Cross Flow VIV Analysis of a Subsea Pipeline and Jumper using FSI Method

Abstract

Abstract When a current impacts on a circular pipe, fluctuating forces are created due to vortex-shedding in the wake. In offshore industry the interest for vortex induced vibration (VIV) is focused on the fatigue that pipe can experience. The fatigue due to VIV can be the dominant fatigue in some pipelines, subsea structures and risers. The assessment of VIV fatigue for pipelines and subsea structures involves two steps. The step one is to determine the structures response under the combined current and/or wave conditions, using analytical, semi-analytical or numerical approach. The second step is to identify the hot spots in the structure and process their loading states to calculate the corresponding damage or life, such as using S-N curve, which is a common practice in the industry. Since simulating the structures response under fluid loads is the key challenge in the VIV fatigue assessment, this paper focuses on the first step with an emphasis on the FSI approach. The current study developed a finite element model in the frame work of the ABAQUS that can be used in the cross flow VIV analysis of the pipelines and jumpers. The fully three dimensional computational fluid dynamics (CFD) solutions are combined with structural models of pipeline and jumper to predict vortex induced motion. The use of three dimensional CFD solutions is aimed to eliminate the guess work for VIV analysis. The proposed method uses finite element methods that are tolerant of sparse meshes and high element aspect ratios. This allows economical solutions of large fluid domains while retaining the important features of the large fluid vortex structures. The method can also be extended to sheared currents whose velocity varies with depth. The proposed method is applied to pipeline and jumper and benchmarked against published results. It also confirms the validity of the simplification of a jumper to a straight pipe during jumper VIV analysis based on DNV RP-F105, which is a common practice in offshore industry. The developed model might be used to reduce the conservatism in the fatigue assessments of pipeline guided by codes, such as DNV RP-F105.