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The wave-induced liquefaction of seabed is responsible for causing damage to marine structures. Particle composition and consolidation degree are the key factors affecting the pore water pressure response and liquefaction behavior of the seabed under wave action. The present study conducted wave flume experiments on silt and silty fine sand beds with varying particle compositions. Furthermore, a comprehensive analysis of the differences and underlying reasons for liquefaction behavior in two different types of soil was conducted from both macroscopic and microscopic perspectives. The experimental results indicate that the silt bed necessitates a lower wave load intensity to attain the liquefaction state in comparison to the silty fine sand bed. Additionally, the duration and development depth of liquefaction are greater in the silt bed. The dissimilarity in liquefaction behavior between the two types of soil can be attributed to the variation in their permeability and plastic deformation capacity. The permeability coefficient and compression modulus of silt are lower than those of silty fine sand. Consequently, silt is more prone to the accumulation of pore pressure and subsequent liquefaction under external loading. Prior research has demonstrated that silt beds with varying consolidation degrees exhibit distinct initial failure modes. Specifically, a dense bed undergoes shear failure, whereas a loose bed experiences initial liquefaction failure. This study utilized discrete element simulation to examine the microscopic mechanisms that underlie this phenomenon. [ABSTRACT FROM AUTHOR]

CFD models (Computational Fluid Dynamics) provide valuable tools to evaluate the interaction of complex flows with coastal works, beyond empirical formulas for overtopping, which are limited to the range of values used in the experiments. However, its use is still incipient in the Chilean context, thus posing various challenges to users. This study presents the calibration and validation of a numerical wave channel using the OpenFOAM CFD model with the olaFlow solver. Cases of waves in progressive, quasistationary and stationary regimes are analyzed. A sensitivity analysis is applied to the main variables and configurations of the model, among which the size of the mesh, the modeling time, the time interval, the turbulence models, and the boundary conditions are examined. Then breaking waves are modeled and compared with a physical model developed by Kamath et al. (2017). Finally, the ability of OpenFOAM to represent the interaction of waves with a pier, with particular focus on the pressures under the deck, is studied. [ABSTRACT FROM AUTHOR]

Reef islands are composed of unconsolidated carbonate sediment from the reef that has been organized and deposited on an atoll and platform reef by ocean hydrodynamics. They are frequently found in remote mid-ocean locations within tropical and subtropical waters and are the sole source for habitable land of some island nations. It is anticipated that sea level rise and more frequent and intense storms resulting from global climate change will destabilize these low-lying reef islands, thus there is increasing concern about the persistence and habitability of these islands during future extreme wave events. The reef island morphodynamic response to the action of regular waves has not been reported in the literature. Therefore, this study performed laboratory experiments based on a horizontally one-dimensional reef island physical model in a wave flume. The temporal variation of the island profile under regular waves was measured to analyze the effects of island morphological factors (initial island height and width) and initial island location on its topographic evolution. The results showed that the reef island lost crest elevation and migrated and extended toward its lagoon side under the action of regular waves. Accretion also occurred on the lagoon side beach and random ripples appeared. The time required for the island to reach its equilibrium profile decreased with increasing of initial island height, initial island width, and initial island distance from reef edge. The island crest lowering due to scouring increased with increase of initial island height, but it decreased with increasing of initial island width and initial island distance from the reef edge. Among the three factors, initial island height had the greatest impact on the crest lowering. The island lagoonward migration decreased with increasing of both initial island height and initial island distance from reef edge, but it increased with the increase of initial island width. Among the three factors, initial island location was the most influential factor to lagoonward migration, but no island lagoonward migration was detected when the initial island distance D≥2 m. Regression analysis was used to obtain empirical formulae to predict the island crest lowering and island lagoonward migration, respectively. The outcomes of this study provide a habitability assessment for such low-lying island nations in the context of global climate change.

