Perforated Breakwater Research Articles

Study of effects of perforation layouts on wave energy dissipation caused by a submerged perforated breakwater in front of a vertical seawall

Perforated structures are a promising alternative to traditional breakwaters for constructing harbors and protecting coastlines. Perforated structures can effectively remove wave energy from ocean waves by the energy dissipation associated with the turbulence generated by the flow through the perforations in the structure. Understanding the factors that may affect the hydrodynamic characteristics of flow through a perforated plate is important for designing perforated marine structures. The purpose of this research was to determine the wave energy dissipation performance of thin-walled plates with various perforation configurations using OpenFOAM-based CFD simulation. Ten different plate configurations were designed and tested with a constant porosity while varying the distribution, shape, and size of the perforations, to determine the impacts to energy dissipation performance. The energy dissipation was quantified by CFD simulations of wave-interaction with a submerged perforated plate placed vertically in front of a vertical backwall (“seawall”). Physical wave flume experiments were also conducted to verify and validate the numerical models. The results showed that the perforation distribution, shape, and size play a minimal role in the energy dissipation performance when porosity is held constant. The minimal performance deviation between the perforation configurations was consistent across a range of wave periods and amplitudes.

Study on the impact of the perforated floating breakwater on coastal bridge with box-girder superstructure under two-dimensional focused waves

The advantages of Floating Breakwater encompass its adaptability to varying water depths and tidal ranges, as well as its economic viability, mobility, and ease of installation. However, limited research has been conducted on the wave damping performance of floating breakwaters on the box-girder superstructure of coastal bridges during extreme wave conditions. In this study, a two-dimensional numerical model was established using the RANS equations and SST k-ω turbulence model in OpenFOAM. The breakwater was constrained by mooring forces, with linear elastic deformation, and underwent horizontal, vertical, and torsional movements under the action of ocean waves. The validity of the numerical model was confirmed by comparing it with existing numerical simulations and experimental data. The study examined influential factors, including the cross-sectional shape, submergence depth, and spacing of the floating breakwater, with a specific emphasis on the dimensions of the upper and lower openings for perforated breakwaters. Combined with attenuation rates and fluid-structure coupling analysis, the wave damping performance of the floating breakwater on the box-girder superstructure of coastal bridges under extreme wave conditions was evaluated. The research results demonstrate that the perforated floating breakwater, with Cs = 0.75, L = 10 m, and upper opening B1 = 0.1 B and lower opening B2 = 0.4 B, maximizes the wave damping performance on the box-girder superstructure of coastal bridges, which holds crucial significance for studying wave attenuation and disaster prevention on the box-girder superstructure of coastal bridges.

Evolution of porous boundary condition in numerical wave tank

A vertical porous or perforated structure can be considered an effective breakwater due to its efficient use in deep water when compared to conventional breakwaters. The hydrodynamic performance of this breakwater can be evaluated by studying the wave reflection and transmission through it. Various experimental studies in the past have shown the performance characteristics of this structure, but their application is limited due to the required effort, time, and manpower (Rajendra et al., 2017). As an alternative, a numerical model can be advantageous in representing exact situations and providing additional benefits. Therefore, as a preliminary study, the wave reflection and transmission of the vertical perforated breakwater are simulated in a numerical wave tank using a unique approach to defining porous boundary conditions. The numerical wave tank is developed using a finite volume-based FLUNET tool with a viscous-laminar model configuration. However, the porous boundary condition is defined in terms of the inertial resistance coefficient, which was derived from pressure drop measurements taken across the perforated structure during lab experiments. The wave reflection and transmission obtained from the numerical wave tank show good agreement with the experimental data. Interestingly, a closer examination of the flow field in the vicinity of the breakwater indicates partial standing wave formation, which contributes to an increase in wave reflection for a limited case.

