Showing papers on "Breakwater published in 2016"

The Effectiveness, Costs and Coastal Protection Benefits of Natural and Nature-Based Defences.

Abstract: There is great interest in the restoration and conservation of coastal habitats for protection from flooding and erosion. This is evidenced by the growing number of analyses and reviews of the effectiveness of habitats as natural defences and increasing funding world-wide for nature-based defences-i.e. restoration projects aimed at coastal protection; yet, there is no synthetic information on what kinds of projects are effective and cost effective for this purpose. This paper addresses two issues critical for designing restoration projects for coastal protection: (i) a synthesis of the costs and benefits of projects designed for coastal protection (nature-based defences) and (ii) analyses of the effectiveness of coastal habitats (natural defences) in reducing wave heights and the biophysical parameters that influence this effectiveness. We (i) analyse data from sixty-nine field measurements in coastal habitats globally and examine measures of effectiveness of mangroves, salt-marshes, coral reefs and seagrass/kelp beds for wave height reduction; (ii) synthesise the costs and coastal protection benefits of fifty-two nature-based defence projects and; (iii) estimate the benefits of each restoration project by combining information on restoration costs with data from nearby field measurements. The analyses of field measurements show that coastal habitats have significant potential for reducing wave heights that varies by habitat and site. In general, coral reefs and salt-marshes have the highest overall potential. Habitat effectiveness is influenced by: a) the ratios of wave height-to-water depth and habitat width-to-wavelength in coral reefs; and b) the ratio of vegetation height-to-water depth in salt-marshes. The comparison of costs of nature-based defence projects and engineering structures show that salt-marshes and mangroves can be two to five times cheaper than a submerged breakwater for wave heights up to half a metre and, within their limits, become more cost effective at greater depths. Nature-based defence projects also report benefits ranging from reductions in storm damage to reductions in coastal structure costs.

Economic Assessment of Overtopping BReakwater for Energy Conversion (OBREC): A Case Study in Western Australia

Abstract: This paper constructs an optimal configuration assessment, in terms of the financial returns, of the Overtopping BReakwater for wave Energy Conversion (OBREC). This technology represents a hybrid wave energy harvester, totally embedded in traditional rubble mound breakwaters. Nine case studies along the southern coast of Western Australia have been analysed. The technique provides tips on how to estimate the quality of the investments, for benchmarking with different turbine strategy layouts and overlapping with the costs of traditional rubble mound breakwaters. Analyses of the offshore and nearshore wave climate have been studied by a high resolution coastal propagation model, forced with wave data from the European Centre for Medium-Range Weather Forecasts (ECMWF). Inshore wave conditions have been used to quantify the exploitable resources. It has been demonstrated that the optimal investment strategy is nonlinearly dependent on potential electricity production due to outer technical constraints. The work emphasizes the importance of integrating energy production predictions in an economic decision framework for prioritizing adaptation investments.

Prototype Overtopping Breakwater for Wave Energy Conversion at Port of Naples

Abstract: The integration of the wave energy devices (WECs) into existing or new coastal structures could be a realistic solution to reducing their very high costs (Vicinanza et al., 2014). Nowadays very few devices have been constructed in full scale and no one is in commercial phase. The paper presents the prototype of an innovative breakwater for wave energy conversion installed in the port of Naples in 2015. The device is denominated OBREC (Overtoppin g BReakwater for Energy Conversion) and represents the world’s first WEC prototype completely embedded into a breakwater, which exploits the wave overtopping process. This article shares the entire design process, from concept, the preliminary design in small scale to the full-scale prototype construction.

Interaction between oblique waves and perforated caisson breakwaters with perforated partition walls

Abstract: This study gives an analytical solution for oblique wave interaction with perforated caisson breakwaters having perforated partition walls. The periodic boundary conditions of the velocity potential and its derivative in the caisson length direction are incorporated into the solution. A velocity potential decomposition method is used to obtain velocity potentials inside caisson chambers. The newly developed analytical solution is confirmed by the solutions for several special cases of the present breakwater and an independently developed multi-domain boundary element method solution for the present problem. The analytical solution is also validated by experimental data. The reflection coefficients, the wave forces and the surface amplitudes near the breakwater are examined, and some useful results are presented. This study may give a better understanding of the effect of perforated partition walls on the hydrodynamic performance of perforated caisson breakwaters.