Reef islands are composed of unconsolidated carbonate sediment from the reef that has been organized and deposited on an atoll and platform reef by ocean hydrodynamics. They are frequently found in remote midocean locations within tropical and subtropical waters and are the sole source for habitable land of some island nations. It is anticipated that sea level rise and more frequent and intense storms resulting from global climate change will destabilize these low-lying reef islands, thus there is increasing concern about the persistence and habitability of these islands during future extreme wave events. The reef island morphodynamic response to the action of regular waves has not been reported in the literature. Therefore, this study performed laboratory experiments based on a horizontally one-dimensional reef island physical model in a wave flume. The temporal variation of the island profile under regular waves was measured to analyze the effects of island morphological factors (initial island height and width) and initial island location on its topographic evolution. The results showed that the reef island lost crest elevation and migrated and extended toward its lagoon side under the action of regular waves. Accretion also occurred on the lagoon side beach and random ripples appeared. The time required for the island to reach its equilibrium profile decreased with increasing of initial island height, initial island width, and initial island distance from reef edge. The island crest lowering due to scouring increased with increase of initial island height, but it decreased with increasing of initial island width and initial island distance from the reef edge. Among the three factors, initial island height had the greatest impact on the crest lowering. The island lagoonward migration decreased with increasing of both initial island height and initial island distance from reef edge, but it increased with the increase of initial island width. Among the three factors, initial island location was the most influential factor to lagoonward migration, but no island lagoonward migration was detected when the initial island distance D≥2 m. Regression analysis was used to obtain empirical formulae to predict the island crest lowering and island lagoonward migration, respectively. The outcomes of this study provide a habitability assessment for such low-lying island nations in the context of global climate change. [ABSTRACT FROM AUTHOR]

The importance of coastal protection increases with the increase in coastal development. Soft and hard protection measures are the most used techniques; however, hard structures are still preferable. Hard structures are characterized by a long lifetime and high stability in rough sea states. Many innovative, environmentally friendly hard coastal protections measured have been proposed and used for specific applications. This research’s main objective is to develop and check a new coastal structure, Corrugated Semi-circular Breakwater (CBW). This structure is modified from the Semi-circular Breakwater (SCBW), one of the hard protections used in Japan and China, to increase its efficiency in coastal protection and electricity generation. A comparative study between CBW and SCBW is carried out physically in a two dimensions wide wave flume with dimensions 1.2*1.2*40 m and numerically using the Flow-3D model. The study checked the effect of the structures in merged, semi-merged, and submerged conditions and increased structure permeability. The reflection, transmission, and dissipation coefficients are used as the efficiency indicators. The results show that CBW is more efficient in wave dissipation, current velocity reductions, and bed stability than SCBW. It is recommended to use the CBW as a submerged protected structure within the recreational coastal areas.

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. [ABSTRACT FROM AUTHOR]

This paper experimentally explored the influence of the wave spectrum shape variation on breakwater design. The energy spectrum function generally considered for the design of coastal structures is the JONSWAP spectrum. The laboratory results were therefore used to assess the impact of changing the spectrum shape parameter (PEF). We analysed armour stability and wave overtopping in a wave flume with a geometric similarity ratio of 1:30. The experimental results showed that the PEF has maximum influence on overtopping and wave pressures on the crown wall. For a PEF value of 3.3, overtopping was much higher (30% to 100% higher) than with a PEF of 1. Pressure on the crown wall was 20% higher with a PEF of 3.3 in comparison with that for a PEF equal to 1. The stability of the breakwater's block armour is less sensitive to the PEF variation. [ABSTRACT FROM AUTHOR]

To protect the coastal areas of the seas and oceans from the destructive force of tsunami waves, coastal and surface barriers are usually built. However, for high waves, these barriers turn into underwater barriers through which tsunami waves pass practically without losing their energy. In this paper, we study a new principle of suppression of the energy of tsunami waves by underwater barriers. The problems of experimental and numerical modeling of the processes of generation, propagation, and interaction of gravity wave of the tsunami type with underwater barriers are considered. It is shown that, under certain conditions near the underwater barriers, large-scale vortex structures occur that accumulate a significant part of the energy of the incident wave. Here, if the barriers parameter h/(H + A) = 0.84 ÷ 0.85 (h—height of the barriers, A—amplitude of incident wave on a barrier, H—depth of the reservoir), then the vortex structures accumulate up to 50% of the wave energy incident on the barrier. A theoretical model explaining the effect of anomalous vortex suppression of tsunami wave energy by underwater barriers has been developed. Theoretical calculations and results of numerical modeling based on the Navier–Stokes Equations are consistent with experimental studies in a hydrodynamic wave flume.

