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This paper presents the results of laboratory tests on a hybrid wave energy converter concept, the O2WC (Oscillating-Overtopping Water Column) device. The proposed device aims at providing an alternative to the classical OWC concept,... more
This paper presents the results of laboratory tests on a hybrid wave energy converter concept, the O2WC (Oscillating-Overtopping Water Column) device. The proposed device aims at providing an alternative to the classical OWC concept, storing part of the wave energy of the highly energetic sea states in a second chamber at atmospheric pressure, through overtopping phenomena. In this way, the maximum airflow rate and air pressure in the OWC chamber are reduced, possibly aiding the safe functioning of the air turbine, and allowing to exploit the excess of energy instead of dissipating it through by-pass valves. The performance of the device is investigated under different incident wave conditions, for different design parameters. The height of the overtopping threshold from the second chamber of the device which allows to maximize the performance has been selected. Results show that the decrease of the primary conversion efficiency of the OWC component of the device caused by the decre...
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Research Interests: Humanities and Art
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Coasts of low lying countries are often comprised of a gentle foreshore and shallow waters, followed by a dike and a promenade. At the end of the promenade buildings or storm walls are constructed. This setting makes it possible for waves... more
Coasts of low lying countries are often comprised of a gentle foreshore and shallow waters, followed by a dike and a promenade. At the end of the promenade buildings or storm walls are constructed. This setting makes it possible for waves to overtop the dike and impact on the storm wall or building. Especially during storm season the overtopping waves induce large loads on these structures. New scenarios for climate change and sea level rise make it worthwhile to invest in research regarding overtopping wave loads. Within the European project 'Wave Loads on Walls' (WaLoWa) model tests in the Delta flume (The Netherlands) were conducted. It is the aim to study overtopping wave loads on storm walls and buildings. The project is coordinated by Ghent University (Belgium), in cooperation with TU Delft (The Netherlands), RWTH Aachen (Germany), University of Bari, University of L'Aquila, University of Calabria and University of Florence (Italy) and Flanders Hydraulics Research ...
WaLoWa stands for Wave Loads on Walls and is a Hydralab+ project funded by the European Union. Ghent University (Belgium), TU Delft (The Netherlands), RWTH Aachen (Germany), Politechnico Bari and University of Florence (Italy) and... more
WaLoWa stands for Wave Loads on Walls and is a Hydralab+ project funded by the European Union. Ghent University (Belgium), TU Delft (The Netherlands), RWTH Aachen (Germany), Politechnico Bari and University of Florence (Italy) and Flanders Hydraulics Research (Belgium) are jointly working on the WaLoWa project. The user team leader is Ghent University. The WaLoWa project is hosted by Deltares and the Delta Flume facility. When storm walls and buildings are located on top of a dike or promenade, overtopping waves can induce large forces on these structures as has e.g. been observed at the Belgian coast which has a specifically shallow foreshore. Especially during storm season and in times of sea level rise these loads can be highly destructive. It is therefore the key objective of WaLoWa to study overtopped wave loads on structures situated on top of a dike and in shallow foreshore conditions.
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The importance of properly modelling the effects of air compressibility in the selection of the optimal design parameters for an Oscillating Water Column wave energy converter is investigated. For this purpose, a wide dataset of capture... more
The importance of properly modelling the effects of air compressibility in the selection of the optimal design parameters for an Oscillating Water Column wave energy converter is investigated. For this purpose, a wide dataset of capture width ratios, obtained from both experimental tests and Computational Fluid Dynamic simulations, is used to formulate an empirical model able to predict the performance of the device as a function of its basic design parameters (chamber width and draught, turbine damping) and of the wave conditions (wave period, wave height). A multiple non-linear regression approach is used to determine the model numerical coefficients. The data used to formulate the model include the effects of air compressibility. The impact of considering such effects on the selection of the optimal geometry of the device is evaluated and discussed by means of the model application for the optimization of a device to be installed in a site located in the Mediterranean Sea (in fro...
