The waves in the numerical wave-tank (NWT) were generated by the piston see more type wave maker which was located at one end of the NWT. The wave maker plate was assigned a sinusoidal motion with the general formula given in Eq. (1). equation(1) xdis=Asinω0twhere xdis is displacement of the wave maker plate in x-direction, A is the amplitude, ω0 is the frequency and t is the simulation time-step.
Fig. 6 shows the schematic of the numerical wave-tank. This is a multi-phase simulation where there are two phases present – namely water and air. To capture the air–water interface, Volume of Fluid (VOF) method similar to the one used by Lui et al. (2008) was used. An unsteady simulation (transient simulation) was performed based on Reynolds averaged Navier–Stokes (RANS) equations with k−ε turbulence model. The time discertization of the equations was achieved with the implicit second order Backward Euler scheme ( Lais et al., 2009). The computational grid was divided into five domains; moving mesh section, NWT, front guide nozzle, augmentation channel (houses the turbine) and the rear chamber as shown
in Fig. 7. Ribociclib clinical trial The right hand boundary is the wave maker plate which moved sinusoidally with a specified displacement. The side walls and the bottom wall of the moving mesh section were modeled as walls with unspecified mesh motion. The top wall of the moving mesh section, NWT and the rear chamber was open to the atmosphere hence; the boundary condition was set as opening with relative pressure
set to 0 Pa. To prevent the influence from this boundary on the formation of the surface waves, the Cepharanthine distance between the free surface and the upper boundary has to be sufficient (Clauss et al., 2005). For this reason, the influence of the wave-tank height on the flow was first studied in detail. The instantaneous velocity profiles at the inlet and outlet of the front guide nozzle for wave-tank heights of 1 m and 1.5 m are shown in Fig. 8. The results show very little to no difference in the velocity and hence the wave-tank height of 1.5 m was chosen for the detailed study. The rest of the outside walls of the computational domain were modeled as solid walls with no-slip boundary condition. The no-slip condition ensures that the fluid moving over the solid surface does not have a velocity relative to the surface at the point of contact. Lastly, appropriate interface regions were created. For interface, the mesh connection method was automatic. A total of five different wave periods were chosen. It was between 2 s and 3 s with increments of 0.25 s. The objective was to see how different wave conditions affect the water power and hence the primary energy conversion. In Fig.