The importance of coastal protection increases with the increase in coastal development. Soft and hard protection measures are the most used techniques; however, hard structures are still preferable. Hard structures are characterized by a long lifetime and high stability in rough sea states. Many innovative, environmentally friendly hard coastal protections measured have been proposed and used for specific applications. This research's main objective is to develop and check a new coastal structure, Corrugated Semi-circular Breakwater (CBW). This structure is modified from the Semi-circular Breakwater (SCBW), one of the hard protections used in Japan and China, to increase its efficiency in coastal protection and electricity generation. A comparative study between CBW and SCBW is carried out physically in a two dimensions wide wave flume with dimensions 1.2*1.2*40 m and numerically using the Flow-3D model. The study checked the effect of the structures in merged, semi-merged, and submerged conditions and increased structure permeability. The reflection, transmission, and dissipation coefficients are used as the efficiency indicators. The results show that CBW is more efficient in wave dissipation, current velocity reductions, and bed stability than SCBW. It is recommended to use the CBW as a submerged protected structure within the recreational coastal areas. [ABSTRACT FROM AUTHOR]

A novel concept of a surge wave energy converter for nearshore applications is investigated experimentally. The centimetre-sized prototype developed in this work represents a proof of concept of a submerged system, which entails a hybrid transduction solution for the electrical conversion of wave energy, that uses piezoelectric elements (PZEs) and dielectric elastomer generators (DEG). The idea is to exploit the horizontal pressure gradient and horizontal water velocity underneath the waves to compress the PZE and inflate each half wave period a soft variable capacitance, which composes the DEG. The electrical charges created by the PZE are used to polarize the DEG, which is able to multiply the input energy. This hybridization is conceived to allow the system to generate electrical energy from waves without conventional high voltage supplies, thus reducing production costs and allowing standalone clean electrical generation. The article provides the preliminary fluid-mechanical measurements performed in a wave flume with a first version of the prototype and supported by a model comprising the fluid/structure interaction, the materials response, and the electrical operations. An estimation of the output energy of a small-sized prototype in constant charge mode is computed, and perspectives for optimizing the system are presented. [ABSTRACT FROM AUTHOR]

This paper experimentally explored the influence of the wave spectrum shape variation on breakwater design. The energy spectrum function generally considered for the design of coastal structures is the JONSWAP spectrum. The laboratory results were therefore used to assess the impact of changing the spectrum shape parameter (PEF). We analysed armour stability and wave overtopping in a wave flume with a geometric similarity ratio of 1:30. The experimental results showed that the PEF has maximum influence on overtopping and wave pressures on the crown wall. For a PEF value of 3.3, overtopping was much higher (30% to 100% higher) than with a PEF of 1. Pressure on the crown wall was 20% higher with a PEF of 3.3 in comparison with that for a PEF equal to 1. The stability of the breakwater’s block armour is less sensitive to the PEF variation.

In this article, a meshless method based on exponential basis functions (EBFs) is presented to simulate the harmonic waves with moving free-surfaces generated by the piston-type wave maker. Accordingly, velocity potential is adopted in a Mixed Eulerian-Lagrangian (MEL) approach. Boundary conditions are met through a point-wise collocation approach. In order to update the geometry in the simulation time, the free surface points are only moved vertically. To reduce the reflection in the wave flume, a damping zone is added at the far end opposite to the wave maker, where the velocity is modified by adding an artificial damping term. The results indicated the ability of this numerical method in simulating free surface flow problems like non-linear waves with a good accuracy, as well as suitable performances and the least run time calculation.

