Design Of Breakwaters Research Articles

Community-Based Portable Reefs to Promote Mangrove Vegetation Growth: Bridging between Ecological and Engineering Principles.

Despite all efforts and massive investments, the restoration of mangroves has not always been successful. One critical reason for this failure is the vulnerability of young mangroves, which cannot grow because of hydrodynamic disturbances in the shallow coastal water. For a comprehensive study bridging ecological and engineering principles, a portable community-based reef is proposed to shield mangroves from waves during the early stages of their growth. A series of field observations were conducted on Amami Oshima Island (Japan), to observe the growth of young mangroves and their survival rate under moderate wave conditions. The evolution of young mangroves was also observed in the laboratory under a controlled indoor environment. At the research site, it was confirmed that, after six months of germination, young mangroves could withstand normal high waves. Laboratory-grown plants were lower in height and had fewer leaves compared with the native mangroves on Amami. Based on these results, an economical reef system was designed. For this purpose, the Ahrens formula for the design of a low-crested reef breakwater was revisited. The results showed that a 50-cm-high reef constructed with 15-kg stones can protect mangroves that are a few months old and effectively promote early mangrove growth.

Wave scattering by inverted trapezoidal porous boxes using dual boundary element method

A numerical model is developed based on the dual boundary element method (DBEM) to solve the problem of surface gravity waves past multiple floating inverted trapezoidal porous boxes under the framework of linear potential flow theory. The continuity of velocity and semi-empirical quadratic pressure drop equation is adopted on the porous boundary to incorporate the effect of incident wave amplitude on the energy loss coefficient. Various results by an array of inverted trapezoidal porous boxes are discussed in the form of scattering coefficients (wave reflection, transmission, and energy loss coefficients), and force coefficients (horizontal force, vertical force, and moment). The verification of the numerical model is carried out by an independently developed multi-domain boundary element method (MBEM) code, and also with results available in the literature. The study reveals that, in most cases, the long waves exhibit insignificant hindrance whereas intermediate waves delineate the harmonic oscillations and deep water waves feel maximal hindrance by inverted trapezoidal porous boxes. The wave damping of KL≥0.95 is obtained for structural width B/λ≥0.66 by a pair of identical inverted trapezoidal porous boxes. The angle of porous wings is helpful to alter the scattering coefficients and also helps in the fine-tuning of force coefficients. The angle of partially open wings within 300≤θ≤600 is suggested along with structural porosity μ=0.25 for effective constriction of incident waves. The parametric analysis will be useful in the meticulous design of cost-effective breakwaters.

Bragg scattering of surface gravity waves by a submerged wavy porous plate

Bragg scattering of surface gravity waves by a slender pile-supported submerged wavy porous plate is studied under the assumption of small amplitude water wave theory. The waves past porous barriers are modeled using linearized pressure drop boundary condition known as Darcy law. Numerical solution for the boundary value problem is obtained using the Multi-Domain Boundary Element Method and the outcomes are validated with known results in the literature. For different wave and structural parameters such as the effect of the number of ripples of the wavy plate, effect of the relative ripple amplitude, relative plate length, plate porosities, and relative submergence depth; various physical quantities of interests like reflection and transmission coefficients, vertical force, and horizontal force coefficients are computed and analyzed. The study reveals that Bragg scattering occurs in the water of shallow and intermediate-depth for a wavy plate having more than two ripples and wave reflection increases with an increase in the amplitude of the wavy plate. For higher wavenumber or with an increase in plate length, Bragg scattering with harmonic and sub-harmonic peaks in the reflection coefficients are noticed in the case of wavy plate irrespective of permeability unlike the oscillatory decreasing pattern in the case of a flat plate. Wave forces exerted on the submerged plate decreases significantly with the introduction of structural porosity due to the dissipation of wave energy. Moreover, an increase in the number of ripples and ripple amplitude reduces the wave transmission; thus improving the overall performance for a wide range of frequencies. The study will be useful in the design of effective breakwaters for mitigating wave effects in the marine environment.

