Using strip theory to model vibrations in offshore risers

This paper presents an algorithm for the coupled time-domain solution of flow and structure equations using strip theory. The approach is then adopted for numerical simulation of the multi-mode response of flexible long risers used in the offshore energy industry for vortex-induced vibrations. The various models currently used to solve the problem of vortex-induced vibrations in marine risers are briefly studied and compared. The work reported here initially includes calculation of eigenvalues and eigenmodes of risers, the results of which are subsequently used to predict the response of risers based on a modal analysis. The two-dimensional flow simulations used in the strip theory are validated using experimental and numerical results presented in the literature. The root mean square of the amplitude of the riser movement in the cross-flow direction for various top tensions are studied and compared with similar cases reported in the literature.