Showing papers on "Breakwater published in 1992"

Hydraulic Design of Perforated Breakwaters

Abstract: In the present engineering practice, direct formulas are not given for the preliminary hydraulic design of Jarlan-type breakwaters: Only qualitative observations and heuristic considerations are reported. The writers analyze the wave attenuation produced by the permeable structure and propose design formulas that can be used for the optimized hydraulic design of Jarlan-type breakwaters. The proposed model, based on the linear wave theory, is validated by comparison of the theoretical results with the experimental measurements of other authors. The results show that the Jarlan-type breakwater with a single chamber gives the most effective wave reduction in the range of practical applications and that no particular configuration of the porous wall can be suggested as the best one. The size of the breakwater cannot be standardized, since the optimum hydraulic design of the structure is linked to the parameters of the design wave. Moreover, the proposed design formulas may be used to approximately predict the response of the structure to incident irregular waves.

Conceptual Design of Rubble Mound Breakwaters

Abstract: This paper gives first an overall view of physical processes involved with rubble mound structures and a classification of these structures. After the description of governing parameters, the hydraulic response is treated. This is divided into: - Wave run-up and run-down, - Wave overtopping, - Wave transmission, - Wave reflection. The main part of the paper describes the structural response which is divided into: - Rock armour layers, - Armour layers with concrete units, - Low-crested structures, - Berm breakwaters, - Underlayers and filters, - Toe protection, - Breakwater head, - Longshore transport at berm breakwaters. The design tools given in this paper and by Delft Hydraulics' pc-program BREAKWAT are based on tests of schematised structures. Structures in prototype may differ (substantially) from the test-sections. Results, based on these design tools, can therefore only be used in a conceptual design. The confidence bands given for most formulae support the fact that reality may differ from the mean curve. It is advised to perform physical model investigations for detailed design of all important rubble mound structures.

Reflection and transmission of water wave by porous breakwater

Abstract: A small‐amplitude water wave acting on a vertical porous breakwater in an infinitely long channel is investigated. In the present work, homogeneous water follows conventional assumptions as irrotational, inviscid, incompressible fluid flow. The solid skeleton of the porous breakwater is rigid, and the flow inside the porous breakwater is governed by simplified Biot theory of poroelasticity. A small “porous Reynolds number” is applied to obtain a regular perturbation solution that preserves the surface of seepage on the breakwater/channel flow interface. It is found that there are dramatic variations of velocity distributions among vertical cross sections inside the porous breakwater. It is also found that the reflected wave is greater, while the transmitted wave is less for waves of higher frequency with thicker and less porous breakwaters. However, the thickness of the porous breakwater only has a significant effect on the transmitted wave.

Impact loading and dynamic response of caisson breakwaters

Abstract: The results of large-scale model tests on impact loading and dynamic response of a caisson breakwater are presented. Hydraulic model tests are performed in which the impact loading is induced by breaking waves on the structure. Horizontal impact forces, uplift forces and the related overturning moments are determined. The transmissibility of the impact loads and the accelerations of the structure are investigated (dynamic response).. The hydraulic model tests are supplemented by pendulum tests on the same caisson breakwater model used in the hydraulic model tests in order to determine the characteristics of the structural model itself. The added mass of water oscillating with the structure, the stiffness of the foundation and the damping ratio are evaluated from these tests.

A submerged compliant breakwater

Abstract: A numerical technique is utilised to investigate the dynamics of a submerged compliant breakwater consisting of a flexible, beamlike structure anchored to the seabed and kept under tension by a small buoyancy chamber at the tip. The fluid motion is idealised as linearised, two-dimensional potential flow and the equation of motion of the breakwater is taken to be that of a one-dimensional beam of uniform flexural rigidity and mass per unit length subjected to a constant axial force. The boundary integral equation method is applied to the field domain, modifications are made to the basic formulation to account for the zero thickness of the idealised structure and the singularity in the fluid velocity which occurs at the breakwater tip. The dynamic behaviour of the breakwater is described through an appropriate Green function. Numerical results are presented which illustrate the global influence of the tip singularity on the solution and the effects of the various wave and structural parameters on the efficiency of the breakwater as a barrier to wave action. Small-scale physical model tests were also carried out to validate the foregoing theory. In general, the agreement between experimental and numerical results was reasonable, but with considerable scatter.