Analytical study on an oscillating buoy integrated with a perforated structure with a quadratic pressure drop condition: A case study on a WEC-perforated breakwater integration system

A general analytical method for solving the linear wave interactions with the integration systems comprising an oscillating buoy and perforated structure is presented, with a quadratic pressure drop condition on the perforated surface. Using the method of variable separation and eigenfunction expansion, the motion response of the buoy and total velocity potential can be solved using a two-loop iterative method. The method is validated against the published results. The integration system with a heaving WEC arranged inside a perforated breakwater was investigated particularly. Under the quadratic pressure drop condition, the symmetry of the hydrodynamic coefficients and Haskind relation, are found no longer satisfied, and the dissipation through the perforated wall also contribute to the damping coefficient. Effects of the damping of the power take-off system, front wall porosity, wave amplitude, and position of the WEC are investigated in particular. It was found that the horizontal and vertical wave forces on the WEC increase significantly as wave amplitude increases; however, the hydrodynamic efficiency decreases. When the WEC is near the solid rear wall, the horizontal wave forces on the WEC and solid rear wall increase significantly at the frequencies of piston mode gap resonance and heave motion resonance.

Experimental Study on Hydrodynamic Performance of Partially Perforated-Wall Caisson Breakwaters Designed for the Southeast Coast of Korea

Lee, B.W.; Baek, D.; Ha, T.; Lee, K.J., and Yoon, J.-S., 2023. Experimental study on hydrodynamic performance of partially perforated-wall caisson breakwaters designed for the southeast coast of Korea. Journal of Coastal Research, 39(1), 167–174. Charlotte (North Carolina), ISSN 0749-0208. If a perforated wall is installed on the front and rear surfaces of the caisson, then it is possible to reduce the wave reflection and the discharge of wave overtopping caused by energy dissipation. Consequently, the energy dissipation helps reduce the transmitted wave and improve the stability of the breakwater. This paper discusses the hydraulic performance (i.e. the wave reflection, wave transmission, discharge of wave overtopping, and stability of breakwater) of four perforated breakwaters as measured by physical experiments in a wave flume. The irregular wave was generated by the wave condition of the target site. Three breakwaters were designed: a perforated wall with a single chamber for a 50-year return period and two perforated walls with double chambers for a 100-year return period. Based on experimental results, the breakwater with a double chamber showed the best performance of 0.612, 0.102, and 0.076 m3/(m · s) for the reflection, transmission coefficient, and overtopping discharge, respectively. In particular, in the stability experiment of the armor units and perforated caissons, the breakwater with double chamber has not experienced any failure in any of the test cases.

An effective approach for VARANS-VOF modelling interactions of wave and perforated breakwater using gradient boosting decision tree algorithm

In this paper, we propose a systematic and time-efficient approach to calibrate 2D VARANS-VOF models for simulation of wave interaction with porous plate in numerical wave tank. To reach this goal, we develop a data-driven approach in combination with numerical and experimental data to figure out the optimal empirical coefficient associated with linear and non-linear drag force coefficients (α, β). Advanced gradient boosting decision trees algorithms (GBDT) are adopted to capture the accuracy of the prediction model. Although only limited samples, for instance 72 samples are generated and chosen to train and test the prediction model, the GBDT model is able to identify the trend in non-linear influence of model parameters. The advantage of GBDT algorithm can obviously be seen through the regression analysis with very high regression coefficient (R2 > 0.99). The developed model is subsequently employed for a large range of considered parameters as input features of the models to predict the possible hydrodynamics characteristics. The smallest mean squared error between predicted and experimental results, which is 0.00204, is found and used to determine the best performing combination of these model parameters. The numerical model together with selected values of empirical coefficients is then validated using available experimental data in literature. The free surface elevations in front of and behind the structure from the numerical model are nearly identical with the experimental data.

Optimization of double-layer perforated breakwater based on risk assessment of uncertainties

