Semicircular Breakwater Research Articles

Two-dimensional one-way coupled modelling for fluid-structure-seabed interactions around a semicircular breakwater using OpenFOAM

Semicircular breakwaters, preferred for their lighter weight, wider base and superior resistance to overturning and sliding, have seen focused research on wave forces and hydrodynamic performance. Despite documented failures due to seabed instability, numerical examinations of the seabed response and stability around these structures are lacking in the literature. This study establishes an OpenFOAM model to numerically investigate hydrodynamic interactions, structural dynamics, seabed consolidation and liquefaction potential near a semicircular breakwater in two-dimensional, addressing complex fluid–structure-seabed interactions in a one-way coupling manner. A novel method for determining the compressibility of the pore fluid has been implemented, which integrates geostatic stress, atmospheric pressure and wave-induced excessive pore pressure within the seabed. The numerical results indicate that seabed responses are sensitive to the bulk modulus of pore air in partially saturated cases, where a decrease in pore pressure, an increase in the vertical effective stress and a decrease in the horizontal effective stress are observed. Further numerical analysis reveals that the most vulnerable part of the breakwater appears on the wave-facing side of the caisson, where reinforcement measurements are recommended during construction. A pronounced liquefaction zone is observed ahead of the breakwater, corresponding to the area with upward seepage, which is attributed to the combined effect of hydrodynamic interactions and direct stress action transferred from the semicircular breakwater.

Hydrodynamic Performance Assessment of Emerged, Alternatively Submerged and Submerged Semicircular Breakwater: An Experimental and Computational Study

Coastal protection structures are essential defenses against wave energy, safeguarding coastal communities. This study aims to refine coastal protection strategies by employing a semicircular breakwater (SBW) model. Through a combination of physical and computational models, the hydrodynamic properties of the SBW under regular wave conditions were thoroughly examined. The primary objectives included delineating the hydrodynamic characteristics of SBWs, developing a computational model to validate experimental findings. Hydrodynamic characteristics of the SBW model were scrutinized across various wave conditions. Experimental testing in a wave flume covered a range of relative water depths (d/h) from 0.667 to 1.667, wave steepness (Hi/L) spanning 0.02 to 0.06 and wave periods ranging from 0.8 to 2.5 s. Notably, analysis of an emerged SBW with d/h = 0.667 revealed superior wave reflection, while an alternative submerged SBW with d/h = 1.000 showed the highest energy loss. These findings are further corroborated by the validation of computational models against experimental outcomes for d/h = 0.667, 1.000, 1.333 and 1.667. Moreover, the investigation of forces revealed an inverse correlation between horizontal forces and wave height, while vertical forces showed nuanced variations, including a slightly decreasing average vertical force with greater relative wave period (B/L) for different immersion scenarios.

Numerical Investigation of the Seabed Dynamic Response to a Perforated Semi-Circular Breakwater

Numerical Investigation of the Seabed Dynamic Response to a Perforated Semi-Circular Breakwater

Numerical investigations on the hydrodynamic performances of an isolated OWC and its integration with a semi-circular breakwater

The exploration of multifunctional systems to harvest wave energy has become increasingly prominent in recent research. This paper presents a comprehensive investigation into the effectiveness of utilizing a wave energy converter (WEC) not only for energy generation but also as a coastal protection measure. Among the various types of WECs, the Oscillating Water Column (OWC) stands out as particularly promising due to its inherent advantages and notable efficiency. The versatility of the OWC allows for standalone installation or integration into hybrid systems, such as combining it with breakwaters. While numerous studies have examined the integration of OWCs with Caisson-type breakwaters, research on their integration with Semi-circular breakwaters (SCBW) is scarce. This study fills this gap by utilizing the open-source computational fluid dynamics (CFD) tool, OpenFOAM, to analyze the hydrodynamic performance of an OWC embedded within an SCBW. The numerical findings are validated against existing experimental data, enabling a thorough comparative analysis between the performance of an isolated OWC and a hybrid OWC integrated with SCBW. The investigation delves into various parameters, including wave amplification factor, chamber air and water pressure, external water pressure, energy transfer efficiency from chamber water to air, and wave run-up over the SCBW face. The results conclusively demonstrate that an OWC integrated with SCBW exhibits superior hydrodynamic performance compared to standalone configurations.

