Numerical wave tank for the application in ocean engineering

In this paper,a numerical wave tank (NWT) which is capable of generating regular waves,irregular waves based on wave spectrum and predetermined irregular wave train,is presented. This numerical wave tank integrated with dynamic boundary generating waves,dissipation zone dealing with wave reflection and volume of fluid method capturing free surface,was developed based on secondary development on professional CFD software FLUENT. Grid size test and time step test were performed to acquire accurate and economical mesh resolution and time step benchmark. Simulation of irregular wave was conducted based on Jonswap Spectrum by equally dividing the energy range to get the circular frequency of wave component. Simulated results reveal that calculated spectrum agrees well with theoretical spectrum in terms of statistical characteristics of irregular waves. The deficiency of simulating irregular wave spectrum is the heavy time consumption. In real sea states,damage incidents on offshore floating structures may not due to the whole time series of waves but due to few extreme waves or wave groups in irregular wave train. So,using CFD tools to precisely simulate irregular wave train is of great help in understanding the local characteristics of flow field when the incidents occur to offshore structures. In this paper,an extreme wave was modeled successfully. The key step in this new method of simulating irregular wave train is to determine the wave-maker motion. Similarly,decomposition was made on the wave elevation at the wave-maker into certain number of small amplitude waves. The wave parameters of each wave component were determined by Fourier Series Expansion. The same as simulating irregular wave spectrum a transfer function derived for piston type paddle from potential theory was used to calculate the wave-maker motion corresponding to each wave component. Superposition was made over all the wave components to get the final wave-maker motion.