Design of rubble mound breakwaters

Abstract: This rapport includes two main topics for designing a rubble mound breakwater: 1. Geometrical properties and durability of rock materials 2. Structural integrity of concrete armour units Included in this rapport are some design diagrams for Dolos of different waist ratios.

Armor Stability on Submerged Breakwaters

Abstract: Armor stability on submerged conventional breakwaters is examined using a hybrid method based on experimental, numerical, and empirical results. Four test runs are conducted to measure the horizontal fluid velocities and free-surface elevations over a submerged breakwater caused by a solitary wave. These measurements are used to evaluate the numerical model called IBREAK. The agreement between the measured and computed results is found to be fair except that IBREAK overestimates the velocities immediately landward of the crest of the submerged breakwater for the case of small submergence. The comparison also shows that the horizontal velocity over the breakwater decreases with the increase of its submergence. The reduction of the horizontal velocity is then related to the increase of armor stability on the breakwater with the increase of its submergence. The present method predicts the significant increase of the armor stability resulting from the moderate reduction of the maximum horizontal velocity with...

Dynamic breakwater and pumping system

Abstract: A dynamic breakwater system pumps water from a body of water in response to wave action or underwater currents. A submerged stationary base is fixed to a solid subsurface. A breakwater protrudes upwardly through the surface of the water. Wheels support the breakwater for displacement on the base along a generally horizontal displacement axis. Springs acting against opposing sides of the breakwater urge it to a rest position between two horizontally extreme positions, and wave action and underwater currents against either side of the breakwater produce a reciprocating movement of the breakwater along its displacement axis. A pump pumps water in response to the reciprocating movement. The pump has a large piston spaced from the pump housing by roller assemblies. A door permits access to the pump interior for removal of debris or for repair, and a locking mechanism fixes the breakwater to the base to arrest pumping action for such purposes. Brush assemblies attached to the breakwater sweep debris from the base in response to the reciprocating motion ensuring that the breakwater continues to displace.

Modelling Siltation at Chukpyon Harbour, Korea

Abstract: The present paper describes the application of a range of computer models to describe the seasonal variation of seabed bathymetry in the vicinity of Chukpyon Harbour, which is situated on the east coast of Korea. The coastal conditions at the harbour site are dominated by waves and wave-induced currents. Consequently, wave-period-average models were used to predict waves and wave-induced-currents for three wave conditions for two wave directions. A new three-dimensional wave-period-average sediment model was then used to describe particular patterns of seabed change, which were, in turn, combined to predict seasonal changes. Use was made of a variety of field data on waves, currents, and sediment transport rates to set up and calibrate the model. Comparison of model results with field data confirmed the presence of residual sediment movement towards the harbour entrance and the location of shoal zones near the west groyne and east breakwater. The model was subsequently used to study new additions to the existing structures to control nearshore siltation.

Detached Breakwaters and their Use in Italy

Abstract: Detached (or "offshore") breakwaters of emerging type are a common and effective approach for beach protection, particularly for areas with small tidal oscillations. This kind of breakwaters aims at acting on sediment transport by decreasing the transport capacity of long-shore currents, thus locally causing settlement of sediments. Unlike groins, which act directly on long-shore currents, detached breakwaters act on incoming waves decreasing their height in the protected areas and thus also decreasing the strength of associated currents and causing settlement of sediments. Another functional aspect of detached breakwaters is that they influence not only long-shore transport, but also on-offshore transport of sediments. The use of detached breakwaters is quite common along the coasts of the Mediterranean (particularly in Italy) and in Japan. It is well known that, as for all protective structures of the "rigid" type, the benefit for the protected beach, following the increased deposition of sediment, is usually offset by reduced supply of sediments to and subsequent erosion phenomena of the downdrift beaches. After a brief review of general characteristics and performance of detached breakwaters of emerging and submerged type, in this report some applications of this kind of protective system along the coasts of Italy will he illustrated and discussed.

Joseph whidbey and the building of the plymouth breakwater

Abstract: (1992). JOSEPH WHIDBEY AND THE BUILDING OF THE PLYMOUTH BREAKWATER. The Mariner's Mirror: Vol. 78, No. 1, pp. 37-56.

