Showing papers on "Breakwater published in 2009"

Coastal, Estuarial and Harbour Engineers’ Reference Book

Abstract: Introduction. Part 1: The dynamic environment. The deep-water origins of the physical environment of coastal, estuarial and harbour regions. An introduction to nearly-horizontal flows. Element of the theory of turbulence. Diffusion, dispersion and sub-grid parametization. Elements of non-cohesive sediment transport. Elements of cohesive sediment deposition, consolidation and erosion. Three-dimensional hydrodynamic models. Quasi-three-dimensional modelling using mixed finite difference and spectral models. Two-dimensional nearly-horizontal flow models. One-dimensional nearly-horizontal flow models. Numerical modelling of short-period waves. Three-dimensional advection-diffusion models. Two-dimensional advection-diffusion models. One-dimensional transport-dispersion and water quality. Three-dimensional sediment-transport models. Two-dimensional models of sediment transport due to waves and currents. One-dimensional models of sediment-transport under the influence of currents. Physical short-period-wave models. Hydraulic-structure interaction. Part 2: The physical environment. Groynes, offshore breakwaters and artifical islands. Beach response modelling. Beach nourishment, offshore dredging and sand bypassing. Marinas. Physical and mathematical models in the optimisation of breakwater layout. Design of breakwaters and selected design wave height. Rock for maritime structures. Wave forces on structures. Wave loads on sea dikes. Coastal pollution and water quality. Hydromechanics of porous media in the maritime. Geotextiles in coastal and harbour engineering. Dredging and dredgers. Disposal of dredged material at sea. Field studies and the analysis of data. Coastal management. Construction of maritime works. Materials in the marine environment. Maintenance of coastal structures. Economic appraisal of coastal engineering works. Cohesive sediments. Hydraulic behaviour of fine sediment. Contamination in estuarine sendiments. Cohesive sediments in coastal engineering applications. Determining depth and navigability. Maintenance dredging. Estuarial problems. Barrages and barriers. Tendering, coastal management, site supervision and control. Arbitration. Index.

Coupled FEMDEM/Fluids for coastal engineers with special reference to armour stability and breakage

Abstract: Sea-level rise and increased storminess present huge challenges to coastal engineers worldwide. The seaward slope of many breakwaters and shoreline defence structures consists of thousands of interlocking units of concrete or rock making up a massive granular defence against wave attack. The units are placed freely to form an armour layer which is intended to both dissipate wave energy and remain structurally stable. Design guidance on the mass and shape of these units is based on empirical equations derived from Froude scale physical model tests. The two main failure modes for concrete armour layers are displacement (hydraulic instability) and breakage (structural instability) which are strongly coupled. Breakage mechanisms cannot all be faithfully reproduced under scaled physical models. Fundamental understanding of the forces governing such wave-structure interaction remains poor and unit breakages continue to baffle the designers of concrete armour units. This paper illustrates a range of DEM and FEMD...

Wave interaction with a perforated circular breakwater of non-uniform porosity

Abstract: Wave interaction with a porous cylindrical breakwater is studied analytically by linear potential wave theory. The breakwater is assumed to have a thin skin, is bottom-mounted and surface-piercing. The porosity of the breakwater is uniform vertically but varies in the circumferencial direction. This allows the choice of a partially impermeable wall or a vertical slot in the breakwater. Three different basic configurations of the breakwater are investigated, namely, (1) uniformly porous cylinder; (2) porous cylinder with partial impermeable wall; and (3) porous cylinder with an opening. The performance of these types of breakwaters is studied vs. wave parameters and breakwater configurations including angle and position of opening or partial impermeable wall as well as porosity. Parametric studies with regard to the wave-amplification factor, wave forces, and elevation contours are made. The results should be found useful in the design of coastal and offshore structures.

Practical design and investigation of the breakwater OWC facility in China

Abstract: The breakwaters are utilized for absorbing wave energy to provide suitable berthing conditions for the harbors. The caisson breakwater can be modified as the air chamber of the Oscillating Water Column (OWC)Wave Energy Conversion (WEC) facilities. In the present paper, the integrated structure of Caisson breakwater- OWC chamber is practically designed. The experiments are performed in the wave flume to obtain the oscillating amplitude of inner water column inside the chamber, which are usually employed to demonstrate the operating performance of the OWC chamber. A numerical wave tank based on the twophase VOF model is established to generate 3D incident waves. The numerical wave tank consists of the continuity equation, Reynolds-averaged NavierStokes equations and two-phase VOF volume fraction equations. The standard k-e turbulence model, finite volume method, NITA-PISO algorithm and dynamic mesh technique are employed. The numerical results are compared and validated by the above corresponding experimental data. The effects of several incident wave conditions and shape parameters on the wave energy converting efficiency and performance of integrated system are investigated.