Hydroelastic Response of a Flexible Submerged Porous Plate for Wave Energy Absorption

The application of flexible horizontal porous structure has a significant impact on the design of breakwaters and wave energy absorption devices for coastal protection and wave energy extraction, respectively. This type of structure is more economical compared to a rigid type structure. Therefore, the hydroelastic response of the flexible porous structure can be investigated to widen the influence of structural deformations in design parameters. This paper presents a generalized expansion formula for the said problem based on Green’s function in the water of finite depth (FD) and infinite depth (ID). The series form of the velocity potentials for the wave-maker problem is also derived using Green’s second identity. The derived expansion formula is applied to a real physical problem and the analytical solution is obtained utilizing a matched eigenfunction expansion method under velocity potential decompositions. The convergence study of the series solution is checked. The present results and the published experimental datasets, as well as analysis, are compared. The effect of design parameters on the hydroelastic response of the submerged flexible porous plate is analyzed. It is observed that the analysis of the results will be useful for gaining insight into how to design a wave energy absorption device.

Wave Model for the Design of Sustainable Coastal Infrastructures at an Industrial Site in Tuban, East Java

This study focuses on the use of computational model in the design of a breakwater structure, which aims to determine the propagation pattern of the long-term ocean waves, in order to understand their propagation from the deep waters, and to determine the distribution of their energy around a proposed breakwater construction site. The method used is computational simulation of the wave model using the 2D Boussinesq Wave (BW) Module of MIKE21 software. The simulation used an incoming wave of 4.6 m high, which corresponds to the 100 years return-period value. The results show that the existing breakwater layout can protect the harbour by reducing the incoming waveheight by up to 75%. At the proposed design condition, the propagation pattern of the incoming wave slightly differs from the existing condition. The presence of the slopes on both sides of the channel changes the wave direction outwards due to shoaling effects, and consequently, larger concentration of wave energy occurs at some parts of the proposed breakwater design. Results from the model are useful for the design of the new breakwater structures, which is designed according to the predicted wave energy distribution.

Joint probability analysis of marine environmental elements

Reasonably determining the fortification criterion is one of the important links in the design of breakwaters and flood walls, and it is directly related to the construction cost and protection efficiency of these engineering works. Wave height is one of the most important element of the marine environment determined by the breakwater and flood protection standards. Based on the stochastic process theory, this paper gives a mathematical description of the stochastic process that can reflect the deeper level of statistical characteristics regarding the wave heights. By regarding the number of typhoons in a certain sea area as a Poisson process, this paper establishes a new model for the joint probability analysis of marine environmental elements: the nested random composite distribution model, and it gives the display expression of the new model. We also take typhoon data, wave height, and water increase data under typhoon influence from Weizhou Hydrological Station in western Guangdong, China from 1990 to 2016 as samples, and use the Gumbel-Pareto distribution as the edge distribution to apply the nested random composite distribution model to typhoon-affected sea areas. The joint recurrence period under different time combinations is calculated, and the joint statistical characteristics of the same element or different elements in different periods are also given.

Adaptation strategies for port infrastructure and facilities under climate change at the Kaohsiung port

The growing impact of climate change on port infrastructure and facilities currently may lead to a rising frequency of such serious natural disasters or accidents as rising sea level, increasing extreme weather, increasing intensity of tropical storms and typhoons, rising wave height surmounting breakwater design levels, heavy rain exceeding quay well drainage capacity, rising ocean temperatures, and deteriorating harbor water quality. The paper aims to apply a risk management matrix approach to vulnerability assessment and identification of desirable adaptation strategies. The data for this investigation is first collected by means of questionnaire survey of experts in shipping companies or port management offices at the Kaohsiung port. Then, a vulnerability analysis of port infrastructure and facilities is carried out under the impact of severe typhoons. Subsequently, adaptation strategies are identified for infrastructure and facilities at the Kaohsiung port to address the adverse impacts of climate change. One intellectual merit of this paper is that ten vulnerability assessment criteria are proposed for addressing the impacts of climate change on port infrastructure and facilities. Second, both ground and access roads in the port area, and drainage facilities in flooding-prone areas are shown to be damaged in the moderate risk areas potentially impacted by typhoons. The third merit is that a set of adaptation strategies has been identified for the moderate risk areas impacted by serious typhoons.

