Query: Submerged porous breakwater

title: Wave interaction with a submerged floating tunnel in the presence of a bottom mounted submerged porous breakwater
abstract: A coupled model of wave interaction with a submerged floating sea tunnel in the presence of a bottom mounted submerged porous breakwater is proposed to study the role of porous breakwater in mitigating wave effects on tunnel. In this study, three configurations of the porous breakwater namely trapezoidal, circular and wedge shapes are analyzed. The Sollitt and Cross' model is adopted for fluid flow inside the porous medium. For solution, the problem is handled with eigenfunction expansion for uniform seabed whereas it is handled with mild slope equation as an approximate technique for arbitrary shape of porous breakwater. Solutions from both the methods are matched at the interface boundaries under certain physical conditions. Reflection and transmission coefficients, and wave forces are calculated for wave and structural parameters. This study reveals that trapezoidal breakwater shows less transmission of waves by dissipating much wave energy and thereby wave forces are mitigated substantially on the tunnel. Parameters are investigated for optimum wave reflection, transmission and wave forces. When the gap between free surface and tunnel becomes zero, considerable phase shift is found in reflection and transmission coefficients of wave. The present study may be useful for understanding the performance of a porous submerged breakwater having different configurations to protect sea tunnel from wave action.

title: Numerical investigation on performance of submerged porous breakwater to mitigate hydrodynamic loads of coastal bridge deck under solitary wave
abstract: Coastal bridges are vulnerable to extreme surges and waves generated during hurricanes and tsunamis. Over the past few decades, extensive research works were conducted to study the damage mechanisms of coastal bridges under the impact of extreme surges and waves. However, these research efforts mainly focused on the hydrodynamic characteristics involved in surge waves impinging bridges. However, there has been little research on mitigation measures to protect coastal bridges. This study examines the installation of a submerged porous breakwater to protect coastal bridge decks from the impacts of solitary waves. As an environmentally friendly wave reduction device, submerged porous breakwater structures have been widely implemented in coastal regions due to their ease of installation and cost effectiveness. To investigate the performance of the submerged porous breakwater on the hydrodynamic loads of a coastal bridge deck under the impact of a solitary wave, a high resolution numerical wave tank is established based on an open source flow solver REEF3D, which numerically solves the governing equations of incompressible two phase flow on a staggered mesh arrangement and captures the interface between air and water using a high resolution level set method. The hydrodynamic characteristics of coastal bridge decks with the installations of submerged porous breakwater are systematically investigated by considering the effects of six prominent factors, i.e. wave height, submersion depth, water depth, permeability, spacing distance between breakwater and bridge, and aspect ratios of breakwaters. Results show that the submerged porous breakwater is effective in reducing the hydrodynamic loads applied to the coastal bridge decks under most of the situations. Therefore, it is believed that the findings drawn from this paper can further enhance our understanding on the damage mechanism of coastal bridges under extreme waves and should be instructive for future bridge designs.

title: Hydrodynamic conditions in a submerged porous breakwater
abstract: In the present work the applicability of an extended Boussinesq type model in simulating wave propagation over submerged porous breakwaters, as well as predicting the velocity distribution inside them was studied. The basic solver is able to reproduce wave propagation in practically any water depth over mild sloping bottom. Extension of this model is presented here to cover porous structures and predict wave kinematics in the interior of a permeable rubble mound covering 2DH configurations. Laboratory experiments were undertaken in the Hydraulic Engineering Laboratory, Department of Civil Engineering, University of Patras. Tests with a physical model were performed in order to measure the 2DH free surface elevation and 3D flow velocity in the interior of a porous submerged breakwater under regular and irregular, breaking and non breaking, short or longer wave attack. The numerical results when compared with test data showed that adequate agreement was achieved in most cases.

