A new three-dimensional numerical wave tank is developed for the calculation of wave propagation and wave hydrodynamics by solving the incompressible Navier-Stokes equations. The free surface is modeled with the level set method based on a two-phase flow approximation, allowing for the simulation of complex phenomena such as wave breaking. The convection terms of the momentum and the level set equations are discretized with the finite di↵erence version of the fifth-order WENO scheme. Time stepping is handled with the third-order TVD Runge-Kutta scheme. The equations are solved on a staggered Cartesian grid, with a ghost cell immersed boundary method for the treatment of irregular cells. Waves are generated at the inlet and dissipated at the numerical beach with the relaxation method. The choice of the numerical grid and discretization methods leads to excellent accuracy and stability for the challenging calculation of free surface waves. The performance of the numerical model is validated and verified through several benchmark cases: solitary wave interaction with a rectangular abutment, wave forces on a vertical cylinder, wave propagation over a submerged bar and plunging breaking waves on a sloping bed.

The open-source CFD model REEF3D is used to simulate plunging breaking wave forces on a vertical cylinder. The numerical results are compared with data from the experiments carried out at the Large Wave Channel, Hannover, Germany to validate the model. Further, the location of the cylinder is changed so that the breaking wave impacts the cylinder at different stages of wave breaking and the resulting wave forces are evaluated. The different locations for the cylinder placement based on the breaker location are determined from the results obtained for the wave breaking process in a two-dimensional numerical wave tank. Maximum wave forces are found to occur when the breaking wave tongue impacts the cylinder just below the wave crest in all the cases simulated and the lowest wave forces are generally obtained when the wave breaks behind the cylinder. Several wave features such as the splashing on impact, the splitting and rejoining of the wave around the cylinder resulting in a chute-like jet formation are identified. The model provides a good representation of the breaking wave process and can be a useful tool to evaluate breaking wave forces on structures.

An Oscillating Water Column (OWC) device is a renewable energy device that is used to extract ocean wave energy through the action of waves on a partially submerged chamber consisting of an air and a water column. The operation of an OWC device involves complex hydrodynamic interactions between the waves and the device and a good understanding of these interactions is essential for the design of hydrodynamically efficient and structurally stable devices.In this paper, a two-dimensional numerical wave tank is utilized to simulate the interaction of an OWC device with waves of different wavelengths and steepnesses. The chamber pressure, provided by a turbine in a prototype, is simulated using porous media flow theory in the numerical model. The pressure in the chamber and the velocity of the free surface is calculated to evaluate the efficiency of the device and the model is validated by comparing the numerical results with experimental data. The performance of the device under a range of wavelengths for different wave steepnesses is evaluated. The effect of wave steepness on the device efficiency at a lower wave steepness was found to be low, but a large reduction in performance was found in the presence of steep non-linear waves.

The paper presents the numerical modelling of wave-induced scour around piles in a side-byside arrangement using the open-source CFD model REEF3D. The model solves the Reynolds-Averaged Navier-Stokes equations to calculate wave hydrodynamics. The turbulence under the wave action is calculated using the k-ω model. The free surface is captured with the level set method. The simulated flow field is coupled with the morphological module in REEF3D to simulate the scouring process. The morphological evolution of the sediment bed is based on the Exner formula. For a more realistic calculation of bed scouring and deposition, the modified critical bed shear stress on a sloping bed together with a sand slide algorithm is implemented in the morphological model. First, the model is tested for numerical modelling of wave-induced scour around a single pile. The study presents wave generation and the scouring process in a full-sized and a reduced-length numerical wave tank (NWT) using the relaxation and the active wave absorption method. Furthermore, a discussion on the partial temporal decoupling for the time scales of the morphological and the hydrodynamic models is made. The simulated result shows that the fully developed waves and resulting scouring can be modelled in a reduced-length NWT with the same quality as seen for a full-sized NWT. The validated model is then used to simulate the wave-induced scour around piles in a side-by-side arrangement. The capacity of the model to simulate wave-induced scour in the gap between two piles along with the free surface is demonstrated. The results show the variation of the normalised maximum scour depth S/D with the gap ratios G/D and the Keulegan-Carpenter number. The formation of the jet effect between the piles with different G/D values is also discussed.

An Oscillating Water Column (OWC) is a wave energy converter consisting of a partially submerged chamber with an air column over the water column. The work done by the air column under excitation by the incident waves is used to generate electrical energy through a power take-off (PTO) device. The air column is under pressure due to the damping from the PTO device and this pressure is essential for the extraction of wave energy using the OWC. The relationship between the PTO damping and the hydrodynamic efficiency of the OWC provides more insight into the wave energy extraction using an OWC. namic efficiency increases with increasing incident wavelength. The formation of stagnation zones in the water due to high velocities for lower values of PTO damping is found to reduce the hydrodynamic efficiency.