Showing papers on "Breakwater published in 2012"

Dynamics of the Douro estuary sand spit before and after breakwater construction

Abstract: The Douro estuary sand spit (NW Portugal) is an important natural defence against the impact of storm events. Aiming to improve navigation safety, a breakwater was built to stabilise the spit. In 2001, a monitoring programme was set up to understand the dynamics of the sand spit and, later, to evaluate breakwater efficiency on stabilising the spit's shape and volume. Nine years of periodic, accurate 3D digital elevation models obtained from kinematic differential Global Positioning System surveys were used to assess spatial and temporal changes in the spit morphology before and after the breakwater construction. Temporal and spatial spit dynamics were further related to river discharge flows, wave action and wind energy. Although the breakwater had a stabilising effect on most of the spit's area and volume, it caused a clear change in the morphology of the spit's head and in the previously observed patterns of erosion and accretion. Before breakwater construction, erosion was significantly correlated with extreme river discharge and wind conditions; accretion was significantly correlated with extreme wind conditions; and spit area and volume at 1–2 m elevation with extreme wave conditions. After breakwater construction, these correlations were not found, but the eastern (inland) face of the spit and particularly its southern part became more susceptible to the observed extreme river discharge flows, wave and wind conditions. The instability in the SE part of the spit may pose a threat to an existing local Nature Reserve. Furthermore, before breakwater construction, the spit often breached during severe floods favouring river discharges. The strengthening of the spit after breakwater construction may reduce the likelihood of breaching and lead to more severe flood effects in the estuary.

Breaking wave-induced response and instability of seabed around caisson breakwater

Abstract: SUMMARY Breaking-wave-induced dynamic response and instability of seabed around a caisson breakwater are investigated. A seabed-rubble-breakwater system is modeled using finite elements. The impact response of the porous seabed and rubble foundation is assumed to be governed by the coupled Biot equations, and three possible formulations are considered with respect to the inclusion of inertial terms. The response is presented in terms of shear stress and pore pressure distributions at three locations underneath the breakwater. The effect of seabed and wave parameters and the inertial terms on the impact response is investigated through parametric studies. Analyses show that usually partly dynamic formulation yields the largest response amplitudes as compared to the fully dynamic formulation, which is the most complete form. The instability of seabed and rubble mound as a result of instantaneous liquefaction is also studied. Breaking wave-induced pressures in some cases are found to cause liquefaction in the rubble and the seabed. The effect of some parameters on the instability is found to be significant. Copyright © 2011 John Wiley & Sons, Ltd.

Seismic response of poro-elastic seabed and composite breakwater under strong earthquake loading

Abstract: The marine structures in offshore area, such as composite breakwater, are generally vulnerable to the strong seismic wave propagating through their seabed foundation. There are a lot of failure examples during the strong earthquake events in the world in the past 20 years. However, attention given to the seismic response of marine structures under strong seismic wave is limited. In this study, taking the dynamic Biot’s equation “u − p” as the governing equation for porous seabed foundation, the seismic response of a composite breakwater and its porous seabed foundation under the seismic wave recorded in the Japan 311 off the pacific coast of Tohoku earthquake (M L = 9.0) is investigated using a FEM numerical model. The numerical results indicate that the seismic response of composite breakwater is very strong in the earthquake process. The amplification of the input seismic wave occurs both in seabed foundation and composite breakwater; and this amplification is positively related to the buried depth of points. The horizontal seismic response is much strong than the vertical seismic response. The seismic wave induced excess pore pressure and effective stresses in seabed foundation vibrates; the vibration amplitude is also positively related to the buried depth of points. Under strong seismic loading, the surface region of seabed foundation could liquefy. The parametric study shows that the young’s modulus of seabed foundation has significant effect on the seismic response of composite breakwater.

