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A marine geophysical survey was carried out over the ruins of the ancient Eunostos harbor, in front of the recent western harbor of Alexandria. The survey works aimed to study the seafloor and the subsurface layers over the survey area using side-scan sonar and sub-bottom profiler. It is attempted to identify the impact of nature and geo-hazards on the coast of the submerged ancient harbor. Numerous ridges, reefs and breakwaters which protected the port from the northern swells were detected on the acoustic images of the side-scan sonar. In addition to some undefined artifacts and ancient coastal scars were noticed across the seafloor. Seismic interpretations also showed series of shallow diffractions that generally intensified towards east and north. Also deformed and disturbed subsurface layers were noticed beneath the area of the submerged ancient harbor. Side-scan sonar and sub-bottom profiler findings are concordant with the descriptions of the ancient literature and succeeded to confirm the vulnerability of the ancient coastal harbor to natural disasters during the past times. [ABSTRACT FROM AUTHOR]

In ocean engineering, breakwater plays a crucial role in protecting coastal structures such as bridge pier from the impact of extreme sea waves. However, enhancing the existing breakwaters' ability to withstand extreme wave remains an urgent issue to address. This study explores the reinforcement strategy of breakwater against extreme sea waves by installing seawalls on the breakwater. Utilizing dam-break wave generation techniques to simulate tsunamis, the study experimentally evaluates the effectiveness of seawalls in reducing the tsunami forces exerted on bridge pier model and numerically investigates the tsunami forces on the seawalls. The focus of this research is to analyze the pressure distribution on seawalls and the impact of different seawall configurations on the reduction of tsunami forces on bridge pier model. Results show that: Under the tested wave condition (a) The height of the seawall on the breakwater is a critical parameter, as increasing wall height reduces the tsunami forces exerted on the bridge pier behind it. The taller seawalls are subjected to greater tsunami forces in tested cases; (b) The trend of extreme pressure values for different seawalls starts increasing at the bottom and then decreases; (c) There is a critical distance that the breakwater being most effective at reducing tsunami impact forces between the bridge pier model and the breakwater. This study not only deepens the understanding of the interaction between tsunami waves and seawalls but also offers practical guidance for designing structures with disaster resilience, significantly influencing the future design and construction of tsunami-resistant coastal infrastructure. • New designs for protecting bridge piers from tsunamis are presented. • Efficacy of setting seawalls on breakwaters are experimentally tested. • Various seawall and breakwater configurations are comparatively studied. • Hydrodynamic behaviors of seawall structures are numerically analyzed. [ABSTRACT FROM AUTHOR]

In a complex marine dynamics environment, the consideration of fluid-structure-seabed interaction (FSSI) plays a vital role in reliably analyzing the dynamic response of marine structures, and in assessing their structural dynamic stability. Currently, the predominant numerical analysis used worldwide for the problems of wave-seabed interaction and seawater-structure-seabed interaction is primarily the one-way coupling method. While only a few two-way coupled models are being developed. Consequently, two issues are brought up: (1) For the cases involving small deformation and displacement, the degree of discrepancy can't be quantitatively identified between the results obtained respectively from one-way coupling models and two-way coupled models which are more rigorous in mathematics and physics. (2) For the cases involving large deformation and displacement, one-way coupling models should be non-applicable. To address this problem, this study first proposes an explicit two-way coupling theory for the fluid-structure-seabed interaction. Then, a two-way coupled numerical model is developed by integrating the soil-structure dynamics software FssiCAS, and an OpenFOAM-based CFD solver OlaFlow by utilizing the data exchange library preCICE. This two-way coupled model has been embedded into the software FssiCAS. The reliability of the developed two-way coupled model is systematically validated through a rigorous verification process. Subsequently, a comparative study is conducted between the newly developed two-way coupled model and the existing one-way coupling model, to investigate the ocean wave-seabed interaction, as well as the interaction process between ocean wave, a breakwater, and seabed foundation. A comprehensive analysis is performed by comparing the differences in the wave profiles in fluid domain, dynamic displacement of structure and seabed foundation, seepage, pore pressure accumulation, and liquefaction in seabed foundation solved by the two-way and one-way coupled models. Finally, the suitability of the one-way and two-way coupled models in different applicable scenarios was discussed. • A generalized framework of two-way coupled numerical model is developed for Fluid-Structure-Seabed Interaction. • FssiCAS and OlaFlow are taken as the soil-structure dynamics module, fluid dynamics module respectively. • The open-source library preCICE is taken as the data exchanger coupling FssiCAS and OlaFlow together. • The two-way coupled model is utilized to explore the intrinsic interaction between waves, structures, and seabed foundations. • Unique streamlines structure of seeping in seabed, and liquefaction behind breakwater by seawater overtopping are observed by adopting the two-way coupled model. [ABSTRACT FROM AUTHOR]

A theoretical model based on the linear potential flow theory and eigenfunction expansion-matching method is developed to analyze the interaction between water waves and multi-chamber oscillating water columns (OWCs) embedded in a caisson array. The semi-analytical solution consists of the diffraction and radiation components of periodic OWCs. The velocity singularity at the tip of the OWC chamber walls is resolved by implementing a Chebyshev polynomial expansion. The unknown expansion coefficients are determined by the continuity equations of velocity and pressure at the interface of subdomains. The semi-analytical solution is verified using the Haskind relation and the conservation law of wave energy flux. It is found that multi-chamber OWCs have higher hydrodynamic efficiency over a broader frequency bandwidth than traditional single- and dual-chamber OWCs. The maximum hydrodynamic efficiency η increases with increasing of chamber number (J), from 0.5 (J = 1) to nearly 1.0 (J = 8 and 12). It is also found that a larger incident wave angle leads to a narrower frequency bandwidth for energy capturing. Increasing the incident wave angle from π/3 to 5π/12 results in a decrease of the first cutoff frequency k c from 2.41 to 2.02, and therefore results in the energy capture bandwidth narrowing accordingly. Both constructive and destructive hydrodynamic interactions between caissons array and OWCs are observed over the tested frequency range. Interestingly, when configuration of the OWC chambers is reversed, the transmission coefficient remains unchanged. • A theoretical model for wave interaction with multi-chamber OWCs embedded in a caisson array is developed. • Multi-chamber OWCs achieve a higher hydrodynamic efficiency than the single- and dual-chamber OWCs. • Both constructive and destructive hydrodynamic interactions between OWCs and the caisson array are observed. [ABSTRACT FROM AUTHOR]

This study aims to propose an efficient approach to calibrate the load and resistance factors (LRFs) for the limit state design of breakwater foundations. The spatial variability of soil was considered by employing the Cholesky decomposition technique. To overcome the low computational efficiency of the Monte Carlo simulation (MCS), a response surface method (RSM) was utilized. Additionally, an efficient algorithm, namely the adaptive boundary-based particle filtering algorithm (ABB-PFA), was proposed with the use of RSM to automatically and quickly search optimal nominal values of random variables in the LRF calibration process. Noticeably, the optimal number of particles and values of the modification factor used in the ABB-PFA were observed to enhance the efficiency of the calibration process. The results showed that the computational efficiency of the calibration process is significantly increased by utilizing the response surface method and the proposed ABB-PFA. The efficiency increases the most if the number of particles is one and the value of the modification factor is 0.5 or 0.6. The influences of the random field element size on the efficiency of the calibration process were also investigated. By using the appropriate size, the efficiency is significantly increased while still obtaining a high accuracy of the LRFs calibration process. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive investigation of the storm damage at a commercial port located in the Southwestern Black Sea Region that occurred on January 18–19, 2018. One week after the event, a field survey was conducted at the port focusing on significantly damaged mound breakwaters and protection structures that failed at several sections. A numerical wave modeling study is carried out to estimate the wave characteristics at deep sea, nearshore, and inside the port to assess the observed damage during the field survey. Widely used numerical models WAVEWATCH III, SWAN, and SWASH are utilized using nested computational domains and calibrated based on satellite measurements. As a result, the significant wave height of the storm is estimated as 7.8 m with a peak period of 12.4 s near the port area, approaching mainly from the northwest direction. The damage mechanisms of the mound structures are discussed based on the field observations and the wave modeling studies. The insufficient seaside armor unit sizes and the orientation of the breakwaters are found to be the main reasons for the damage. • Major damage, including failure of mound breakwaters at a port, is investigated. • The characteristics of the waves that caused the damage were estimated using calibrated models. • Damage mechanisms of the protection structures are discussed in detail. [ABSTRACT FROM AUTHOR]