Performance Characteristics of a Submerged Semicircular Breakwater Exposed to Regular Waves: An Experimental Study

Many mangrove replanting programs fail due to the drifting of the mangrove sapling by waves and coastal currents soon after the replanting. Hence, adequate wave protection for the mangrove planting site is required to enhance the survivability rates of the newly planted saplings. A small scaled modular submerged semicircular breakwater (SBW) is perceived to be a viable option to provide the required level of wave protection to mangroves. The study is set to investigate wave transmission, reflection, and energy loss by a SBW subjected to different immersion depths under a regular wave environment via physical modelling. The SBW model was tested in a wave flume and was subjected to relative immersion depth, i.e., a ratio of water depth to the height of the SBW, of 1.00 and 1.33, and wave steepness ranging from 0.02 to 0.06. The alternatively submerged SBW was found to be an effective breakwater design to provide the required level of wave tranquility to various coastal applications.

Numerical Analysis of Dynamic Response and Liquefaction Phenomena in Sandy Seabed Foundation around a Semi-Circular Breakwater under Wave Loading

Understanding the stability of the seabed foundation holds paramount significance in guaranteeing the safety and structural soundness of the breakwater alongside additional offshore structures. This study aimed to investigate the stability of a sandy seabed foundation around a semi-circular breakwater under wave loading in nearshore areas. A coupled numerical model of waves, a semi-circular breakwater, and the seabed was developed based on the OpenFOAM platform. The VARANS equations were used to govern the wave behavior. Meanwhile, the Biot’s partially dynamic model was employed to numerically simulate the seabed response considering both consolidation under self-weight and dynamic response under wave loading. The effects of various wave parameters, seabed properties, and the radius of the structure on the dynamic response of the seabed and the depth of liquefaction were investigated. The numerical results indicate that an increase in wave height, period, and permeability coefficient intensifies the dynamic response of the seabed soil. Furthermore, an increase in water depth weakened the soil’s dynamic response. There was a negative correlation between the radius of the semi-circular breakwater and the dynamic response. The influence of Poisson’s ratio on the dynamic response of the seabed was relatively small. Furthermore, a stronger dynamic pore pressure response was observed at the connection between the semi-circular breakwater and the rubble foundation.

Multipole solution with nonlinear pressure loss for oblique waves action on a submerged partially perforated semi-circular breakwater

This study is an extension of the research on semi-circular breakwater based on Lyu et al. (2020). This time, we focus on the changes in the flow field when waves obliquely interact with the axis of the partially perforated semi-circular breakwater, as well as the nonlinear effects resulting from variations in wave height to some extent. The analytical solution of the flow field is still obtained using the multipole expansion method based on potential flow theory and the method of separation of variables. The analytical solution for oblique incidence is primarily achieved through the cylindrical form of the Bessel equation. Separately considering viscous effects and potential flow, we estimate the impact of wave height variation on the perforated boundary through the quadratic pressure loss term. By employing an iterative solving approach, we comprehensively discuss the influence of wave height, water depth, perforation form, and oblique incidence angle on the flow field and the forces acting on the breakwater.

Numerical simulation and PIV measurements of the wave-induced flow field near semi-circular breakwaters