Rubble-mound bank constructing method

Abstract: PURPOSE:To enable a bank to be constructed easily and sturdily in the sea, lakes, or the like. CONSTITUTION:In a shape for forming a revetment breakwater space SP with bag-shaped networks 6, 6, the networks 6, 6 are set at positions for the execution of work in seawater. In the bag-shaped sections of the networks 6, 6, rubbles 5a are cast, and rubble structural-bodies 5, 5 are formed, and into the revetment breakwater space SP, sand 7a is cast from a seawater surface 2b, via silt protectors 9, 9 inside the networks 6, 6, and a sand structural-body 7 is formed. In a state that the sand 7a is densely heaped up according to a repose angle, the sand structural-body 7 is formed, and so the rubble-mound bank 1 of steady construction is constructed.

Hydraulic Design of Offshore Breakwater in Sergipe, Brazil

Abstract: A Petrobras (Petroleo Brasileiro S.A.) marine terminal was recently constructed in Sergipe, Brazil (Figure 1). The offshore breakwater was initially designed in a conventional way, but alternative breakwater designs were developed based on the berm breakwater concept. The features of this concept were: relatively lower costs of construction; considerably lighter stones on the main armour when compared with a conventional two-stone armour design; and simpler construction procedures which enabled better control during construction. This paper describes the details of the hydraulic model testing carried out during the designing stages of the offshore breakwater. This design was developed by means of two separate physical model testing, firstly an alternative berm design and then a redesign due to changed geotechnical conditions. The testing program assisted in preparing a cost-effective, hydraulically stable breakwater structure, considering the armour stability, wave runup and overtopping and overall integrity of the structure.

Influence of superstructure geometry on the behaviour of vertical breakwaters: two case studies

Abstract: Traditionally, vertical breakwaters were referred to as reflecting breakwaters, to distinguish them from the rubble mound breakwater. With this distinction it seemed clear under which design wave conditions the two types should be used, i.e., the vertical breakwater ought only to be constructed in areas where the calculation wave is not going to break. However, greater knowledge of the behaviour of these breakwaters in physical model tests is bringing about a change in this attitude. This article presents two case studies, in which different vertical breakwater designs are subjected to breaking waves and non-breaking waves. Modifications to the superstructure geometry (parapet) of the caisson and activity taking place in front of the breakwater itself have achieved an important reduction in the stress caused by the wind waves, because they affect not only the face of the breakwater, but also overtopping. This has become apparent from the results obtained from tests carried out on physical models.

Wave dissipation breakwater having artificial tidal pool construction to promote breeding of useful seaweed

Abstract: PURPOSE:To obtain an environment for breeding seaweeds not to generate any fault in the life cycle of the seaweeds through four seasons by forming wave dissipation breakwaters in the shape of steps, and by providing the breakwaters with tidal pool construction CONSTITUTION:Wave dissipation breakwaters 1, 2, 3, 4 are formed in the shape of steps, and on the respective steps, frames formed integrally with a main body so that tidal pools 5, 6, 7, 8 may be formed along edges not to dry seaweeds at a tidal time are manufactured Then, the gamest and zygots of sea lettuces and the like are attached to the tidal pools 5, 6, 7, 8, and all year round, the seaweeds are bread

Diagonal wave dissipation type breakwater

Abstract: PURPOSE:To improve capability of wave dissipation by a method wherein a breakwater main body, stretching horizontal and having a slope facing the direction from which waves approach, and a breakwater equipped with partitions, some of which have openings and others do not, are provided and a recessed part for producing of diagonal waves is provided on the offshore side along the longitudinal direction of the breakwater. CONSTITUTION:A breakwater 6, stretching horizontal and having a slope that faces the direction C from which waves approach, is arranged. A diagonal wave producing recessed part 7 is provided to the ground 2 on the offshore side so that it gradually extends in the width along the longitudinal direction of the breakwater 6, and thereby the waves progressing toward the breakwater alter the course, and waves diagonal to the breakwater 6 are produced therewith. Projections and recesses provided to the breakwater 6, and openings 3 for passing through of diagonal waves provided to partition walls 4 with openings of the breakwater 6 make the diagonal waves reflected and collide with the following waves. The waves progressing diagonally in the projections and recesses of the breakwater 6 meet with resistance when passing through the openings 3 and lose energy thereby, as well as by colliding with the following waves.