To facilitate a comprehensive exploration of the wave energy conversion process of a full-scale Oscillating Water Column (OWC), encompassing primary-stage (from wave energy to pneumatic power), secondary-stage (from pneumatic power to mechanical power), and third-stage (from mechanical power to electric power) conversions, together with an estimation on the electric power output, a fully coupled model aimed at an OWC-turbine-generator-breakwater integrated system is established, in which an impulse turbine with a U-shaped air duct is employed. Owing to the superior steady-state characteristics (working independently) of the U-shaped air duct turbine, the transient-state (characterized by reciprocating airflow induced by incident waves and embedded into an OWC-breakwater system) characteristics is further explored across a wide spectrum of external excitation conditions. The integration of the chamber-turbine-generator system into a vertical breakwater reveals that an increase in the load torque coefficient corresponds to a consistent rise in the primary-stage conversion efficiency. Opting for a medium load torque coefficient maintains a satisfactory overall efficiency and results in a maximum electric power output of 11.59 kW. In addition, the height of guide vanes significantly influences airflow through the air duct, impacting primary-stage conversion efficiency. Optimal turbine efficiency is attainable under the medium guide vane height, with electric power output ranging from 4.08 kW to 11.66 kW. Moreover, in both free-spinning and forced-spinning modes, the adoption of the U-shaped air duct turbine surpasses the I-shaped turbine in overall conversion efficiency of the integrated system, indicating its superior potential for the utilization of wave energy in nearshore areas. The coupled analysis and power generation prediction model of the OWC-turbine-generator-breakwater integrated system established in this study can serve as a basis for the array deployment of such devices and the scalable development of wave energy. • A system with an OWC device, impulse turbine, generator and breakwater was studied. • Multi-stage wave energy conversion process and electric power output were evaluated. • A novel impulse turbine with a U-shaped air duct was studied under two scenarios. • Effects of the load torque and guide vane height on the power generation were tested. • The integrated system employing a U-shaped turbine surpasses the I-shaped turbine. [ABSTRACT FROM AUTHOR]

In order to enhance the conversion efficiency and optimize the hydrodynamic performance of the OWC device, a novel combined system composed of a pile-based OWC chamber and a perforated wave-eliminator is proposed. The schemes with rectangular front wall M1, elliptical front wall M2, M3 are designed. Physical tests and numerical simulations were conducted for the hydrodynamic process under the action of wave of the system with H / d = 0.16, 0.20, 0.24 and L / B = 3.3, 3.8, 4.3, 4.7, 5.2, 5.5, 6.4. The obtained-results show that the system has better energy converting and wave eliminating performance than the other existing systems. Its maximum conversion efficiency ξ is up to 70%, while its transmission coefficient C t is less than 0.45. Compared to M1 and M2, M3 can improve the efficiency ξ of the system (up to approximately 35%) and reduce the maximum force exerted on the system (up to 10%). When studying the forces on the combined system, the horizontal force (in the direction of wave propagation) can be primarily calculated by considering the force exerted on the chamber. However, when investigating the vertical forces (opposite to gravity) acting on the system, both the OWC chamber and the wave-eliminator need to be considered. The research results can provide valuable references for further design optimization of OWC devices. • A novel OWC- breakwater combined system was proposed. • The energy conversion and wave dissipation effect were studied. • The force and flow flied characteristics were analyzed. • The effect of wave elements on system performance was considered. • The efficiency is up to 0.7, max-transmission coefficient is less than 0.45. [ABSTRACT FROM AUTHOR]

A low-cost methodology is proposed to provide settlement data for solid blocks in order to improve the design of future coastal structures. Two methods were used to determine how far the block was sinking at the sandy bottom: topographically (four field campaigns) and continuously (with two pressure sensors) for 7.5 months. Settlement values obtained were similar in both cases. The difference between both methods at most 2 cm. Half of the sink occurred in the first week. Over the next month, the rate of sinking slowed down until a storm ended it all. Subsequently, the blocks remained stable. A comparison with other researchers' data was performed and significant differences were found. This heterogeneity in behaviour necessitate the use of these types of low-cost tests that would help calibrate both physical and numerical models. • A new affordable way to find out absolute and relative values of concrete block sinking in the sea bottom is shown. • The methodology showed here is a very low cost technique. • Real data of a practical case of great utility for the calibration and validation of physical and mathematical models are also presented. • Amount the results, it is worthy of to highlight that most of the sinking was observed in the first week. [ABSTRACT FROM AUTHOR]

In this paper, oblique water wave interaction with a surface piercing box-type porous structure placed in front of a vertical rigid wall is investigated in the presence of current, which flows parallel to vertical wall. The current speed is considered distinct in different subdomains. However, in a particular subdomain current speed is uniform throughout the water depth. In this analysis, Sollitt and Cross model is used for the study of wave motion inside the porous structure. Employing small amplitude linear water wave theory, the present model of our interest is developed into a boundary value problem and solved analytically using the eigenfunction expansion method. Using the developed solution, the reflection coefficient and hydrodynamic wave forces on porous structure are computed for different values of parameters: the dimension of porous structure, the friction coefficient of porous structure, the current speed of following current and opposing current. This research paper suggests that suitable arrangement of rigid walls and surface-piercing partially extended porous structures can be an effective and economical approach for guiding ocean currents and protecting marine facilities against wave attacks. • Oblique wave trapping in the presence of current and porous structure is discussed. • Boundary value problem solved analytically using the eigenfunction expansion method. • Wave forces are higher for following current speed than the opposing current speed. • Node of standing waves are formed on the rear face of the porous breakwater. [ABSTRACT FROM AUTHOR]

A wave resource characterisation is presented for the French Basque coastal region, with a specific focus on Bayonne nearshore area. The study is derived from a 10-year hindcast computation performed with a very high-resolution coastal implementation of a SWAN model. After a detailed validation of the model in intermediate and shallow water, the spatial, temporal, and spectral distributions of the local nearshore wave energy climate are characterized. Refraction over a local submarine canyon splits the coastal domain into two main regions with different general characteristics. In the southern Basque region, the spatial fluctuations of the wave resource increase drastically in shallow water. Variability nearshore was shown to be significantly higher than over the deeper part of the shelf. Noticeable hot-spots are found in the nearshore area around Bayonne, where the local wave resource substantially exceeds the outer shelf incident energy flux. Seasonal to hourly temporal fluctuations are also characterized at different nearshore locations and found to be very pronounced. The major wave resource variations found at reduced space-time scales highlight the strong influence of local small-scale bathymetry features in the Basque nearshore region. [ABSTRACT FROM AUTHOR]

Harnessing the advantages of geotextile sand containers (GSCs), numerous submerged breakwaters and shoreline protection structures have been constructed worldwide. But an emerged breakwater structure with geotextile armour units, capable of replacing the conventional structures, is rarely discussed. A 1:30 scaled physical experimentation is chosen as a preliminary investigation to test the feasibility of using GSCs as breakwater armour units. Structural design is evolved based on a comprehensive literature survey. The paper focuses on the stability parameters and damage characteristics of the proposed structure. Four different configurations are subjected to waves, confining to Mangaluru's wave parameters. Effect of armour unit size and sand fill ratio on the stability of the structure is analysed and it is concluded that changing sand fill ratio from 80% to 100% shot up the structural stability to a maximum of 14%. Increasing bag size also resulted in the increased stability up to 8%. Experiments revealed that the best performing configuration could withstand wave heights up to 2.7 m. Stability curves for all tested configurations are discussed and can serve as an effective guideline for designing GSC breakwaters. • Feasibility of using geotextile sand containers (GSCs) as armour units of breakwaters is investigated. • Existing GSC protection works and its design recommendations are extensively reviewed. • Novel stability curves developed through experimentation can be used as a design guideline for GSC structures. • Effect of GSC size, sand fill ratio and water depth in the stability of the structure is identified. • Serves as pilot data for numerous studies that may be adopted by changing various structural parameters. [ABSTRACT FROM AUTHOR]

