An accurate and efficient time-domain numerical model for simulating water-axisymmetric structure subjected to horizontal earthquakes

Abstract

The seismic response of offshore structures is generally influenced by water-structure interaction. This study focuses on the earthquake-induced hydrodynamic forces on axisymmetric offshore structures. Based on the finite element method, an accurate and efficient time-domain numerical model for simulating water-axisymmetric structures subjected to horizontal earthquakes is developed. First, according to interface boundary condition and using the method of separation of variables, the three-dimensional (3D) wave equation governing the compressible water is transformed into a two-dimensional (2D) governing equation in the vertical and radial directions, where the solution in the circumferential direction is analytical. Secondly, an exact artificial boundary condition (ABC) in frequency domain is developed by using the separation of variables method. Third, a high-accuracy ABC that is local in time but global in space is obtained by applying the temporal localization method. Furthermore, the high-accuracy artificial boundary condition is discretized and coupled with the finite element equation of the near field, leading to a symmetric second-order ordinary differential equations. Finally, the coupled finite element equation for the water-axisymmetric cylinder is presented. The proposed method is used to study the effect of water compressibility on the seismic response of and evaluate the seismic responses of a composite bucket foundation.