Effect of Climate Change on Performance-Based Design of Caisson Breakwaters

Abstract: This paper presents a method to incorporate the effect of climate change on the performance-based design of a caisson breakwater and its application to the East Breakwater of the Port of Hitachinaka in Honshu, Japan. The up-to-date projection estimated a future sea-level rise of 0.25-0.6 m and a wave-height increase of 1.7 m (from 8.3 to 10 m) during the 21st century in this area. The influence of a sea-level rise on caisson sliding was minimal; the sea-level rise was much smaller than the water depth at the breakwater site. When the effects of climate change were not included, the performance-based design method calculated the same caisson width as that of the constructed breakwater, partly validating the consistency between conventional deterministic methods and performance-based design methods. The effects of climate change dictate an increase in caisson width of approximately 1.5 and 0.5 m for linear and parabolic increases of wave height, respectively, which are approximately 6.8 and 2.3% of the present caisson width of 22 m. Finally, it is recommended that the caisson breakwater be designed using the projected wave height and water level in 30 years from construction, if the deterministic design method is used and the effects of climate change are to be taken into account. DOI: 10.1061/(ASCE)WW.1943-5460.0000126. © 2012 American Society of Civil Engineers. CE Database subject headings: Breakwaters; Caissons; Climate change; Design; Sea level. Author keywords: Breakwaters; Caisson; Climate change; Performance-based design; Sea-level rise.

Hydrodynamic Characteristics of a Free-Surface Semicircular Breakwater Exposed to Irregular Waves

Abstract: A free-surface semicircular breakwater (SCB) has been developed for protecting coastal and marine infrastructures against ocean waves. The hydrodynamic characteristics of the breakwater are investigated in irregular seas through an experimental program. A test model of the semicircular breakwater has been constructed with front wall porosity varied at 0 (i.e., no perforations), 9, 18, and 27%. The wave surface elevations are measured at different locations upstream and downstream of the models, and the coefficients of wave transmission, reflection, and energy dissipation are evaluated. Wave climate in the vicinity of the breakwater models and horizontal wave force on them are also measured. On the basis of the measured data, empirical models are proposed to provide design formulas for wave transmission, wave reflection, and horizontal wave force. The proposed empirical models show good agreement with the measured data; however, sensible engineering judgment must be taken while using these because the equa...

Consolidation and dynamics of 3D unsaturated porous seabed under rigid caisson breakwater loaded by hydrostatic pressure and wave

Abstract: In this study, based on the dynamic Biot’s theory “u-p” approximation, a 3D finite element method (FEM) numerical soil model is developed, in which the Generalized Newmark-method is adopted to determine the time integration. The developed 3D FEM soil model is a part of the coupled model PORO-WSSI 3D for 3D wave-seabed-marine structures interaction problem, and is validated by the analytical solution proposed by Wang (2000) for a laterally infinite seabed loaded by a uniform force. By adopting the developed 3D soil model, the consolidation of seabed under a caisson breakwater and hydrostatic pressure is investigated. The numerical results show that the caisson breakwater built on seabed has very significant effect on the stresses/displacements fields in the seabed foundation after the transient deformation and primary consolidation are completed. The parametric study indicates that the Young’s modulus E of seabed is the most important parameter to affect the settlement of breakwater, and the displacement fields in seabed foundation. Taking the consolidation status as the initial condition, the interaction between ocean wave, caisson breakwater and seabed foundation is briefly investigated. The 3D ocean wave is determined by solving the Navier-Stokes equations with finite volume method (FVM). The numerical results indicate that there is intensive interaction between ocean wave, caisson breakwater and seabed foundation; and the breakwater indeed can effectively block the wave energy propagating to the coastline.

Time-domain hydrodynamic analysis of pontoon-plate floating breakwater

Abstract: The hydrodynamic behaviors of a floating breakwater consisting of a rectangular pontoon and horizontal plates are studied theoretically. The fluid motion is idealized as two-dimensional linear potential flow. The motions of the floating breakwater are assumed to be two-dimensional in sway, heave, and roll. The solution to the fluid motion is derived by transforming the governing differential equation into the integral equation on the boundary in time domain with the Green's function method. The motion equations of the floating breakwater are established and solved with the fourth-order Runge-Kutta method to obtain the displacement and velocity of the breakwater. The mooring forces are computed with the static method. The computational results of the wave transmission coefficient, the motion responses, and the mooring forces of the pontoon-plate floating breakwater are given. It is indicated that the relative width of the pontoon is an important factor influencing the wave transmission coefficient of the floating breakwater. The transmission coefficient decreases obviously as the relative width of the pontoon increases. The horizontal plates help to reduce the wave transmission over the floating breakwater. The motion responses and the mooring forces of the pontoon-plate floating breakwater are less than those of the pontoon floating breakwater. The mooring force at the offshore side is larger than that at the onshore side.