Nonlinear Dynamic Simulation of Offshore Breakwater on Sloping Liquefied Seabed

Abstract: Offshore structures are generally vulnerable to strong seismic waves propagating through a loose seabed foundation. However, only limited attention has been paid to the seismic stability of composite breakwaters. In this study, a coupled numerical analysis is performed to study the seismic dynamics of a composite breakwater on a sloping loose seabed foundation under a seismic wave recorded during the 2011 Tohoku earthquake (M L = 9.0) in Japan. Computation results show that the developed numerical model is capable of capturing a variety of nonlinear phenomena in the interaction process between offshore structures and their loose seabed foundation. Under seismic loading, the loose seabed foundation away from the composite breakwater becomes completely liquefied. Because of the presence of the structure, the seabed foundation beneath the composite breakwater is partially liquefied. The composite breakwater undergoes significant subsidence, translation, and rotation; meanwhile, large lateral spreading occurs in the sloping seabed foundation. This investigation demonstrates that an advanced numerical method is promising in realistic evaluation of seismic performance of offshore structures.

Experimental study of the short-term efficiency of different breakwater configurations on beach protection

Abstract: A campaign of experimental tests on a 2D movable-bed physical model, reproducing an Italian beach on the Adriatic Sea, has been performed in the wave flume of the “Laboratorio di Idraulica e Costruzioni Marittime” of the Universita Politecnica delle Marche (Ancona, Italy), with the aim to assess the fundamental features of various breakwater configurations to be used in a beach-defence system typical of sandy, low-coastline beaches. Three emerged and three submerged configurations of rubble-mound detached breakwaters, for beach protection, placed at different distances from the shore, were tested, as well as a free beach configuration. The short-term hydrodynamic performances of the different configurations were assessed using as forcing some typical real-life intense sea-storm conditions. Wave transmission and beach protection efficiency under various intense wave conditions were obtained and related to some dimensionless parameters, amongst which a recently introduced one, $$\chi $$ , that combines both wave and breakwater properties. Transmission coefficients were found to be about 0.4 for emerged breakwaters and in the range 0.5–0.8 for submerged breakwaters. A net damping coefficient, defined as the wave height decay solely due to the effect of the breakwater, was measured as 0.2 for submerged breakwaters and 0.4 for the emerged ones. Further, submerged breakwaters induce an inshore mean water superelevation that increases with $$\chi $$ , whilst it decreases in the case of emerged breakwaters. Wave transmission is well represented by existing literature relations for both emerged and submerged breakwaters. Emerged breakwaters are more protective than submerged ones, but, at the same time, are more sensitive to changes in structure dimensions or positions. This is confirmed by the analysis of the momentum flux within the nearshore region, which is much larger for the submerged breakwaters. Such structures induce large swash-zone motions and sediment transport, comparable to those occurring at an unprotected beach.

Numerical Analysis on Wave Characteristics around Submerged Breakwater in Wave and Current Coexisting Field by OLAFOAM

Abstract: OLAFOAM is the powerful CFD code and is an expanded version of OpenFOAM ® , for wave mechanics simulation. The OpenFOAM ® does provide many solvers to correspond to each object of the numerical calculation in a variety of fields. OLAFOAM’s governing equation bases on VARANS (Volume-Averaged Reynolds-Averaged Navier-Stokes) equation, and the finite volume method is applied to numerical techniques. The program is coded in C++ and run on the Linux operating system. First of all, in this study, OLAFOAM was validated for 1) wave transformation inside porous structure under bore and regular wave conditions, 2) wave transformation by submerged breakwater under regular wave condition, and 3) regular wave transformation and resultant vertical velocity distribution under current by comparison with existing laboratory measurements. Hereafter, this study, which is almost no examination carried out until now, analyzed closely variation characteristics of water surface level, wave height, frequency spectrum, breaking waves, averaged velocity and turbulent kinetic energy around porous submerged breakwater in the wave and current coexisting field for the case of permeable or impermeable rear beach. It was revealed that the wave height fluctuation according to current direction(following or opposing) was closely related to the turbulent kinetic energy, and others.

Shape optimization of a breakwater

Abstract: In this paper, we optimize the shape of a breakwater which protects a harbour basin from incoming waves. More specifically, our objective is reducing the harbour resonance due to long-range ocean waves. We consider the complex-valued Helmholtz equation as our model state equation and minimize the average wave height in the harbour basin with the shape of the breakwater as optimization variable. The geometry is described by the level set method, i.e. the domain is given as the subzero level set of a function. In contrast to many publications we use the volume expression of the shape derivative, which lends itself naturally to a level set update via a transport equation. The model problem features intrinsic geometric constraints which we treat in the form of forbidden regions. We guarantee feasibility of the iterates by projecting the gradient onto a suitable admissible set.

