CFD Simulation of Waves over Mound Breakwater

Coastal Engineering Proceedings

The wave field around a rectangular submerged breakwater is investigated by means of an experiment in numerical wave flume. The results were compared with those obtained making use of the Boundary Element Method. The numerical experiment is carried out to determine the share of the incident wave energy that are reflected, dissipated over the roof of the breakwater, and transmitted in the lee. The wave field before the breakwater (i.e. the quasi standing field) obtained with the CFD simulations is quite similar to that obtained with the BEM. Some relevant differences between the two models arise in the lee of the breakwater, because the wave motion is strongly affected by the dissipation occuring over the breakwater roof by friction and wave breaking. They cannot be foreseen with BEM, being the motion ideal. Their analysis show that the dissipation is more than halves the transmission of energy, despite the relevant submergence of the considerated breakwater.

2007

Experimental tests on interaction between a wave and a submerged rubble-mound breakwater were performed in wave flume at University of Napoli Federico II. Different incident wave conditions were tested, including both non-breaking and breaking waves over the barrier. In cases of breaking, different breaker types at structure were described and classified according to hydraulic-morphological criteria. Experimental results show, according to early literature, that wave breaking induces a saturation in non-linear processes that characterize wave-structure interaction. Effect of saturation on 2 nd order transmitted free waves amplitude was investigated, and a best-fit formula was derived. A simple approximate method for wave profile prediction leeward of the barrier is finally proposed.

Journal of Waterway Port Coastal and Ocean Engineering-asce, 1994

Laboratory experiments are presented for the breaking of solitary waves over breakwaters. A variety of behaviors is observed, depending on both breakwater and incident wave height: for emerged breakwaters, waves may collapse over the crown, or break backward during rundown; and for submerged breakwaters, waves may break forward or backward, downstream of the breakwater. The limit of overtopping and wave transmission and reflection coefficients are experimentally determined. It is seen that transmission is large over submerged breakwaters (55-90%), and may also reach 20-40% over emerged breakwaters. Computations using a fully nonlinear potential model agree well with experimental results for the submerged breakwaters, particularly for the smaller waves (Hid < 0.4). For emerged breakwaters, computations correctly predict the limit of overtopping, and the backward collapsing during rundown.

2014

Until recently, physical models were the only way to investigate into the details of breakwaters behavior under wave attack. From the numerical point of view, the complexity of the fluid dynamic processes involved has so far hindered the direct application of Navier-Stokes equations within the armour blocks, due to the complex geometry and the presence of strongly non stationary flows, free boundaries and turbulence. In the present work the most recent CFD technology is used to provide a new and more reliable approach to the design analysis of breakwaters, especially in connection with run-up and reflection. The solid structure is simulated within the numerical domain by overlapping individual virtual elements to form the empty spaces delimited by the blocks. Thus, by defining a fine computational grid, an adequate number of nodes is located within the interstices and a complete solution of the full hydrodynamic equations is carried out. In the work presented here the numerical simu...

Ocean Engineering, 2008

Using COBRAS-UC, a numerical model based on the Volume-Averaged Reynolds Average Navier-Stokes (VARANS) equations, 2-D wave interaction with low-mound breakwaters is analyzed. The model uses a Volume of Fluid (VOF) technique method to capture the free surface which allows the modeling of complicated processes such as breakwater overtopping. Furthermore, thanks to the VARANS equations, the flow in the permeable layers underneath the caisson is quantitatively correct. In order to validate the model's performance, a new set of experimental studies are carried out in a wave flume at a 1:20 scale using regular and irregular waves. Comparisons between numerical and experimental free surface, pressure time histories, and overtopping layer thickness for regular and irregular waves show a good agreement. Further comparisons of numerically predicted overtopping magnitudes with existing semiempirical formulae and experimental data indicate that the model can be used as a complementary tool for the functional design of this kind of structures.

Experimental tests on interaction between a wave and a submerged rubble-mound breakwater were performed in wave flume at University of Napoli Federico II. Different incident wave conditions were tested, including both non-breaking and breaking waves over the barrier. In cases of breaking, different breaker types at structure were described and classified according to hydraulic-morphological criteria. Experimental results show, according to early literature, that wave breaking induces a saturation in non-linear processes that characterize wave-structure interaction. Effect of saturation on 2 nd order transmitted free waves amplitude was investigated, and a best-fit formula was derived. A simple approximate method for wave profile prediction leeward of the barrier is finally proposed.

In the present article a new procedure is proposed to study the interactions between maritime breakwaters (submerged or emerged) and the waves, by integrating CAD and CFD software. The approach is meant to match closely the physical laboratory test procedure, and it is oriented at analyzing the hydrodynamic aspects of the phenomenon (overtopping, breaking, run-up, reflection, transmission) and the stability of primary armour elements. Methodology and results

Coastal Engineering, 2007

The paper presents a series of analytical and numerical investigations of oblique wave transmission at low-crested breakwaters. For a smooth breakwater, two important features of wave height and direction are analyzed to establish the generic nature of the wave transmission process at oblique incidence. The proposed framework of research is validated against laboratory data from the EU-sponsored project, DELOS. The numerical simulations exhibit a significant decrease of the transmission coefficient with increasingly oblique incidence at a smooth breakwater. The roles of wave-breaking, nonlinearity, wave-induced currents and set-up in determining the characteristics of oblique wave transmission are demonstrated in the paper. It is found that both the amplitude-dependent phase velocity and the decrease of mean wave period contribute to the change of mean wave direction on the transmission side. An attempt has also been made to qualitatively explain the different behaviour of oblique wave transmission at a rubble-mound breakwater.

Journal of Marine Science and Engineering

This study focuses on the prediction of technical efficiency of narrow-crested submerged permeable rubble-mound breakwaters, in terms of wave attenuation. A number of existing formulae for estimating wave transmission coefficient for submerged breakwaters can be found in the literature, whereas in this work further improvement for that estimation has been achieved mainly through physical modelling. A series of 2D experiments under scale were conducted for regular and random waves providing data on wave transmission coefficient and respective wave breaking characteristics. A Boussinesq-type wave model capable of simulating wave propagation for regular waves over porous submerged breakwaters was also used in order to provide additional wave transmission information. Data analysis showed that wave breaking mechanism significantly affects wave energy dissipation and, therefore, wave breaking occurrence and type can be directly linked to wave transmission coefficient for a given structur...

2019

Breakwaters with semi-immersed curtains are suitable for locations with low to moderate wave conditions (Hs≤1,2-1,4m, fetch≤5-10km). Such structures enable water circulations through the body of breakwater and this way better water quality in closed port basin. The wave transmission through the body of breakwater depends on the curtain immersion, water depth and wave length. Investigations on wave transmission for regular waves have already been conducted and used in engineering practice for years. The lack of the knowledge is about wave transmission for irregular waves which are in their hydrodynamics much closer to the real wind surface waves. This paper gives results of laboratory investigations in wave flume for irregular waves and their comparison to the models developed for regular waves. The paper gives relations between transmission and reflection coefficients, energy losses and transmission of wave periods.