In this work, the optimal dimensions of a double-layer perforated breakwater were determined by considering the risk of uncertainties in marine conditions, including wave height and wavelength. To do so, the CVaR-NINP technique combines Conditional Value-at-Risk (CVaR) and Nonlinear Interval Number Programming (NINP), which are useful in dealing with discrete interval uncertainties and probabilistic. Based on experimental data, two Extreme Learning Machine (ELM) models were developed to simulate the hydraulic behavior of the breakwater. To increase accuracy and performance, the parameters of these two models were optimized using single and multi-objective optimization algorithms. The obtained results indicate that the non-dominated sorting genetic algorithm (NSGA-II) exhibited better performance in optimizing ELM. Subsequently, optimized ELM, which better modeled the hydraulic performance of perforated breakwater, was selected to link to the NSGA-III algorithm to determine the trade-off between the defined objective functions based on the CVaR-NINP technique, namely, minimize CVaR of (Ct), minimize the radius of the interval number of (Ct), minimize CVaR of (Cr), minimize the radius of the interval number of (Cr). Pareto optimal solutions, obtained from NSGA-III, using the multi-attribute decision-making (MADM) method, also called the R-method, were ranked and applied to select the best solutions.

STUDY OF MODIFIED PERFORATED BREAKWATER AS RENEWABLE ENERGY DEVICE

Aim: This study investigates to determine the influence of wave steepness, relative freeboard, and breaker parameters on overtopping discharge at a perforated breakwater. Methodology and results: The research method used was using both a numerical model simulations on three-dimensional computational fluid dynamics (CFD) modelling software namely FLOW-3D; and empirical equation computation. The evaluation of both approaches were performed for understanding the characteristics of wave discharge that overtopping the perforated breakwater. The experimental results of modified perforated breakwater revealed that the lowest slope possible with the highest porosity possible can generate the highest value of dimensionless overtopping discharge for wave energy harvesting. Conclusion, significance and impact study: The findings of this study formulated the optimum slope and porosity to the highest wave energy harvested. Further studies recommend that data collection from onsite trials of modified perforated breakwater are performed.

Theoretical study on arranging heaving wave energy converters in front of jarlan-type breakwater

A hybrid wave energy extraction (HWEE) system consisting of a heaving wave energy converter (WEC) and a Jarlan-type breakwater was theoretically investigated using the linear potential theory. The law of wave energy flux conservation was used for verification. The effect of several critical geometry parameters on the hydrodynamic performance of the HWEE system was discussed. Then, appropriate parameter ranges were recommended in terms of the stability of the structure and the wave energy capture performance. The contribution of the wave radiation force to the total force was discussed, it was found that, compared with the wave excitation force, the wave radiation force can be ignored in most frequency ranges, except near the natural frequency of the heaving WEC. By a contrastive study, it was found that the hydrodynamic performance of the heaving WEC is greatly adjusted by the rear perforated breakwater, and the wave attenuation performance of the proposed HWEE system is much better than an isolated perforated breakwater. Furthermore, it was also found that, in irregular waves, the proposed HWEE system can still maintain a rather good wave energy capture performance.

Numerical Analysis of Velocity Magnitude on Wave Energy Converter System in Perforated Breakwater

Waves are an alternative energy source that can be used for electricity generation. Wave Energy Converter (WEC) system in perforated breakwater is potentially applicable WEC system for coastal area. The magnitude of wave energy generated is determined by the volume of sea water inside the perforated breakwater. This volumetric flow rate is calculated using the flow velocity at perforated holes on the structure slope. Therefore, this research aims to study the velocity magnitude by analyzing the interrelation among wave steepness, wave run-up and relative velocity. The method used consists of applying numeric 3D flow model in the perforated structure of the breakwater with the variation of wave height, wave period and structure slope. The result shows that, the steeper the structure, the bigger is the relative run up (Ru/H). The higher the relative run up, the higher are the relative run-up velocities (V/Vru). As the velocity increase, the volumetric flow rate inside perforated breakwater will be higher, which leads to higher wave energy. Hence, it can be concluded that the higher the velocities (V/Vru), the higher is the wave energy generated.