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Research Interests: Geology and Meteorology
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Floating Oscillating Water Column (OWC) type Wave Energy Converters (WECs), compared to fixed OWC WECs that are installed near the coastline, can be more effective as they are subject to offshore waves before the occurrence of wave... more
Floating Oscillating Water Column (OWC) type Wave Energy Converters (WECs), compared to fixed OWC WECs that are installed near the coastline, can be more effective as they are subject to offshore waves before the occurrence of wave dissipation of a nearshore location. The performance of floating OWC WECs has been widely studied using both numerical and experimental methods. However, due to the complexity of fluid-structure interaction of floating OWC WECs, most of the available studies focus on 2D problems with limited Degrees-Of-Freedom (DOF) motion while 3D mooring effects and multiple-DOF motion have not been extensively investigated yet. Therefore, in order to gain a deeper insight of these problems, the present study focuses on wave flume experiments to investigate the motion and mooring performance of a 1:25 scaled floating OWC WEC model. As a preparatory phase for the MaRINET2 EsfLOWC (Efficiency & survivability of floating OWC) project completed by the end of 2017, the main ...
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Overtopping bore impact forces on a dike mounted vertical wall were measured in similar large-scale (Froude length scale factor 1-to-4.3) and small-scale (Froude length scale factor 1-to-25) models. The differences due to scale effects... more
Overtopping bore impact forces on a dike mounted vertical wall were measured in similar large-scale (Froude length scale factor 1-to-4.3) and small-scale (Froude length scale factor 1-to-25) models. The differences due to scale effects were studied, by comparing the up-scaled force measurements from both models in prototype. It was noted that if a minimum layer thickness, velocity of the overtopping flow and water depth at the dike toe were maintained in the small-scale model, the resulting differences in impact force due to scale effects are within the range of differences due to non-repeatability and model effects.
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... Figure 12: Numerical simulations of the short term morphodynamics induced by groins of different lengths. ... References Aminti PL, Cappietti L., 2003, Sea bottom scour near gaps in coastal protectionstructures. In Int. ... Physical... more
... Figure 12: Numerical simulations of the short term morphodynamics induced by groins of different lengths. ... References Aminti PL, Cappietti L., 2003, Sea bottom scour near gaps in coastal protectionstructures. In Int. ... Physical Modelling in Coastal Engineering, Dalrymple RA, pp. ...
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Wave-Overtopping loads on vertical walls, such as those located on top of a dike, have been investigated in several small-scale experiments in the past. A large-scale validation for a mild foreshore situation is still missing. Hence the... more
Wave-Overtopping loads on vertical walls, such as those located on top of a dike, have been investigated in several small-scale experiments in the past. A large-scale validation for a mild foreshore situation is still missing. Hence the WALOWA (WAve LOads on WAlls) experimental campaign was carried out to address this topic. This paper, first presents a description of the large-scale model, the measurement set-up and the experimental methodologies, then it focuses on the layer thicknesses and velocities of the flows created on the promenade by the wave overtopping. A set of resistive wave gauges, ultrasonic distance sensors and velocimeters have been used to conduct these measurements. Preliminary data analysis and results, related to a 1000 irregular waves long test, are discussed. The momentum flux of these flows is studied and its implications, for the wave-overtopping loads acting on the vertical walls, are highlighted.
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Abstract This paper aims at assessing the effectiveness of an oscillating water column device, generally conceived and studied as a wave energy converter, as an anti-reflective system to be integrated into vertical wall harbour... more
Abstract This paper aims at assessing the effectiveness of an oscillating water column device, generally conceived and studied as a wave energy converter, as an anti-reflective system to be integrated into vertical wall harbour structures. The wave-structure interaction is studied with simulations carried out in a numerical wave tank, implemented in the computational fluid dynamics environment OpenFOAM®. Reflected and radiated wave components are decomposed and the interaction between these components is studied. A quasi-standing wave field is present in front of the structure. The effect of design parameters and hydrodynamic conditions on the reflection properties and on the wave field in front of the structure is discussed. Results are analysed in terms of dimensionless parameters and original empirical formulae to predict the wave reflection are given. Minimum reflection coefficients (including both properly reflected and radiated waves) around 15% are found, suggesting that the OWC could efficiently be used to reduce wave agitation in front of vertical wall harbour structures. The reflection coefficient is primarily influenced by the ratio of the camber length W to the incident wavelength L, with minimum values for W/L = 0.1–0.17. Minimum values of the ratio of the quasi-antinode height to the incident wave height around 1.1 are found.