Scattering of Gravity Waves by Multiple Submerged Rubble-Mound Breakwaters

A numerical model based on multi-domain is developed to investigate the scattering of surface gravity waves by an array of submerged rubble-mound breakwaters. The boundary value problem is analysed in two dimensions under the assumption of small-amplitude wave theory in the water of finite depth. Analytical solution based on the eigenfunction expansion method is independently developed to validate the numerical model in addition to available results in the literature. Various configurations such as trapezoidal, triangular, and circular shapes are investigated parametrically. The performance characteristics are discussed by analysing the scattering coefficients (such as reflection, transmission, and damping coefficient) for different physical parameters like relative water depth, relative structural dimensions, relative spacing, and the number of submerged breakwaters. In the case of trapezoidal breakwaters, the crest width plays a major role in dampening the wave energy by a whopping 90%. Moreover, the wave damping performance of triangular breakwaters is very poor. The Bragg resonant reflection is observed to be a trivariate function, which depends on structural porosity, structural thickness, and the number of submerged breakwaters. The free spacing is evident in adjusting the position of Bragg resonant reflection by multiple equi-spaced structures of several shapes. The present study will be useful in the effective design of Bragg breakwaters for establishing a calm wave environment near the harbour regions.

Numerical and Experimental Analyses of Breakwater Designs for Turbulent Flow Characteristics and Sediment Transport Under Coastal Wave Actions

Abstract The goal of the study is to identify optimal breakwater designs to be placed on the banks of various water bodies in coastal Louisiana, to prevent the coastal erosion. Coastal erosion is a significant concern for Louisiana's wavy coastline. The loss of coastal wetlands is threatening the environment and the economic development. One of the ways to prevent coastal erosion and wetland losses is by using breakwaters designed to reduce the wave energy and change the transport of sediments brought by the waves. The objective of this research is to analyze the turbulent characteristics around specially designed three-dimensional (3D) breakwaters, and its impact on sediment deposition under coastal wave actions. Both computational fluid dynamics (CFD) simulations and experimental measurements were conducted. In order to validate the CFD models used for this study, the simulation results were compared to data measured from a scale-down experiment. Once the validity of the CFD models has been confirmed on three miniature panels, namely, a solid panel, a panel with three holes, and a panel with eight holes, the simulations were scaled up to the actual size of the designed breakwater panels for tests. The breakwater designs aim to allow sediment pass through the holes, to deposit sediment at target areas, and to reduce wave actions. There were three different panel-design cases simulated in this study. The results of 3D CFD simulations of these panels were compared and analyzed to determine the performance of each design in terms of wave reduction and sediment retention.

A Field Experiment on Wave Forces on an Energy-Absorbing Breakwater

The U-OWC is a caisson breakwater embodying a device for wave energy absorption. Under the wave action, the pressure acting on the upper opening of the vertical duct fluctuates, producing a water discharge alternatively entering/exiting the plant through the U-duct, formed by the duct and the chamber. The interaction between incoming waves and the water discharge alters the wave pressure distribution along the wave-beaten wall of this breakwater compared with the pressure distributions on a vertical pure reflecting wall. As a consequence, the horizontal wave forces produced on the breakwater are also different. A small scale U-OWC breakwater was put off the eastern coast of the Strait of Messina (Southern Italy) to measure the horizontal wave force. Experimental results were compared with Boccotti’s and Goda’s wave pressure formulas, carried out for conventional upright breakwaters, to check their applicability on the U-OWC breakwaters. Both models are suitable for design of U-OWC breakwaters even if they tend to overestimate by up to 25% the actual horizontal loads on the breakwater. Indeed, the greater the absorption of the energy is, the lower the wave pressure on the breakwater wall is.

Bulk Wave Dissipation in the Armor Layer of Slope Rock and Cube Armored Breakwaters

The objective of this research is to analyze the interaction of the incident wave train with a mound breakwater (specifically, dissipation in the armor layer) and to quantify the performance of the structure built with different types and sizes of armor units. The generalized Π -Buckingham theorem is invoked to choose a complete set of independent variables that govern the principal interaction processes. The analysis is based on two sets of experimental data obtained in the wave flume of IISTA, University of Granada, and in the wave flume of Aalborg University. The bulk dissipation depends on the product of the relative water depth and the incident wave steepness, (h/L)(HI/L), the relative size of the armor diameter, Da/HI, the relative thickness, e/L, the shape and specific placement criterion, the characteristics of the porous core, B*/L, D50,p/L, and the slope angle of the breakwater. For a given breakwater, the product of (h/L)(HI/L) can be used to identify and quantify three hydrodynamic performance regimes: reflective, dissipative and transitional, based on the prevalent interaction processes. Moreover, the dimensional analysis provides a functional relationship between the stability parameter and the bulk dissipation. For two mound breakwaters, one built with cubes of Da=49.6 mm and the other one with rocks of Da=44.0 mm, the bulk dissipation is almost similar over the entire range of (h/L)(HI/L). These results could be useful for the assimilation of data obtained in different wave flumes, the optimization of the breakwater design and to revise the notional permeability parameter.