Numerical investigation into effect of the rubble mound inside perforated caisson breakwaters under random sea states

The paper reports a numerical investigation into the effect of rubble mounds inside perforated caisson breakwaters (PCBs), in which a line-shaped mass source wavemaker is proposed for generating random waves. A series of experiments are employed to validate the numerical model, and good agreements are observed in the comparison of the experimental and numerical results. With the use of the validated numerical model, the numerical investigation is performed, in which the attention is mainly paid to two parameters: the slope angle and porosity of the inner rubble mound. The result shows that, as the slope angle of the inner rubble mound increases, the reflection coefficient is observed to decrease first and then increase, and compared to the experiment, both the positive and negative hydrodynamic pressure acting on the solid rear wall of PCBs is weakened. On the other hand, although a larger inner rubble mound porosity is beneficial to diminish the reflection coefficient, the reduction is not obvious especially when the front wall porosity is small. Furthermore, as the increase of front wall porosity and relative wave absorption chamber length (the ratio of wave absorption chamber length to significant wavelength), the effect of the slope angle and porosity of the inner rubble mound becomes more significant because more waves could enter the wave absorption chamber. The relative wave absorption chamber length considered in the present study ranges from 0.06 to 0.21, and the recommended slope angle is approximately 45 degrees.

Modelling wide perforated breakwater with horizontal slits using Hybrid-BEM method

A hybrid boundary element method has been developed to efficiently solve the hydrodynamic response of a wide perforated breakwater with arbitrary hull geometry and multiple horizontal slits. The fluid subdomains inside the slits were considered as rectangular and analytical eigenfunctions of the slit area were applied to derive the boundary condition at the interface. The involvement of analytical solutions in the numerical boundary element method (BEM) is the novelty of the present approach. The 2D numerical solution was verified with analytical solution of perforated rectangular breakwater to show the validity of the proposed hybrid BEM. Parametric studies have been performed to study the effect of porosity, position and layout of the slits. It has been found that the slits generally reduce the diffracted and radiation potentials, and would be most effective when placed near the free surface. The approach was also extended to 3D channel flow and the results were calibrated against an experimental study performed in the wave flume.

Waves and structure interaction using multi-domain couplings for Navier-Stokes solvers in OpenFOAM®. Part II: Validation and application to complex cases

In this work, we present several applications of the 2D-3D multi-domain couplings for Navier-Stokes models developed and validated in its companion (Di Paolo et al., submitted). The methodology is used to carry out some relevant simulations which include long regular and irregular waves, solitary wave propagation on a shallow foreshore, focused wave group transformation on a planar beach, wave impact on a cylinder and finally, the numerical twin of a complex laboratory experiment to analyse the performance of a perforated breakwater under wave action.Results agree well with the full 3D simulations and laboratory experiments and demonstrate the feasibility of using the 2D-3D coupled methodologies presented in Part I to successfully replace full 3D modelling. For all the cases considered, the application of coupled methodologies have resulted in a drastic reducing of the computational time without decreasing the accuracy of the full solution.

Iterative analytical solution for wave reflection by a multi-chamber partially perforated caisson breakwater

This study examines wave reflection by a multi-chamber partially perforated caisson breakwater based on potential theory. A quadratic pressure drop boundary condition at perforated walls is adopted, which can well consider the effect of wave height on the wave dissipation by perforated walls. The matched eigenfunction expansions with iterative calculations are applied to develop an analytical solution for the present problem. The convergences of both the iterative calculations and the series solution itself are confirmed to be satisfactory. The calculation results of the present analytical solution are in excellent agreement with the numerical results of a multi-domain boundary element solution. Also, the predictions by the present solution are in reasonable agreement with experimental data in literature. Major factors that affect the reflection coefficient of the perforated caisson breakwater are examined by calculation examples. The analysis results show that the multi-chamber perforated caisson breakwater has a better wave energy dissipation function (lower reflection coefficient) than the single-chamber type over a broad range of wave frequency and may perform better if the perforated walls have larger porosities. When the porosities of the perforated walls decrease along the incident wave direction, the perforated caisson breakwater can achieve a lower reflection coefficient. The present analytical solution is simple and reliable, and it can be used as an efficient tool for analyzing the hydrodynamic performance of perforated breakwaters in preliminary engineering design.

