3D Finite Element Analysis of Marine Risers under Random Loads

Rizwan A. Khan; Suhail Ahmad

Abstract

The dynamic response of marine risers under long crested random sea is obtained in time domain using finite element solver ABAQUS/AQUA. The response analysis is based on a simulation technique which duly considers various nonlinear effects such as relative velocity squared drag force, variable added mass due to variable submergence and nonlinearity due to large excursions. It also accounts for variable tension in the riser due to variable submergence, variable buoyancy and wave forces. Results are presented which illustrates the effects of nonlinearities, long-term drift oscillations and instantaneous motion of the vessel and current velocity on the bending stress in the marine risers. The response time histories are obtained and presented in terms of bending stress envelopes and spectra showing contribution of various harmonics which is significant because of a nonlinear system. Keywords: Marine risers, random waves, vessel motion, drift oscillation, dynamic response