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In this paper, a novel approach for simulating Oscillating Water Column (OWC) using lattice Boltzmann method (LBM) is presented. A direct comparison between a real wave flume and a 3D-Large Eddy Simulation (LES) numerical lattice... more
In this paper, a novel approach for simulating Oscillating Water Column (OWC) using lattice Boltzmann method (LBM) is presented. A direct comparison between a real wave flume and a 3D-Large Eddy Simulation (LES) numerical lattice Boltzmann (LB) wave flume is developed through the analysis of an OWC energy converter in order to validate the LBM approach for simulating OWCs. The numerical model uses a Volume-of-Fluid (VOF) approach and handles the water–air coupling into the OWC air chamber. The experimental and numerical setup are described. Comparisons for water level during free oscillation test, water level and air pressure under regular wave attacks are given and show that the LB model is accurate. We also discuss the efficiency of the simulated OWC. The 3D numerical model offers a powerful tool in order to study the 3D phenomena occurring into OWCs.
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An empirical model, to be used as a tool to aid in the definition of the optimal values of the main design parameters of oscillating water column wave energy converter devices, is proposed. An extensive dataset of capture width ratio of... more
An empirical model, to be used as a tool to aid in the definition of the optimal values of the main design parameters of oscillating water column wave energy converter devices, is proposed. An extensive dataset of capture width ratio of the device, obtained from both experimental tests and Computational Fluid Dynamics simulations, is used to formulate the model. The model has been developed by applying the dimensional analysis to select the non-dimensional independent variables of the functional form. A multiple non-linear regression method is used to compute the model power coefficients and empirical constants. The model can predict the capture width ratio of the oscillating water column device given the wave conditions, the water depth, the geometrical parameters of the device and the turbine damping as input variables. It can be used in the preliminary stage of the device design, allowing to comparatively test a considerable number of design alternatives with reduced computationa...
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Wave reflection at harbor structures negatively affects the navigability of entrance canals and harbor tranquility. In case of rubble-mound structures this phenomenon is relatively limited if compared to vertical-wall structures. However,... more
Wave reflection at harbor structures negatively affects the navigability of entrance canals and harbor tranquility. In case of rubble-mound structures this phenomenon is relatively limited if compared to vertical-wall structures. However, in case of deep waters, the use of the latter is an obliged choice due to economic reasons. Furthermore, vertical wall structures are also the preferred choice of harbor managers since they permit a better design of the berthing structures and help the effective use of space inside the harbor. Reducing the wave reflection at vertical wall structures is thus an important measure. To date, several approaches have been presented in the literature (see for instance Huang et al., 2011, and references therein). The effectiveness of slotted vertical perforated-walls has been studied since many years (most recently: Neelamani et al., 2017). Such kind of structure is often also adopted as frontal and internal wall of caisson breakwaters embodying one or mul...
Oscillating water column (OWC) systems are among the most credited solutions for an effective conversion of the notable energy potential conveyed by sea waves. Despite a renewed interest, however, they are often still at a demonstration... more
Oscillating water column (OWC) systems are among the most credited solutions for an effective conversion of the notable energy potential conveyed by sea waves. Despite a renewed interest, however, they are often still at a demonstration phase and additional research is required to reach industrial maturity. Within this framework, this study provides a wave-to-wire model for OWC systems based on an impulse air turbine. The model performs a comprehensive simulation of the system to estimate the attendant electric energy production for a specific sea state, based on analytical models of the primary (fixed chamber) and secondary (air turbine) converters coupled with the tertiary converter (electric generator). A rigid piston model is proposed to solve the hydrodynamics, thermodynamics, and hydrodynamics of the chamber, in a coupled fashion with the impulse turbine aerodynamics. This is solved with a novel method by considering the cascades as sets of blades, each one consisting of a fin...
