The semicircular breakwater (SBW) is a composite breakwater consisting of a semicircular caisson resting on a rubble mound. The SBW function as a barrier dissipates the incident wave energy and creates tranquility on its leeside. The dynamic pressures due to regular waves exerted on seaside perforated SBWs with 7 and 11% of exposed surface area with perforations were measured. The measured pressures are compared with those exerted on impermeable SBWs. In addition, the forces exerted on the caisson alone are measured. The reflection coefficient, measured total forces on the caisson of the models, and the pressures are presented as functions of relative water depth. The effect of the water depth and the percentage of perforations on the above stated variables are examined, details of which are reported in this paper. © 2002 Elsevier Science Ltd. All rights reserved.

V Sundar

Department of Ocean Engineering

Ranganathan Sundaravadivelu

breakwaters

Caissons

Reflection

Water waves

water depth

Wave energy

Ocean Engineering

Breakwater

Dynamic characteristics

WAVE FORCE

Wave-structure interaction

Dynamic analysis

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IIT Madras

Dynamic pressures and forces exerted on impermeable and seaside perforated semicircular breakwaters due to regular waves

Reef breakwaters are submerged structures usually made out of rubble mound construction. Wave attenuation could be achieved off-shore by the introduction of such reef breakwaters. This offshore wave attenuation helps to protect a coast subjected to erosion. Such submerged structures are suitable when moderate wave transmission is acceptable on the lee side of the structure. This present work aims at providing a basis for the design of reef breakwaters using results from physical model tests. The hydrodynamic performance characteristics of the reef breakwaters, namely the transmission and reflection coefficients are examined in the study for varying wave parameters and geometric configurations of the reef. Further, the present experiments have helped shed light on Reef Induced wave Breaking (RIB) and its role in the hydrodynamic performance of the reef breakwater. The present investigations bring out those parameters which are involved in RIB so that a designer would be able to identify and provide-for the RIB. Design equations for prediction of transmission and reflection coefficients for submerged porous reef breakwaters in regular and random waves are proposed and compared with other such equations. It is shown that the present equations reproduce dependence of hydrodynamic performance on reef and wave parameters. © 2019 International Association for Hydro-environment Engineering and Research, Asia Pacific Division

Journal of Hydro-Environment Research

Functional performance of modular porous reef breakwaters

The present experimental research work focused on how a semicircular breakwater performs hydrodynamically under submerged conditions. In the field, a submerged semicircular breakwater may be preferred in front of the vertical breakwater to mitigate the wave forces and to minimize coastal erosion on its lee side. Various parameters affect the hydrodynamic performance of a semicircular breakwater such as the reflection and transmission characteristics, the dimensionless pressures, the horizontal forces and the vertical forces, and these are considered in the present study. Experiments were performed for three different perforations, namely 7%, 11% and 17%, of the exposed surface area with perforations on its sea side (sea-side perforated) and on both sides (fully perforated) owing to regular and random waves. The effect of the water depth was also studied in addition to the effect of perforation. All the hydrodynamic characteristics considered for the present study on the semicircular caisson are presented as functions of the relative water depth, and optimal conditions were determined. The results on the above-stated variables for sea-side-perforated semicircular breakwaters and fully perforated semicircular breakwaters are compared with the results of an impermeable semicircular breakwater. © Institution of Mechanical Engineers 2011.

Fulltext

Proceedings of the Institution of Mechanical Engineers Part M: Journal of Engineering for the Maritime Environment

Performance of a perforated submerged semicircular breakwater due to non-breaking waves

