Breakwater System Research Articles

Effect of resonance and wave reflection in semi-enclosed moonpool on performance enhancement of point absorber arrays

This paper presents a novel means to enhance the energy generation of the wave energy converters (WECs) array by deploying it in a semi-enclosed moonpool. The resonance phenomenon in a moonpool and the wave reflection from the wall of the moonpool result in an amplification of wave amplitude thus increase the energy generation of the wave farm. The wave diffraction and radiation analyses, based on the boundary element method are used to assess the performance of the array. An array of five-point absorbers in a semi-enclosed moonpool is considered and the energy generation, interaction effect and wave climate surrounding the wave farm are investigated. The results show that the width of the moonpool opening affects the performance of the WEC array. The wave climate surrounding the moonpool platform is studied to assess the effectiveness of the moonpool platform as a floating breakwater. The results show that the proposed integrated wave farm and floating breakwater system (moonpool platform) could generate a substantial amount of wave energy and at the same time is effective in attenuating the wave forces. The characteristics of the WECs reveal that the energy generation bandwidth could be increased by deploying the WECs in the semi-enclosed moonpool.

Modeling The Hydrodynamic Characteristics of Tidal And Monsoonal Currents In Pondok Dayung Port of Tanjung Priok Harbor, Jakarta

The Pondok Dayung port forms a significant segment of the Tanjung Priok harbor in the Jakarta coastal bay. Studies on the hydrodynamic characteristics of tidal and monsoonal currents appear very important to ship movement and laid/dock operations in port basins/jetties. These flow conditions have been simulated using a two-dimensional shallow water equation, while the tidal and monsoonal wind were coupled to model the ocean current. In general, the simulation results of the ocean current characteristics were dominated by tidal effects, as well as the interactions with the coastlines, jetties, and breakwaters. Also, the geometric replica has been validated satisfactorily, using time series sea elevation from the tidal station in the research area managed by the National Geospatial Agency (BIG). Strong RMSE and linear correlation values ranging from 0.0405-0.0458 m and 0.9648-0.9843 were obtained, respectively. During the flood tides, the ocean current is directed towards the basin area, while an outward flow is observed under ebb conditions. Furthermore, the maximum tidal current speed of ±0.26 m/s was recorded at the port waterways. A similar outcome was also reported during the west and east monsoon, in addition to a minimum ocean current speed of approximately 0.00 m/s. These conditions implied that the Pondok Dayung port and its breakwater system served as protective structures to the surrounding vessels and the harsh ocean current impacts.

Hydraulic performance of perforated enlarged pile head breakwaters through laboratory investigation

An economical, ecofriendly and efficient breakwater system is vital for coastal protection and harbour tranquility. In this regard, various researchers are working to develop the appropriate solutions to encounter site-specific challenges. With this viewpoint, concept of enlarged pile head breakwater is developed. The study focuses on improving the hydraulic efficiency of pile breakwater by enlarging the structure near the free surface and providing it with perforations. Effect of percentage distribution of perforations, size of perforations and percentage of perforations on wave transmission, reflection and dissipation characteristics of the structure is investigated. The physical experiments are conducted in a two-dimensional wave flume under varying monochromatic wave climates. Results indicate that the pore size highly dominants the wave attenuation than considering the increasing percentage of perforations with the small size of the pore. Perforations effectively reduce the Kt of about 10%–18% to that of non-perforated pile head breakwater. Hydraulic efficiency of enlarged pile head breakwater is optimum when D/Hmax = 0.6, Y/Hmax = 1.0, b/D = 0.2, S = 0.25D, pa = 75% and P = 22.5 at 0.3 m water depth. A hybrid theoretical solution is developed based on the current set of experimental data for the quick estimate of hydraulic coefficients. The proposed hybrid equation for the perforated pile breakwater predicts more desirable values of Kt, Kr and Kd. The proposed concept of breakwater gives a reasonably enhanced hydraulic efficiency than the compared type of breakwaters.

