Research On Pipe-soil Interaction And Fatigue Analysis Of Steel Catenary Riser In Deep Water

A lot of research and engineering investigations show that the fatigue damage of touch down zone of steel catenary riser is pretty serious and it is the key factor that influences the riser design. However, traditional studies generally use the conservative method to model the complicated interaction between the soil and the riser with linear elastic spring. For more accurate numerical simulation, it needs to set up a nonlinear model to describe the interaction between the riser and the seabed.The explicit dynamic analysis of ABAQUS is used to simulate the process of pipe soil interaction and the bone curve is obtained,as well as the curve of force and displacement under once cycle of the pipe soil interaction which is in accordance with NGI experimental results. Then the influence of the soil cohesion, friction angle, the outer diameter and the wall thickness of riser to the interaction of riser and soil were discussed. Based on the vertical pipe soil interaction numerical model and the horizontal pipe soil coulomb friction interaction model, the secondary development of the nonlinear element of pipe soil interaction was conducted and then the nonlinear dynamic analysis model of steel catenary riser was established to research the burial depth,the stress distribution and fatigue life of the touchdown zone and to analysis the influence of various factors.The analysis shows that the soil cohesion, friction angle and the outer diameter of riser have an effect on pipe soil interaction. With the increase of these parameters, the reaction of soil under the same displacement is increased. The parameters of soil and riser have effect on burial depth of touchdown zone and the displacements of the platform have effect on location and scope of touchdown zone. The increase of soil cohesion, friction angle and riser diameter leads to the increase of fatigue damage but the increase of wall thickness of the riser is good for fatigue performance of the riser. In the three directions of displacement of platform, the heave has the largest effect on the touch down zone. The loop displacement of this direction leads to the most serious fatigue damage of the touch down zone, the expansion of touch down zone and increase of the scope of the serious fatigue damage.