1D physical modelling of wave transmission at submerged breakwater

Ibrahim, 'Izzat Na'im (2017) 1D physical modelling of wave transmission at submerged breakwater. [Project Paper] (Submitted)

Text lp FK 2017 56.pdf Download (9MB)

Abstract

Breakwaters are used around the globe as a mean of protection against beach erosion by reducing the height of incoming waves into smaller transmitted waves. In addition, breakwaters can efficiently be used to preserve tranquillity inside the harbour basin, to decrease the deposition of sediments that can lead to water pollution at the harbour entrances, and to be a sanctuary for marine habitats. The main purpose of this study is to determine wave transmission coefficient, KT at submerged breakwaters through 1 D physical modelling. In addition to the main objective, several research objectives are constructed such as to determine the relationship between freeboard of the structures, R and wave height, Hi and relationship between the crest width of structure, B and the wavelength, L0 for two different breakwaters, to find the energy reduction of the waves passing through the submerged breakwaters and to compare the performance between vertical and sloping front face. The experiment took place in a small scale laboratory wave flume equipped with wave generator. A total number of 24 sets of experiments has been conducted on four type of breakwater models by using various parameters. Two different heights of wave (25 mm and 35 mm) are generated by the wave generator for cases with three different freeboards (20 mm, 40 mm and 60 mm). Two wave probes were positioned inside the wave flume before and after the breakwater model to record the incident wave and transmitted wave heights respective) y. Sponge was placed at the end of the wave flume to act as absorber to reduce the impact of reflection of the wave. The wave was propagated to the breakwater model for duration of two minutes. The wave heights were recorded and processed by using HR-DAQ software. Results show that the freeboard of 20 mm gives the lowest wave transmission coefficient compare to the freeboard of 40 mm and 60 mm. Apart from that, the results confirm that the top crest width of 200 mm has reduced the wavelength of incident wave compared to the top crest width of I 00 mm. For the type of slope, the 1 :2 front slope shows better reduction of incident wave compared to the vertical front slope. In addition, when experimented with 60 mm of freeboard, the wave coefficient transmissions exceed 1.0 which indicated that reflection occurs at the lee of the structures for all type of models. It can be concluded that wave transmission at submerged breakwaters in 1 D physical can be modelled. The submerged breakwaters are capable of reducing the height of the transmitted wave. In addition, the relationship between the crest width of structure, B and the wavelength, L0 for two different breakwaters is that the wider the length of B, the lower the wavelength at the lee of the breakwater models. This study implies that submerged breakwater is able to reduce incoming wave heights into smaller transmitted wave heights given the ratio of freeboard to structural height is equal to 0.67 or lower and the ratio of freeboard to incoming wave height is equal to 1.14 or greater. If the ratio of freeboard to structural height is greater than 0.67 or ratio of freeboard to incoming wave height is lower than 1.14, Furthermore, the relationship between the freeboard of the structures, R and wave height, Ht is found that the lower the freeboard, the lower the wave transmission coefficient. reflection coefficient needs to be taken into account.

Item Type:	Project Paper
Faculty:	Faculty of Engineering
Depositing User:	Ms Siti Mariam Giman
Date Deposited:	25 Oct 2023 07:21
Last Modified:	25 Oct 2023 07:21
URI:	http://psaspb.upm.edu.my/id/eprint/1580

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