Rubble mound breakwater overtopping: estimation of the reliability of a 3d numerical simulation

Abstract: Until recently, physical models were the only way to investigate into the details of breakwaters behavior under wave attack. From the numerical point of view, the complexity of the fluid dynamic processes involved has so far hindered the direct application of Navier-Stokes equations within the armour blocks, due to the complex geometry and the presence of strongly non stationary flows, free boundaries and turbulence. In the present work the most recent CFD technology is used to provide a new and more reliable approach to the design analysis of breakwaters, especially in connection with run-up and overtopping. The solid structure is simulated within the numerical domain by overlapping individual virtual elements to form the empty spaces delimited by the blocks. Thus, by defining a fine computational grid, an adequate number of nodes is located within the interstices and a complete solution of the full hydrodynamic equations is carried out. In the work presented here the numerical simulations are carried out by integrating the three-dimensional Reynolds Average Navier-Stokes Equations coupled with the RNG turbulence model and a Volume of Fluid Method used to handle the dynamics of the free surface. The aim of the present work is to investigate the reliability of this approach as a design tool. Two different breakwaters are considered, both located in Southern Sicily: one a typical quarry stone breakwater, another a more complex design incorporating a spill basin and an armoured layer made up by Coreloc® blocks.

Design of detached breakwaters for coastal protection: development and application of an advanced numerical model

Abstract: An advanced nonlinear wave, sediment transport and bed morphology evolution 2DH model, for the design of coastal protection structures, has been developed. The extended Boussinesq equations, including higher order non-linear terms, which can describe the propagation of highly nonlinear waves in the shoaling region, surf and swash zone, are used. The bed and suspended load transport are estimated with a quasi-steady, semi-empirical formulation, developed by Camenen, and Larson (‘A unified sediment transport formulation for coastal inlet application’, Technical report ERDC/CHL CR-07-1, US Army Engineer Research and Development Center, Vicksburg, MS, 2007) for an oscillatory flow combined with a superimposed current under an arbitrary angle, involving phase-lag effects in the sheet flow layer. Model results are compared with experimental data (morphology evolution behind detached breakwaters). The agreement between numerical simulations and data is quite satisfactory. Also, model predictions agree with the tombolo/salient criteria found in the literature. The methodology can be applied to the design of detached breakwaters, which are used as coastal protection structures.

Wave diffraction on arc-shaped floating perforated breakwaters

Abstract: An analytical method is developed to study the sheltering effects on arc-shaped floating perforated breakwaters. In the process of analysis, the floating breakwater is assumed to be rigid, thin, vertical, and immovable and located in water with constant depth. The fluid domain is divided into two regions by imaginary interface. The velocity potential in each region is expanded by eigenfunction in the context of linear theory. By satisfying continuity of pressure and normal velocity across the imaginary fluid interface, a set of linear algebraic equations can be obtained to determine the unknown coefficients for eigenfunction expansions. The accuracy of the present model was verified by a comparison with existing results for the case of arc-shaped floating breakwater. Numerical results, in the form of contour maps of the non-dimensional wave amplitude around the breakwater and diffracted wave amplitude at typical sections, are presented for a range of wave and breakwater parameters. Results show that the sheltering effects on the arc-shaped floating perforated breakwater are closely related to the incident wavelength, the draft and the porosity of the breakwater.

