Showing papers on "Breakwater published in 1993"

Numerical simulation of nonlinear wave interacting with permeable breakwaters

Abstract: A fully nonlinear simulation model was developed to predict the wave transformation interacting with a permeable breakwater. The present model was applied to simulate wave transformations due to a rubble-mound breakwater and due to a caisson breakwater covered with armor units and verified by hydraulic model tests. Numerical experiments were also performed to interpret the stability of armor units and the wave-induced pressure on the caisson through the pile of armor units.

Water waves on flexible and porous breakwaters

Abstract: This is a theoretical study of the reflection and transmission of small‐amplitude waves by a flexible, porous, and thin beam‐like breakwater held fixed in the seabed. The fluid motion is idealized as a linearized, two‐dimensional potential flow and the breakwater is idealized as a one‐dimensional beam of uniform flexural rigidity and uniform mass per unit length. The velocity potentials of the wave motion are coupled with the equation of motion of the breakwater. Analytical solutions in closed forms are obtained for the reflected and transmitted velocity potentials together with the displacement of the breakwater. The free‐surface elevation, hydrodynamic force acting on the breakwater, and the overturning moment are determined. The dynamic response of the breakwater in terms of bending moment and shear force are also evaluated. It is found in general that hydrodynamic force increases as structural rigidity increases. The magnitude of the force is reduced dramatically for a stiffer porous breakwater. It is...

Wave power conversion by a prototype wave power extracting caisson in sakata port

Abstract: Ocean wave energy is clean and inexhaustible. Repeated oil crises and the urgent need for environmental preservation on a global scale have made utilization of ocean wave energy increasingly important. The Japanese Ministry of Transport has been developing a wave power extracting caisson breakwater which can absorb wave power and convert it into electric power. The breakwater shown in Fig.l is a composite breakwater with a special caisson for absorption and conversion of wave power. The caisson has a so-called air chamber where wave power is converted into air power. The air power activates a turbine-generator in the machine room on the caisson. The use of the breakwater as a wave power converter will effectively cut down the power generation cost. This breakwater also aims at the improvement of the wave resisting stability and performance as a breakwater by absorbing the wave energy.

Wave Diffraction through Submerged Breakwaters

Abstract: The water‐wave interaction with submerged breakwaters is examined to determine the reflection and transmission coefficients. Three types of breakwaters are considered, namely, a submerged breakwater extending from the sea bed until below the waterline, a breakwater extending from above the seawater to some distance below, and a breakwater extending all the way from the seabed with a slit at some distance from the bed. In all three cases the breakwaters are assumed to be rigid, thin, and impermeable, and subjected to linear monochromatic waves, and the fluid motion is idealized as linearized, two‐dimensional potential flow. A computationally efficient method—an eigenfunction technique with a mixed boundary condition—is used to determine the velocity potential anywhere in the region of flow. The least‐square method has been utilized in the solution for the mixed boundary condition. The accuracy of the solution is demonstrated by comparing the numerical values for the transmission coefficient with those obta...

Water Waves on Crown Breakwaters

Abstract: The linear theory for waves impinging obliquely on a vertical, porous breakwater with an impermeable crown is examined. The wave‐induced flow within the breakwater is modeled by the 1972 theory of Sollitt and Cross. Using eigen‐function expansions for the velocity potentials seaward of the breakwater, beneath the crown, and behind the structure, the reflection and transmission coefficients are calculated to determine the sheltering provided by the breakwater. The results agree well with other methods, including a plane wave analysis, obtained by neglecting the evanescent wave modes. The distribution of the wave‐induced pressure along the base of the crown is also calculated, showing that the linear pressure gradient assumption usually applied for uplift forces on the breakwater crown is inaccurate.

Equilibrium Shoreline Response to Breakwaters

Abstract: An empirical analysis of the shoreline response to both single and multiple detached breakwaters is presented. In the analysis, equilibrium conditions are assumed. The analysis is based, in part, on previously published experimental data, which are also the basis of a previous study of equilibrium shoreline response to breakwaters. The current analysis differs from the previous analysis in several ways: (1) The effects of wave steepness and beach slope are included; (2) waves are allowed to approach from any direction in deep water; and (3) the effects of segmented breakwaters can be analyzed. Neither analysis includes the effects of grain size. The current analysis can be used to predict the formation of tombolos and salients, and to predict the maximum shoreline retreat or shoreline advance. To demonstrate the utility of the analysis, the shoreline response to the 11‐unit breakwater system at Bay Ridge, Md., is predicted. The predicted and actual shorelines are shown to be in good agreement.