Scientists and researchers are currently focusing considerable attention on the hydrodynamic characteristics of semicircular breakwaters worldwide, particularly in Japan and the People's Republic of China. A semicircular breakwater is a composite breakwater made of prestressed concrete and has several merits over a conventional rubble mound breakwater, e.g. it is technically advanced, economically viable and aesthetically pleasing. At low water levels, it serves as a rubble mound breakwater and, at high water levels, it acts as a composite breakwater in the emerged condition. It reduces the considerable magnitude of dynamic forces if constructed in front of a vertical wall (the main structure) under the submerged condition and also reduces coastal erosion along the shoreline. Many research studies are being carried out all over the world to evaluate the performance of a semicircular breakwater in the laboratory and in the field. The authors of this review paper have also conducted a large number of experiments to study the hydrodynamic characteristics of a semicircular breakwater and to optimize the parameters such as the rubble mound height, the water depth and the size of perforations. The experiments were conducted for both the emerged condition and the submerged condition subjected to regular and random waves with various wave heights and periods to find the suitability of a semicircular breakwater in the field, and the optimum parameters were recommended in their previous publications. Hence, a sincere attempt has been made in this review paper to present the ongoing research on semicircular breakwaters, which has been carried out all over the world to facilitate the studies of researchers and to provide related information to people working in the area of semicircular breakwaters. © 2012 IMechE.

Review of the research on emerged and submerged semicircular breakwaters

The submerged semicircular breakwater (SBW) is mainly adopted to prevent beach erosion and to reduce the incident wave energy on its leeside, if it is used in front of a vertical breakwater. In addition, it facilitates the premature wave breaking, which in turn causes the reduction in wave energy. The dynamic pressures and forces exerted on the submerged SBW with 7%, 11%, and 17% of the exposed surface area with perforations on its seaside due to regular waves were measured. The hydrodynamic characteristics such as variations in the dimensionless pressures and forces, reflection and transmission coefficients on the semicircular caisson as a function of scattering parameter for three different water depths are presented and an optimum depth of submergence is arrived. The results on the above stated variables for seaside perforated SBWs are compared with the results of an impermeable SBW to study the effect of perforations. Copyright © 2010 by ASME.

Journal of Offshore Mechanics and Arctic Engineering

Regular wave measurements on a submerged semicircular breakwater

The present study investigated how the perforations, water depth and rubble mound height on fully perforated semicircular breakwater (SBW) affects non-breaking wave transformations. SBW model with surface piercing condition for three different perforation ratios with 7 percentage, 11 percentage and 17 percentage were considered to study the variation of reflection, transmission, run-up characteristics and dimensionless horizontal and vertical forces as a function of relative water depth and the results are compared with an impermeable SBW and seaside perforated SBW models. From the results it is understood that, SBW with perforation ratio 17 percentage in the case of seaside perforated case shows reverse trend in hydrodynamic characteristics and for fully perforated SBW, it transmits large amount of wave energy on the seaside, which affects the tranquillity condition in the harbour. In addition, transmission characteristics of SBW models and conventional rubble mound breakwater model are compared to understand the effect of composite breakwater action and also the reflection characteristics of SBW models are compared with field data of Miyazaki Port after Sasajima et al. (1994). The results reveal that the SBW model with perforation ratio of 11 percentage in seaside and fully perforated type gives an optimum performance in terms of energy dissipation and transmission. © 2009 Elsevier Ltd. All rights reserved.

Effect of perforations and rubble mound height on wave transformation characteristics of surface piercing semicircular breakwaters

The standing wave pressures due to laboratory-generated regular and random waves exerted on a vertical wall were measured in a wave flume. The standing wave pressures were measured at four relative depths of submergence on the test model. The regular wave test conditions ranged from intermediate to deep water conditions. The measured pressures due to regular waves were compared with results obtained using linear theory and third-order solution. In the case of random wave tests, the dynamic pressures due to the time histories of water surface elevation following the spectral characteristics of Pierson-Moskowitz and Bretschneider spectra were measured. These pressures are compared with simulated pressures obtained through the linear filter technique of Reid. The variation of pressure spectra along the depth are presented. In addition, comparison of spectral parameters, i.e. zeroth moment, spectral width parameter and narrowness parameter of measured and simulated pressure spectra, are reported and discussed. The behaviour of the coherence function between the wave elevation on the wall and the corresponding pressures is also discussed. © 1995.

Journal	Ocean Engineering
ISSN	00298018
Open Access	No