Three-dimensional dynamic analysis of deep-water steel steep wave riser considering internal solitary wave

This paper aims to investigate the nonlinear dynamic response of steel steep wave risers (SSWRs) considering the excitation of internal solitary waves (ISWs). Considering ISWs and the combined excitation of vessel motion (VM), surface wave (SW), this paper proposes a three-dimensional nonlinear dynamic model of the SSWRs based on the slender rod model. The finite element method and the Newmark-beta method are applied to discretize the governing equations and solve the dynamic response of the SSWRs, respectively. Then, a computational program, DRSSWR, was developed in this paper. The accuracy of DRSSWR is verified with experimental data and published results. Further, the nonlinear dynamic response of the SSWR is obtained. Analysis results indicate that ISW causes extremely large displacements and shear deformations in the X, Y, and Z directions of the SSWR like a slow, massive shock load, particularly in the Y direction. Extreme values of displacement and stress occur mainly around critical points (i.e., seawater interface, arc bend point, sag bend point). ISW shows both " weakening effect" and "strengthening effect" on the dynamic response induced by VM and SW.