Laboratory study on protection of tsunami-induced scour by offshore breakwaters

Abstract: Devastating tsunami waves can mobilize substantial amount of coastal sediment. Scouring is the primary damage caused by tsunamis. Offshore submerged or emerged breakwaters are coastal structures that are commonly employed to provide protection to valuable coastal beaches from energetic ocean waves. However, the protection capabilities of tsunami scour by submerged or emerged breakwater are less understood compared to tsunami runup and tsunami inundation. A set of laboratory experiments are reported in this study on protection of tsunami-induced scour by submerged or emerged breakwaters on a sandy beach. FLOW-3D is used in this paper to calculate flow field of tsunami wave propagation over the breakwater in order to help us to understand the sediment transport and tsunami scour process. Our experiments show that the submerged breakwater could not effectively reduce the tsunami scouring and only could affect the height and position of deposition sand bar. The emerged breakwater could significantly effectively reduce the tsunami scouring on the sandy beach; meanwhile, local scouring caused by plunging jet occurs mainly on the both sides of the structure. It is also found that for typical tsunamis, the scour depth at shoreward is unlikely to reach its equilibrium stage. Local scouring damage is one of the main factors leading to the destruction of coastal structures during a tsunami event. The most important governing parameters on local scouring around breakwater were defined. The final empirical relations that define the magnitude and position of local scouring around the breakwater were presented. The information reported in this study is useful for local authorities to assess potential tsunami damage of structure and to have a better plan for tsunami preventing and reducing.

Assessing the Hydro-Morphodynamic Response of a Beach Protected by Detached, Impermeable, Submerged Breakwaters: A Numerical Approach

Abstract: Postacchini, M.; Russo, A.; Carniel, S., and Brocchini, M., 2016. Assessing the hydro-morphodynamic response of a beach protected by detached, impermeable, submerged breakwaters: A numerical approach. Coastal areas host a large fraction of the world's population and are exposed to natural extreme events, which are a serious threat to human life, as well as to economies. For this reason, sea storms are increasingly the object of studies, and the design of traditional coastal defenses is being carried out in conjunction with modeling analyses. Relying on numerical simulations performed by means of an innovative shallow-water hydro-morphodynamic model, the present work explores the overall response of a protected beach to sea storms. Numerical tests evaluate the effects of sea states extracted from realistic sea storms having different spectral characteristics, as well as the influence on beach morphology of positioning shore-parallel, impermeable, submerged breakwaters. Simulation results revealed ...

Instability of a Caisson-Type Breakwater Induced by an Earthquake–Tsunami Event

Abstract: The Tohoku coastal area in Japan suffered massive damage in the Great Tohoku Earthquake, in which a prolonged major earthquake was followed by a large tsunami. The damage mechanisms of coastal structures during earthquake–tsunami events have not been fully explained. Thus, this study elucidates the damage mechanism of breakwaters by focusing on the interactions among earthquake–tsunami events, caisson structures, and soil composed of rubble mounds and seabed components. Centrifuge model tests, finite-element analyses, and smoothed particle hydrodynamics simulations with tsunami–soil–structure interactions were performed. The simulated breakwater was destabilized by not only wave pressure, but also long-acting tsunami seepage flow and overflow into the rubble mound and the seabed. These processes resulted in scour and fluidization/liquefaction, which decreased the bearing capacity. Moreover, the liquefaction resulting from earthquake motion caused caisson subsidence and excess pore water pressure i...

Application of X-Band Wave Radar for coastal dynamic analysis: case test of Bagnara Calabra (south Tyrrhenian Sea, Italy)

Abstract: Sea state knowledge has a key role in evaluation of coastal erosion, the assessment of vulnerability and potential in coastal zone utilization, and development of numerical models to predict its evolution. X-band radar measurements were conducted to observe the spatial and temporal variation of the sea-state parameters along a 3 km long sandy-gravelly pocket beaches forming a littoral cell on Bagnara Calabra. We produced a sequence of 1000 images of the sea state extending offshore up to 1 mile. The survey has allowed monitoring the coastline, the directional wave spectra, the sea surface current fields, and the significant wave heights and detecting strong rip currents which cause scours around the open inlets and affect the stability of the submerged reef-type breakwaters. The possibility to validate the data acquired with other datasets (e.g., LaMMA Consortium) demonstrates the potential of the X-band radar technology as a monitoring tool to advance the understanding of the linkages between sea conditions, nearshore sediment dynamics, and coastal change. This work proves the possibility to obtain relevant information (e.g., wave number, period, and direction) for evaluation of local erosion phenomena and of morphological changes in the nearshore and surf zone.

