Nonlinear Dynamic Analysis of Deepwater Risers With the Irregular Seabed

Abstract

The stress of a steel catenary riser (SCR) at touch-down zone (TDZ) is substantially affected by its interaction with the seabed. Based on the slender rod theory, the paper adopts a realistic nonlinear load-deflection (P-y) curve to simulate soil deformation and resistance force. This seabed model can better reflect the change of soil stiffness along the vertical direction. According to the P-y curve, the equivalent stiffness at different points are obtained by an iterative method. In order to add the soil resistance force to the equation of motion, the seabed force is multiplied by the shape function a(s) and integrated from 0 to L of an element length. This paper use Gauss integral method to get the seabed force. In fact, the element may be not entirely in contact with the seabed. Therefore, the first step is to get the contact point between element and soil, and then to determine the real integral range. Meanwhile, existing riser-soil models mostly take the support of the seabed as a horizontal plane. However, many SCRs are unavoidable to be laid on the irregular seabed. It makes the strength characteristics of riser flow-line more complicated. This paper has studied the effect of irregular seabed on riser stress. The results indicate that there is a stress peak value at the irregular seabed. This value is almost equal to the value at TDP.

Research on the Dynamic Response of a Steel Catenary Riser in the Touchdown Zone under Pigging Conditions

“…Wang et al [25] proposed a non-linear dynamic model for a characteristic analysis of an SCR under pipe-soil contact by using the Aqua module in ABAQUS. Sun et al [26] investigated the static and dynamic characteristics of an SCR under an irregular seabed using a finite element method. Dong and Shiri [27,28] studied the node response and overall response of a non-linear contact model of a steel catenary riser with the seabed.…”