Careful design of the high-tech semi-circular breakwaters (SBW), which are used for protection against sea waves, is essential to avoid the failure of these large-scale projects. An improved design tool adopting numerical simulations, complemented with experimental measurements is introduced. Unstructured boundary-fitted grids are used to model the curved SBW boundary accurately and resolve the flow adjacent to it. Experimental measurements based on Particle Image Velocimetry (PIV) are introduced and the numerically simulated velocity fields are validated. For the first time, the strong free surface deformation upstream of the SBW, termed trough-breaking, is reproduced numerically. The phenomenon is investigated in detail and its impact on several SBW advantages and stability is emphasized. The improved accuracy due to unstructured boundary-fitted grids complemented by the PIV data set, offers valuable prospects for performing complex designs and exploring future applications.Article HighlightsAn efficient design tool for the high-tech semi-circular breakwater is introduced adopting numerical simulations and experimental measurements.The numerical results agree well with the experimental measurements. Hence, this experimental data set should be used extensively for validation in future studies.The important flow phenomenon of “trough-breaking” is reproduced numerically for the first time, and its impact on the semi-circular breakwater features is clarified.

Effect of data normalisation in estimating wave overtopping discharge parameter of semicircular breakwater using ANN and Random Forest.

Breakwaters are the structures constructed in the coastal areas to maintain calm inside the port or prevent beach erosion. Semi-circular Breakwater (SCB) is an innovative type of Breakwater made of hollow caisson on a base slab with or without perforations. In this study, the wave overtopping discharge parameter of an SCB is estimated using Artificial Neural Network and Random Forest. The data is collected and used in the current research from an experimental investigation conducted in the Wave Mechanics Laboratory of the Department of Water Resources and Ocean Engineering (WROE), NITK Surathkal. Using this experimental data, the ANN and Random Forest models are developed for the prediction of the wave overtopping discharge parameter of an SCB. The performance of the models is evaluated using different statistical parameters. Data with and without normalisation are used separately to check the effect of normalisation in the prediction of wave overtopping discharge parameter using ANN and Random Forest. From the results, it is found that ANN gives better results when the data is normalised. The performance of Random Forest is independent of the data normalisation.

Wave Action Analysis of Multiple Bottom Fixed Semi-Circular Breakwaters in the Presence of a Floating Dock

Abstract The comprehensive usage of an array of natural or artificial semi-circular breakwaters (SCBs) as supporting structures to secure the floating/fixed structures are received increasingly more consideration in recent years. The performance characteristics of bottom-fixed SCB in the presence of a floating dock are investigated under the framework of linear wave theory. The edge conditions such as continuity of velocity and pressure along the SCB and zero-flow condition near rigid surfaces are adopted. The multi-domain boundary element method (MBEM) is used to examine the wave attenuation performance of the whole breakwater system in two dimensions. The correctness of the present study's numerical results is confirmed by performing the comparative study with the readily available experimental and analytical results reported by various researchers. The reflection, transmission, energy loss coefficients, and fluid force experienced by floating dock are examined as a function of incident wave properties and breakwater physical properties. The Bragg resonant reflection and performance comparison with other shapes are also studied. The study results strongly suggest that the damage of floating structures and leeward locales due to incident wave stroke is minimized with the introduction of porosity for SCB located on the seabed by dissipating the wave energy. A pair of bottom-fixed SCBs having 10–20% breakwater porosity placed far away from the dock is identified as the optimal choice to reduce the fluid force experienced by the dock and wave transmission coefficient.

Eksperimentalna i numerička analiza hidrodinamičkih svojstava visećih zakrivljenih valobrana

The purpose of breakwaters is to protect the ports, beaches, or beach facilities from strong waves and storms, as they help establish calm inside the port and thus achieve safety for ships and ease of operation. This paper presents an experimental and numerical study of unconventional alternatives to the vertical breakwater in order to evaluate the hydrodynamic performance of the proposed models. Two proposed cases for a semi-submerged breakwater were selected in the form of a half-pipe section with an inside diameter of 20 cm and a thickness of 1 cm. Case (a) was of the concave type of semicircular breakwater, while case (b) was of the convex type. Numerical modeling FLOW 3D was used to construct numerous scenarios for numerical simulation of the proposed breakwaters. The obtained results indicates that, when comparing the wave transmission coefficient (Kt) and its reflection coefficient (Kr) with the relative water depth (h/L), the transmission coefficient decreased with the relative height of the wave, while the reflection coefficient was completely reversed. In case (a), Kt was less than in case (b) at a range of 10% to 15%, while Kr in case (a) was bigger than in case (b) at a range of 5% to 10%. When the wave hit the breakwater, it was reflected back as its energy is dissipated in less water depth and its speed decreases as it approaches the port. The velocity of the wave decreases as it approaches the bottom, which means that the wave is affected by the depth of the water, i.e. the lower the water depth, the lower the wave velocity. Case (a) was more efficient and effective in wave dissipation, current velocity, and bed stability than case (b), so it is recommended to use case (a) due to its efficiency in protecting coastal areas and generating electricity.