Hydrodynamics of a dual-module pontoon-net floating breakwater system: Numerical simulations and prototype tests

Floating breakwaters with a mooring system have been widely applied to protect marine infrastructures (e.g., artificial beach or island, aquaculture farm or marine vessels in harbors) from being destroyed by severe waves. In this paper, an innovative cylindrical dual pontoon-net floating breakwater was developed to enhance the wave attenuation capacity. This dual-module floating breakwater system was constructed as the prototype for on-site testing. A fully nonlinear time-domain model based on the coupled iterative solutions of the fluid integral equation and the pontoon-net dynamic equations was proposed to simulate the interactions between waves and the floating breakwater system. The flow field around the nets was simulated by introducing a porous-media model with Darcy’s law, while the deformation of the flexible nets was solved by using the lumped mass model. The instantaneous free surface was captured using the mixed Eulerian-Lagrangian (MEL) approach which employs an improved moving-grid technique based on the spring analysis to re-mesh the instantaneous water surface and the body wetted surface. On-site tests were also conducted to evaluate wave transmission performance of the floating breakwater system and to validate the numerical model. The comparisons show that the numerical solutions are in good agreement with the measured data. The effects of incident wave direction, wave period, wave height, net height, net number and net porosity on the hydrodynamic performance of the floating breakwater system were emphatically examined.

Study on Brain Plasticity of Music Training Based on Network Technology

Spectral wave models have experienced constant development and vast improvements over the past decades. They are constantly being extended and refined in order to cover the complex wave transformation processes that take place in the coastal zone. Nevertheless, wave transmission due to overtopping has not been treated similarly yet. In this paper, a methodology to include wave generation due to overtopping in spectral wave models is presented. Incorporation of overtopping aims at better simulating the wave disturbance in the lee side of a system of offshore breakwaters and the induced hydrodynamic processes. So far, the waves generated due to wave overtopping were being neglected. The methodology consists of executing sequential simulations at small time step intervals and whenever wave overtopping occurs in a breakwater, waves are generated and transmitted in the lee side of the structure. This is achieved by modifying the boundary condition at the lee of a coastal structure to account for wave generation due to overtopping. Additionally, the transmitted spectrum source function was modified, to capture the observed transfer of energy in the higher frequencies of the spectrum due to the aforementioned overtopping process. The above methodology was implemented in the open source wave model TOMAWAC and verification with experimental measurements was carried out yielding satisfactory results. Inclusion of wave transmission due to overtopping in spectral wave models is considered to be a valuable asset, especially for the simulation of inshore hydrodynamic processes.

Surface Gravity Wave Interaction With a Submerged Composite Wavy Porous Plate Attached to a Vertical Wall

Abstract The hydrodynamic performance of composite wavy submerged porous plate attached to a wall is investigated using numerical method multi-domain boundary element method in the linearized water wave theory in which wave past the porous barriers are modeled using Darcy’s law. Effect of the presence of wall on the hydrodynamic parameters like reflection coefficient, dimensionless wave height, wave force and moment acting on the composite wavy porous structure, and horizontal force on the vertical rigid wall is analyzed for various physical parameters like the number of ripple wavelength, structural porosity, submergence depth, and relative amplitude of composite wavy porous plate. The study demonstrates that the efficiency of hydrodynamic characteristics of the composite wavy porous plate attached to the wall is better compared to a horizontal porous plate attached to the wall of the same applicability conditions (around 27% reduction in wave reflection). Moreover, optimum performance of this kind of breakwater system is increased by considering the lower submergence, higher relative ripple amplitude, appropriate relative amplitude, and suitable moderate porosity of the structure in the range of wavenumber 1 < k0h < 5. Dimensionless wave height, horizontal load on the impermeable wall are reduced to zero, while substantial minimization of vertical load on the structure with suitable consideration of the other influencing parameters of porosity Gp = 0.3, relative amplitude Ds/h = 0.1, relative ripple wavelength m > 3, and submergence depth h1/h = 0.3. The present structural arrangement will be useful for attenuating wave effects on the sea wall.