Design optimization of floating breakwaters with an interdisciplinary fluid-solid structural problem

Abstract: The design optimization of floating breakwaters implicates solving an interdisciplinary problem consisting of three models. The first one arises from the interaction of linear waves with a moored floating breakwater with a leeward boundary that is composed of a vertical sidewall representing the quay wall in ports. The second covers the dynamical behaviour of the oscillating structure caused by the incoming waves. These two assemble the hydrodynamic performance of the floating breakwater; while the third concerns its structural mechanics subject to hydrostatic and hydrodynamic forces. The goal of the optimization problem is to design an optimal floating breakwater that can attenuate the waves to the minimum height inside the port and fulfill several constraints related to floating, stability, and structural resistance. The objective function and constraints are expressed in terms of geometrical parameters of the breakwater as mathematical expressions assembled in an optimization algorithm based on the seq...

Performance of rigidly interconnected multiple floating pontoons

Abstract: A floating system consisting of three pontoons equispaced, rigidly interconnected and taut moored to act as a single unit is analyzed. The theoretical formulation of the problem is based on the assumptions of irrotational fluid flow, an inviscid fluid, and small incident waves. The breakwater is assumed to be long and uniform in the direction parallel to the incident wave crests. The diffracted and the scattered potentials are obtained from the solution of boundary value problem using Green's identity method. The potentials and hence the free surface oscillations in between the spacing are also determined. The results of parametric study of varying space and drafts of the pontoons have been presented as a function of relative width of breakwater (Ratio of width of the breakwater to the wavelength) .It is evident from the results that the spaces between the pontoons have a definite effect on transmission and reflection characteristics of a floating breakwater system. As the draft of the floating breakwater increases the bandwidth of incident wave frequencies for which K t (Ratio of transmitted wave height to incident wave height) is less than 0.2, also increases, thus ensuring a wider spectrum of operation. In addition the paper discusses on forces, oscillations in the interspaces and reflection coefficient. Keywords: breakwater, pontoon, taut moored, free surface oscillations . doi: 10.3329/jname.v1i1.2031 Journal of Naval Architecture and Marine Engineering 1(2004) 3-17

Optimum Safety Levels and Design Rules for the Icelandic-Type Berm Breakwater

Abstract: acceptance number: 60. Paper title: OPTIMUM SAFETY LEVELS AND DESIGN RULES FOR THE ICELANDIC-TYPE BERM BREAKWATER Authors: Sigurdur Sigurdarson, Jentsje W. van der Meer, Hans F. Burcharth and John Dalsgaard Sorensen,

Experimental and numerical investigations on zigzag porous screen breakwater

Abstract: Pile supported porous breakwaters are commonly adopted for shielding small-scale harbors, such as marinas, fishing harbors, and recreational harbors from external waves. To improve efficiency of such breakwaters, attempts have been made to provide a filter screen containing porous material. Possible alternative to the existing pile supported screen breakwaters is the zigzag breakwater. This article details on the numerical and experimental investigations carried out on the performance of zigzag porous screen breakwater. Results related to the wave amplification in front of the structure, wave reflection, and transmission, forces exerted by the waves on the structure are discussed. The studies clearly indicate that the transmission coefficient of the order of 0.5 can be achieved for H i/gT 2 > 0.008 for 50% submergence, whereas the reflection coefficient can be effectively reduced to 0.2. Reduction in wave force is of the order of 50% which is primarily due to reduction in reflection coefficient. Substantial reduction in wave force contributes directly to reduction in the cost of construction of the breakwater, a definite advantage over other similar breakwaters.

