Showing papers on "Breakwater published in 1982"

Wave Scattering by a Rigid Thin Barrier

Abstract: The boundary integral equation method (BIEM) is applied to examine the effectiveness of both the vertical and the inclined thin breakwater. The BIEM has been used widely for free surface flow problems in both ground-water flows and water waves. For the present problems, modifications of the method are made to treat the velocity singularity at the tip of the breakwater and the zero thickness of the breakwater. The computational domain is truncated by introducing two auxiliary boundaries at some distance away from the break-water. Analytical solutions, which satisfy the governing equations and the radiation boundary condition, with unknown coefficients are used along the auxiliary boundaries. The accuracy of the numerical technique is demonstrated by comparing numerical results with analytical solutions for a vertical breakwater in a deep water. Numerical results in terms of both reflection coefficient and transmission coefficient are presented for both vertical and inclined thin breakwater.

Sedimentological Influences of Detached Breakwaters

Abstract: Wave diffraction and refraction in the surroundings of a new detached breakwater induce currents strong enough to cause substantial local sediment transport and consequently morphologic changes, the main feature of which are sand spits or tombolos. As shown by field studies the morphologic changes cause an equilibrium state with some minor fluctuations due to changing wave climate. Model studies have also proved the existance of such an equilibrium state for any given geometry and sea state The present paper treats mainly this equilibrium state, but also attempts to explain the mechanism of sand transport characterizing the initial and transitional states. According to observations by the authors in small scale models, the transporting mechanism in the transitional state involves sea bottom erosion, especially near the breakwater heads outside the protected area, and transport of sand towards the shore of the sheltered area in the form of small migrating sand bars, which finally join the shore line and widen it. Results of experimental investigations conducted by the authors, for the particular case of high impervious breakwaters attacked by waves of normal incidence, as well as results of field and model studies given by others, are used to define relationships among the factors determining the equilibrium state and to base a new hypothesis regarding the equilibrium state. This hypothesis states that a morphologic and sedimentologic equilibrium is reached behind a detached breakwater, when the shape of the contour lines becomes such, that along the sheltered beach the diffracted waves have components of momentum opposed to the gradients of the mean sea level induced by radiation stress due to non uniform wave heights along the wave fronts approaching from both sides of the breakwater. The significant parameters characterizing the dimensions of the spit or tombolo in the equilibrium state are shown to be the relative length of the breakwater (compared to its distance from the original shore line), the relative distance from the original shore line (compared to the position of the breakers' line) and the relative height of the breakwater crest (above M.S.L, compared to the incident wave height).

Floating Tire Breakwater Design Comparison

Abstract: The design curves from two independent studies of the wave transmission and mooring force characteristics of Goodyear-type floating tire breakwaters are compared. The CERC wave transmission results from prototype scale tests and the mooring force results of Harms from model scale tests are recommended for use in design. Both wave transmission and mooring forces are seen to depend primarily on the ratio of wavelength to breakwater beam, and less importantly on the relative draft and the wave steepness. Differences between the results of the two studies are attributed to scale effects and to different methods of data analysis.

Variation of Foreshore Due to Detached Breakwaters

Abstract: As coastal areas are very valuable for mountainious Japan, many countermeasures against beach erosion have been taken. The length of seawalls for beach erosion amounts to 5,600 kilometers, which is much longer than the length of seadikes for flood tide, which is 2,900 kilometers. In addition, 10,000 groins and 2,300 detached breakwaters have already been constructed for beach erosion. Especially, we used many detached breakwaters for the last ten years. Fig.1 showes the increase of total length of seawalls and seadikes for the last twenty years.

Combined refraction and diffraction: Comparison between theory and experiments

Abstract: Laboratory experiments (Hales, 1980) concerning the wave field near a breakwater are used to compare with a uniform asymptotic theory developed by Liu et al. (1979). The breakwater was installed on a linear plane beach, and the orientation of the breakwater is perpendicular to the bottom contours. Excellent agreement between the theory and experimental data is observed. Numerical solutions based on the asymptotic theory are also given for the wave field near a detached breakwater.

A numerical model of wave/breakwater interactions

Abstract: A numerical model has been developed to simulate breakwater response to wave impacts with special reference to armor unit behavior and breakwater stability. The model uses a finite difference hydrodynamic code to follow the wave impacts and determine wave forces upon the breakwater components. A discrete element code models the breakwater response and motions. The model rationale and numerical basis are followed by three examples used in this, the concept validation, stage of model development.

The monitoring of rubble mound breakwater stability using a photographic survey method

Abstract: A method of surveying the above-water slope of breakwaters by means of photography has been developed at the National Research Institute for Oceanology. The method is simple and inexpensive and yet capable of detecting movement or displacement of a single armour unit on a breakwater. This poster paper describes the method and presents some examples of its application in the field.

Floating breakwater field experience, West Coast

Abstract: : Existing literature on floating breakwaters is lacking field information on the construction and subsequent performance of these structures. This report partially addresses this deficiency by evaluating 11 existing floating breakwaters located in the Pacific Northwest. The breakwaters consist of five concrete caisson units, three Alaskan-catamaran or ladder-type breakwaters constructed of posttensioned concrete segments, one constructed of surplus oil pipeline sections, one Goodyear floating-tire module breakwater, and one with units consisting of four rows of plastic pontoons. The report includes a description of each site and breakwater structure, a discussion of the breakwater's performance based on site inspections and discussions with owners, marina operators, etc., and a set of conclusions for the overall evaluation of the structures.

