1D TIME-DOMAIN METHOD FOR 2D WAVE MOTION IN UNDERWATER SITE WITH OBLIQUELY INCIDENT PLANE WAVE

The problem of ground motion input of underwater foundation site under oblique incidence of seismic wave is a complex problem involving the coupling of water layer, saturated porous media and bedrock. At present, the theoretical results are still very scarce. Thusly, the 1-D time-domain method for underwater site is successfully established by the base of a 1-D time-domain method of porous media. Firstly, according to Snell law, the displacement of adjacent nodes in the horizontal direction can be replaced by that of the node in adjacent time, and 2-D equations can be transformed equivalently into 1-D equations, solved to compute the displacement of nodes along the vertical direction in time-domain method due to plane wave oblique incidence. Secondly, an exact artificial boundary condition of single-phase elastic media is introduced to represent the wave absorption and input characteristics of truncated bedrock, and the global finite element equations of the underwater site are assembled with the 1-D time-domain finite element equations of the porous media and water layer. Finally, with the aid of the central difference method and Newmark constant average acceleration method, the explicitnumerical solutions of displacement and acceleration are obtained. The reliability and rationality of the time-domain method are verified by comparing with the theoretical solutions obtained by Fourier transform and the existing literatures, which give convincing evidence for 1-D time domain finite element method of underwater site. It provides a new and efficient input method of seismic wave to deal with the dynamic response of underwater site.