A finite element solution of earthquake-induced hydrodynamic forces and wave forces on multiple circular cylinders

Abstract

This paper investigates the interaction of water with multiple circular cylinders subjected to earthquake ground motion and incident linear waves respectively. Accurate and efficient finite element models are firstly presented to calculate the earthquake-induced hydrodynamic forces and wave forces on uniform vertical cylinders with arbitrary cross-section. An elliptical boundary surrounding all the cylinders is introduced so that the whole domain is partitioned into unbounded and bounded domains. The elliptical exact absorbing boundary condition for simulating unbounded domain is derived in the elliptical coordinate system. A coupled equation is obtained by adding the impedance matrix of unbounded domain to that of bounded domain. The proposed models are furtherly used to investigate the earthquake-induced hydrodynamic forces and wave forces on pile group with two, three and four piles, where the coefficients of pile group are given. The results indicate that interaction of water with multiple cylinders is significant when the relative distance between two adjacent piles is less than three. This phenomenon depends on the relative distance between piles, width-depth ratio, wave numbers, and the direction of earthquake or incident wave. In addition, the simplified formulas of the coefficients of pile group of added mass are proposed for engineering application.