Numerical investigation on the hydrodynamic performance of a new designed breakwater using smoothed particle hydrodynamic method

Floating breakwaters have better performance than fixed breakwaters in deep water conditions owing to their higher durability and lower cost. To evaluate the hydrodynamics of a floating breakwater system, a coupling model between smoothed particle hydrodynamics and a multisegmented quasi-Static method is developed. The free-floating and the moored cases are firstly employed as benchmarks to validate the accuracy and stability of the proposed numerical procedure. The coupling model is then utilized to investigate the wave-attenuating performance of a novel configuration of floating breakwater under different environmental conditions. It is demonstrated that the induced response and the tension characteristics are both in good agreement with experimental results, which means that the developed coupling model is capable of predicting the hydrodynamics of the floating breakwater system. Moreover, it is also suggested that the newly-proposed configuration shows more satisfactory wave-attenuating performance than the classical type by inducing more complex velocity fields surrounding the breakwater.

Experimental investigation of a triple pontoon wave energy converter and breakwater hybrid system

In this paper, a novel hybrid wave energy converter (WEC)-floating breakwater system consisting of three floating pontoons with power take-off (PTO) modules is developed to extract wave energy from heave motion and attenuate waves to protect the coast. Unlike previous studies of this subject, the present three pontoons are in close proximity so that they may share the same foundation to reduce the cost further and both pontoons with step change drafts and same drafts are investigated. A systematic experimental study was carried out in a wave flume to examine the hydrodynamic characteristics of the hybrid system under regular waves. The experimental results are used to assess the influences of the WEC-breakwater integration and the configuration of pontoons on the hydrodynamic performance of the hybrid system as a WEC and a breakwater. It was found that the integration of multiple energy-extracting pontoons is robust in smoothing out the power output fluctuations, and the floating pontoons with same drafts gave arise to higher energy conversion efficiency while the floating pontoons with step change drafts are more effective in attenuating wave energy. A parametric analysis is able to identify the balanced performance of the system as a WEC and a breakwater.

Performance characteristics and parametric analysis of a novel multi-purpose platform combining a moonpool-type floating breakwater and an array of wave energy converters

Integration of Wave Energy Converters (WECs) with floating breakwater system provides a multi-function solution to wave energy extraction and offshore infrastructural protection. The contribution of this work is to guide the optimal size and configuration of a multi-purpose platform including a moonpool-type floating breakwater and an array of heaving oscillating-buoy (OB) WECs. The investigation is performed using a developed time-domain numerical wave tank (NWT) based on the three-dimensional (3D) potential flow theory with fully nonlinear boundary conditions on transient wetted body surfaces and free surfaces. The comparison of the hydrodynamic performance among the multi-purpose platform, the isolated array WECs, and the isolated floating breakwater are examined. The internal fluid motion in the moonpools has a positive effect on the wave energy absorption of WECs, which in turn enhances the wave attenuation capacity of the floating breakwater. WECs with larger diameter have a larger water-plane area, which leads to more extracted wave energy. The wave nonlinearity reduces the optimal PTO damping value and has an adverse effect on the wave energy extraction. However, when wave nonlinearity becomes prominent, the wave attenuation capacity is improved with increasing PTO damping. For an unequal layout of moonpools, the thinner moonpools are the major contributor to wave energy extraction, especially in the short wave region. As a result of mass exchange of fluid from the moonpool to the outer domain, the multi-purpose platform indicates favorable performance of wave energy absorption. The novel floating system makes the utilization of wave energy over a wider frequency range.

Integration of a heaving-type wave energy converter with a chambered breakwater system

This paper examines the response of a heaving plate wave energy converter integrated with a chambered breakwater system through experimental and numerical simulations. A porous seaside wall with 20% porosity and an impermeable back wall constitutes a chambered breakwater under investigation. The time-domain response of the wave energy converter before and after integration with the chambered breakwater is evaluated using an open-source code WEC-Sim implemented in MATLAB and Simulink. The performance of WEC subjected to regular wave conditions and the wave elevations measured from the experiments are examined in the present investigation. The reflection characteristics of the chambered breakwater system after integrating with the wave energy converter have been found to decrease. The heave RAO of the wave energy converter installed at a location toward the porous wall is observed to have improved by 22% after integrating with the chambered breakwater than the stand-alone wave energy converter. A similar increase in the power generation performance of the wave energy converter is also observed. The proposed system can improve the economic competitiveness of the wave energy converter by serving dual purposes.