Load & Resistance Factors Calibration for Limit State Design of Non-Perforated Caisson Breakwater

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Influence of Mild Bottom Slopes on the Overtopping Flow over Mound Breakwaters under Depth-Limited Breaking Wave Conditions

The crest elevation of mound breakwaters is usually designed considering a tolerable mean wave overtopping discharge. However, pedestrian safety, characterized by the overtopping layer thickness (OLT) and the overtopping flow velocity (OFV), is becoming more relevant due to the reduction of the crest freeboards of coastal structures. Studies in the literature focusing on OLT and OFV do not consider the bottom slope effect, even if it has a remarkable impact on mound breakwater design under depth-limited breaking wave conditions. Therefore, this research focuses on the influence of the bottom slope on OLT and OFV exceeded by 2% of incoming waves, hc,2% and uc,2%. A total of 235 2D physical tests were conducted on conventional mound breakwaters with a single-layer Cubipod® and double-layer rock and cube armors with 2% and 4% bottom slopes. Neural networks were used to determine the optimum point to estimate wave characteristics for hc,2% and uc,2% calculation; that point was located at a distance from the model toe of three times the water depth at the toe (hs) of the structure. The influence of the bottom slope is studied using trained neural networks with fixed wave conditions in the wave generation zone; hc,2% slightly decreases and uc,2% increases as the gradient of the bottom slope increases.

An experimental study on the hydraulic stability of Icelandic-Type berm breakwaters

One of the key aspects of breakwater design and safety assessment is their stability evaluation. In the present paper, hydraulic stability of a multi-layer berm breakwater (MLBB) has been studied through varying the parameter of eroded area. To this end, a 2-D experimental model has been carried out in the wave flume of Tarbiat Modares University using irregular waves with a JONSWAP spectrum. A total of 150 tests have been performed to cover a wide range of sea state conditions and geometrical parameters such as wave height, wave period, water depth, berm width, berm elevation, stone class I height, front slope and nominal diameter of stone class I. In this study, a new dimensionless parameter is introduced to indicate that the wave breaking type plays a fundamental role in stability of MLBBs. Eventually; a new formula is derived to estimate the damage of MLBBs, based on different sea state conditions and various geometrical parameters. Comparisons are made between the estimated damage parameter of MLBBs by the proposed formula and those estimated by existing formulae. The results denote that the present formula not only performs well for MLBBs experimental data, but also indicates a reliable performance for some of Lykke Andersen's (2006) data in statically homogenous berm breakwaters (HBBs) outside the range of given formula. Furthermore, an innovative approach is presented to examine the eroded area based on the berm recession and the intersection point of reshaped and initial profile from SWL, which performs faultlessly rather than the existing one.

Overtopping layer thickness and overtopping flow velocity on mound breakwaters

Mound breakwater design is evolving owing to rising sea levels caused by climate change and social concern regarding the visual impact of coastal structures. The crest freeboard of coastal structures tends to decrease while overtopping hazard increases over time. Pedestrian safety when facing overtopping events on coastal structures has been assessed considering the overtopping layer thickness (OLT) and overtopping flow velocity (OFV). This paper proposes a new method to estimate the OLT and OFV on mound breakwater crests during extreme overtopping events, based on 123 2D small-scale physical tests of conventional low-crested mound breakwaters with a single-layer Cubipod® and double-layer rock and cube armors. The new method to estimate OLT exceeded by 2% of incoming waves is based on formulas given in literature for dikes, but adapted and calibrated for mound breakwaters. The formula to estimate the OFV exceeded by 2% of incoming waves is based on the correlation between the statistics of the OLT and OFV, considering an empirical coefficient calibrated for each type of armor layer. Exponential and Rayleigh distribution functions are proposed for estimating the OLT and OFV with exceedance probabilities under 2%. Although the statistics of OLT and OFV depend on similar variables, contrary to intuition, specific OLT and OFV corresponding to the same overtopping event appear to be independent.

Stability Assessment of Rubble Mound Breakwaters Using Extreme Learning Machine Models

The stability number of a breakwater can determine the armor unit’s weight, which is an important parameter in the breakwater design process. In this paper, a novel and simple machine learning approach is proposed to evaluate the stability of rubble-mound breakwaters by using Extreme Learning Machine (ELM) models. The data-driven stability assessment models were built based on a small size of training samples with a simple establishment procedure. By comparing them with other approaches, the simulation results showed that the proposed models had good assessment performances. The least user intervention and the good generalization ability could be seen as the advantages of using the stability assessment models.

