Riser Vortex‐Induced Vibrations

Abstract

Vortex‐induced vibration (VIV) fatigue is one of the failure mechanisms of riser systems. Failure occurs due to the fatigue of the structure in vibration. VIV is caused by the motion of risers or other structures to shed vortices when exposed to fluid flow (such as currents and waves) impinging on the structure. The response of the structure is dependent on the natural frequencies of the structure and the frequency at which the structure sheds vortices (shedding frequency). Several physical quantities affect the VIV response such as the dimensions, stiffness, damping, and mass of the structure. VIV results in catastrophic failure of the riser system and is a critical that either the structure by design has low fatigue damage due to VIV or some external VIV suppressing devices are used to ensure safe operations. This article discusses the theory/concepts of VIV and the unique aspects of each riser system (TTRs, SCRs, flexibles, etc.) that need to be accounted for in the fatigue evaluation. The final section of this article introduces the typical suppressing devices that are used. This article focuses on the concepts relevant for riser VIV, and further reading is presented toward the end, for those readers interested in gaining more in‐depth understanding of the topic.