Experimental modeling of bed morphological changes and toe erosion of emerged breakwaters due to wave-structure interactions in a deltaic coast

Large-scale coastal erosion in the Mekong Delta has been dramatically increasing in severity in recent decades. There are several effective hard engineering solutions that have been implemented in this delta to efficiently prevent coastal erosion and stimulate sedimentation while supporting the local ecosystem conservation. These measures include Pile-Rock Breakwaters (PRBW), Hollow Triangle Breakwaters (HTB) and Semicircular Breakwaters (SBW). However, research on the sediment transport, morphological changes and toe erosion for these offshore breakwaters is very limited and is currently in the initial stages of understanding the specific conditions of sediment characteristics and foundations. The objective of this study was to reproduce the morphological changes and toe erosion of three breakwaters due to wave-structure interactions. This was investigated using 2D physical models with 3000 irregular waves during 8 experimental hours (equal to 15,000*Tp). To extract the bed morphological changes and toe erosion both specialized laser measurements (SW50M laser ruler) and analysis of high-speed video recording by images digitalization were applied. The experimental results show that the shape and structural design of offshore breakwaters can have a significant influence on the bed morphology on both the seaside and the leeside. We found that generally the toe of the construction on the seaside was eroded due to the occurrence of reflected waves, and that the flow is narrowed while passing through the construction, increasing the flow velocity and causing toe erosion. Additionally, the accretion of sediment at the leeside of the breakwaters was found to be mainly driven by the transport of sediment through the construction. Comparing the breakwater designs the experimental results showed that the HTB has the maximum accretion rate behind the structure, as well as the fastest accretion rate behind the breakwater. The SBW has high wave energy dissipation efficiency, although the toe erosion rate is faster than the other classes of breakwaters. The PRBW shows the fastest toe erosion rate in front of the structure and causes accretion at the leeside of the construction but at a lower rate than the HTB. The findings from this study will help practical designers to reinforce the foot of construction during real breakwater designing and inform stability calculations. We recommendation is to apply these three classes of breakwaters, especially the HTB and SBW, for stimulating sedimentation for mangrove restoration in the mangrove mud-coast delta.

Wave reduction efficiency for three classes of breakwaters on the coastal Mekong Delta

This study presents a laboratory scale implementation of breakwaters and their ability to mitigate extreme wave erosion on the coast of Mekong Delta. Three classes of breakwaters are tested in this study: Hollow Triangle breakwaters (HTBW), pile-Rock breakwaters (PRBW), and semi-circular breakwaters (SBW) using physical models in the laboratory. The investigation includes 210 experimental tests using a physical model under various incident waves and water levels. The experimental results show that the SBW has the lowest wave transmission coefficient (Kt). The HTBW has the highest Kt. The Kt of SBW, PRBW and HTBW in the submerged state (Rc/Hm0,i < 0) varies between 0.45 – 0.73; 0.55 – 0.73 and 0.64 – 0.82, respectively. The wave reflected coefficient of the PRBW is found larger than SBW and HTBW. The SBW demonstrates the largest wave energy dissipation capacity. The wave reflection coefficients (Kr) in the submerged state for SBW, PRBW and HTBW have a similar range of Kr with varying range i.e., 0.16 – 0.30, 0.16 – 0.27 and 0.16 – 0.28, respectively. Meanwhile, the Kr of the HTBW and the SBW in the emerged state (Rc/Hm0,i > 0) varies in a range, 0.17 – 0.35 and 0.19 – 0.33, respectively, while the Kr of the PRBW has a larger variation with a range of 0.22 – 0.48. From the field measurements, the Kt and wave spectrum is verified with the physical model results. The average wave dissipation capacity of the three breakwaters is obtained about 54-80% for PRBW, 75-81% for HTBW, and 51-90% for SBW, respectively. The observed Kt for the field scale breakwaters shows non-linearity rather than the physical models due to the large variability of incident wave conditions in the East and West Seas. HTBW and SBW are highly efficient in dissipating the longer period waves peak, while PRBW is highly efficient in dissipating the short period waves peak. The results indicate that three breakwaters particularly the PRBW have a great capacity to dissipate wave energy under the different sea states in the Mekong Delta.