A wave flume is used to study a scaled model of a stepped bottom dual-chamber Oscillating Water Column (OWC) installed onshore. Compared to traditional single-chamber OWCs, the use of dual-chambers is expected to widen the range of sea states in which the OWC is more efficient, and the step, in front of the first chamber, boosts the capturing energy capacity of the device. The Power Take-Off (PTO) system is modelled as an air opening in the pneumatic chambers. Several experiments combining regular incident waves and PTO damping conditions are performed. Results of the amplitudes of the free surface elevations inside the chambers show that the device can amplify the incident wave amplitude up to 1.57 times in chamber 2. Results of the primary efficiency show that the device is highly dependent on the PTO damping characteristics and can reach around 40% for a wide range of wave periods. Results of the reflection analysis show that the reflection coefficient is also dependent on the PTO damping characteristics but remain lower than 0.6 for all the studied cases. Sloshing phenomenon (mostly in the cross-section direction) was observed for a wavelength close to the cross-section dimension, impacting negatively on the device pneumatic performance. • A wave flume is used to study a scaled model of a dual-chamber Oscillating Water Column device installed onshore. • The Power Take-Off system is modelled as an air opening in the pneumatic chambers. • Results show that the primary efficiency of the device is highly dependent on the Power Take-Off damping characteristics. • For the studied cases with higher damping configurations, the primary efficiency of the device can reach around 40%. [ABSTRACT FROM AUTHOR]

A novel triple oscillating floater wave energy converter (WEC)-breakwater hybrid system was proposed to harvest wave energy and protect coast. A series of comprehensive laboratory experiments were conducted to investigate the effects of varying power take-off (PTO) and configuration of floaters on wave energy conversion and attenuation efficiency under regular and irregular waves. Wave energy reflection, transmission, loss and conversion are derived from experimental data to identify the optimum PTO damping force and draft of the floaters. It was found that as the initial draft gradient of floaters or PTO damping increases, the floater displacement and the wave transmission decreases, and the system makes the transition from a dissipative to reflective state. When the PTO damping of three floaters increases towards the wave maker, the wave energy absorption is largely determined by the draft gradient of three floaters, as the draft of each floater dictates the energy losses. In addition, the hybrid system with different PTO damping for each of the three floaters, exhibits an optimum frequency bandwidth for both wave power conversion efficiency (K e exceeding 20%) and wave attenuation. Remarkably, the present WEC-breakwater hybrid system is capable to achieve high efficiency in wave power conversion and wave attenuation at the same time, particularly for irregular waves. [ABSTRACT FROM AUTHOR]

Details of the failure characteristics of composite-type breakwaters reinforced by rubble have not been clarified, including the prehension of some failure modes and the conditions that cause each mode. In this study, details of the failure characteristics and a performance assessment method were studied using two approaches, namely, centrifuge model tests and a circular slip analysis. The model tests showed that sliding failure could occur when the friction between the mound and the caisson was low, the caisson was wide, and the reinforcing embankment was high and/or wide. In contrary cases, bearing capacity failure was liable to occur. Basically, the larger the reinforcing embankment size, the greater the strength and stiffness. The performance assessment using a circular slip analysis and considering failure modes was verified through discussions. The analysis resulted in the underestimation of the stability of the reinforced breakwaters when the rubble was angular. However, the caisson moved to a certain degree even with a relatively lower load and the displacement reached that which is allowable by the structure. Consequently, a circular slip analysis was deemed suitable for evaluating the performance of reinforced breakwaters. [ABSTRACT FROM AUTHOR]

This paper presents a formula to estimate the stable weight of a rubble mound for breakwaters, considering the tsunami-induced overflow and seepage flow, based on the theoretical force balance among the frictional resistance of the rubble mound, the tractive force of the water flow over the caisson to the rubble mound and the seepage force of the rubble mound through the breakwaters. A series of hydraulic model tests was conducted on the scale of 1/100 for the Kamaishi Harbor Mouth Breakwaters in order to confirm the effectiveness of the proposed formula. Using the test results, the stability of rubble mounds for breakwaters was evaluated from the geotechnical engineering and hydrodynamical points of view. [ABSTRACT FROM AUTHOR]

• The wave diffraction problem by arrays of cylinders in front of a vertical wall, with infinite or finite length is examined. • The employed solution method relied on the multiple scattering approach and the direct matrix inversion method. • Two different cylinder arrangements have been investigated (i.e. a bottom-fixed and a floating cylinder array). • Additional resonances arising around the trapped and the near trapped modes for the array in front of a breakwater. The present paper deals with the investigation of the interaction phenomena of regular waves with arrays of circular cylinders either bottom-mounted or floating in front of a vertical breakwater of infinite and finite length. The acting loads on the array have been modeled using an analytical solution to the diffraction problem. The method of images is applied to define the fluid flow around the bodies of the array in front of a breakwater of infinite length, whereas the finite-length breakwater is represented by an elliptical cylinder with zero semi–minor axis. The multiple scattering approach and the direct matrix inversion method are compared to describe the hydrodynamic interaction phenomena among the members of the array. Focus is placed on the so called "near trapped" mode phenomena, created by an array of finite length, associated to the presence of the breakwater supplemented by representative numerical results concerning the exciting loads on the cylindrical bodies. [ABSTRACT FROM AUTHOR]

Since Gangneung Harbor breakwaters were built in the east coast of Korea from 1992 to 2002, the shoreline inside the harbor had severely changed as it was accreted in the area inside the harbor but eroded further south during the observation period (1979–2005). We investigated this process using Telemac-2DH model to calculate flows, waves, sediments and morphological changes in unstructured grids. The performance of the model was validated using the experiment data by Graven and Wang (2007). The model was run in two cases by turning on/off the diffraction mode using the formula by Holthujisen et al. (2003). For this, we tuned the model by setting a shadow zone behind the breakwaters and by applying the diffraction formula only inside the shadow zone. The model results showed that wave heights significantly increased inside the shadow zone when the diffraction mode was on, compared to the case when the diffraction mode was off. This effect of diffraction was confirmed by the observations as the wave heights measured inside the shadow zone became 10–20% lower than those measured outside, which were nicely simulated by the model. In addition to the wave height, the wave-induced currents became stronger in the innermost area of the shadow zone with the diffraction mode. The model also successfully predicted the observed morphological change pattern because it simulated the shoreline erosion at the southern end of the shadow zone where the currents were bifurcated. Inside the shadow zone, sediment deposition occurred, corresponding to the observation, when the diffraction mode was on, whereas this deposition process was not simulated when the mode was off. The results support that the observed shoreline accretion in the harbor was mainly due to the reduced wave and current energy, which emphasizes the importance of accurate modelling of diffraction effect in the prediction of shoreline evolution. [ABSTRACT FROM AUTHOR]

The combined method, in which the design shear strength is determined based on the comparison between the unconfined compressive strength and the CU (Consolidated Undrained) triaxial test, called the combined method, was applied in the extension project of the breakwater at the Port of Sakai. The existing breakwater had been constructed on intermediate soil after ground improvement, as the design strength of the ground was determined by the unconfined compressive strength. Based on the design strength determined by the combined method, the breakwater was constructed without any improvement. Hence, it was confirmed that the use of the combined method to determine the strength of intermediate soil is an effective approach for reducing the costs and time of constructing a breakwater. [ABSTRACT FROM AUTHOR]