Multiple reflections of the waves between structure and wavemaker in hydraulic flumes could change the frequency content of the desired incident wave or result in resonance. A prominent approach to avoid multiple reflections is active control of the wavemaker. This paper proposes a simple and practical active control algorithm for piston-type wavemaker. The block diagram of the control system is presented in real time domain. It is shown that there is no need to use any transfer function or filter in the feedback and feed forward loops and the use of constant gains can yield acceptable results. In the operating frequency range (0.25–2 Hz), it is revealed that the proposed system is very effective at suppressing the excitation of resonant sloshing for regular wave. In the case of irregular waves, it is depicted that the experimental waves agree quite well with the desired wave elevation in frequency domain. In addition, comparison of the results obtained both with and without absorption discloses the good characteristics in time domain. [ABSTRACT FROM AUTHOR]

Emerged breakwaters are structures that give protection to the ports infrastructure, so it is essential to have an appropriate knowledge of its behavior under the wave action. Waves generate several hydrodynamic effects on the breakwater, the stability of which is the object of this study. The study was realized in the Laboratorio de Ingeniería Hidráulica de la Escuela Superior de Ingeniería y Arquitectura - Unidad Zacatenco del Instituto Politécnico Nacional de México, in a wave flume with hydraulic generator of irregular waves and wave meter equipment controlled by computer. It was possible to analyze the behavior of two structures through wave measurement, photography and video, giving information that was compared with criteria found in the literature. [ABSTRACT FROM AUTHOR]

The horizontal elements of maritime structures are susceptible to both wave impact and resulting vibrations. These vibrations can lead to a partial or complete failure of structures and require detailed investigations. To address this issue, laboratory experiments were conducted in a wave flume. The aim of this study was to investigate the problem of standing wave impact underneath a horizontal deck. The main focus was on the effect of the wave-induced vertical forces on the global response of the structure. The physical model of the deck was installed above a still water level in front of a vertical barrier. The model was supported by a system of strings and springs. The mechanical system had one degree of freedom corresponding to a small rotational displacement around rear deck edge. Among other physical parameters, the impact pressure generated under the structure due to wave impact was measured. The high sampling frequency of the data acquisition system allowed to capture momentary slamming pressure. The systems of accelerometers and displacement gauges were installed to measure induced vibrations. Thorough analysis of the influence of wave parameters and the deck clearance on the structure response was performed based on the measurements. The rapid slamming force increase, recorded at the moment of impact is not revealed in the dynamic response of the plate. [ABSTRACT FROM AUTHOR]

Green water events may present different features in the initial stage of interaction with the deck of a structure. It is therefore important to investigate the evolution of different types of green water, since not all the events interact with the deck at the same time. In this paper, the evolution of three types of green water events (dam-break, plunging-dam-break, and hammer-fist) are studied. The water surface elevations and volumes over the deck in consecutive green water events, generated by incident [wave trains in a wave flume, were analyzed using image-based methods. The results show multiple-valued water surface elevations in the early stage of plunging-dam-break and hammer-fist type events. Detailed experimental measurements of this stage are shown for the first time. The effect of wave steepness on the duration of the events, maximum freeboard exceedance, and volumes were also investigated. Although the hammer-fist type showed high freeboard exceedances, the plunging-dam-break type presented the largest volumes over the deck. Some challenges for further assessments of green water propagation are reported.

This article presents a method for obtaining the spatial free surface elevation and velocity field for the water surface in a wave flume over a relatively large measurement area for this type of application (approximately 1.5 m × 1.5 m). The technique employs proprietary videogrammetry software to post-process stereo images captured by multiple synchronised machine vision cameras. Dimensional resolution and other limitations are similar to that experienced for particle imaging velocimetry systems (x, y resolution of 2 mm). Imaging of the free surface was enabled by the use of millions of bespoke slightly positively buoyant fluorescent flakes. Ultraviolet light was used as the primary light source to excite the fluorescent flakes. Reflected ultraviolet light was attenuated by a high-pass filter fitted to the cameras so that only the emitted light from the fluorescent flakes was visible. The software was validated using a simple linear translation experiment. An application is demonstrated for the radiated wave field generated from a submerged sinusoidal heaving sphere for two cases: one single and five consecutive oscillations. Results agree with linear wave theory which indicates that the floating flakes had minimal impact on the water surface particle motion at the scale tested. It is, therefore, concluded that spatial measurement of the free surface elevation and velocity using the method presented has good resolution over a large measurement field. The flakes were found to follow the free surface well, but the measurement area is constrained to where the pattern of flakes exists in the image. Hence, application of floating markers is not suitable for experiments with significant outflow/upwelling which would wash away the floating markers from the intended measurement area. [ABSTRACT FROM AUTHOR]

