Internal Generation of Wave in 3D RANS Equation Model using Mass Source and Mass Flux

Abstract

For the internal generation of wave in the Navier-Stokes equation model using the VOF scheme, Lin and Liu (1999) developed the internal wave-maker method for which the mass source function of the continuity equation was used to generate target wave trains. Choi and Yoon (2009) also developed the internal generation of wave scheme using momentum source to produce the target waves, which is applied to the RANS equation model in a CFD code, FLUENT. The above-mentioned approaches make it possible to achieve the accurate velocity profiles after the waves are propagated with the sufficient distances. In this study, two approaches including mass source and mass flux methods were devised for the application in a CFD code, FLOW-3D. In addition, the sponge layer scheme using the porous media was introduced to remove the reflected waves into the computational area as proposed by Choi and Yoon (2009). The achieved results were compared with the analytical solution according to the applied wave theories including the Airy, Stokes’ 2nd order and Stokes’ 5th order theories. The self-adaptive wave generator was also devised to produce the accurate mass flux according to the change of the surface elevation, which the vertical profiles of horizontal particle velocities are changed based on the position of free surface. This method will be expanded to the application of short waves, which the vertical particle velocities are more important for the accurate generation of free surface than the case of long wave. The comparisons between the numerical results and the analytical solutions showed good agreements in the free surface elevation. This achievement can be applied to the 3 dimensional wave simulations such as the wave tranquility study in harbor areas and the wave propagation from the offshore to the near-shore, especially the shallow water areas where wave breaking and intensive turbulence may occur. The physical model tests were carried out to verify the application of an internal wave-maker in the 3D CFD model with the pile-supported perforated wall breakwater. Two dimensional laboratory experiments have been carried out in the wave flume with the width of 1.4 m, the height of 1.5m, and the length of 40m. In the physical model tests, the wave heights in the wave chambers were measured to investigate the reduction ratio of wave height in accordance with various slit wall shapes and several wave conditions. The achieved results from the physical model tests were compared with those of the CFD simulations to check the appropriateness of the internal generation of wave in the 3D CFD model. From the comparisons, the CFD test results shows good agreement with those of the physical model tests and the applicability of the internal wave-maker in CFD model is verified.