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ABSTRACT The Oscillating Water Column (OWC) is one of the oldest and simplest concepts for wave energy conversion. However, the device optimization is still required as a fundamental step towards the technology commercial scale diffusion.... more
ABSTRACT The Oscillating Water Column (OWC) is one of the oldest and simplest concepts for wave energy conversion. However, the device optimization is still required as a fundamental step towards the technology commercial scale diffusion. Numerical modelling, validated and calibrated with results from physical tests, is an essential tool, allowing the study of more configurations than those practically feasible with physical modelling and measurement in an undisturbed flow field. In this study, the state of the art of OWC numerical modelling as well as a CFD model (with turbulence modelling) of an OWC device implemented in OpenFOAM® are presented. The multiphase (air-water) model adopts a Volume of Fluid (VOF) method to track the air-water interface. The implemented model solves the incompressible 3D Navier-Stokes equations, using Large Eddy Simulation (LES) for turbulence modelling. Preliminary results are compared to physical tests performed on the same configurations in a physical wave flume. The approach seems to be promising for the simulation of the different steps of energy conversion hydraulic chain, allowing the evaluation of the conversion efficiency and a deeper understanding of the relevant processes involved in the wave-structure interaction.
Floating oscillating water column (OWC) type wave energy converters (WECs), compared to fixed OWC WECs that are installed near the coastline, can be more effective as they are subject to offshore waves before the occurrence of wave... more
Floating oscillating water column (OWC) type wave energy converters (WECs), compared to fixed OWC WECs that are installed near the coastline, can be more effective as they are subject to offshore waves before the occurrence of wave dissipation at a nearshore location. The performance of floating OWC WECs has been widely studied using both numerical and experimental methods. However, due to the complexity of fluid–structure interaction of floating OWC WECs, most of the available studies focus on 2D problems with WEC models of limited degrees-of-freedom (DOF) of motion, while 3D mooring effects and multiple-DOF OWC WECs have not been extensively investigated yet under 2D and 3D wave conditions. Therefore, in order to gain a deeper insight into these problems, the present study focuses on wave flume experiments to investigate the motion and mooring performance of a scaled floating OWC WEC model under 2D wave conditions. As a preparatory phase for the present MaRINET2 EsflOWC (efficienc...
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This article presents an assessment of water exchange between sea and the Orbetello Lagoon, Italy. The work methodology is based both on field measurements and on numerical simulations. The assessment is related to tidal, wind and... more
This article presents an assessment of water exchange between sea and the Orbetello Lagoon, Italy. The work methodology is based both on field measurements and on numerical simulations. The assessment is related to tidal, wind and atmospheric pressure for the whole 2016, taken as exemplary year. Field measurements have been conducted by means of level gauges, installed at four internal lagoon points, and one anemometer installed at a central internal point. Moreover, two tidal gages, one located at Civitavecchia harbor and the other at Marina di Campo (Elba Island) have been used to set the offshore boundary conditions for the numerical model. The numerical simulations have been conducted with the HD FM module of the MIKE21 software package, a fully non-linear shallow water solver. The numerical results match closely the field measurements, in terms of total sea-lagoon water exchange, but the former also permits to simulate the whole lagoon hydrodynamics thus allowing much deeper un...