A bottom-hinged flap breakwater is proposed for the wave attenuation and coastal protection. A series of laboratory experiments and a CFD numerical model were conducted to investigate the hydrodynamic characteristics in regular waves. The hydrodynamic coefficients, dimensionless maximum point pressure and average pitching amplitude of flap were examined with the parameters of incident waves and flap property. As the incident wave steepness increased, the wave reflection coefficient K r , wave transmission coefficient K t , dimensionless maximum point pressure p max / ρ w gh , and average pitching amplitude of flap θ a increased for a given wave period; however, the wave dissipation coefficient K d decreased. As the flap relative height increased, K r and θ a increased for a given wave period; whereas, K t decreased. Furthermore, as the flap density ratio increased, K r , p max / ρ w gh , and fitted K d increased; however, K t and θ a decreased. As the equivalent damping coefficient ratio increased, K r and p max / ρ w gh increased; however, K t and θ a decreased. Additionally, a series of dimensionless parameters of incident waves and flap property were used to derive formulas for K r , K t and K d , which were validated using the related data. • A bottom-hinged pitching flap breakwater is proposed for the wave attenuation and coastal protection. • Laboratory experiments are conducted to study the hydrodynamic characteristics of the device in regular waves. • A numerical model is used to simulate the pitching motion of the bottom-hinged flap. • The hydrodynamic coefficients and flap average pitching amplitude are examined with the wave and flap parameters. • The prediction formulas are conducted to assess the hydrodynamic coefficients of the flap with an acceptable accuracy. [ABSTRACT FROM AUTHOR]

Breakwaters are coastal structures typically used to protect shorelines from coastal erosion by providing wave energy attenuation and reflecting amounts of wave currents. Traditional breakwaters made of impervious materials can have a significant environmental impact, disrupting the coastal ecosystem and altering natural wave patterns. In general, permeability has become an acquainted characteristic since it directly influences the interaction between the structure, the coastal zone behind it, and the lateral zone without structural protection, which makes pervious concrete a sustainable alternative to traditional concrete. In this study, pervious concrete is utilised as a permeable breakwater considering the influence of permeability introduced to deliver ecological friendliness defence for shorelines. A physical experiment was used to evaluate four models of structures that varied in porosity in order to study the physical properties and then analyse the performance of the pervious concrete breakwater over the solitary wave impact. Subsequently, the hydrodynamic scattering coefficient is analysed by considering changes in physical parameters. The results indicated that pervious concrete breakwater (PCB) could effectively work in the case of emergence due to the increased interaction between wave and structure. PCBs can effectively reduce wave reflection and increase wave transmission, with the magnitude of these effects increasing with porosity. The result indicated the potentiality of PCB to serve as a feasible alternative to traditional breakwaters for a prospective coastal protection structure by reducing the environmental impact as PCBs allow for the passage of water and other marine organisms, which can help maintain the health of coastal ecosystems. Finally, the structure of PCBs, which can be prefabricated, could reduce the complexity and time of installation, making them a cost-effective solution for coastal protection. • Sustainable Coastal Defense: Explore pervious concrete breakwaters (PCBs) as eco-friendly alternatives, minimizing environmental impact on coastal ecosystems. • Enhanced Permeability: Pervious concrete's inherent permeability benefits ecological balance, enabling water flow and marine life passage, supporting coastal ecosystem health. • Wave Attenuation Boost: Physical experiments show porous concrete breakwaters (PCBs) effectively dampen solitary wave impacts, lessening reflection and enhancing transmission. Increased porosity amplifies these effects. • Cost-Efficient Defense: Emphasizing prefabrication, porous concrete breakwaters (PCBs) offer a streamlined and cost-effective coastal protection solution, reducing complexity and installation time versus traditional options. [ABSTRACT FROM AUTHOR]

This paper develops a Smoothed Particle Hydrodynamics (SPH) model to simulate wave interaction with elastic thin structures. This is achieved by coupling the δ -SPH and the Total Lagrangian SPH (TL-SPH) models for solving the fluid and structure phases, respectively. To this aim, a multiresolution algorithm within the ghost particles framework is introduced in order to treat the thin elastic components of the structure. The main idea of the proposed technology is to evaluate the hydrodynamic forces acting on the structure and the elastic dynamic at the finest solid particle resolution. Then, the information is transferred to the coarse solid particles, which act as a non-penetrating boundary condition for the fluid phase. The present enforcement is introduced with the aim of overcoming the disadvantages in terms of CPU time for heavy SPH simulations, in which the choice of the initial spatial resolution is driven by the presence of elastic thin structures immersed in the fluid environment. The present elastic thin-wall boundary treatment is verified through several numerical cases, in which it is proved that the proposed technology can block non-physical interaction of fluid particles located at opposite sides of the elastic thin-wall boundary, ensures the stability of the fluid pressure field, and reasonably predicts the motion of elastic structures when these are subjected to hydrodynamic loads. Successively, the proposed numerical model is applied to simulate wave interaction with an elastic horizontal plate breakwater. The hydrodynamic performances of the breakwater, with focus on the reflection and transmission coefficients, are analyzed. The results of elastic and rigid horizontal plate breakwaters are compared in order to better understand the effects of the structure deformation on the hydrodynamics. Finally, an analysis of the structural deformation of the breakwater is also reported. • A SPH numerical model to study wave interaction with elastic thin structures is developed. In this context, the δ -SPH and TL-SPH models for solving fluid and structure phases respectively are used, and a multiresolution strategy for treating elastic thin structures is proposed to couple them. • The proposed multiresolution strategy is verified through several numerical cases, in which it is proved that it can ensure the stability of the fluid pressure field, and reasonably predicts the motion of elastic structures when these are subjected to hydrodynamic loads. • The proposed numerical model is applied to simulate wave interaction with an elastic horizontal plate breakwater, in which the hydrodynamic performances of the breakwater are analyzed. [ABSTRACT FROM AUTHOR]

In this paper, we theoretically investigate a multi-resonant oscillating water column (OWC) breakwater array. Based on linear potential flow theory, an extension of semi-analytical solution for wave interaction with periodic OWCs was developed for periodic OWCs with arbitrary chamber number. Both the diffraction and radiation problem for periodic multi-chamber OWCs are solved and verified using Haskind relation and wave energy flux conservation law. Parametrical analysis was conducted to examine the hydrodynamic characteristics of the present OWC breakwater system. Results indicate that multiple resonance of OWCs in piston mode led to multiple peaks of hydrodynamic efficiency, therefore broaden the effective frequency bandwidth with significant wave power absorption and coastal protection capability. However, the resonance of OWCs in sloshing mode in along-shore direction significantly weakens the wave power extraction. The triggering of the sloshing mode resonance mainly depends on the along-shore length of OWC unit and the incident wave angle. For larger along-shore OWC unit length (2 l > h, within the present calculations), the effective frequency bandwidth is significantly influenced by the incident wave angle. Notably, when the incident wave angle exceeds π/4, the effective bandwidth decreases by half approximately. However, for narrower lengths (2 l < h) , the hydrodynamic performance of the OWC array demonstrates reduced sensitivity to the variations of the incident wave angle. [ABSTRACT FROM AUTHOR]