title: NUMERICAL STUDY OF WAVE INTERACTION WITH A SUBMERGED POROUS BREAKWATER IN COMBINATION WITH A FLOATING BREAKWATER
abstract: Conventional emerged rubble mound breakwaters are commonly built to protect ports and marinas from direct wave action. With increased high valued developments in the coastal region, engineers have to design innovative coastal protection structures that can provide adequate harbor tranquility with minimum visual impact. One such solution is the combination of a submerged breakwater with a floating breakwater. In this paper, the open source CFD model REEF3D (Bihs et al. 2016) is used to simulate wave interaction with a submerged porous breakwater with a floating breakwater on the lee side. The wave interaction with the submerged porous breakwater is validated by comparison with experimental data from Hieu and Tanimoto (2006) The validated model is then used to simulate the wave interaction with a combination of the submerged breakwater and the floating breakwater. The transmission coefficient across the combination is calculated to be about 12.5% demonstrating the possibility to provide harbor tranquility with minimum visual impact.

title: OBLIQUE WAVE SCATTERING BY A SUBMERGED POROUS BREAKWATER WITH A PARTIALLY REFLECTING SIDEWALL
abstract: This study develops an analytical solution for oblique wave scattering by a submerged porous breakwater with a leeside partially reflecting vertical wall. The matched eigenfunction expansion method is used to develop the analytical solution. The whole fluid domain is divided into three regions according to the geometries of the structures. The series solution of the velocity potential in each region is obtained by the separation of the variables, and the unknown expansion coefficients are determined using the pressure and velocity continuous conditions on interfaces of different regions. The newly developed analytical solution is confirmed by an independently developed multi domain boundary element method (BEM) solution and two known solutions for special cases. Numerical examples are presented to examine the reflection and transmission coefficients of the porous breakwater. Some useful results for engineering design are provided. The present solution may be used to determine the optimal breakwater parameters under an oblique wave attack at a preliminary engineering design stage.

title: Wave propagation over a submerged porous breakwater with steep slopes
abstract: The applicability of a Boussinesq type wave model in simulating wave propagation over submerged breakwaters is studied. The original model is able to reproduce wave propagation including wave breaking in practically any water depth over impermeable mild sloping bottom. Extension of that model is presented to cover steep slopes, permeable structures and breaking conditions typically out of the applicability range of the main solver. This extension is attained by coupling the main solver with a nonlinear Darcy Forchheimer equation and with a modified wave breaking module. Experiments in a wave flume were conducted to measure free surface elevation for regular waves propagating over such structures. The modified model is able to accurately capture the nonlinear phenomena due to wave propagation over submerged structures of any porosity. Also, the wave breaking prediction technique, introducing breaker type categorization in terms of the dominant form, shows that the modified model is able to adequately simulate breaking effects, including spilling, plunging and collapsing breakers, for long and short waves. The numerical simulations when compared with measurements show very good agreement in most cases.

