Abstract
The vortex-induced-motion (VIM) of a hollow monopile is investigated using a three-dimensional two-phase Computational Fluid Dynamic (CFD) model in ANSYS CFX. The turbulence effects are modelled using the k-omega SST turbulence model. Both air and water phases are included in the numerical model to consider the variation of the buoyancy due to the rigid body motion. Dynamic mesh techniques with six-degree-of-freedom (DOF) rigid body are used to capture the motion of the monopile. The mesh and time step convergence studies are conducted first, and the converged numerical set-up is used for the other cases. The numerical model is validated against the model test measurements for VIM of a scaled monopile foundation by Seaway7 to show the applicability of the present numerical model for the VIM prediction in subcritical flow regions. The characteristics of the inline and cross-flow motions, hydrodynamic coefficients and flow fields are discussed.