Empirical formulae of wave loads on quasi-ellipsoid-type foundations surrounded by cylindrical perforated breakwaters

This study provides empirical formulae of wave loads on quasi-ellipsoid-type foundations coaxially surrounded by perforated breakwaters. The variation of the wave load on each structure versus wave number is characterized as a polygonal line by four key points. The coordinates of these points can be directly obtained from the empirical formulae, which are developed by using mathematical models in the framework of potential theory. The empirical formulae can consider not only the geometric parameters and porous parameters but also the wave exposures and wave numbers. Comparison with the experimental results indicates that the empirical formulae can effectively determine the wave loads on the models under different wave scenarios. Further investigation is conducted on circular foundations, which are the most distinct case of quasi-ellipsoid-type foundations. The wave load magnitudes and phase differences are investigated by experimental and theoretical methods with the consideration of porous parameters and geometric parameters. The experimental results also validate the occurrence of the “phase jump” when the wave loads on the breakwater are minimum. Empirical formulae for the distribution of the “phase jump” points are also presented.

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.

Wave reflection and transmission test with pipe wall roughness and without roughness on the perforated breakwater

Waves towards the shore that have a porous breakwater building will experience reflection and transmission, to determine the height of reflection and transmission wave is needed a study by the process of generating waves on the flume with a porous breakwater building, the effect of wave changes in its propagation requires an experiment in the laboratory. This study was aimed to determine the height ratio of reflection and transmission wave by using a model of pipe structure as a wave reducer by adding the friction plane of the roughness of the walls in the pipe. A method of laboratory experiment on the wave generation flume has several variations consisting of 3 periods (T; 1,0 seconds, T; 1,1 seconds, T; 1.2 seconds) and 3 water depth (d) are 15, 30 and 36 cm, stroke to regulate the flap motion that determines the wave height (H) as a wave generator that is 4, 5 and 6 by comparing the model that uses pipe wall roughness and without roughness. The result of testing indicates that the height of reflection wave (Hr) and transmission (Ht) is strongly influenced by the period (T). If the period increases, Hr and Ht significantly decrease, the height ratio of reflection wave using pipe wall roughness is greater than without roughness. However, it inversely proportional to the height of transmission wave (Ht) were a model using pipe roughness is more efficient to reduce Ht than a model without pipe roughness.

Numerical Study on Performance of Perforated Breakwater for Green Water

AbstractIn this work, the influence of the geometry of lightweight perforated breakwaters on its performance against green water impact loads is investigated systematically through a series of nume...

Applying Finite Difference Method to Simulate the Performance of a Perforated Breakwater Under Regular Waves

Using a discretized finite difference method, a numerical model was developed to study the interaction of regular waves with a perforated breakwater. Considering a non-viscous, non-rotational fluid, the governing equations of Laplacian velocity potential were developed, and specific conditions for every single boundary were defined. The final developed model was evaluated based on an existing experimental result. The evaluated model was used to simulate the condition for various wave periods from 0.6 to 2 s. The reflection coefficient and transmission coefficient of waves were examined with different breakwater porosities, wave steepnesses, and angular frequencies. The results show that the developed model can suitably present the effect of the structural and hydraulic parameters on the reflection and transmission coefficients. It was also found that with the increase in wave steepness, the reflection coefficient increased logarithmically, while the transmission coefficient decreased logarithmically.

Below the Data Range Prediction of Soft Computing Wave Reflection of Semicircular Breakwater

Coastal defenses such as the breakwaters are important structures to maintain the navigation conditions in a harbor. The estimation of their hydrodynamic characteristics is conventionally done using physical models, subjecting to higher costs and prolonged procedures. Soft computing methods prove to be useful tools, in cases where the data availability from physical models is limited. The present paper employs adaptive neuro-fuzzy inference system (ANFIS) and artificial neural network (ANN) models to the data obtained from physical model studies to develop a novel methodology to predict the reflection coefficient (Kr) of seaside perforated semicircular breakwaters under low wave heights, for which no physical model data is available. The prediction was done using the input parameters viz., incident wave height (Hi), wave period (T), center-to-center spacing of perforations (S), diameter of perforations (D), radius of semicircular caisson (R), water depth (d), and semicircular breakwater structure height (hs). The study shows the prediction below the available data range of wave heights is possible by ANFIS and ANN models. However, the ANFIS performed better with R2 = 0.9775 and the error reduced in comparison with the ANN model with R2 = 0.9751. Study includes conventional data segregation and prediction using ANN and ANFIS.