Hydrodynamic Efficiency of Floating Breakwaters WITH Plates (Dept.C)

The efficiency of the floating breakwaters was experimentally studied under normal and regular waves with wide ranges of wave heights and periods. The efficiency of the breakwater is presented as a function of the transmission, reflection, and dissipation coefficients. Different parameters affecting the breakwater efficiency such as, the connection of the virtical plates under the floating body at different positions, length of mooring wires and the wave length were tested. It was found that, the transmission coefficient decreases with the increase of relative breakwater width (B/L), the number of plates and also with the increase of the relative wire length (l/h) whereas the reflection coefficient takes the opposite trend. In addition, the suggested floating breakwater system dissipates about 15% to 30% from the incident wave energy. Also, the suggested floating breakwater model is efficient compared with other types of pontoon breakwaters.

Simulating wave transmission in the lee of a breakwater in spectral models due to overtopping

Spectral wave models have experienced constant development and vast improvements over the past decades. They are constantly being extended and refined in order to cover the complex wave transformation processes that take place in the coastal zone. Nevertheless, wave transmission due to overtopping has not been treated similarly yet. In this paper, a methodology to include wave generation due to overtopping in spectral wave models is presented. Incorporation of overtopping aims at better simulating the wave disturbance in the lee side of a system of offshore breakwaters and the induced hydrodynamic processes. So far, the waves generated due to wave overtopping were being neglected. The methodology consists of executing sequential simulations at small time step intervals and whenever wave overtopping occurs in a breakwater, waves are generated and transmitted in the lee side of the structure. This is achieved by modifying the boundary condition at the lee of a coastal structure to account for wave generation due to overtopping. Additionally, the transmitted spectrum source function was modified, to capture the observed transfer of energy in the higher frequencies of the spectrum due to the aforementioned overtopping process. The above methodology was implemented in the open source wave model TOMAWAC and verification with experimental measurements was carried out yielding satisfactory results. Inclusion of wave transmission due to overtopping in spectral wave models is considered to be a valuable asset, especially for the simulation of inshore hydrodynamic processes.

Performance analysis of dual sphere wave energy converter integrated with a chambered breakwater system

The integration of a dual sphere wave energy converter with a chambered breakwater system is found to enhance the performance of both structures. Such an integrated system is well suited for regions that receive medium wave energy potential at an estimated annual mean wave power less than 30 kW/m. The hydrodynamic efficiency of the integrated system is investigated through experiments. The dual sphere wave energy converter was installed near to the porous and impermeable wall of the chambered breakwater system in the integrated system. The power generation capability of the dual sphere wave energy converter exposed to the wave elevations measured inside the chamber is numerically investigated in the present study. The average power generation capability of the dual sphere wave energy converter is found to be enhanced by 63% after integration with the chambered breakwater. The significance of the position of installing the wave energy converter inside the chamber has been highlighted. The economic competitiveness of the wave energy converter is found to be improved after its integration with the chambered breakwater system.

Coastal Morphological Response to the Effects of Protection Structures against Erosion

Garcia, I.; Negro, V.; Lopez, J.S.; Esteban, M.D., and Del Campo, J.M., 2020. Coastal morphological response to the effect of structures of protection against erosion. In: Malvarez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 220–224. Coconut Creek (Florida), ISSN 0749-0208.The prediction of sandy tombolo formation by the presence of detached breakwaters is key to the use of these elements as beach protection systems. The distance from the shoreline is a relevant factor and must be determined based on the characteristics of the incident waves, the dimensions of the artificial protections themselves, the typologies of the beach and the coastal sedimentary transport zone. In the cases analysed of detached breakwater systems with sandy tombolo formation, linear trends are obtained in between said characteristics. These results can be extrapolated to other cases located in other countries on the Mediterranean coast. Obtaining these relationships has led us to propose a new sizing method that sets the separation of the structures from the shore.

