Analysis On Riser-soil Interaction Based On Rod Theory

The steel catenary riser(SCR)is important equipment in the exploration of oil and gas resources.The interaction between touchdown zone and seabed will easily lead to fatigue damage.The interaction model depends on several factors,such as soil suction,seabed trench and soil stiffness degradation.Therefore,the choice of soil model plays an important role for the dynamic analysis of SCR.A realistic nonlinear load-deflection(P-y)curves be used to simulate soil deformation and resistance forces,where P is the seabed force and y is the vertical penetration of the riser into the seabed.To improve the program of “The software of analyzing static and dynamic response of Deepwater rod”,this thesis use Fortran language to write a subroutine.This thesis researched the effects of soil suction.The coefficients of soil suction are equal to 0,0.004 and 0.005 under the same external load conditions.The results shown that the range of moment of the riser at touchdown point are decreasing with the coefficients varies from 0,0.004 to 0.005.This thesis also researched the effects of the seabed trench.The results shown that the range of moment of the riser at touchdown point with initial seabed trench is smaller than the one with flat seabed.To consider the effects of the degradation of stiffness of soil,this thesis presents a degradating P-y model.The results shown that the maximum seabed force,the maximum soil suction and the maximum deflection at touchdown point are increasing with the coefficients of the degradation of stiffness of soil varying from 0,0.004 to 0.005.