Numerical simulation of nonlinear water waves based on fully nonlinear potential flow theory in OpenFOAM®-extend

We develop a free surface tracking solver for numerical simulation of unsteady irrotational fully non-linear water waves in a freely available open-source computational fluid dynamics toolbox OpenFOAM®-Ext, which is community-driven release of OpenFOAM®. The solver is based on the solution of the Laplacian of the velocity potential with moving free surface. The free surface is tracked by solving the kinematic boundary condition based on the normal flux out of the surface. We also develop the necessary boundary conditions for the realistic wave generation at inlet and the absorption boundary condition at the outlet boundary. To avoid numerical instability, a 5-point smoothing technique is used to smooth the free surface elevation. Solution of Laplace's equation for the velocity potential, the non-linear free surface boundary conditions, the wave generation and the absorption boundary conditions are all not part of the standard OpenFOAM® distribution. The potential flow solver is able to simulate large amplitude standing and progressive waves. We validate the solver by comparing the numerical results with analytical results for second order standing waves, and progressive waves with experimental results and satisfactory agreement is found.