THE NUMERICAL INVESTIGATION OF THE RESPONSE OF RISERS INDUCED BY INTERNAL SOLITARY WAVES BASED ON POTENTIAL FLOW THEORY

Internal solitary waves are large waves that occur below the ocean surface and are widely present in all sea areas of the world. The huge wave profile undulations and energy pose a serious threat to marine structures like marine risers. Analysis of the flow field characteristics in the propagation and evolution process of internal solitary waves and the dynamic response law of the risers under the action of internal solitary waves are of great significance to the design of the marine risers. Multi-domain boundary element method is adopted to establish a numerical model to analyse and calculate the flow field of internal solitary wave based on the nonlinear potential flow theory in stratified fluids in this paper, and the flow field characteristics of internal solitary wave in real time can be obtained. The Morison equation is used to calculate the load distribution including inertia force and drag force induced by the internal solitary wave on the marine risers according to the flow field information calculated using the numerical simulations. The nonlinear potential flow calculation model of the internal solitary wave flow field is coupled with the dynamic finite element model to solve the dynamic response characteristics of the marine riser under the action of the nonlinear internal solitary wave. The influences of the internal solitary wave parameters, the top tension and the internal fluid densities on the dynamics of the riser are calculated and discussed. It is found that the displacement in flow direction of the ocean riser increases significantly as the amplitude of the internal solitary wave increases. The top tension has a significant impact on the response of the marine risers by changing the value of the geometric stiffness matrix. However, the density of the internal fluid has little effect on the displacement of the pipeline at flow direction for the weakly restrained risers.