Performance Assessment of a Semi-Circular Breakwater through CFD Modelling

Coastal defence works, such as breakwaters, are structures that aim to support the action of waves and dissipate their energy. Therefore, they provide conditions for stabilizing the coast, protecting ports, beaches and other coastal infrastructures and ecosystems. Semicircular breakwaters have been applied in different locations around the world due to their aesthetic advantages and high structural performance. Marine structures are subject to hydrodynamic actions normally estimated through physical models. However, these models are complex to implement, involving high costs and long experimental procedures. Thus, alternative methodologies for studying the hydrodynamic performance of these structures are of great use. This work presents the results of the application of a computational fluid dynamics (CFD) tool to study the stability of a perforated semicircular breakwater, based on a rubble mound foundation. The model was validated against experimental results of the critical weight necessary to resist sliding, taking into account the effects of water depth and different characteristics of the waves. A comparison is made between the perforated and the non-perforated solution in terms of the breakwater’s performance to dissipate wave energy. Dissipation conditions of this energy, in the exposed face, are also evaluated in detail, in order to assess the potential of this structure as a biological refuge for marine species. Both solutions show similar performance in terms of results obtained for the wave reflectivity coefficient. The turbulence dissipation on the exposed face of the perforated breakwater is limited to a region of restricted extension around it, which is advantageous in terms of the passage of species into the breakwater.

Optimization of Hydraulic Efficiency of a Free Surface Semicircular Breakwater Using Wave Screens

A free surface semicircular breakwater (SCB) with rectangular perforations has been developed to serve as a wave defence structure. Hydrodynamic performance of the breakwaters of various perforations has been thoroughly investigated through wave measurements in a wave flume under random waves. The SCBs were experimentally confirmed to be good anti-reflection wave structures; however, the level of wave transmission at the leeside of the SCBs was rather high particularly when immersed in limited depth and confronted by waves of longer period. This study aims at optimizing the hydraulic characteristics of the SCB by extending its draft by means of wave screens. Three test configurations have been identified in this study, namely (1) the SCB with front screen, (2) the SCB with rear screen, and (3) the SCB with double screens. For each wave screen, three porosities (i.e. 25, 40 and 50%) have been considered in the experiments. The models of shallow immersion depths have been tested in random waves of different characteristics in a wave flume. Wave transformation at different locations upstream and downstream of the test models has been recorded by wave probes. The hydraulic performance of the breakwater are quantified by the coefficients of wave transmission, reflection and energy dissipation, and the wave climate in the vicinity of the breakwater are presented in the form of a ratio relative to the incident wave height. The optimum design of SCB supplemented by truncated wave screen(s) is proposed at the end of the study.