Nonlinear wave transformation over a submerged permeable breakwater

Abstract: A set of nonlinear vertically integrated equations has been derived to predict the transformation of waves over a submerged permeable breakwater on a onedimensional topography. The square of the relative water depth is assumed to be of the same order as the wave height to water depth ratio and a set of second-order governing equations which are equivalent to the Boussinesq equations is derived. The equations have been applied to simulate non-breaking and breaking wave transformations obtained from laboratory experiments, in the latter incorporating a model for breaking wave energy dissipation. When breaking is nonexistent on the breakwater, the wave height as well as the wave profile is well predicted. However, the disintegrating character of the transmitted waves is weakly predicted. For breaking transformation, the wave profiles are predicted well prior to the lee of the breakwater where disintegration occurs.

Preliminary analysis of the stability of rubblemound breakwater crown walls

Abstract: A series of two-dimensional hydraulic model tests was carried out to investigate the stability of rubblemound breakwater crown walls. The effect of seven design parameters on the minimum mass required for a crown wall to remain stable was studied: wave height, wave period, crown wall height, water level, front slope of the breakwater, position of the crown wall and length of stabilizing legs. Observations regarding the type of wave interaction, degree of overtopping, superstructure movement and overall hydraulic stability were studied. The coefficient of friction at the crown wall/breakwater interface was also measured. The crown wall superstructure was located on the crest of a conventional multi-layer breakwater and was subjected to both regular and irregular wave attack. Preliminary analysis of this data set is presented which shows trends established for each of the seven design parameters.

Laboratory tests on the interaction between nonlinear long waves and submerged breakwaters

Abstract: This paper deals with the use of submerged detached breakwaters as beach protection, a use that today has become quite popular. This type of structure has been largely studied both theoretically and through experimental analyses in recent years, however its behaviour has not been completely understood, specially if related to the real irregular wave attacks. In particular some laboratory studies carried out by the authors have pointed out some interesting phenomena associated with the interaction between the nonlinearities of wave transformations in shallow water and submerged breakwaters. Aiming at discerning between the phenomena related to the structure (beach and breakwater) and flume geometry, a new series of laboratory tests have been carried out in a 50 m long wave flume; these tests and the results obtained are described in this work. Besides the study of the behaviour of submerged structures related to the bounded-long-waves, some current velocities have also been measured during this research through directional micro-propeller fluid meters.

Water Particle Velocities on a Berm Breakwater

Abstract: Water particle velocities in waves running up and down a berm breakwater have been measured for several wave heights and wave periods with a Laser Doppler Velocimeter (LDV). The measured water particle velocities have been compared with velocities computed with the numerical model ODIFLOCS. There is a fanagreement between the calculated and measured velocities.

Armour displacements on reshaping breakwaters

Abstract: A computer simulation model for the reshaping of dynamically stable breakwaters under normally incident, monochromatic waves has been developed. The proposed model is used to simulate initial reshaping as well as transport on the developed profile. Preliminary validation of the model has been carried out by comparison with data obtained from experimental tests on a berm breakwater.

Model testing of wave transmission past low-crested breakwaters

Abstract: Small-scale model tests were conducted to assess the wave transmission characteristics of low-crested breakwaters. The goals of this study are to quantify the wave transmission characteristics of these breakwaters for various structure heights, water depths, and wave conditions. The tests were conducted on crosssections of solid and rubble breakwater models using both regular and irregular waves. A new parameter, (F-Ru)/Hf, is then proposed to represent transmission past a breakwater for all values of breakwater freeboard.

Field experiments on a dual cylindrical caisson breakwater

Abstract: A deepwater caisson breakwater as shown in Fig.l has been developed by the Ministry of Transport, Japan. The new breakwater is a composite breakwater with a cylindrical caisson named as dual cylinder caisson. The caisson has dual cylindrical walls and its outer cylinder has a perforation in the fore half of the upper portion, forming a wave chamber of a doughnut shape bounded by its inner impermeable cylinder. A series of laboratory experiments had been carried out at the Port and Harbour Research Institute from 1985 to 19881'3). According to the laboratory experiments, the caisson was found to have advantages of low reflection and high stability. The design method of the caisson was proposed through intensive laboratory studies in 1988. Prototype experiments of the dual cylindrical caisson breakwater have been conducted in order to verify its proposed design method against waves at Sakai Port by the Third District Port Construction Bureau, since 1989. A distinguished attempt in the field experiments was tried to measure the displacement of caisson as well as wave pressures during sliding due to high waves. This attempt was accomplished by a storm occurred on February 17, 1991.