Stability of wave-dissipating concrete blocks of detached breakwaters against tsunami

Abstract: In recent years, the risk of occurrence of tsunamis generated by near shore earthquakes, such as, Tokai, Tonankai, Nankai and off-Miyagi is considered to be higher than before, as well as off shore tsunamis traveling long distances, e.g., the 2010 Chilean tsunami. On March, 11th, 2011 the huge, devastating tsunami generated by The 2011 off the Pacific coast of Tohoku Earthquake attacked and damaged the east coast area of Japan. Tsunami forces onto vertical walls, such as seawalls, has already been studied in detail, e.g., Asakura et al.(2002) and Kato et al.(2006). In Japan, detached breakwaters made with wave-dissipating concrete blocks such as Tetrapods have been widely applied. However, the effects of detached breakwater on tsunami disaster mitigation have not been studied. In our study, hydraulic model tests have been systematically and carefully carried out using solitary tsunami waves to evaluate the stability of concrete blocks following the our previous study on the effect of detached breakwaters from the viewpoint of reducing run-up and wave pressure onto seawalls behind the detached breakwaters (Hanzawa et al., 2011).

An environmental and economic analysis for geotube coastal structures retaining dredge material

Abstract: This paper investigates the environmental and economic sensitivity of coastal structures for two different construction methods; a traditional rubble mound structure and a geotube coastal structure using dredged material. The analysis is undertaken for two projects: a small scale coastal protection project using a revetment and a medium size capital harbour expansion using a breakwater. This work provides further insight into previously published work by Sheehan et al. (2009) on the economic aspects of geotube technology and identifies the optimum method of construction for each type of coastal structure. An economic sensitivity analysis is undertaken on the key logistical parameters involved in the construction of these coastal structures. An environmental sensitivity analysis focuses on the CO 2 emissions produced from the construction of the coastal structures for both construction methods. These sensitivity analyses are undertaken using a decision support software program (DMMAP), developed to assist users at the planning stages of a project to achieve sustainable dredge material management. The key logistical parameters are analysed to generate environmental and economic ranking tables. The analyses highlight that the size of the structure and the distance to the source of the quarry material are crucial factors in determining the optimum construction method. This work shows that geotubes are a viable alternative to traditional rubble mound coastal structures. It also shows that traditional construction methods may be more economical than geotube structures when considering small coastal structures. In general, the larger the scale of the project the greater the potential savings in CO 2 emissions and cost that can be achieved through the use of geotube technology. Geotubes, with the use of dredge material, may provide a sustainable beneficial use for dredge material and offer a serious economic and environmental alternative to traditional rubble mound structures.

Numerical modelling of consolidation of 2-D porous unsaturated seabed under a composite breakwater

Abstract: The investigation of seabed consolidation under a breakwater is not available in previous literatures. In this study, taking the dynamic Biot's equation known as “u-p” approximation as the governing equation, a FEM program PORO-WSSI 2D is developed for the consolidation and dynamic response of porous medium. By adopting PORO-WSSI 2D, the consolidation of unsaturated seabed under a composite breakwater and hydrostatic pressure is investigated. The floating force acting on the bottom of caisson has been considered in numerical computation. The excess pore pressure dissipation, growth of effective stresses, settlement of breakwater and the shear stress concentration in seabed foundation all can be monitored. The developed FEM program provides coastal engineers with an effective analysis tool to predict the shear failure in seabed foundation.DOI: http://dx.doi.org/10.5755/j01.mech.18.4.2337

Innovative breakwaters design for wave energy conversion

Abstract: This paper intends contributing to an economically and environmentally sustainable development of coastal infrastructures by investigating the possibility of combining together breakwaters and Wave Energy Converters (WEC). The latter change the wave energy to electricity, which may serve both the rubble mound breakwaters and seawalls related activity and the energy demand of small human communities. Wave loadings and overtopping on a seawall and rubble mound breakwater with front reservoir are discussed on the basis of physical 2-D model tests carried out at University of Southampton (UK) and Aalborg University (DK).

Geometry Optimization of an Overtopping Wave Energy Device Implemented into the New Breakwater of the Hanstholm Port Expansion

Abstract: The study presented here describes the geometry optimization of the Sea wave Slot cone Generator (SSG) overtopping wave energy converter as part of the feasibility study for the implementation of the device in the development plan of Hanstholm harbour in Denmark. The total length of the new planned breakwater is 1.5 km and the water depth ranges approximately from 8.0 m up to 14 m with localized influences on the wave climate. The study is conducted numerically in order to present the expected power production and overall performance of the SSG breakwater in Hanstholm. The price par kWh is also presented.