A study of the energy losses of tsunami-like waves due to the formation of large eddies near the underwater barriers has been gaining importance in recent years. However, the conditions of the birth of the large-scale vortex behind the barriers are not yet fully understood. The paper presents the results of theoretical, experimental and numerical studies of the interaction between the long gravitational tsunami-like waves and the impermeable underwater barrier. The proposed mathematical model is based on the approximation of two-dimensional incompressible Navier-Stokes equations. The OpenFOAM toolbox is used to perform the numerical simulation with the method of finite volumes. The air-water interface is identified by the volume of fluid method (VOF). The numerical simulation is tested via a comparison with test activities and experiments carried out in a hydrodynamic wave flume, at the Institute of Applied Mechanics Russian Academy of Sciences. The efficiency of the underwater barrier is assessed as the percentage of the energy loss to the incident wave energy. It is shown that the barrier effectiveness depends on its relative height and the incident wave parameters. New experimental and numerical results are consistent with the theoretical model proposed earlier and research results of other authors. • Detail reviewed the vortex-induced tsunami wave suppression mechanism using by experimental and numerical methods. • Theoretical justification for tsunami wave suppression through the recovery coefficient. • Clarified the optimum conditions at which the total energy of wave suppression would be the highest. [ABSTRACT FROM AUTHOR]

A comprehensive experimental study was carried out on the regular wave attenuation with a trapezoidal pontoontype floating breakwater (FB) in deep water. The functionalities of two simple FB geometries consist of a rectangle and a trapezoid with the slope of 60° were investigated under the wave attack. A two-dimensional wave flume was used in the experiment; the incident, transmitted waves, mooring line forces and motion responses of the floating breakwaters were measured. Also the influence of the sea state conditions (incident wave height and wave period) and structural parameters (draught of the structure) were investigated using the trapezoidal FB. Our experimental results indicated that the trapezoidal FB significantly reduced the wave transmission and mooring line force when compared with rectangular FBs. A new formula was developed in order to predict the value of the transmission coefficient in trapezoidal FBs with the slope of 60°. Experimental data showed to be consistent with the results of the formula. [ABSTRACT FROM AUTHOR]

The wave overtopping discharge at coastal defense structures is directly linked to the freeboard height. By means of physical modelling, experiments on wave overtopping volumes at sloped coastal structures are customarily determined for constant water levels and static wave steepness conditions (e.g., specific wave spectrum). These experiments are the basis for the formulation of empirically derived and widely acknowledged wave overtopping estimations for practical design purposes. By analysis and laboratory reproduction of typical features from exemplarily regarded real storm surge time series in German coastal waters, the role of non-stationary water level and wave steepness were analyzed and adjusted in experiments. The robustness of wave overtopping estimation formulae (i.e., the capabilities and limitations of such a static projection of dynamic boundary conditions) are outlined. Therefore, the classic static approach is contrasted with data stemming from tests in which both water level and wave steepness were dynamically altered in representative arrangements. The analysis reveals that mean overtopping discharges for simple sloping structures in an almost deep water environment could be robustly estimated for dynamic water level changes by means of the present design formulae. In contrast, the role of dynamic changes of the wave steepness led to a substantial discrepancy of overtopping volumes by a factor of two. This finding opens new discussion on methodology and criteria design of coastal protection infrastructure under dynamic exposure to storm surges and in lieu of alterations stemming from projected sea level rise.

The use of LiDAR as an alternative to an array of in-situ instruments for water elevation measurement, specifically in the surf zone, is covered in detail. This paper outlines the advances in remote sensing of the coastal environment and provide both laboratory and field observations obtained through the application of LIDAR scanning devices. The results of this paper show a good correlation between LiDAR and pressure transducer measurements of water elevation in both a wave flume and within the surf zone (mean coefficient of determination of 0.76 and 0.89 respectively). The water surface reflectivity of the study area needs to be maximised in order for the LiDAR to provide suitable measurements, therefore a method of seeding in the wave flume is described. Points to consider for the setup of the LiDAR instrument in both the laboratory and the field are discussed, as well as the influence that wave parameters such as wave height and wave period have on the quality of results. Free surface elevation data across the spatial and temporal domain can be obtained with LiDAR and used for a wide range of wave analyses. [ABSTRACT FROM AUTHOR]