The Reflection of Normal Incident Waves by Absorbing-Type Breakwaters

Abstract: This paper investigates the reflection of normal incident waves produced by absorbing-type breakwaters. The absorbing-type breakwaters in this study consist of a vertical porous plate, a submerged permeable caisson, and an impermeable back wall. The flow field is divided into four regions: a porous caisson region, and three pure water regions. Under the assumptions of linear wave theory, Darcy's law in the perforated wall, and the pore velocity potential theory of Sollitt and Cross (1972) in the porous caisson region, this study creates a 2-D BEM model to calculate the reflection coefficients of water waves using several breakwater properties. This numerical model is calibrated by previous numerical studies and limiting cases for a partially perforated-wall caisson breakwater and a vertical porous breakwater with an impermeable back wall. Generally speaking, the wave dissipation in absorbing-type breakwaters is bigger than that for a partially perforated-wall caisson breakwater. The reflection coefficient values imply the performance of wave absorbers in this study. Therefore, we examine the major factors that affect the reflection coefficient.

Building a breakwater with prefabricated caissons on soft clay

Abstract: This paper presents a case history of the construction of an offshore breakwater on soft clay using prefabricated, semicircular-shaped concrete caissons. The project was located near Shanghai Port, China. The breakwaters were designed as gravity-retaining structures, and used for deepening of the navigation channels along the Yangtze estuary. Some sections of the breakwaters were installed on a thick layer of soft deposit. During the construction, the caissons in one section failed under a heavy storm. The causes of failure were investigated. The design of the breakwater and the soil improvement works are described in this paper. Surcharge preloading and prefabricated vertical drains were adopted to improve the soft soils below the caissons. Some other measures, such as the use of anti-sliding mats for the base of the caissons to increase the base friction, and the use of geotextile with sand-filled geotextile tubes and geotextile and concrete block composites to prevent scour, were also adopted. These measures were proven to be effective in maintaining the stability of the breakwaters against subsequent heavy storms.

Analysis of Wave Reflection from Wave Energy Converters Installed as Breakwaters in Harbours

Abstract: Amplification and renovation of harbours, none the last for the need of straitening existing structures because of the increased storminess due to climate change, is a practice that is repeating itself all around the world. To this purpose, integration of breakwaters and Wave Energy Converters (WECs) based on two different technologies, one based on the overtopping principle and the other of Oscillating Water Column (OWC) type, revealed to be suitable with different advantages compared to offshore installations, among the others: sharing of costs, cheaper accessibility and maintenance, lower loads on the structure, i.e. better survivability. Nevertheless these devices must comply with the requirements of harbour protection structures and thus cope with problems due to reflection of incoming waves, i.e. dangerous sea states close to harbors entrances and intensified sediment scour, which can lead to structure destabilization. The present paper aims to analyse wave reflection from OWC and Sea Slot-cone Generator (SSG) converters, based on experimental results obtained in 2D and 3D facilities. The applicability of formulae available in the literature and derived from costal structures experience are checked. Consideration on induced scour and structure stability are also carried out, and solution for design improvements are finally drawn.

Numerical study of options to reduce swell and long wave penetration at port Geraldton

Abstract: The combination of swell waves and long waves penetrating into Geraldton Harbour gives rise to occasions of problematic surging conditions for moored vessels. In order to investigate options for improved harbour tranquillity, a numerical study of the swell and long wave penetration was undertaken. The modelling methods included a 10-year regional and nearshore hindcast (SWAN), harbour penetration modeling (CGWAVE), and modelling to identifying the source / directionality of long waves with a modified version of FUNWAVE. Model results of the exis ting harbour configuration indicates the main breakwater is only partially-effective at preventing swell and long wave penetration into the harbour basin. The adjacent reef platform and shipping channel effectively cause waves to refract and propagate directly toward the harbour entrance, several hundred metres beyond the breakwater terminus. Boussinesq modelling confirms that most of the long wave energy is being generated during the swell wave transformations over the wide reef platform; propagating shoreward and entering the harbour by refraction and diffraction into the entrance channel region, as well as reflection off the adjacent armoured shoreline. A range of control structures (including detached options) were tested, and the most effective solution was found to be a 350m linear extension to the breakwater. This outcome is expected to provide approx. 50% reduction in swell wave heights and 30% reduction in the long wave heights throughout the harbour basin.