• The WEC model oscillated in heaving direction and integrated with a fixed breakwater. • The geometry shape and distance influence hydrodynamic performance of WEC. • The integration of breakwater can improve the performance of the WEC device. • The hydrodynamic and power capture performance calculation using CFD and experiment. The hydrodynamic and power capture performance of an asymmetric floating device called "Dolphin" wave energy converter (WEC) integrated with a fixed breakwater has been proposed. The operation of the floating WEC device is restricted to the vertical direction called heaving motion. In this research, the theories of heaving motion, wave energy conversion, and computational fluid dynamics (CFD) were studied. A numerical simulation of the CFD with the laminar model was conducted; namely, the effects of four different model shapes were investigated, distance effect between the WEC device and breakwater, WEC integrated with/without breakwater, and vorticity effect analysis using STAR-CCM+ software based on the viscous flow theory in the time domain. The optimal power take-off (PTO) system was considered during the numerical calculation, including the parameters of the WEC model, which were optimized to exploit a higher efficiency by analyzing the motion response in order to obtain the response amplitude operator (RAO) and capture width ratio (CWR) values. From the RAO and vortex field analysis, the RAO value of the Dolphin WEC was exhibited better than that of the other models. A vortex method was applied to verify the CFD simulation results. From the vortex simulation, it can be clearly seen that the integration of breakwater also affected the hydrodynamic performance of the WEC. The Dolphin WEC model with breakwater integration at experimental scale was built and tested in wave tank at Harbin Engineering University under various wave conditions. The breakwater was welded with the steel plate to restrict movement. The displacement sensor and linear generator were installed on top of the WEC device during the experiment. To modify the damping in the system, the heaving motion and power generation characteristics were analyzed and electrical resistance was assumed. The displacement and power in the time domain, RAO, and CWR for different wave periods and wave heights were investigated in the experiment, where the maximum motion response and power efficiency of the WEC model were 1.57 and 0.376, respectively. [ABSTRACT FROM AUTHOR]

The submerged horizontal plate (SHP) has been extensively studied as an open-type breakwater, and some research explored its potential as a wave energy converter. However, these two functionalities were seldom combined in the literature. In this study, a 2D numerical model solving the wave-SHP interaction was built by using the weakly compressible smoothed particle hydrodynamics (WCSPH) method. The thin-walled boundary condition was verified through a dam-break impact case. The accuracy of wave profile and flow velocity calculations was validated by comparing with available experiments of solitary and regular waves interactions with SHPs. Comparison of the wave dynamic and flow dynamic between SHP and submerged step were made, which showed the advantages and disadvantages of the SHP. Then a parametric study of regular waves-fixed SHP interaction was conducted. Empirical formulas for the wave transmission coefficient and energy conversion efficiency were obtained by regressing numerical results using the Levenberg-Marquardt algorithm. Finally, a mathematical programming problem concerning the combined functionalities of SHP was established. Using the complex method, the optimal length and submergence of SHP regarding different emphases taken on the regular wave attenuation and energy utilization were solved. The results preliminarily demonstrated the potential application of SHP as a wave energy breakwater and provided reference on its parameter design, although this work was carried out in 2D and ignored the effects of energy convertor and piles on wave and flow patterns. • The WCSPH method is used to simulate the wave-submerged horizontal plate (SHP) interaction. • The numerical model is validated through numerical tests and available experiments. • Formulas for the wave transmission coefficient and energy conversion efficiency of SHP are obtained. • The optimal configuration and performance of the SHP-type wave energy breakwater are discussed. [ABSTRACT FROM AUTHOR]

Hydrodynamic improvement of wave energy converter (WEC)'s performance tends to reach a bottleneck in that it becomes difficult to further jump over the present low-efficiency stage. Instead of focusing on conventional geometry or layout optimization of WECs, this study investigates an alternative way to overcome the efficiency challenge. Inspired by a parabolic reflector that can reflect sound towards a focal point, this study explores the concept of breakwater with parabolic openings to converge propagating waves toward a focus position. The wave energy harvest can be increased when a buoy-type WEC is set at the focus position. A 3D numerical wave tank based on the boundary element method is developed to investigate the wave field around this parabolic breakwater. It is confirmed that reflected waves from the parabolic opening of the breakwater can travel towards a fixed focus position. The maximum wave height of the full wave field appears at a location half, or one wave length away from the vertex of the parabolic opening. For a specified wave environment, the wave height at the focus position can reach over four times the incident wave height, indicating wave energy multiplication. Effects of the neighbouring openings' distance on the wave field are also investigated. As this distance increases, the maximum wave height at the focus position decreases accordingly. Further, the wave field around a parabolic breakwater with its focus inside or outside the parabolic opening area is discussed. It is recommended to design the breakwater with its focus position located inside the parabolic opening area. Finally, a truncated circular cylinder as a simplified buoy-type WEC is placed at the focus position of each parabolic opening in front of the breakwater. Compared with the conventional design, the heave response of the buoy in front of the parabolic breakwater can be amplified by about three times. • Novel breakwater with parabolic openings is proposed for wave energy harvest. • Wave height at the focus position can reach four times incident wave height. • Wave energy harvest of buoy-type WECs can be multiplied effectively. • D numerical wave tank is developed to verify its hydrodynamic performance. [ABSTRACT FROM AUTHOR]

Highlights • Hydrodynamic performance of ring-shaped spar-type VLFS was experimentally evaluated. • Long natural periods enhanced vertical motion performance and afforded favorable condition. • Large surge damping induced by the breakwater significantly affected the surge and pitch motion. • Wave attenuation was frequency-dependent and effective among the common wave frequencies. • Wave attenuation and wave run-ups tended to improve in the absence of the leeward walls. Abstract A ring-shaped spar-type Very Large Floating Structure (VLFS) is proposed as an intermediate base for supporting deepwater resource exploitation far away from the coast line. The proposed VLFS is composed of eight rigidly connected deep-draft spar-type modules and an inside harbor. A double-layered perforated-wall breakwater is vertically attached to the VLFS and pierces through the water surface to attenuate the wave energy in the inside harbor. The hydrodynamic performance characteristics of the ring-shaped VLFS was experimentally evaluated in the present study, focusing on the motion responses, wave elevations, and wave run-ups. The natural periods of the motions in vertical plane were determined to be larger than 40 s, which is much larger than common wave periods. This enhanced the motion performance in vertical plane and afforded favorable habitation and operation condition on the VLFS. A large surge damping was induced by the vertical breakwater, which tended to significantly affect the surge and pitch motions, but had a negligible effect on the heave motion. The component frequencies of the wave elevations in the inside harbor and the wave run-ups were identical with those of the incident waves. The wave attenuation was frequency-dependent and effective for the common wave frequencies, with a smaller loss coefficient observed in higher sea state. The wave attenuation and wave run-ups tended to improve in the absence of the leeward walls. [ABSTRACT FROM AUTHOR]

Abstract This paper introduces a time-domain potential flow method for simulating fully nonlinear wave interaction with a fluid-filled membrane mounted on the seabed. The numerical method is based on a mixed Eulerian-Lagrangian method, which tracks the free water surface and the membrane using a Lagrangian method and solves the flow fields inside and outside the membrane using an Eulerian method. To remove the numerical instability, a method that satisfies the no-flux condition on the membrane at any location and any time was developed to calculate the radial displacement of the membrane at every time step and a Fourier series expression for the radial displacement of the membrane was used to calculate the local curvature of the membrane accurately. Experimental results from an existing experimental study were used for model validation and verification. The response of the membrane and the nonlinear wave scattering were simulated. The simulation results show that the transmission coefficients of the fundamental waves, second harmonic free and locked waves approach zero when a resonant response of the membrane to waves occurs. Sample results of the simulated tension in the membrane and interior pressure are also included in the discussion. [ABSTRACT FROM AUTHOR]

Abstract An integrated breakwater-WEC system, which comprises of an array of heaving Oscillating Buoy Wave Energy Converters (OB-WECs) attached at the weather side of a fixed breakwater, is proposed in this study. Detailed experiments have been undertaken to investigate the heave-response-amplitude operator (HRAO), the wave force on the WEC devices and the transmission coefficient of the breakwater-WEC system. The design of the experiment is validated by comparing the HRAO of the devices with the corresponding numerical results. The hydrodynamic performance of the breakwater-WEC system is compared with that of its isolated counterparts, i.e., the isolated WEC array and the isolated breakwater. Parametric studies are conducted to optimise the draft of the WEC devices and the breakwater-WEC spacing, i.e. the gap between the WEC devices and the breakwater. Results show that, compared with the case of isolated WEC devices, the wave force and HRAO of the WEC devices are amplified for a properly designed breakwater-WEC system. Even though the external damping (caused by viscous damping and the friction loss) plays an important role while evaluating the efficiency of the WECs, the existence of the breakwater significantly improves the performance of the WEC array. The HRAO is sensitive to the draft of the devices and breakwater-WEC spacing. Highlights • The heave response and wave force on WEC devices can be amplified in the breakwater-WEC system. • The transmission coefficient of the breakwater-WEC system is not compromised by comparing with the original breakwater. • The RAO of WEC devices in heave mode is sensitive to the draft of WEC device and the pontoon-WEC spacing. [ABSTRACT FROM AUTHOR]

