show that the fluid-structure interaction theory can simu- late the characteristic feature of fluid and structure in seismic response of bridge piers. The proper initial conditions in fluid domain insure the stability of numerical computation and reduce the computational complexity. Shear force on the bottom of bridge piers is dominant under transversal earthquake excitation and displacement of structure is significant under longitudinal earthquake excitation. A structure with the linear elastie model in the fluid-structure system has a clear nonlinear feature in its seismic response.