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Vincent Gruwez, Ghent University, Vincent.Gruwez@UGent.be Corrado Altomare, Universitat Politecnica de Catalunya & Ghent University, Corrado.Altomare@upc.edu Tomohiro Suzuki, Flanders Hydraulics Research, Tomohiro.Suzuki@mow.vlaanderen.be... more
Vincent Gruwez, Ghent University, Vincent.Gruwez@UGent.be Corrado Altomare, Universitat Politecnica de Catalunya & Ghent University, Corrado.Altomare@upc.edu Tomohiro Suzuki, Flanders Hydraulics Research, Tomohiro.Suzuki@mow.vlaanderen.be Maximilian Streicher, Ghent University, Maximilian.Streicher@UGent.be Lorenzo Cappietti, Università degli Studi di Firenze, Lorenzo.Cappietti@unifi.it Andreas Kortenhaus, Ghent University, Andreas.Kortenhaus@UGent.be Peter Troch, Ghent University, Peter.Troch@UGent.be INTRODUCTION Low-lying countries typically have mildly-sloping beaches as part of their coastal defence system. For countries in north-western Europe high-rise buildings are a common sight close to the coastline. They are usually fronted by a low-crested sea dike with a relatively short promenade, where the long (nourished) beach in front of it acts as a very/extremely shallow foreshore as defined by Hofland et al. (2017). Along the cross-section of this hybrid beachdike coastal defen...
In this paper, a Reynolds-averaged Navier–Stokes (RANS) equations solver, interFoam of OpenFOAM®, is validated for wave interactions with a dike, including a promenade and vertical wall, on a shallow foreshore. Such a coastal defence... more
In this paper, a Reynolds-averaged Navier–Stokes (RANS) equations solver, interFoam of OpenFOAM®, is validated for wave interactions with a dike, including a promenade and vertical wall, on a shallow foreshore. Such a coastal defence system is comprised of both an impermeable dike and a beach in front of it, forming the shallow foreshore depth at the dike toe. This case necessitates the simulation of several processes simultaneously: wave propagation, wave breaking over the beach slope, and wave interactions with the sea dike, consisting of wave overtopping, bore interactions on the promenade, and bore impacts on the dike-mounted vertical wall at the end of the promenade (storm wall or building). The validation is done using rare large-scale experimental data. Model performance and pattern statistics are employed to quantify the ability of the numerical model to reproduce the experimental data. In the evaluation method, a repeated test is used to estimate the experimental uncertaint...
The sea is an important renewable energy resource for its extension and the power conveyed by waves, currents, tides, and thermal gradients. Amongst these physical phenomena, sea waves are the source with the highest energy density and... more
The sea is an important renewable energy resource for its extension and the power conveyed by waves, currents, tides, and thermal gradients. Amongst these physical phenomena, sea waves are the source with the highest energy density and may contribute to fulfilling the global increase of power demand. Despite the potential of sea waves, their harnessing is still a technological challenge. Oscillating water column systems operating with Wells turbines represent one of the most straightforward and reliable solutions for the optimal exploitation of this resource. An analytical model and computational fluid dynamics models were developed to evaluate the functioning of monoplane isolated Wells turbines. For the former modeling typology, a blade element momentum code relying on the actuator disk theory was applied, considering the rotor as a set of airfoils. For the latter modeling typology, a three-dimensional multi-block technique was implemented to create the computational domain with a...
Three open source wave models are applied in 2DV to reproduce a large-scale wave flume experiment of bichromatic wave transformations over a steep-sloped dike with a mildly-sloped and very shallow foreshore: (i) the Reynolds-averaged... more
Three open source wave models are applied in 2DV to reproduce a large-scale wave flume experiment of bichromatic wave transformations over a steep-sloped dike with a mildly-sloped and very shallow foreshore: (i) the Reynolds-averaged Navier–Stokes equations solver interFoam of OpenFOAM® (OF), (ii) the weakly compressible smoothed particle hydrodynamics model DualSPHysics (DSPH) and (iii) the non-hydrostatic nonlinear shallow water equations model SWASH. An inter-model comparison is performed to determine the (standalone) applicability of the three models for this specific case, which requires the simulation of many processes simultaneously, including wave transformations over the foreshore and wave-structure interactions with the dike, promenade and vertical wall. A qualitative comparison is done based on the time series of the measured quantities along the wave flume, and snapshots of bore interactions on the promenade and impacts on the vertical wall. In addition, model performanc...