Identifying Coastal Defence Schemes through Morphodynamic Numerical Simulations along the Northern Coast of Yucatan, Mexico

Abstract: Ruiz-Martinez, G.; Marino-Tapia, I.; Mendoza Baldwin, E.G.; Silva Casarin, R., and Enriquez Ortiz, C.E., 2016. Identifying coastal defence schemes through morphodynamic numerical simulations along the northern coast of Yucatan, Mexico. A beach segment on the northern coast of the Yucatan Peninsula, where sandy beaches have widespread erosion problems, was studied with morphodynamic numerical simulations to identify the most appropriate protection scheme for mitigating coastal erosion in the region. The numerical model Delft3D was used to model hydro-morphodynamic patterns. Three types of solution were simulated: (1) beach nourishment only, (2) beach nourishment and groynes (linear, Y- and T-shaped), and (3) beach nourishment and offshore breakwaters. Measured time series of wind, sea level, and shelf currents were fed into the numerical model. Morphodynamic simulations were validated by comparing the modelled volumetric changes with those observed from beach profiles. The morphodynamic evolution ...

Horizontal loading experiments on reinforced gravity type breakwater with steel walls

Abstract: In the 2011 off the Pacific coast of Tohoku Earthquake, especially coastal areas of the Pacific Ocean suffered extensive damage by tsunami. Then, there were needs to develop reinforcement methods for existing breakwaters against tsunami force. The authors proposed a method to reinforce a breakwater against tsunami with a steel wall behind the breakwater. This report presents the experimental results of the breakwater reinforcing method. In the proposed method, steel piles are inserted behind the breakwater and rubbles are filled between the caisson and the piles. The model caisson failed in sliding mode without this improvement method. When it was reinforced with steel walls and filling, the horizontal resistance of the model caisson improved effectively. The failure mode of the caisson changed from sliding mode to ground failure mode. By analyzing the bending moment of the steel wall, the stress distribution in the wall from the caisson via filling and the ground was obtained and failure surface of the ground can be estimated.

Co-seismic and post-seismic behavior of a wall type breakwater on a natural ground composed of liquefiable layer

Abstract: The tsunami disaster countermeasures such as breakwaters might be damaged or lose their capacity to resist tsunami after a strong earthquake. Therefore, not only the co-seismic behaviors of a breakwater and its foundation system during earthquake loading, but also the post-seismic behavior after the earthquake loading should be investigated and estimated for future tsunami preparation, especially when the foundation ground is composed of liquefiable layer, which may cause large amount of displacement to the breakwater. In this study, the co-seismic and post-seismic behavior of an existing wall type breakwater on a natural ground which is composed of nonuniform liquefiable layer and thick cohesive layer with low permeability is investigated using an effective stress-based soil–water coupling numerical method. In the calculation, the complicated nonlinear dynamic behavior of the foundation soil is described by an advanced elasto-plastic soil constitutive model. A real recorded seismic wave, which consists of a major shock and two aftershocks from the 2011 Great East Japan earthquake, is adopted as the input earthquake loading. The calculation results indicate that the used numerical method is capable of capturing the progressive liquefaction and consolidation process of the foundation soil, as well as the subsidence and differential settlement of the breakwater during and after earthquake loading. The influence of earthquake loading can significantly reduce the capacity of breakwater to resist tsunami which may arrive within 1 h after earthquake; therefore, anti-seismic design should be taken into consideration in future tsunami preparation.

Hybrid Structure Combining a Wave Energy Converter and a Floating Breakwater

Abstract: This experimental study investigates on a hybrid structure consisting in an “active” floating breakwater (FB), coupled with a new type of wave energy converter, named ShoWED. The hybrid structure achieves the double purpose of generating electrical energy and of protecting marinas. The specific objective of the tests is to evaluate the performance of the ShoWED when installed in front of a FB and the effects of the wave energy device on the performance of the FB. Physical model tests were carried out at two different scales: 1) in scale 1:20, necessary to evaluate the performance and dynamics of the FB in the absence of the ShoWED. 2) in scale 1:1, in order to evaluate the efficiency of the ShoWED, at different distances from a rear reflective vertical wall, simulating the presence of the FB. A peculiarity of these latter tests is that the real PTO was tested, allowing to measure the produced electrical energy, as a function of the real external electrical impedance. It is concluded that the ShoWED is able to harvest electrical energy if the incident wave height is larger than 0.05 m, a limit possibly given by some friction threshold in the PTO, and if the wave has a period longer than 1.0 s, a limit possibly caused by the finite width of the floater, 70 cm, not negligible compared to the wavelength associated to periods smaller than 1 s. Maximum excursion of the floater are achieved when the floater location takes advantage of the total reflection of the rear wall: for T=2 s, a 26% efficiency was obtained (measured with a “wave to wire” approach), so that a 10 cm wave height produced 7 W in the laboratory. The reflection and transmission characteristics of the hybrid structures were evaluated indirectly, and the benefits compared to a traditional FB should be appreciable especially for long waves.