The purpose of this paper is to verify and validate the Vortex induced vibration (VIV) of a riser using fluid‐structure interaction (FSI) simulation technology. The aim of this study is to provide a framework to setup challenging FSI test cases like a riser which is a key component of the offshore industry. The challenge associated with the FSI simulation is that these components can be subjected to large deformations caused by VIV.

In this work, we will be rigorously validating FSI algorithms and modeling methods of the structural solver, Altair OptiStruct ™ [1] and the fluid solver, Altair AcuSolve ™ [2]. Studies are performed with respect to parameters like mesh qualities, turbulence models and time integration schemes which affect the stability of the FSI solution. The outcome of these studies is to finally come up with cost effective & efficient processes for solving such complex problems using FSI simulations. The validation is carried out using each of the methods outlined below.

A. A one-way coupling, where the structural solver OptiStruct calculates the eigenvalues and eigenvectors of the structure. These are used for projecting the structural system matrices onto a reduced space. The eigenvectors are projected onto the nodes of the fluid mesh that are contacted with the structure (at the fluid-structure boundary) to facilitate easy mapping of the fluid forces into the structural system. This is called a practical FSI. There are two-time integration strategies supported: Conventional Sequential Staggered and Multi-Iterative Coupling.

B. A two-way coupling where the structural solver OptiStruct calculates the structural deformations, which are then are applied to the geometries/grids in the fluid solver AcuSolve, and an iterative procedure is used until convergence is achieved. This is a fully-coupled FSI. OptiStruct and AcuSolve both include time-domain simulation capabilities that break the coupled solution into several time steps. Since the governing equations of both OptiStruct and AcuSolve are nonlinear, sub-iterations are typically required within each time step.