Functional performance of modular porous reef breakwaters

Reef breakwaters are submerged structures usually made out of rubble mound construction. Wave attenuation could be achieved off-shore by the introduction of such reef breakwaters. This offshore wave attenuation helps to protect a coast subjected to erosion. Such submerged structures are suitable when moderate wave transmission is acceptable on the lee side of the structure. This present work aims at providing a basis for the design of reef breakwaters using results from physical model tests. The hydrodynamic performance characteristics of the reef breakwaters, namely the transmission and reflection coefficients are examined in the study for varying wave parameters and geometric configurations of the reef. Further, the present experiments have helped shed light on Reef Induced wave Breaking (RIB) and its role in the hydrodynamic performance of the reef breakwater. The present investigations bring out those parameters which are involved in RIB so that a designer would be able to identify and provide-for the RIB. Design equations for prediction of transmission and reflection coefficients for submerged porous reef breakwaters in regular and random waves are proposed and compared with other such equations. It is shown that the present equations reproduce dependence of hydrodynamic performance on reef and wave parameters.

Effect of Sea Level Rise on the Wave Overtopping Rate at Berm Breakwater

This study quantitatively assessed the risk in the overtopping performance of berm breakwaters due to sea level rise (SLR). To achieve this, a recent overtopping prediction formula that includes the influence of water depth on the estimated overtopping rate was used for the analysis. Additionally, the probabilities of failure in terms of the overtopping rate for different SLR scenarios were estimated using the Monte Carlo simulations, and the optimal maintenance intervals were determined. The increase in the crest freeboard, required to maintain the design overtopping rate, was estimated to be less than the increase needed in berm width for the different sea level rise scenarios considered. Furthermore, the required crest freeboard was influenced less by the initial configuration of the berm width. Shorter maintenance intervals were required for structures with an initially wide berm compared to those with a high crest freeboard. The results indicated that the future design and maintenance of berm breakwaters need to consider the effects of SLR on the overtopping performance, especially in shallow water zones.

Overtopping wave reduction capability of Rakuna IV armor block used for Rubblemound Breakwater

Run up, overtopping are the main reasons that damage and unstabilize the coastal and basin protective structures. So, overtopping wave is an inevitable load during coastal structures designing process, particularly at present very complicated real situation of global sea level rise and climate change. Based on the early researches, allowable mean overtopping wave discharges play an important roll in determining breakwaters' dimension such as top elevation, slope protective alternatives in the port side and so on. The more permissible average overtopping wave discharges, the lower breakwater top elevation needed. Moreover, the weight of armor blocks used on a seaside slope can be reduced. However, the port side slope needs to be properly protected against the impact of overtopping wave. Thus, researching the application of new armored unit blocks with high overtopping wave reduction capability that is corresponsive to typhoon-generated wave conditions is totally in need. Rakuna IV is one of the newly developed wave-dissipating blocks invented by Nikken Kogaku (Japan) in 2007, and the stability of this block for rubble mound breakwaters has been investigated under non-wave overtopping conditions by many researchers in Japan, Korea, China, and Vietnam. To be more exhaustive in the design of breakwaters with this kind of block, this study carried out experimental research on wave overtopping performance of RAKUNA-IV (overtopping reduction by roughness factor γr) in wave flume at Ha Noi Water Resources University. Based on the physical model tests' results, the author has determined the overtopping wave reduction coefficient γr of Rakuna IV block and its relationship with Irribaren number xm-1,0.

Stability of Rubble Mound Breakwaters—A Study of the Notional Permeability Factor, Based on Physical Model Tests

The Van der Meer formulae for quarry rock armor stability are commonly used in breakwater design. The formulae describe the stability as a function of the wave characteristics, number of waves, front slope angle and rock material properties. The latter includes a so-called notional permeability factor characterizing the permeability of the structure. Based on armor stability model tests with three armor layer compositions, Van der Meer determined three values of the notional permeability. Based on numerical model results he added for a typical layer composition one more value. Based on physical model tests, the present paper provides notional permeability factors for seven layer compositions of which two correspond to the compositions tested by Van der Meer. The results of these two layer compositions are within the scatter of the results by Van der Meer. To help determination of the notional permeability for non-tested layer compositions, a simple empirical formula is presented.