Gravity wave scattering by retrofitted circular breakwaters using dual boundary integral formulation

In the present study, the gravity wave scattering by circular edged breakwaters in the presence of retrofits is analysed within the framework of linearized water wave theory. Various types of retrofits (say, porous shield) such as quarter-circular retrofit, semi-rectangular retrofit, semi-circular retrofit, and rectangular retrofit are investigated to protect the newly developed or existing circular breakwaters from the incident wave stroke. A dual boundary integral formulation is used to solve the boundary value problem considering the quadratic pressure drop boundary condition for the waves past the thin porous barriers. A generalized computer code is developed to accommodate the domain changes and is validated with the known results available in the literature. Various results such as the scattering coefficients (wave reflection, transmission and wave energy loss) and force coefficients (vertical and horizontal force on the breakwater and retrofit) are computed as a function of non-dimensional wave number and discussed. The sharp-edged retrofits (rectangular and semi-rectangular) display a considerable reduction of wave transmission as compared with smooth-edged retrofits, and the semi-circular breakwater with rectangular retrofit is suggested for further development of the porous structures. The effect of porous shield alone, breakwater alone, both breakwater and shield on incident wave energy distribution is also reported. The minimal wave transmission and higher wave damping coefficients attended occurred by the proposed breakwaters are identified when the shield porosity varies within 0.1≤μ≤0.2.

Evaluation of coastal protection strategies and proposing multiple lines of defense under climate change in the Mekong Delta for sustainable shoreline protection

Coastal protection measures and management play an important role in coping with coastal disasters and climate-induced sea-level rise. In this study, the success and failure of typical coastal protection works of the Vietnamese Mekong Delta (VMD) are reported and documented from field observations over a study period of 10–15 years. The coastal protection structures evaluated include revetments, geotubes, t-shaped bamboo fences, Pile-rock breakwaters, Busadco's breakwaters, Semi-Circular breakwaters, and Hollow triangle breakwaters. This paper briefly reviews the current situation of coastline erosion problem and accretion in the VMD and illustrates the severity of the current erosion rate that threatens the safety of coastal communities. The paper then evaluates the advantages and disadvantages of various coastal management approaches currently in practice in the VMD to classify different types of possible measures for coastal management with the aim to find holistic measures for planning which require low construction investment. Integrated coastal management and planning are outlined at a regional scale followed by the lessons learned from the previous coastal protection works, and finally the multiple lines of defense (MLD) solution is proposed, which is a green infrastructure inspired nature-based solution. The MLD solution can improve biodiversity, facilitate mangrove forest restoration, and ensure sustainable livelihoods for local communities. Integrated coastal planning and management solutions that are based on the MLD principle are expected to withstand coastal disasters under future climate change, and sea-level rise on the VMD.

