CFD Modeling of Long Risers With Buoyancy Modules and Complex Shapes

Recent advances in computers and software have enabled the direct simulation of the vortex induced vibrations of long risers. Most of the problems solved to date have focused on bare or straked risers with a mild catenary shape. However fielded risers often make use of large buoyancy elements and may have a very general “lazy wave” shape. These features introduce new problems of solution stability and run time. In this paper we address some of these issues. We develop efficient meshing strategies for risers with buoyancy modules. The models are tested against published laboratory experiments. The CFD solutions show the same effects of changing excitation frequencies with changing buoyancy coverage and other effects as seen in the experiments. A general approach is proposed to build large problems with an L/D of 10,000 and a lazy wave shape. This approach demonstrated with an example problem.