Vortex-induced vibration prediction of a flexible cylinder by three-dimensional strip model

Numerical simulations on vortex-induced vibration (VIV) of a top tensioned flexible cylinder experiencing the uniform flow and the stepped flow conditions have been carried out by our in-house solver viv3D-FOAM-SJTU in this paper, which is developed by using the open source toolbox OpenFOAM and the three-dimensional strip model. Hydrodynamic forces in each three-dimensional fluid strip are calculated through the PIMPLE algorithm in the OpenFOAM adopting the Reynolds-averaged Navier-Stokes (RANS) method. The flexible cylinder is simplified as an Euler-Bernoulli bending beam, while structural vibrations are computed using the finite element method (FEM) in both the crossflow and the inline directions. The connection between three-dimensional fluid strips and the long flexible cylinder is realized through the interpolation of hydrodynamic forces and vibration displacements in each time step. Detailed comparisons on vibration Root Mean Square (RMS) amplitude, vibration frequency and vibration modes in both flow conditions among present simulation results, experimental results and published data are presented the validity of the viv3D-FOAM-SJTU solver. The fluid strip thickness dependence study shows that three-dimensional features of the wake field begins to appear at specific strip with dramatic vibration responses when the strip thickness reaches around 1/100 L (where L is the axial length of the flexible cylinder). The flow field of all fluid strips will be fully developed when the strip thickness reaches 3/100 L. Considering the cost of computational resources and the computational efficiency, the strip thickness around 1/50 L is recommend for future researches.