The interaction between waves, seabed, and structures is a complex phenomenon that involves multiple physical domains and processes. The spatial variability of properties in marine sediment can significantly affect the dynamic response of seabed. A stochastic numerical model is developed to investigate the response in a spatially heterogeneous poro-elastic seabed around a submerged breakwater. The model is implemented using the COMSOL platform, which allows for solving the wave and seabed sub-models within the same framework. The spatial variability of soil properties is simulated using the random field method employing the Karhunen-Loève expansion. To couple the generated random fields in MATLAB with the integrated model in COMSOL, a LiveLink program is developed, which incorporates a cycle algorithm for stochastic finite element analysis, enabling hundreds or thousands of runs. The model is validated by comparing its results with analytical solutions and experimental data from literature. Probabilistic analysis is performed using the stochastic numerical model and Monte Carlo simulations. The effects of coefficient of variation and correlation lengths in random field on the probabilistic analysis are investigated. The present study provides a valuable tool and insights for the probabilistic assessment of soil response in a spatially heterogeneous seabed around structures. • A stochastic model with spatially variable soil properties is developed for WSSI. • Response in a heterogeneous poro-elastic seabed around structures is investigated. • Multiple physical domains are solved within a unified framework. • LiveLink program is developed to integrate the RFs of seabed soil with FEM model. • Effects of COV and correlation lengths in the RF on WSSI are investigated. [ABSTRACT FROM AUTHOR]

A numerical model based on the multi-domain boundary element method is adopted to study surface gravity wave interaction with a finite floating dock in the presence of a submerged composite wavy porous plate in the two-dimensional Cartesian coordinate system. Physical parameters of interest such as reflection coefficient, transmission coefficient, dissipation coefficient, horizontal and vertical wave force coefficients of the wavy plate, vertical force and moment coefficients about the centre of the dock are calculated. The influence of structural parameters such as the number of ripple wavelengths, relative ripple amplitude, structural porosity and relative submergence depth of wavy plate, relative space between the plate and dock are computed and studied. An insight into the comparison of various types of plates such as flat plate, wavy plate and composite wavy plate is also presented. The study reveals that the mitigation of wave force on the dock is significant due to a wavy porous plate. Besides, the study exhibits that placing the wavy porous plate at a finite distance from the floating dock has a significant role in dissipating incident wave energy compared to that placing the submerged plate below the dock. Bragg reflection occurs due to the presence of the submerged wavy plate, which diminishes with an increase in structural porosity and depth of submergence of the wavy plate. • Wave interaction with a dock and a submerged wavy porous plate is studied. • Multi-domain boundary element method is used to analyse the physical problem. • Efficiency of wavy plate to that of other plate configurations is compared. • Suitable gap between the dock and plate is crucial in dissipating wave energy. • Bragg reflection amplitude decreases for moderate porosity of the wavy plate. [ABSTRACT FROM AUTHOR]

Earthquake and tsunami impose great threats on the stability of a breakwater. Foundation of the breakwater is weakened by these forces, and it may result in collapse of the breakwater. Lateral flow of seabed soils take place beneath the breakwater, and excess pore water pressure is generated in the foundation by an earthquake that precedes tsunami. These factors may lead to excessive settlement and horizontal displacement of the breakwater. Tsunami introduces additional instability to the deformed breakwater. Due to water level difference between seaside and harborside of the breakwater during a tsunami, seepage occurs through its foundation, and it may cause pipping of seabed soils. Tsunami induced scouring of mound is also a big problem for the stability of the breakwater foundation. Finally, these result in failure of the breakwater foundation. Due to failure of its foundation, the breakwater may collapse and cannot block the tsunami. It results in entering of the tsunami in coastal areas. In order to make a breakwater resilient against earthquake and tsunami induced damage, reinforcing countermeasures were developed for foundation of a breakwater. Geogrid, gabions and sheet piles were used for reinforcing a foundation model. The effectiveness of the model is evaluated through physical modeling for mitigating the earthquake and tsunami induced damage. Shaking table tests were performed to determine the effectiveness of the reinforced model under different earthquake loadings. Tsunami overflow test was conducted on the same deformed model in order to see the effects of tsunami on the model. Comparisons were made between the unreinforced and reinforced foundations, and it was observed during the tests that the reinforced foundation performed well in reducing the damage of the breakwater brought by the earthquake and tsunami. Overall, this study is useful for practice engineering, and the reinforced foundation model can be adopted for designing a breakwater foundation to reduce damage triggered by an earthquake and tsunami in the future. [ABSTRACT FROM AUTHOR]

Improving the energy conversion performance, especially in shorter waves, may enhance the competitiveness of wave energy converters (WECs) deployed at sea with medium wave conditions. In this paper, a novel system consisting of a front oscillating buoy type WEC and a rear fixed pontoon is proposed to improve the energy conversion performance of the original single pontoon breakwater -type WEC system by Ning et al. (2016). For the purpose of comparison, the experiments for both single pontoon system and two-pontoon system are conducted. Note that, to avoid the significant increase of the construction cost, the total pontoon volume (i.e., the displacement of the pontoon) of the proposed system remains the same with that of the single pontoon system. The two-pontoon system with different draft ratios d 1 / d 2 (where d 1 and d 2 are the draft of the front pontoon and rear pontoon) are considered. The experiment shows that the system with smaller draft ratio gives more excellent energy conversion performance. The current controller-magnetic powder brake system is selected and used as the power take-off (PTO) system. The characteristics of the PTO system are investigated, which shows that the approximate Coulomb damping force can be simulated very well. The results also reveal that the proposed breakwater-type WEC with proper configuration improves the capture width ratio (CWR) effectively without compromising the coastal protection performance (i.e., the transmission coefficient K T  < 0.5) in comparison with the single pontoon system. And the effective frequency range for the transmission coefficient ( K T  < 0.5) and CWR ( η  > 20%) can be broadened by improving the CWR in shorter waves. [ABSTRACT FROM AUTHOR]

Erosion along shorelines is a major cause in the conversion of shoreline wetlands to open water bodies. Conventional shoreline protection structures are expensive to construct and may impede environmental exchanges essential for connectivity and functionality. A novel marsh shoreline protection technology, the Wave Suppressor and Sediment Collection (WSSC) system, addresses these issues. Laboratory studies were conducted on three WSSC units to determine the governing parameters of sediment collection efficiency of this technology. The three units had varying open areas and pipe sizes which enabled those parameters to be directly compared. Two types of sands with median particle diameters ( d 50 ) of 0.43 and 0.34 mm were used to evaluate the effects of particle size on the collection efficiency of the units. A new mathematical model was developed to predict the sediment collection efficiency using Van Rijn’s equation for particle fall velocity, and Ribberink and Al-Salem’s equation for sand concentration distribution in a water column. Results showed that the Unit 1, Unit 2 and Unit 3 are capable of collecting sand at 0.30, 0.21 and 0.21 (kg/h) for sand 1, and at 0.39, 0.29, 0.39 (kg/h) for sand 2 respectively. The mathematical model fit the experimental data well and from the model, mass accumulation coefficient (α) alpha was calculated. Mass accumulation coefficients (α) for sand 1 and sand 2 were- 0.94 and 0.97 for Unit 1, 0.63 and 0.70 for Unit 2 and 0.32 and 0.22 for Unit 3 respectively. A sensitivity study of the mathematical model was also performed to determine the governing factors behind the sand collection. The sensitivity study found that water depth, wave height and particle diameter affected the sand collection efficiency the most. The amount of open area on the units, frequency and wavelength were also found to have some effect on collection efficiency. [ABSTRACT FROM AUTHOR]

