Accurate computation of wave loads on a bottom fixed circular cylinder

This abstract describes recent progress in the development of a fast and accurate tool for computations of wave-structure interactions of realistic sea states that include breaking waves. The practical motivation is extreme wave loads on offshore wind turbine foundations, but the tool is applicable to a range of other problems.

The central idea is to drive an inner CFD model that resolves the flow around the structure with an outer wave model that is based on potential flow theory. By letting the potential flow solver describe the waves in the outer flow domain and the Navier-Stokes solver describe the flow in the inner domain a fast and accurate description of wave loads on offshore structures is obtained, even for breaking waves.

Engsig-Karup et. al [1] have recently developed a fully nonlinear potential flow solver (OceanWave3D) to represent propagation and development of fully nonlinear three-dimensional water waves up to the point of breaking. The CFD solver is the open source CFD toolbox OpenFOAMR in combination with the newly developed waves2Foam utility, which in [5] has been successfully applied to calculations of free surface flows.

The numerical solution is obtained by solving the incompressible Navier-Stokes equations in combination with a surface tracking scheme. The CFD solver has been thoroughly tested for stability and first order grid convergence has been shown for the propagation of stream function waves. Here we present results for the magnitudes, of the third-harmonic forces on a vertical circular cylinder from steep waves.

This partly serves as a validation and further brings insight into third-harmonic wave loads on cylinders which are relevant for ringing. Next, preliminary results for the coupled model are presented in terms of irregular waves propagation and the associated forces on a cylinder.