Stability of rubble mound breakwaters against solitary waves

Abstract: No formulas currently exist to design armour units against tsunami attack. To develop such formulae, laboratory experiments were carried out to clarify the failure mechanism of these types of structures. Also, the behavior of armour units against real cases of tsunami attack during the 2011 Tohoku tsunami were evaluated. Both the results of the laboratory experiments and the breakwaters studied in the field where then analyzed in terms of well established formulas such as that of Van der Meer or Hudson. The design of structures that only fail partially during a given tsunami event ("resilient† or "tenacious† structures) should be prioritized in future counter-measures, and in order to make it possible to construct such structures a modification of the Hudson formula for their design is proposed.

The impact of gaza fishing harbour on the mediterranean coast of gaza

Abstract: The Mediterranean coast of Gaza strip, which is covered about 40 km in length, is rich by coastal resources. The development that occurred along the coastal lines has led to the host of problems such as increased erosion, siltation, loss of coastal resources and the destruction of the fragile marine habitats. In order to conserve the depleting coastal resources, the changes due to development and associated activities must be monitored. Studying the temporal pattern of shoreline change is considered one of the most effective means of monitoring the cumulative effects of different activities. An attempt was made to study the impact of Gaza harbour on shoreline displacement along 6 km. This paper was intended to detect changes of coastal area in Gaza city to provide future database in coastal management studies. The analysis was carried out using image processing technique (ERDAS) and Geographical Information System platform. The variation during 38 years in the shoreline along the Gaza coast was determined by analyzing MSS, TM and ETM Landsat images from 1972 to 2010. The analyses identified the erosion and accretion patterns along the coast. The shoreline was advanced south of the Gaza fishing harbor, where the wave-induced littoral transport was halted by southern breakwater and the annual beach growth rate was 15,900 m2. On the downdrift side of the harbor, the shoreline was retreating and beaches erode at an annual rate of -14,000 m2. This study was emphasized that the coastal band is considered as a critical area, it is therefore necessary to monitor coastal zone changes because of the importance of environmental parameter and human disturbance. In particular, the projections of future shoreline erosion and accretion rates are considered important for long-term planning and environmental assessment for a variety of projects, including the construction and tourism facilities

Stability of Low Crested and Submerged Breakwaters with Single Layer Armouring

Abstract: The stability of single layer armour units on low crested and submerged breakwaters has been investigated in 2D hydraulic model tests. Armour unit movements including settlements, rocking and displacements have been determined. The effect of freeboard, packing density and wave steepness on the armour layer stability on crest, front and rear slope has been investigated. Armour units were mostly displaced in the most upper part of the seaward slope and at the seaward side of the crest. Damage on the crest was progressing towards the rear slope. About 40% to 50% larger armour units are required on the seaward slope and crest of low crested structures (as compared to conventional high crested breakwaters). About 35% larger armour units are required on the rear slope. Larger armour units are not required on submerged breakwaters if the water depth on the crest exceeds 40% of design wave height.

Applicability of CADMAS-SURF to evaluate detached breakwater effects on solitary tsunami wave reduction

Abstract: Detached breakwaters, made with wave-dissipating concrete blocks such as Tetrapods, have been widely applied in Japan, but the effectiveness of such kinds of detached breakwaters on tsunami disaster prevention has never been discussed in detail. A numerical wave flume called CADMAS-SURF has been developed for advanced maritime structure design. CADMAS-SURF has been applied mainly to ordinary wave conditions such as wind waves, and little attempt has been made for expanding its application to tsunami waves. In this study, the applicability of CADMAS-SURF for evaluating the effectiveness of detached breakwaters on a solitary tsunami wave reduction is investigated by comparing the calculated results with those from hydraulic experiments. First, the effectiveness of a detached breakwater on the reduction of wave height and wave pressure was confirmed both by hydraulic experiments and numerical simulations. Finally, CADMAS-SURF has been found to be a useful tool for evaluating the effects of detached breakwaters on tsunami wave height and pressure reduction, as a first step in a challenging study.