Dolos Breakwater Design Improvements

Abstract: There are two different failure modes in Dolos breakwaters: (1) Loss of stability; and (2) overstress. Bending tensile stress in armor units increases with design wave height, and a linear relation has been established for this phenomenon. A wave wall or adjacent vertical wall causes an increase in wave force and damage. Consequences due to settlement and consolidation should be considered in deep water breakwater design. The potential benefit of reinforcement of concrete armor units is proposed.

Spending beach breakwater at saldanha bay

Abstract: This paper describes the design and construction of a sand breakwater at Saldanha Bay exposed to the severe swell conditions of the south Atlantic. The design of this spending beach breakwater was aimed to establish a seaward profile with sufficient "playroom" to incorporate profiles resulting from extreme wave conditions. As far as the construction is concerned the emphasis is put on the sandlosses during execution of the works. Finally the designed profile is compared with the actual established beach profile.

Constructing method for harbor structures such as breakwater and quaywall

Abstract: PURPOSE:To shorten the term of construction of large-sized harbor structures and to improve the reliability thereof by uniting a lower caisson fitted with a buoyancy adjusting structure and a tubular upper caisson and by sinking them on the seabed CONSTITUTION:The box-shaped hollow lower caisson 2 is fitted with cylinder towers 10 for adjusting buoyancy and submerged, and the tubular upper caisson 1 is mounted on the upper part of the submerged lower caisson 2 Next, the buoyancy of the lower caisson 2 being increased, the upper caisson 1 and the lower caisson 2 are united watertightly by a packing 11 inserted intermediately between them are connected wih each other by casting concrete into spaces 12 between them Then, the upper and lower caissons 1 and 2 thus connected are towed to a place of setting thereof and suck on the seabed, and later sand or the like is filled up in the upper and lower caissons 1 and 2 thus sunk

Dredging to minimize wave penetration into a harbour

Abstract: Wave protection within a new harbour development has been achieved by shaped dredging in place of long breakwaters. The dredging shape was initially established through wave refraction calculations and then confirmed and optimized in a physical three dimensional model. The cost of additional dredging for the specified shape was A$100,000 compared to estimated breakwater costs of A$l,000,000.

Coastal protection devices - a review

Abstract: Coastal protection devices include, but are not limited to, dune stabilization, seawalls, groynes, detached breakwaters, sand bypassing and beach nourishment. These are the "tools". The "rules" for their use comes from a knowledge of the beach processes which in many instances are site specific. Systems which work satisfactorily at one location may not necessarily work at another. A plan is made for authors to give more information on these processes when describing case histories. The variability of the physical conditions and the non-linear nature of many of the coastal processes often dictates how coastal protection works will behave; a fact which is not always taken into account by the designer. For coastal protection devices to be developed to their full potential requires improved instrumentation and data bases and a greater knowledge of the coastal processes than is available at the present time.

Zeebrugge's Main Breakwaters

Abstract: The design scheme of the Zeebrugge Outer Harbour, Belgium, consists mainly of two breakwaters protruding into the sea as far as 1,750 m beyond the existing mole or 3.000 m out from the coastline. The west outer breakwater is 4,450 m long, the east breakwater runs 4,300 m out from the seafront. The east outer harbour will accommodate terminals for liquid bulk products such as LNG. The west outer harbour will provide space to install two harbour bassins to suit general cargo, hazardous cargo, container and ferry traffic. In the paper emphasis is put on the environmental design conditions (wave height, wave period, water depth), the development of preliminary designs and the final design. Some design features such as dimensions, wave breaking carpet, armour units, workable limits in respect to rock grade, etc ... are discussed. By developing the design the rubble-mound breakwater has been judged to be the only viable alternative versus the caisson type breakwater, taking into account costs, technical risks, construction problems and flexibility under changing environmental conditions. The main feature of the breakwaters is that a huge concrete parapet will have been avoided. A so called flat semi-cube armour unit has been developed. The main advantage lies in the substantial economic benefit whilst maintaining the same stability performance as a concrete cube armour unit.

Improvements in modelling rubble-mound breakwaters

Abstract: Physical modelling is a technique which is commonly used in the design procedure of rubble-mound breakwaters. For reliable results it is necessary that the model tests accurately represent the prototype situation. In this paper, two significant improvements in modelling of breakwaters are presented. They are the generation of realistic sea states at the test site, and the simulation of the breakage of the armour units by using units which have mechanical properties properly scaled from the prototype units. These techniques have been used to study the recent breakwater failure at Riviere-au-Renard, Canada.

Numerical Modelling of Rubble Mound Breakwaters

Abstract: Rubble-mound structures have been used for thousands of years for harbours and coastal lines protection against wave action. Perhaps the oldest use of rubble-mound breakwaters was that found in the ancient City of Alexandria at the Pharaoh Port. The course of progress in design procedures for rubble-mound has been from mere experience and judgement to physical modelling and the use of empirical equations. The purpose of this paper is to shed some lights on the numerous facets of the problem of wave interaction with rubble-mounds and the possibilities of using numerical modelling in the design of such structures.

Computational algorithm for longshore energy flux incorporating friction

Abstract: The calculation of longshore sand transport on "beaches is a significant coastal engineering problem with application to various areas of coastal structure design (i.e., jetties, groins, and offshore "breakwaters), and inlet navigation channel design (i.e., studies of required maintenance dredging). Longshore sand transport as a first approximation is linearly related to longshore energy flux (see Bruno, et al. (1981)), hence, this paper simply presents a method for computing longshore energy flux as a means of determining longshore sand transport. The approach used herein for calculating longshore energy flux includes an analytical method for incorporating frictional wave energy dissipation. The method is simple enough to program on a hand-held programmable calculator. It therefore provides a method hy which rapid calculations can he made for a site at which offshore wave data exist. If offshore directional random wave data are available (i.e. directional wave spectra) then more advanced techniques should he used (see Walton and Dean (1981)).