title: Experimental and numerical investigation on wave interaction with horizontal slotted submerged porous breakwater
abstract: In this research work the interaction between waves and horizontal slotted submerged porous breakwater has been investigated experimentally as well as using numerical model. To investigate the performance of proposed horizontal slotted submerged breakwater, experimental studies are carried out in a two dimensional wave flume (21.3 m long, 0.76 m wide and 0.74 m deep) at the Hydraulics and River Engineering Laboratory of the Bangladesh University of Engineering and Technology. A set of experiments are carried out at 50 cm still water depth with fixed horizontal slotted submerged breakwaters of three different porosities n 0.4, 0.5 and 0.6) for interaction with regular waves of four different wave periods (T 1.6 sec, 1.7 sec, 1.8 sec and 2.0 sec) in the wave flume. For 12 run conditions, data of water surface at different locations are collected manually by providing a vertical scale on the flume side made of glass. Six different locations both in front of and behind the breakwater are selected for data collection. At each measuring location, water surface data were recorded for 1 min, at 5 sec time interval. Also the position of wave breaking is simultaneously recorded with a digital video camera. Different hydrodynamic co efficient such as transmission co efficient (Kt) reflection co efficient (Kr) and wave energy loss co efficient (KL) are determined from the measured water surface data for various run conditions. These co efficient values were then, analyzed with respect to relative breakwater width (k.B) [where, k wave number (2p/L) B breakwater width] and porosity of breakwater. Experimental results reveal that, for transmitting smaller part of wave energy through the breakwater, minimum transmission co efficient, Kt 0.526 was obtained for breakwater with the lowest porosity (n=0.4) for the shortest wave, i.e. T 1.6 sec. Minimum reflection co efficient, Kr 0.03448 was obtained for breakwater with the highest porosity (n=0.6) for the longest wave, i.e. T 2 sec. It is also seen that wave energy loss co efficient (KL) decreases from 0.68 to 0.47 with increasing porosity. Two dimensional numerical model based on the SOLA VOF (SOLution AlgorithmVolume Of Fluid) method developed for wave interaction with fixed submerged breakwater has been updated in this research to study the wave interaction with horizontal slotted submerged porous breakwater. The SOLA scheme is employed to calculate the pressure and velocities in each time step and the added dissipation zone method is adopted to treat the open boundary. The developed numerical model is verified by comparing the model generated wave with the wave as per Stokes 3 order wave theory. The time series water surface profiles, water particle velocity field, VOF function F, pressure around a breakwater of different porosities (n=0.4, 0.5 and 0.6) are simulated using the numerical model. The water surface profiles and breaking positions simulated by the developed numerical model show good agreement with the experimentally measured data. This study is expected to serve as a useful model to analyze wave deformation due to horizontal slotted submerged porous breakwater and will be important for designing submerged porous breakwater as a coastal protection measure.

title: EXPERIMENTAL STUDY OF WAVE BREAKING CRITERIA AND ENERGY LOSS CAUSED BY A SUBMERGED POROUS BREAKWATER ON HORIZONTAL BOTTOM
abstract: Study on the criteria of wave breaking and energy loss caused by a submerged porous breakwater on a horizontal bottom has been performed experimentally in a 2 D wave tank. Wave conditions as well as the freeboard of the submerged breakwater, with the front slope of 1/2 and 1/5, are varying in the experiments. Results show that almost all tested waves can be triggered to break when the ratio of the estimated equivalent deepwater wave height to the freeboard of the submerged breakwater is greater than one. Results also reveal that a milder front slope of submerged breakwater may not trigger wave breaking more efficiently as that with a steeper front slope does. Furthermore, for a given freeboard of submerged breakwater, longer waves are more difficult to be triggered to break than shorter waves as expected. It is found that a submerged breakwater function much more efficiently if waves can be triggered to break by the structure as expected. Furthermore, it is also found that the submerged breakwater with milder front slope consumes more wave energy than that with steeper one through a wider range of porous structure.

title: Wave Transmission over a Submerged Porous Breakwater an Experimental Study
abstract: The present paper presents an experimental study of wave transmission for a trapezoidal submerged porous breakwater located in the nearshore region. Wave transmission characteristics of the breakwater subjected to unidirectional monochromatic waves have been ascertained via a systematic test program. A series of tests have been conducted to study the effect of porosity of the breakwater on wave transmission, and to assess wave attenuation performance of the breakwater in relation to wave steepness and the relative breakwater width. The test results have indicated that the breakwater of 20% porosity offers the highest hydraulic efficiency, and the breakwater provides higher wave suppression ability when exposed to shorter period waves particularly in shallow waters.

title: Wave propagation passing over a submerged porous breakwater
abstract: A linear model of waves propagating over a submerged porous breakwater is derived from two coupled boundary value problems, each of which represents the governing equation in a different medium. The model is similar to the shallow water equations (SWE) with a damping term proportional to the character of the porous breakwater. Therefore, waves traveling above the breakwater will be absorbed, and the amplitude decreases. The wave propagation passing over the submerged breakwater for monochromatic and solitary waves is analyzed. For monochromatic waves, the numerical solution agrees with the analytical. The amplitude decreases exponentially with respect to the space variable in the region above the breakwater. The reflected wave is also analyzed when the model is combined with a model using the shallow water equations.