Lake Taihu is a typical shallow lake which frequently happens sediment resuspension induced by wind-induced waves. The experiments are carried on to simulate the wave disturbance processes in wave flume by setting a series of wave periods (1.2 s, 1.5 s, 1.8 s) and wave heights (2 cm, 10 cm). It aims to analyze the characteristics of sediment resuspension and the mechanisms of nutrients release and to evaluate the effects of sediment dredging on sediment resuspension and nutrients release in Lake Taihu. The results show that wave shear stress during 2 cm and 10 cm wave height processes ranges 0.018–0.023 N/m 2 and 0.221–0.307 N/m 2 , respectively. Wave shear stress has no significant differences between wave periods. Wave height has much more effects on sediment resuspension. Wave height of 2 cm could induce total suspended solids (TSS) reaching up to 5.21 g/m 2 and resuspension flux of sediment (M) up to 1.74 g/m 2 . TSS sharply increases to 30.33–52.41 g/m 2 and M reached up to 48.94 g/m 2 when wave height reaches to 10 cm. The disturbance depth under different sediment bulk weights ranges from 0.089 to 0.161 mm. Variation of suspended solids in 3 layers (1 cm, 5 cm, 20 cm above sediment interface) has no significant differences. Organic matter, TN and TP have positive relationship with SS. Organic matter is only accounted for 5.7%–7.3% of SS. The experiments under different sediment bulk densities (1.34 g/cm 3 , 1.47 g/cm 3 and 1.59 g/cm 3 ) find that TSS and M fall by 44.2% and 39.8% with sediment bulk density increasing, respectively. Total TN, DTN, TP and DTP decrease by 24.3%–33.6%. It indicates that sediment dredging could effectively reduce SS concentration and nutrient levels in water column. The researches provide a theoretical basis for sediment dredging to control the shore zone of Lake Taihu for lake management. [ABSTRACT FROM AUTHOR]

Wave-induced liquefaction of silty seabed is a common submarine geological hazard that poses a significant risk to the safety of marine structures. The liquefied seabed exhibits fluid properties and fluctuates with the overlying wave. To investigate the interaction between waves and the liquefied seabed, a wave flume experiment was conducted to simulate the wave-induced liquefaction process. During the experiment, the variation in the fluctuation trajectory and viscosity coefficient of liquefied silt with the wave intensity and liquefaction process were measured. Additionally, the wave energy dissipation due to seabed liquefaction was analyzed. The results indicate that the viscosity coefficient of the liquefied seabed is closely related to the wave intensity and liquefaction process, with the viscosity coefficient of the liquefied seabed being larger in the liquefaction deposition stage than in the liquefaction development stage. Seabed liquefaction can lead to a considerable increase in wave energy dissipation, up to 15 times greater than when the seabed is stable. Furthermore, wave energy dissipation is greater for high waves than for low waves conditions. The primary factors causing wave energy dissipation are the viscosity friction inside the liquefied seabed and the suspended sediment in the upper water column. • Motion trajectory and viscosity coefficient of liquefied silt are measured. • Wave attenuation due to silty seabed liquefaction is experimental and numerical investigated. • Mechanisms of wave attenuation caused by stable/liquefied silty seabed are analyzed. [ABSTRACT FROM AUTHOR]

Physical model tests were performed in a wave flume at Deltares with rock armoured slopes. A shallow foreshore was present. At deep water, the same wave conditions were used, but by applying different water levels, the wave loading on the rock armoured slopes increased considerably with increasing water levels. This allowed an assessment of the effects of sea level rise. Damage was measured by using digital stereo photography (DSP), which provides information on each individual stone that is displaced. Two test series were performed five times. This allowed for a statistical analysis of the damage to rock armoured slopes, which is uncommon due to the absence of statistical information based on a systematic repetition of test series. The statistical analysis demonstrates the need for taking the mean damage into account in the design of rock armoured slopes. This is important in addition to characterising the damage itself by erosion areas and erosion depths. The relation between damage parameters, such as the erosion area and erosion depth, was obtained from the tests. Besides tests with a straight slope, tests with a berm in the seaward slopes were also performed. A new method to take the so-called length effect into account is proposed to extrapolate results from physical model tests to real structures. This length effect is important, but is normally overlooked in the design of rubble mound structures. Standard deviations based on the presented model tests were used.

