Numerical analysis of performance of wavebreakers exposed to regular waves in static and floating configuration

In the present paper we investigate, through numerical analysis, the hydrodynamic behavior of wavebreakers both in static and in floating configuration. The aim is to evaluate and compare the performance of wavebreakers in regular waves in the range of intermediate depth waters. The analysis is performed through evaluation of the waves transmitted downward and reflected back and the dissipative behavior of the wavebreaker. We simulate numerically the fluid dynamic field using the Unsteady Reynolds Averaged Navier Stokes equations (URANS) with the 𝑘 − 𝜖 turbulence model, both for the water and the air phases, using the Volume of Fluid (VOF) method to detect the interface. We simulate a numerical wave tank, generating the waves at a lateral boundary of the domain and allowing its own propagation into the domain. First we study the static configuration of the wavebreaker, so it is considered fixed in space. Afterward, we consider the wavebreaker as a rigid body with a Single Degree of Freedom (SDOF) in the vertical direction and we analyze the interaction between the wave system and the structure. With this purpose we use the URANS equations over a dynamic mesh in conjunction with a Fluid–Structure-Interaction (FSI) algorithm, where the mesh displacement is associated to the body’s motion through a diffusive Laplace equation; the motion of the solid body is evaluated using the momentum equation of a rigid body subject to hydrodynamic loading. We study two different wavebreakers, the rectangular one and the 𝛱 shape one, and evaluate the differences in terms of transmitted, reflected and dissipated energy. First we assess the algorithm of generation and propagation of the regular waves comparing numerical results with analytical data. Afterward, we evaluate the performance of the two wavebreakers in terms of coefficients of transmission, reflection and dissipation and we compare our numerical results with data from the standard Wiegel Theory, 1960 and successive modifications. Finally, we study the performance of the wave system in presence of the floating body. This is done in two steps: we initially validate the results with those of the analytical solution of the governing equation of a SDOF rigid body forced by regular wave trains; successively we calculate the transmission coefficients for a number of waves with different length and height and compare the results with literature empirical formulas.