A Robust Armor Design to Face Uncertainties

Abstract: A new rubblemound breakwater cross section design named D-armor breakwater is presented. The D-armor cross section shows a significantly larger active armor area than the conventional cross section. The D-armor breakwater shows a similar resistance to the initiation of damage, but a significant increase of resistance to total failure. The observed structural response has a wave height range about 30% wider than the range corresponding to the conventional breakwater; the new section reshapes to an efficient S-shape armor near the total failure point. The D-armor breakwater appears to be a reasonable first step towards a convenient evolution from the conventional breakwater to more efficient designs; the wider structural response makes it appropriate for construction sites with large uncertainties in the estimation of the worst wave conditions in its lifetime.

Evolution of a Beach With and Without a Submerged Breakwater: Experimental Investigation

Abstract: In the present report experimental results about the efficiency of a submerged structure are presented. The experiment, carried out with random waves, covered about 2500 hours until equilibrium profile was reached. The most significant results are the good behaviour of the tested breakwater as a sand holding structure and its slowing effect produced on the shoreline backing, whereas the final position of the shoreline was nearly the same with and whithout breakwater.

Multi-stage tsunami breakwater

Abstract: PURPOSE:To prevent the casualities to the land section by providing a plurality of levee bodies having levee height allowing overflowing of tsunami in a multistage shape in the advancing direction of tsunami, and having subsequently tsunami cross over the levee bodies before tsunami arrives at a sea-wall on the land to damp tsunami energy. CONSTITUTION:When tsunami surges against a submerged breakwater 13, there are step-ups and -downs on the surface of sea water in that position, and tsunami energy is consumed after the passing. After that, a second tsunami breakwater 20 prevents water force of tsunami running against it and, at the same time, tsunami is partially made to cross over the second breakwater to damp energy. Then, tsunami crossing over the breakwater 20 runs against a wave dissipation dyke 23 to damp energy. Tsunami crossing over the breakwater 20 is shoved and pushed against return waves reflected at a sea-wall 30 in a retarding section 25, and energy is rapidly damped. According to the constitution, tsunami energy in the shallow sea area can be efficiently damped, and the arrival of tsunami to the coastline can be greatly controlled, so that large scale casualties to the land section can be prevented.

Numerical determination of wave induced flow in rubble mound breakwater

Abstract: This paper describes a numerical model of wave action onto and into a rubble mound breakwater. The model is constructed of two parts, the wave action on the exterior of the mound in which a boundary element method is used and flow inside the rubble mound in which a finite element method is used. The two parts of the model are coupled by demanding continuity of flow through the front face of the breakwater. The predicted pressures within the core of the rubble mound are compared with data collected from physical model tests.

Breakwater Design in the Chesapeake Bay: Dealing with the End Effects

Abstract: This paper documents various methods for treating the terminal ends of headland breakwater systems. Twelve sites in Chesapeake Bay were selected for study. In selecting design alternatives, it is important to consider acting coastal processes as well as shoreline management issues such as adjacent habitats, property boundaries and funding limitations. The primary objective is to create a smooth transition in energy levels between the shoreline reach protected by the breakwater system and the adjacent, unprotected shoreline. This can be accomplished by modifying structure crest heights, widths and orientations, such that the energy level is gradually rather than abruptly stepped up (or down) as the breakwater system is terminated. In the case where the adjacent shoreline has already been modified by a structure, termination is somewhat easier, with the primary consideration being to maintain the integrity of both systems.

Two dimensional effects in modelling berm or reshaping breakwaters

Abstract: In recent years, the failure of many large conventional type breakwater structures has led to a careful examination of the physical processes of wavestructure interaction. Although naturally armouring structures, which gain their stability as a consequence of profile readjustment due to wave action, have been around in various forms for hundreds of years, the high incidence of failure of conventional structures has led to their increased use in the past decade. The interaction of an incident wave with a rubblemound breakwater results in complex flow patterns involving unsteady non-uniform flow (Hall (1987)). In most cases, it is desirable to construct a breakwater which works in harmony with the flow field; that is to construct a structure with a geometry and armour stone weight gradation which results in natural profile readjustment and subsequent minimization of the applied hydrodynamic loadings.

Monitoring mound breakwaters. the case of sines

Abstract: The aim of monitoring mound breakwaters is presented. Available techniques and Sines breakwaters monitoring program are described.

Numerical modelling of waves and currents with regard to coastal structures

Abstract: This paper describes a two-dimensional numercial model capable of simulating non-stationary flows. Special emphasis has been put on wave motion on and in porous structures, e.g. a rubble mound breakwater. Comparisons of numerical simulations with analytical solutions and model test results have confirmed the applicability of this model for studies of waves and currents with regard to coastal structures.