This paper investigates on a Wave Energy Converter (WEC) named Energy & Protection, 4th generation (EP4). The WEC couples the energy harvesting function with the purpose of protecting the coast from erosion. It is formed by a flap rolling with a single degree of freedom around a lower hinge. Small-scale tests were carried out in the wave flume of the maritime group of Padua University, aiming at the evaluation of the device efficiency. The test peculiarity is represented by the system used to simulate the Power Take Off (PTO). Such dummy PTO permits a free rotation of two degrees before engaging the shaft, allowing the flap to gain some inertia, and then applying a constant resistive moment. The EP4 was observed to reach a 35% efficiency, under short regular waves. The effects, in terms of coastal protection, are small but not negligible, at least for the shortest waves.

The present paper deals with a study of the damping induced by a turbine in the power take off of an small scale Oscillating Water Column Wave Energy Converter. In order to study the turbine-induced damping, an experimental setup was built. The experimental setup consists of a wave flume 2000 mm long, 190 mm high and 96 mm wide with an impermeable beach as a dissipative system at the end to avoid wave reflections. The system is all built in Plexiglas to allow optical real-time observation. An Oscillating Water Column chamber model was placed in the measurement area between the wave-maker and the dissipative beach. The chamber was 37 mm long, 200 mm high and 96 mm wide also built in Plexiglas. In order to study the effect of turbine-induced damping on the system, a calibrated and variable hole was used to simulate the turbine presence, while outflow and inflow air velocity were measured by means of Particle Image Velocimetry (PIV) method. Pressures and velocities of air and water as well as the free water surfaces evolution were measured at different wave frequencies and heights. [ABSTRACT FROM AUTHOR]

Experimental investigations were carried out to assess the wave reflection characteristics of slotted vertical barriers with an impermeable rear wall. This study was carried out to investigate whether these barriers can be used instead of sloped rubble mounds, which occupy a significant area in ports/harbors/marinas, for wave energy dissipation. Thirty-seven different wave barriers (1 vertical wall, 6 different sloped breakwaters, and 30 slotted vertical barriers with porosity in the range of 10-50% and 1-6 slotted barriers) were tested in random wave fields of the JONSWAP spectra in different combinations of significant wave heights and peak periods. For relatively long waves (water depth/wavelength ratio of d/Lp>0.2), the performances of many combinations of slotted vertical barriers were much better than those of the conventional sloped rubble-mound breakwaters. The results of this study show that by increasing the number of porous walls from one to six, it is possible to reduce the value of the reflection coefficient from 0.9 to 0.3, especially for a d/Lp greater than 0.2. Also, the results show that for a d/Lp less than 0.2, increasing the number of porous walls did not significantly reduce wave reflection. Overall, these results suggest that slotted barriers can be a good alternative to sloped rubble breakwaters for ports, harbors, and marinas, especially in places where good-quality stones are expensive. In addition, this solution helps increase the effective use of space inside the harbor better than do sloped rubble-mound structures. [ABSTRACT FROM AUTHOR]

Experimental tests on the interaction between waves and a submerged rubble-mound breakwater (SBW) were performed in the wave flume at the Institute of Hydroengineering PAS in Gdańsk (Poland). A model of a submerged breakwater was prepared based on the constructions built in 2006 in the Polish zone of the Baltic coast, in Gdańsk Bay, in the region of Gdynia Orłowo (Orłowo Cliff). The tests were carried out for regular waves (varying parameters: height, period, length, and steepness) whose parameters were determined on the basis of the actual wind field occurring in Gdańsk Bay. The experiment was conducted for two water levels corresponding to the actual long-term mean sea level (msl) of 500 cm as well as a storm surge of 550 cm. The research has focused on the analysis of the amount of wave energy transmitted into the lee region and the determination of parameters that affect the transmission size. Types of wave-breaking were described based on the extensive video and photographic documentation prepared during the measurements. Based on the results obtained from the experiment and the previous research on the functioning of submerged breakwaters in the coastal zone, including both numerical modelling as well as field research and field observations, the efficiency of the structure was assessed. [ABSTRACT FROM AUTHOR]