Development Of A Numerical Wave Tank With Active Absorption Using OpenFOAM

The wave is one of the predominant hydrodynamic phenomena in the marine environment, and the numerical wave tank is widely applied to the investigations on waves and the interactions between waves and structures. However, the numerical wave tank is an enclosed water of a limited scale. Thus the reflected waves will re-reflect at the wave maker. The re-reflections which do not exist in the real ocean environment, will spoil the wave fields in the test domain, especially for long test durations. Consequently, the accuracy and stability of numerical simulations are out of control. An active absorption wave maker combines the functions of wave generators and absorbers, generating progressive waves and absorbing re-reflections at the wave maker simultaneously. Therefore, the development of a numerical wave tank with active absorption is very important.Based on the theory of active absorption piston-type wave-making, an active absorption numerical wave tank is established on the open source platform of OpenFOAM. The main research contents and conclusions are summerised as follows.(1) The wave fields are solved by the two-phase flow dynamic mesh solver. A tailored oscillating boundary condition is used to generate target waves and absorb reflected waves. The surface elevation at the wave maker is taken as the feedback signal to adjust the real-time motion of the wave maker in order to eliminate the re-reflected waves. The time-domain governing equations of the wave maker are derived based on the linear wave theory.(2)The model is used to simulate regular and irregular waves by both active absorption wave maker and the traditional piston-type wave maker. The numerical results show that the model is accurate to reproduce the target waves for both of the two wave-generating methods.(3)The slow shift of piston arising in the active absorption wave maker is analyzed. Two modifications, i.e., linear compensation and PID control are proposed to minimize the piston’s slow shift. The two methods are both proved effective and fruitful, which enable the active absorption numerical wave tank to conduct long-duration simulations.(4)The established model is applied to investigate the wave fields under regular and irregular waves for submerged breakwaters of different heights. The numerical results demonstrate that the active absorption efficiency of the proposed model is high regardless of different reflectivities.