Structural control of the floating breakwaters by implementation of tuned liquid column damper

The growing maritime activities have led offshore engineers to the application of floating breakwaters to protect coastlines from erosion and to provide a layer of support to ports in the case of strong wave actions. In these applications, minimizing the floating part responses to wave-induced excitations as one of the most critical operational characteristics would be a key factor. In this article, the structural responses of the floating breakwaters are studied through modeling and simulation. To mitigate the floating part wave-induced vibrations, an attached tuned liquid column damper is integrated into the simulation. In the first stage, the numerical model of the floating breakwater system containing the floating body and the mooring system is created. Then, by proposing an iterative coupling procedure, the joint tuned liquid column damper-floating breakwater model is developed. Several rigorous study cases are defined to evaluate the effect of tuned liquid column damper on controlling the floating body unwanted vibrations. In this application, the Airy wave theory and the Joint North Sea Wave Observation Project wave spectrum are used for wave excitations. In order to evaluate the effect of tuned liquid column damper on floating breakwaters, some design parameters like floating body motions and mooring system-mobilized tensile stresses are evaluated. The simulations are conducted in both the time domain and the frequency domain for cases with and without tuned liquid column damper. The rain flow counting method is applied to perform the mooring system fatigue analysis. The study results clearly proved that implementation of tuned liquid column damper would mitigate the floating body responses compared to the original floating breakwater system. In addition, it is indicated that the fatigue-induced failure risks in tuned liquid column damper-floating breakwater mooring system is decreased that would reduce the procurement costs and increase the operational safety of the floating breakwater system.

Vibration characteristics of caisson breakwater for various waves, sea levels, and foundations

In this study, vibration characteristics of a gravity-based caisson-foundation breakwater system are investigated for ambient and geometric parameters such as various waves, sea levels, and foundation conditions. To achieve the objective, following approaches are implemented. Firstly, operational modal analysis methods are selected to identify vibration modes from output-only dynamic responses. Secondly, a finite element model of an existing caisson-foundation breakwater system is established by using a structural analysis program, ANSYS. Thirdly, forced vibration analyses are performed on the caisson-foundation system for two types of external forces such as controlled impacts and wave-induced dynamic pressures. For the ideal impact, the wave force is converted to a triangular impulse function. For the wave flow, the wave pressure acting on the system is obtained from wave field analysis. Fourthly, vibration modes of the caisson-foundation system are identified from the forced vibration responses by combined use of the operational modal analysis methods. Finally, vibration characteristics of the caisson-foundation system are investigated under various waves, sea levels, and foundations. Relative effects of foundation conditions on vibration characteristics are distinguished from that induced by waves and sea levels.

Performance Evaluation of Bottom-Standing Submerged Breakwaters in Regular Waves Using the Meshless Singular Boundary Method

In this paper, the improved version of the meshless singular boundary method (ISBM) is developed for analyzing the hydrodynamic performance of bottom-standing submerged breakwaters in regular normally incident waves. Both the single and dual prismatic breakwaters of rectangular and trapezoidal forms are examined. Only the impermeable breakwaters are considered in this study. The physical problem is cast in terms of the Laplace equation governing an irrotational flow and incompressible fluid motion with the appropriate mixed-type boundary conditions, and it is solved numerically using the ISBM. The numerical results are presented in terms of the hydrodynamic quantities of reflection and transmission coefficients. The values are first validated against the data of previous studies, computed, and discussed for a variety of structural conditions, including the height, width, and spacing of breakwater submergence. An excellent agreement is observed between the ISBM results and those of other methods. The breakwater width is found to feature marginal effects compared with the height. The present method is shown to accurately predict the resonant conditions at which the maximum reflection and transmission occur. The trapezoidal breakwaters are found to generally present a wide spectrum of reflections, suggesting that they would function better than the rectangular breakwaters. The dual breakwater systems are confirmed to perform much better than single structures.