Recent tragic tsunami events, like those that occurred in the Indian Ocean in 2004, and in Japan in 2011, have revealed the need of further work to reduce tsunami risk in coastal areas. An important aspect towards risk reduction is the study of the interaction between tsunami waves and coastal structures as these are the first to receive the tsunami's energy. Dikes and breakwaters must have an adequate structural behavior and maintain some functionality and operability under tsunami attacks to be able to contribute to the reduction of its consequences. Within this scope, laboratory experiments on scaled models of two typical Mediterranean rubble-mound breakwater typologies under tsunami waves were conducted for the first time. The tsunami's action was split into 2 parts: (1) the first impact of solitons was tested by means of large solitary waves and, (2) the subsequent overflow was approached by applying a pump-driven wave maker. The damage on the breakwaters due to these actions was measured and assessed. The result is an in-deep analysis of the relationships among Stability Number, Damage Level and Number of tsunami waves. The outcome of this analysis includes the development of a set of formulae that provide, in the range of the conducted tests, the value of the Damage Parameter, so that tsunami actions can be taken into account in the design of rubble mound structures. Finally, based on the results of these experiments, the threshold values of the Damage Parameter used to characterize damage in armors (Initiation of damage, initiation of destruction, destruction) was particularized for tsunami actions. [ABSTRACT FROM AUTHOR]

Minimizing coastal wetland loss is a high priority in coastal areas worldwide. Typical shoreline protection consists of hard structures placed near areas affected by wave action. These commonly used protection methods are costly, and may have negative impacts on the surrounding areas. The Wave Suppression and Sediment Collection (WSSC) system, made of multiple Wave Robber ® units, is an alternative shoreline protection structure. The primary goal of this study is to determine the performance characteristics of the technology in terms of energy coefficients. Experiments were performed on three scaled units within a laboratory wave tank. Performance characterization showed that the units have wave energy reflections of 0.47–0.83, transmission ranging from 0.10 to 0.42, and wave energy dissipation between 0.49 and 0.88, depending upon unit geometry and wave conditions. Performance data were also compared to other studies on shoreline protection structures. WSSC units reflect more wave energy and transmit less energy compared to other breakwater systems. These units could be utilized in coastal marshes with a large fetch, to reduce wave-induced erosion. [ABSTRACT FROM AUTHOR]

Many breakwaters were failed due to the geo-disaster caused by the 2011 off the Pacific Coast of Tohoku Earthquake and Tsunami. Investigations were carried out, and it was found that the breakwater failed mainly due to the failure of its foundation. However, mechanism of the failure of the breakwater has not yet been completely explained. This paper focuses on the stability evaluation of a breakwater foundation subjected to an earthquake and a tsunami. The main feature of the study is application of centrifuge technique for a geo-disaster caused by an earthquake and a tsunami. Results of the study show that in the case of a geo-disaster brought by an earthquake and a tsunami, excessive pore water pressure generated in the sandy ground, and consequently liquefaction occurred during the earthquake. That resulted in deformation of the foundation ground and settlement of the breakwater. During the tsunami, scouring could occur around the harbor side mound, and seepage took place beneath the breakwater. These were the main reasons of decrease in bearing capacity of the foundation ground and failure of the breakwater. Numerical simulations were also performed to make clear the mechanism and behavior of the breakwater under an earthquake and a tsunami. Overall, this study can be useful to understand the failure process of a breakwater under an earthquake and a tsunami, and it can be helpful to develop countermeasures in order to reduce the earthquake and tsunami induced damage of a breakwater in the future. [ABSTRACT FROM AUTHOR]

The present study combines numerical and experimental approaches to investigate cross flow problems in the entrance channel of a harbor. The combined numerical-experimental approach is illustrated by an application to Lanshan Port (Shandong, China) where large tidal ranges and a newly planned harbor layout may give rise to strong cross flow in the entrance channel of the planned harbor. The resulting flow field with the numerical prediction shows that the layout of newly planned harbor has a major impact on the cross flow speeds in the entrance channel. This will affect the navigation safety of ship entering or leaving the harbor. A corresponding protective scheme related to breakwaters was put forward. A series of physical model experiments under the given flow provided by the numerical approach, were conducted to design the length and crest elevation of a previously proposed breakwater. Results from a series of laboratory model tests show a significant reduction of flow velocities across the entrance channel with longer breakwater length and higher crest elevation. However, a longer or higher breakwater obviously can expand the cross flow influenced zone into the entrance channel. The acceptable breakwater length and crest elevation were determined by taking account the maximum cross flow speed and cross flow influenced zone in addition to the construction cost. [ABSTRACT FROM AUTHOR]

One of the most abundant energy sources exists in this world is the ocean wave energy. By far, it has shown to be the most clean, renewable, predicted energy and has raised the potential to compete with the current use of non-renewable energy sources. Recent research conducted on wave energy invention has opened a new dimension to slowly reduce the dependency on fossil fuel by introducing new technology on the renewable world but relatively lacking in economical aspect. This review brings the latest status on integration of wave energy device with other marine facilities, which is the breakwater structure that may possibly aid to cost sharing. Most researches done on this field highlighted countries experiencing rough sea condition and focused less on countries with medium wave condition as faced by the Asian continent. The potential for energy extraction and wave dissipation for medium wave condition will be discussed in this review by considering several aspects including reliability, effectiveness and performance. Finally, this review shows that the integration opens up a new dimension to acknowledge the technology harnessing ocean wave, especially for the Asian countries experiencing medium wave condition. [ABSTRACT FROM AUTHOR]

This study provides a numerical model to investigate the influences of breakwater layout on coastal waves, wave-induced currents, sediment transport and beach morphological evolution in the vicinity of breakwater. The numerical model is developed based on the sub-models for nearshore wave, wave-induced current, sediment transport and beach morphological evolution. Nearshore wave is simulated based on the parabolic mild-slope equation considering wave refraction, diffraction and breaking effects. Wave-induced nearshore current is modeled using the nonlinear shallow water equations in which wave radiation stresses are provided by wave model for driving current. Then, the two-dimensional suspended sediment transport equation, bed-load equation and coast beach morphological evolution are coupled with the wave and current models for simulating sediment transport and morphological evolution in coastal waves and wave-induced currents. The numerical model is firstly tested by the experiment results for coastal waves, near-shore currents, sediment transport and beach morphological evolution around breakwater from the Large-scale Sediment Transport Facility at the US Army Corps of Engineer Research and Development Center ( Gravens and Wang, 2007 ). Then the model is used to study the influences of breakwater layout on coastal waves, wave-induced currents, sediment transport and beach morphological evolution by set several breakwater layouts in the LSTF basin. [ABSTRACT FROM AUTHOR]

The paper offers a novel comparative case study on the performance of solid versus porous breakwater physically modeled under similar laboratory and wave conditions. Unidirectional waves were generated in a two dimensional laboratory flume having dimensions of 21.3 m length, 0.76 m width and 0.74 m height. Keeping still water depth of 50 cm, waves with T=1.6 sec, 1.7 sec, 1.8 sec and 2 sec were generated from a piston type wave generator. At 800 cm from the wave generator, horizontally slotted submerged breakwater of 100cm width,75cm length and 40 cm height were constructed with varying porosities of n=0.4, 0.5 and 0.6. Water level data were collected at six different locations for 12 unique run conditions. Using the measured data different hydrodynamic coefficients were calculated which include transmission co-efficient K t , reflection co-efficient, K r and wave energy loss co-efficient, K L . These co-efficient values were then, analyzed with respect to relative breakwater width (k.B), [where, k = wave number (2π/L), B = breakwater width] and porosity of breakwater. For the comparison, hydraulic performance of solid rectangular submerged breakwater of 40 cm height and 100 cm width was also reviewed which was modeled in the same laboratory under same wave condition of T=1.6,1.7 1.8 and 2.0 seconds and a still water depth of 50 cm. Experimental results from the porous breakwater and subsequent comparison of the results with solid breakwater indicate that, for transmitting less wave energy through the breakwater, maximum transmission co-efficient, K t = 0.526 was obtained for porous breakwater with the lowest porosity (n=0.4) for T = 1.6 sec whereas for the solid breakwater maximum K t = 0.5 was obtained for T=1.6 second. In terms of wave height, percentage wave height reduction was maximum 47% for porous breakwater whereas it was 68% for solid breakwater both at T=1.6 second. The hydrodynamic performance shows a significantly higher wave height reduction percentage for solid breakwater as anticipated by the physics of the interaction of the breakwater and the wave too. Besides, the position of wave breaking for different case scenario for both types of breakwater were recorded and analyzed which demonstrates that for porous breakwater waves tend to transmit through the slots and break at a certain distance beyond the breakwater whereas in case of solid breakwater, waves tend to break before or on the breakwater. [ABSTRACT FROM AUTHOR]

