Numerical wave generation in Open FOAM®

Abstract

Abstract An open source CFD solver,OpenFOAMR, has been used to create a numerical wave tank. The study is based on the interFoam solver, i.e. a solver for incompressible multiphase flow problems. The solver uses the finite volume method for the spatial discretization of equations and applies the VOF approach for the free surface modeling. Initially a convergence study was carried out. The study was based on the propagation of fifth order Stokes waves in deep water condition. To this end two separate applications, waveWriter and errorCalculator, were created. With the former the initial conditions for the velocities and pressure of fifth order Stokes wave can been specified directly for interFoam. The errorCalculator is a post-processing tool that estimate the computational errors at each time step. The study revealed that the model exhibits only first order convergence. The loss of one order is due to the waveWriter setting only first order initial conditions. Wave generation and absorption in the wave tank are performed by the relaxation method. For this purpose the existing interFoam solver has been partially modified in order for replacing the computational solutions with desired analytical ones inside the relaxation zones. In this manner the modified solver is able to generate and dissipate different wave types in the numerical wave tank. It is shown that outgoing waves are absorbed efficiently by extending the damping relaxation zone to at least three wavelengths, while one wavelength extension is required for the wave-generating zone. To validate the numerical wave tank, the Whalin shoaling test was considered. Unfortunately, inadequacies in the then existing version of interFoam, (version 1.6.x), in the handling of the pressure force balance on non-orthogonal and distorted meshes, hindered and finally stopped the validation test process. Subsequently it was found that the newer version OpenFOAM-1.7.x, can be used promisingly for the validation of wave tank by Whalin test and this has been defined as a recommended future work. Keywords: OpenFOAM, interFoam, NumericalWave Tank, Nonlinear waves, Free surface flow, Relaxation Method, Wave Generation and Absorption.