Apparatus for generating offshore wind power combined with tidal current power and wave force generation by utilizing a breakwater

Abstract: PURPOSE: A combined tidal and wave power generating system using a breakwater is provided to facilitate management of generating system by combining wind power, tidal power, and wave power generating units CONSTITUTION: A combined tidal and wave power generating system comprises a base(10), a breakwater(20), a wind power generating unit(30), and a combined tidal and wave power generating unit(40) The base is installed on the underwater bottom and supports an upper structure The breakwater is formed of concrete on the base to block waves from the open sea The wind power generating unit is installed on the top of the breakwater and generates power from the torque by the wind The combined tidal and wave power generating unit is installed inside the breakwater and rotates by tidal and wave forces according to seawater level The breakwater is settled on the base, including a bottom part to keep the structure stable

Parametrical and Motion Analysis of a Moored Rectangular Floating Breakwater

Abstract: Moored floating breakwaters with a leeward boundary, assimilating the port quay walls are described by a large number of coupled variables. This complicates their design and requires a detailed parametrical and motion analysis to assess their hydrodynamic performance. A diffraction-radiation boundary value problem is developed. It arises from the interaction of linear waves on a moored floating breakwater with a leeward boundary described by a partial reflective sidewall. The effects of the sidewall clearance, structural parameters, mooring lines stiffness, and their angle of inclination on the transmission coefficient and the dynamic motion of the floating breakwater are considered. The transmission coefficient is strongly affected by the motion itself and the allowable length change in the mooring lines.

Application of remote sensing video systems to coastal defence monitoring

Abstract: Shoreline stability is an important issue along much of the Mediterranean’s Coasts. European project MEDDOOC INTERREG BEACHMED-e focused on the strategic management of beach protection for the sustainable development of the Mediterranean coastal zone. In the framework of this project, a video system has been installed in Valras (Gulf of Lions / France) to monitor coastal evolutions and recent protection works. Over the past 20 years, coastal video remote sensing techniques represent an efficient alternative tool to classical in situ surveying techniques. Coastal video monitoring is based on Time exposure images (Timex) acquisition and photogrammetry technique which allows transforming 2D image coordinates into the corresponding 2D real world coordinates. This paper presents the use of video monitoring technique to estimate the impact of engineering works. Important beach retreat has been observed for decades along the 3 km of Valras beaches and 12 breakwaters have been built until 2007. From January to May 2008, a new similar protection, a submerged breakwater and 95,000 m sand nourishment have been added. As Empirical Orthogonal Function (EOF) analysis has become an established method for investigating temporal beach fluctuation, EOF is performed using weekly video monitored shorelines over a 6 months period. The results show: (1) the natural erosion / accretion phases of the already protected shoreline, (2) the impact of beach nourishment and the trend toward the equilibrium position of the restored shoreline, (3) the efficiency of video monitoring for shoreline management.

Numerical modelling of breakwater overtopping using a nlsw equation model with a porous layer

Abstract: This paper illustrates the application of a non-linear shallow water numerical model, AMAZON, to study the mean wave overtopping discharge at a breakwater protecting the Portuguese harbour of Povoa de Varzim. The results are compared with two-dimensional physical model data collected at the National Civil Engineering Laboratory, Portugal. The implications are considered of using two different governing equations for flow within the porous layer of the breakwater: firstly, the Darcy equation for stationary laminar flow; secondly, the Forchheimer equation for stationary turbulent flow. The results suggest that the type of flow is of secondary importance in determining the mean overtopping discharge. The parameter which most affects the results is the specified maximum velocity of the flow during the exchange of water between the surface and porous layers. Choosing suitable values of the porous flow parameters leads to a good agreement between the AMAZON results and the data.

Effect of core permeability on armour layer stability

Abstract: The permeability of a breakwater core affects the stability of the breakwater armour. No design guidelines are available to account for the effect of a geotextile container core on armour stability. This paper discusses the present knowledge on the effect of core permeability on armour layer stability, both for rock and concrete armour units. Results are presented from project specific model tests on Xbloc armoured breakwaters with geotextile container cores. A prototype case is presented where damage has occurred, which may be attributed to low core permeability. Recommendations are given for the design of breakwaters and seawalls with low permeability cores.

Coastal Morphology and Coastal Protection

Abstract: Lecture notes ct5309. Tides, currents and water; coastal problems; sediment transport processes; coastal transport modes; longshore transport; cross-shore transport; fundamentals of mud; channels and trenches; coastal protection; application of structures; application of nourishments.