Reflection effects on wave field within a harbour

Abstract: The present paper outlines a numerical model for predicting the wave field in a harbour with partially reflecting boundaries, and describes laboratory tests undertaken to assess the model. The numerical model is based on linear diffraction theory and involves the application of a partial reflection boundary condition. By utilizing a wave doublet representation of the fluid boundaries instead of the usual wave source representation, the extension is made to general harbour configurations that include breakwaters. Numerical results are compared with known solutions for specific reference configurations. Laboratory measurements have been made of the wave field within a particular harbour model having portions of the boundary corresponding to different degrees of wave reflection. A comparison with the numerical predictions is summarized and highlights the importance of adequately modelling the partial reflections within the harbour. Key words: breakwaters, coastal engineering, harbours, waves, wave diffractio...

Rubble-Mound Breakwater Stability: Results of In-Situ Measurements

Abstract: When the construction of the Zeebrugge Outer Harbour was finished a full scale monitoring system was realized as a part of the global monitoring and inspection programme. The monitoring system was designed to follow the water level- and the water pressure fluctuation inside and in front of the breakwater. A general description is given of the instrumentation of a section of the NW-breakwater followed by a global overview of the data-acquisition system and off-line data processing. Results from the primary analysis of the raw data of relevant storm measuring sessions are presented.

Artificial Gravel Beaches in the Coastal Protection

Abstract: Gravel beaches on the Caucasian Black Sea coast are intensively eroded mainly because of man meddling in natural course of coastal processes (sediment withdrawal from beaches and river beds, adjustment of river runoff, construction of port jetties and local systems of coastal protection etc.) That results in intensification of coast and bottom abrasion and destruction of buildings and communications. To withstand this occurrence different kinds of concrete erections such as sea walls, groynes, submerged breakwaters, concrete block fills were used for a long time. Such a method did not favor the solution of this problem but only complicated it. Since 1981 artificial gravel beaches, as the most effective and inexpensive method of coastal protection, are being used more widely on the Caucasian Black Sea Coast.

Beach Changes Caused by Elongation of Breakwater of Kashiwazaki Port

Abstract: Beach changes associated with the elongation of the harbor breakwater were analyzed through the case study of the Arahama coast, Niigata Prefecture, as an example. On this coast next to Kashiwazaki port, a long breakwater was extended to form a shelter zone from waves. A large amount of sand was carried from the outside to the inside of this calm wave zone by longshore sand transport. The sea bottom changes were analyzed on the basis of bottom sounding data. It was found that the total sand volume which accumulated for twelve years from 1980 to 1992 in the shelter zone was approximately 1.6 × 106 m3. The average longshore sand transport rate was estimated at 1.5 × 105 m3/yr. The closure depth was determined to be approximately 10 m, from comparison of the beach profiles. It was concluded that, since the long breakwater was built at Kashiwazaki port under the condition of seasonally changing wave direction without enough preventive works against littoral transport, a large amount of sand accumulate...

Ecolocy-Conscious Submerged Breakwater

Abstract: A submerged breakwater makes incident rough waves small when their heights exceed a certain level on the site, though the other waves lower than the level are not so much affected by the structure when they pass it over. The structure may be preferable on a coast where a clear view of sea is required, and on a water area fisheries and marine leisure activities need to keep an adequate water depth at the constructed site for their operations. The structure is also desirable for fishermen because they have empirically known that high-values marine products, like abalone, top-shell and spiny lobster, are prefer to live on the under water parts of coastal structures therefore fishermen expect submerged breakwaters will be used as fish habitat more effectively than other coastal structures.

Motions of Floating Breakwaters

Abstract: Floating Breakwaters have long been an economic structure for providing sheltered water for developments such as marinas. Whilst the transmission of waves has long been understood the motions of the breakwater has received less attention. This study concentrated upon the translation and rotation of the breakwater caused by a variety of incident waves. The intention being to gain a better understanding of the mechanisms involved in the dissipation of wave energy.

Design and Execution of Beach Nourishments in Belgium

Abstract: When a severe coastal erosion problem has to be solved, two kinds of remedial coastal protection works are usually taken in view; the first one most often used in the past, requires the construction of structures such as groynes and breakwaters; the second one aims at providing a coastal protection solution by restoring or modifying the beach profile. Factors to be considered when evaluating the possible solutions are environmental conditions and sediment transport mechanisms. In fact, engineering design methods and human concern, are evolving, which leads to a new concept of coastal defence works. This trend is illustrated by case studies of project carried out along the Belgian coast.