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Oscillating water column (OWC) systems are among the most credited solutions for an effective conversion of the notable energy potential conveyed by sea waves. Despite a renewed interest, however, they are often still at a demonstration... more
Oscillating water column (OWC) systems are among the most credited solutions for an effective conversion of the notable energy potential conveyed by sea waves. Despite a renewed interest, however, they are often still at a demonstration phase and additional research is required to reach industrial maturity. Within this framework, this study provides a wave-to-wire model for OWC systems based on an impulse air turbine. The model performs a comprehensive simulation of the system to estimate the attendant electric energy production for a specific sea state, based on analytical models of the primary (fixed chamber) and secondary (air turbine) converters coupled with the tertiary converter (electric generator). A rigid piston model is proposed to solve the hydrodynamics, thermodynamics, and hydrodynamics of the chamber, in a coupled fashion with the impulse turbine aerodynamics. This is solved with a novel method by considering the cascades as sets of blades, each one consisting of a fin...
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Floating oscillating water column (OWC) type wave energy converters (WECs), compared to fixed OWC WECs that are installed near the coastline, can be more effective as they are subject to offshore waves before the occurrence of wave... more
Floating oscillating water column (OWC) type wave energy converters (WECs), compared to fixed OWC WECs that are installed near the coastline, can be more effective as they are subject to offshore waves before the occurrence of wave dissipation at a nearshore location. The performance of floating OWC WECs has been widely studied using both numerical and experimental methods. However, due to the complexity of fluid–structure interaction of floating OWC WECs, most of the available studies focus on 2D problems with WEC models of limited degrees-of-freedom (DOF) of motion, while 3D mooring effects and multiple-DOF OWC WECs have not been extensively investigated yet under 2D and 3D wave conditions. Therefore, in order to gain a deeper insight into these problems, the present study focuses on wave flume experiments to investigate the motion and mooring performance of a scaled floating OWC WEC model under 2D wave conditions. As a preparatory phase for the present MaRINET2 EsflOWC (efficienc...
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This paper describes experimental research on a floating moored Oscillating Water Column (OWC)-type Wave-Energy Converter (WEC) carried out in the wave flume of the Coastal Engineering Research Group of Ghent University. This research has... more
This paper describes experimental research on a floating moored Oscillating Water Column (OWC)-type Wave-Energy Converter (WEC) carried out in the wave flume of the Coastal Engineering Research Group of Ghent University. This research has been introduced to cover the existing data scarcity and knowledge gaps regarding response of moored floating OWC WECs. The obtained data will be available in the future for the validation of nonlinear numerical models. The experiment focuses on the assessment of the nonlinear motion and mooring-line response of a 1:25 floating moored OWC WEC model to regular waves. The OWC WEC model motion has 6 degrees of freedom and is limited by a symmetrical 4-point mooring system. The model is composed of a chamber with an orifice on top of it to simulate the power-take-off (PTO) system and the associated damping of the motion of the OWC WEC model. In the first place, the motion response in waves of the moored floating OWC WEC model is investigated and the wat...
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Wave reflection at harbor structures negatively affects the navigability of entrance canals and harbor tranquility. In case of rubble-mound structures this phenomenon is relatively limited if compared to vertical-wall structures. However,... more
Wave reflection at harbor structures negatively affects the navigability of entrance canals and harbor tranquility. In case of rubble-mound structures this phenomenon is relatively limited if compared to vertical-wall structures. However, in case of deep waters, the use of the latter is an obliged choice due to economic reasons. Furthermore, vertical wall structures are also the preferred choice of harbor managers since they permit a better design of the berthing structures and help the effective use of space inside the harbor. Reducing the wave reflection at vertical wall structures is thus an important measure. To date, several approaches have been presented in the literature (see for instance Huang et al., 2011, and references therein). The effectiveness of slotted vertical perforated-walls has been studied since many years (most recently: Neelamani et al., 2017). Such kind of structure is often also adopted as frontal and internal wall of caisson breakwaters embodying one or mul...