This paper describes an effective reinforcement technique for foundation of breakwater in order to provide resiliency to the breakwater against earthquake and tsunami related compound geo-disaster. As reinforcing measures, the technique uses gabions and sheet piles in the foundation of the breakwater. A series of shaking table tests were performed to evaluate the effectiveness of the technique under different earthquake loadings, and comparisons were made between conventional and reinforced foundation. The results of these tests reveal the advantages of the reinforcing foundation technique in terms of reduction in settlement and horizontal displacement of the breakwater during the earthquake loadings. Duration and level of acceleration of earthquake loadings had significant impacts on the settlement and horizontal displacement of the breakwater. It was found that one of the reasons of settlement of the breakwater is lateral flow of foundation soils during earthquake, and the sheet piles could reduce the lateral flow. The excess pore water pressures could be reduced significantly during earthquake due to the reinforcing technique. Numerical analyses were also performed to confirm the effectiveness of the technique, and to determine behavior of the reinforcement-soil-breakwater system during the earthquakes. [ABSTRACT FROM AUTHOR]

Powerful tsunami waves were generated by the 2011 off the Pacific Coast of Tohoku Earthquake, and they struck the coast of Japan after few minutes of the main shock. Seismic aftershocks continued for several hours. Many coastal structures such as breakwaters, seawalls were damaged due to the earthquake and tsunami. It may be possible that some coastal structures were hit by the aftershock and the tsunami together. This paper focuses on this fact, and analyzes stability of breakwater under combined effect of earthquake and tsunami. For estimating seismic inertia forces on breakwater, the pseudo-dynamic method was used, which considers seismic waves passing through body of breakwater with respect to depth and time. Stability of breakwater was assessed in terms of factors of safety against sliding and overturning modes of failure. It was found that stability of breakwater reduces drastically under combined effect of earthquake and tsunami as compared to only earthquake and only tsunami. Parameters such as seismic accelerations, height of tsunami wave, seawater level and width of breakwater have significant impacts on stability of breakwater under combined action of earthquake and tsunami. The design charts and tables, presented in this paper, will be helpful for design engineer to design a breakwater under combined effect of earthquake and tsunami in future. [ABSTRACT FROM AUTHOR]

Scour may act as a threat to coastal structures stability and reduce their functionality. Thus, protection against scour can guarantee these structures’ intended performance, which can be achieved by the accurate prediction of the maximum scour depth. Since the hydrodynamics of scour is very complex, existing formulas cannot produce good predictions. Therefore, in this paper, Genetic Programming (GP) and Artificial Neural Networks (ANNs) have been used to predict the maximum scour depth at breakwaters due to non-breaking waves ( S max / H n b ). The models have been built using the relative water depth at the toe ( h t o e / L n b ), the Shields parameter ( θ ), the non-breaking wave steepness ( H n b / L n b ), and the reflection coefficient ( C r ), where in the case of irregular waves, H nb =H rms , T nb =T peak and L nb is the wavelength associated with the peak period ( L nb =L p ). 95 experimental datasets gathered from published literature on small-scale experiments have been used to develop the GP and ANNs models. The results indicate that the developed models perform significantly better than the empirical formulas derived from the mentioned experiments. The GP model is to be preferred, because it performed marginally better than the ANNs model and also produced an accurate and physically-sound equation for the prediction of the maximum scour depth. Furthermore, the average percentage change (APC) of input parameters in the GP and ANNs models shows that the maximum scour depth dependence on the reflection coefficient is larger than that of other input parameters. [ABSTRACT FROM AUTHOR]

Solitary waves have been commonly used as an initial condition in the experimental and numerical modelling of tsunamis for decades. However, the main component of a tsunami waves acts at completely different spatial and temporal scales than solitary waves. Thus, use of solitary waves as approximation of a tsunami wave may not yield realistic model results, especially in the coastal region where the shoaling effect restrains the development of the tsunami wave. Alternatively, N-shaped waves may be used to give a more realistic approximation of the tsunami wave profile. Based on the superposition of the sech 2 (*) waves, the observed tsunami wave profile could be approximated with the N-shaped wave method, and this paper presents numerical simulation results based on the tsunami-like wave generated based on the observed tsunami wave profile measured in the Tohoku tsunami. This tsunami-like wave was numerically generated with an internal wave source method based on the two-phase incompressible flow model with a Volume of Fluid (VOF) method to capture the free surface, and a finite volume scheme was used to solve all the governing equations. The model is first validated for the case of a solitary wave propagating within a straight channel, by comparing its analytical solutions to model results. Further, model comparisons between the solitary and tsunami-like wave are then made for (a) the simulation of wave run-up on shore and (b) wave transport over breakwater. Comparisons show that use of these largely different waveform shapes as inputs produces significant differences in overall wave evolution, hydrodynamic load characteristics as well as velocity and vortex fields. Further, it was found that the solitary wave uses underestimated the total energy and hence underestimated the run-up distance. [ABSTRACT FROM AUTHOR]

In this study, centrifuge model tests and effective stress analyses are performed on a tsunami-affected breakwater similar to those that were seriously damaged during the magnitude-9.0 East Japan Earthquake in 2011. The centrifuge model tests are performed at a scale of 1/200 to simulate the failure of the breakwater. This study is a significant improvement on a previous one [1] by the same authors. The centrifuge model tests now allow the seepage flow to be blocked as well as admitted, and the effective stress analyses are now performed based on the finite strain formulation in order to take large deformations into account instead of just the infinitesimal strain formulation that is applicable only to small displacements. Both the centrifuge model tests and the effective stress analyses demonstrate the important part played by the seepage of pore water in the failure of the rubble mound, in addition to the wave force of the tsunami action. In particular, it is shown that the breakwater damage of 2011 could have been prevented or at least mitigated by preventing seepage flow in the rubble mound. [ABSTRACT FROM AUTHOR]

This paper presents a numerical study on erosion and deposition of a sandy beach installed with a breakwater bearing spill holes, aiming to understand its performance in erosion reduction. The two-dimensional (2D) governing equations for the water-sand mixture are solved by the VOF method and other techniques. The numerical approaches are validated against experimental data for wave propagation on an impermeable beach with a breakwater, scour underneath a pipeline, scour in front of a breakwater, and erosion and deposition of a sandy beach. On these bases, numerical simulations are made for three scenarios: a sandy beach, a sandy beach with a breakwater, and a sandy beach with a breakwater with spill holes. Then, the study proceeds to a detailed investigation of the third scenario with different breakwater locations, spill hole sizes, water depths, and wave heights. The results indicate that the breakwater indeed reduces beach erosion, and the breakwater location and wave height have a pronounced influence on the erosion. The breakwater's performance in reducing beach erosion achieves a maximum at a specific size of the hole opening. It is anticipated that the understanding revealed in this study sheds light on the design and application of breakwaters. • Beach deposition and erosion in the presence of a breakwater with spill hole are studied. • Effects of breakwater location, water depth, spill hole size, and wave height are examined. • Maximum erosion protection is achieved at specific values of water depth and spill hole size. [ABSTRACT FROM AUTHOR]