Numerical Simulation and Piv Measurements of the Wave-Induced Flow Field Near Semi-Circular Breakwaters

Numerical Simulation and Piv Measurements of the Wave-Induced Flow Field Near Semi-Circular Breakwaters

Prediction of wave reflection for quarter circle breakwaters using soft computing techniques

The modified form of the semi-circular breakwater is called Quarter-Circle Breakwater (QBW). It consists of a quarter-circular surface facing incident waves, a horizontal bottom, a rear wall, and is built on a rubble mound foundation. In general, QCB may be constructed as emerged, with and without perforations that may be on one side or either side based on the coastal designer. These perforations dissipate the energy due to the formation of eddies and turbulence created inside the hollow chamber. In the present study, experimental data obtained from Binumol, 2017 are fed as input to both the models. This data is used to predict the reflection coefficient of QBW by adopting the ANN system approach. The reliability of the Artificial Neural Network (ANN) approach is done with statistical parameters, namely Model Performance Analysis (MPA) viz., Correlation Coefficient (CC), Root Mean Square Error (RMSE), Nash-Sutcliffe Efficiency (NSE), and Scatter Index (SI). The results of the MPA indicate that the ANN is suited for predicting the reflection coefficient of QBW.

Performance assessment of corrugated semi-circular breakwaters for coastal protection

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

Performance of submerged semi-circular breakwater under solitary wave in consideration of porous media

Submerged breakwater as the main structure of coastal engineering to protect coast is widely laid on the seabed because of its significant wave-dissipation performance. To reveal the interaction mechanism between waves and submerged breakwater, the hydrodynamic characteristics of a wave passing over different solid breakwaters were numerically and experimentally studied. Compared with the previous research, considering breakwater made up of porous media and the effects of extreme waves generated by hurricanes or tsunamis, this paper systematically investigates the effects of the semi-circular porous medium breakwater on the breaking solitary wave run-up based on a numerical model with the immersed boundary (IB) method. The computational capability of this model is verified firstly. Then, depending on the model, a series of cases are carried out to research the effects of different breakwaters on the run-up of solitary waves. The results show that the influence of porous breakwater on wave propagation is more significant than that of the solid breakwater. With the increase of the gravel particle median diameter, the maximum run-up height and the horizontal hydrodynamic force on the breakwater decrease, while the vertical hydrodynamic force on the breakwater increases. Increasing the size of the breakwater is beneficial to reducing the wave run-up height and the forces on the sloping beach. Compared with the single breakwater, the impact of the tandem breakwater on the wave propagation is more significant.

Numerical study on the performance of semicircular and rectangular submerged breakwaters

A systematic numerical comparative study of the performance of semicircular and rectangular submerged breakwaters interacting with solitary waves is the basis of this paper. To accomplish this task, Nwogu\'s extended Boussinesq model equations are employed to simulate the interaction of the wave with breakwaters. The finite difference technique has been used to discretize the spatial terms while a fourth-order predictor-corrector method is employed for time discretization in our numerical model. The proposed computational scheme uses a staggered-grid system where the first-order spatial derivatives have been discretized with fourth-order accuracy. For validation purposes, five test cases are considered and numerical results have been successfully compared with the existing analytical and experimental results. The performances of the rectangular and semicircular breakwaters have been examined in terms of the wave reflection, transmission, and dissipation coefficients (RTD coefficients) denoted by K_R, K_T, K_D. The latter coefficient K_D emerges due to the non-energy conserving K_R and K_T,. Our computational results and graphical illustrations show that the rectangular breakwater has higher reflection coefficients than semicircular breakwater for a fixed crest height, but as the wave height increases, the two reflection coefficients approach each other. On the other hand, the rectangular breakwater has larger dissipation coefficients compared to that of the semicircular breakwater and the difference between them increases as the height of the crest increases. However, the transmission coefficient for the semicircular breakwater is greater than that of the rectangular breakwater and the difference in their transmission coefficients increases with the crest height. Quantitatively, for rectangular breakwaters the reflection coefficients K_R are 5-15% higher while the diffusion coefficients K_D are 3-23% higher than that for the semicircular breakwaters, respectively. The transmission coefficients K_T for rectangular breakwater shows the better performance up to 2.47% than that for the semicircular breakwaters. Based on our computational results, one may conclude that the rectangular breakwater has a better overall performance than the semicircular breakwater. Although the model equations are non-dissipative, the non-energy conserving transmission and reflection coefficients due to wave-breakwater interactions lead to dissipation type contribution.