Lifecycle Environmental Impact Assessment of an Overtopping Wave Energy Converter Embedded in Breakwater Systems

Overtopping breakwater systems are among the most promising technologies for exploiting wave energy to generate electricity. They consist in water reservoirs, embedded in piers, placed on top of ramps, higher than sea-level. Pushed by wave energy, seawater fills up the reservoirs and produces electricity by flowing back down through low head hydro turbines. Different overtopping breakwater systems have been tested worldwide in recent years. This study focuses on the Overtopping BReakwater for Energy Conversion (OBREC) system that has been implemented and tested in the harbor of Naples (Italy). The Life Cycle Assessment of a single replicable module of OBREC has been performed for analyzing potential environmental impacts, in terms of Greenhouse Gas Emissions, considering construction, installation, maintenance, and the operational phases. The Carbon Footprint (i.e. mass of CO2eq) to build wave energy converters integrated in breakwater systems has been estimated, more specifically the “environmental investment” (i.e. the share of Carbon Footprint due to the integration of wave energy converter) needed to generate renewable electricity has been assessed. The Carbon Intensity of Electricity (i.e. the ratio between the CO2eq emitted and the electricity produced) has been then assessed in order to demonstrate the profitability and the opportunity to foster innovation in the field of blue energy. Considering the impact for implementing an operational OBREC module (Carbon Footprint = 1.08 t CO2eq; Environmental Investment = 0.48 t CO2eq) and the electricity production (12.6 MWh/yr per module), environmental benefits (avoided emissions) would compensate environmental costs (i.e. Carbon Footprint; Environmental Investment) those provided within a range of 25 and 13 months respectively.

Meshless Method for Analysis of Permeable Breakwaters in the Proximity of A Vertical Wall

In the present work, the improved version of the meshless singular boundary method (ISBM) is developed for analyzing the performance of bottom standing submerged permeable breakwaters in regular normally incident waves and in the proximity of a vertical wall. Both single and dual prismatic breakwaters of rectangular and trapezoidal forms are examined. The physical problem is cast in terms of the Laplace equation governing an irrotational flow and incompressible fluid motion with appropriate mixed type boundary conditions, and solved numerically using the ISBM. To model the permeability of the breakwaters fully absorbing boundary conditions are assumed. Numerical results are presented in terms of hydrodynamic quantities of the reflection coefficients. These are firstly validated against the results of a multi-domain boundary element method (BEM) developed independently for a previous study. The agreement between the results of the two methods is excellent. The coefficients of reflection are then computed and discussed for a variety of structural conditions including the breakwaters height, width, spacing, and absorbing permeability. Effects of the proximity of the vertical plane wall are also investigated. The breakwater’s width is found to have only marginal effects compared with its height. Permeability tends to decrease the minimum reflections. These coefficients show periodic variations with the spacing relative to the wavelength. Trapezoidal breakwaters are found to be more cost-effective than the rectangular breakwaters. Dual breakwater systems are confirmed to perform much better than single structures.

Enhancement the Fatigue Life of Floating Breakwater Mooring System Using Tuned Liquid Column Damper

Abstract Safety is a key design criterion for floating structures. A high rate of mooring accidents has been reported over the past decades. Preventing mooring line failure is a key design objective for floating breakwater systems. The mooring system comprises sets of mooring lines anchored to the seabed. These components are exposed to highly cyclic nonlinear load fluctuations induced by an irregular wave climate during their service life. DNVGL-OS-E301 classifies the mooring lines for floating breakwaters as long-term elements that should be evaluated according to the fatigue limit state. Fatigue of mooring lines needs to be monitored and evaluated to warrant the station keeping and integrity of overall system. Applying an additional control device to a floating breakwater mitigates the structural response and hence mobilized tension in mooring system. The focus of present study was to examine the effect of an additional control device on fatigue life of mooring lines for floating breakwaters. To evaluate the effect of a control device on the fatigue behavior of mooring lines, a floating breakwater was simulated with a tuned liquid column damper (TLCD) attached. A time-dependent approach based on S-N curves in conjunction with the Palmgren-Miner rule was employed to evaluate the mooring line fatigue. This paper presents a further parametric study focused on the effect of TLCD on fairlead point displacement, mobilized tension, damage rate, and fatigue life of mooring lines. The results showed that TLCD increased the fatigue life of mooring line and thus dramatically decreased the likelihood of the mooring system being damaged by fatigue. This would reduce the maintenance costs and increase the lifetime and operational safety of floating breakwater. In addition, the presented case study showed that failure probability of mooring lines against fatigue damage was also reduced and was acceptable for the safety factor defined in DNVGL-OS-E301. This proposed approach of applying a TLCD is a practical tool for designing the components of a floating breakwater more efficiently.