Wednesday, November 13, 2019

Breakwater Essay -- Marine Infrastructures

Conventional breakwaters are massive in size and generally associated with large scales in construction materials, effort and cost. The development of large breakwater schemes with poor design and management may trigger a number of adverse effects on neighbouring coastal environment, e.g. large amount of wave reflection, alteration of beach morphology, water quality deterioration and change of marine ecosystem. To alleviate the above problems, various ingenious designs of light-weight breakwaters have been proposed, tested and constructed in the past as alternatives to the conventional breakwaters, one of which is the free surface breakwaters. Free surface breakwaters are essentially barriers located near the water surface where the energy flux is maximal. The total height of such barriers is usually far smaller than the water depth which helps water circulation around the structures. These barriers can be constructed on a group of piles driven into sea floor, or held floating as floating breakwaters. Wave reflection and dissipation are the primary energy damping mechanisms inherited by these barriers. Free surface breakwaters are most suitable to be built at semi-protected sites where the soil condition is poor. The present investigation is motivated by the construction of bottom-mounted semicircular breakwaters in Miyazaki Port (Japan), Tianjin Port (China) and Yangtze River Estuary (China) for sea defence. Extensive studies on such breakwaters were undertaken by several researchers from Japan, China and India, e.g. Tanimoto et al. (1989), Sasajima et al. (1994), Xie (1999), Dhinakaran et al. (2002), Yuan and Tao (2003) and Zhang et al. (2005). Although a number of studies have been reported in the literature associated with... ...hat comprise a large number of discrete constituents for energy dissipation. Examples of such breakwaters are multiple-layer breakwater (Wang et al., 2006) and porous-pile breakwater (Hsiao et al., 2008). These structures are usually highly porous to water flow, resulting in relatively small wave reflection and the horizontal wave forces on the structures. One of the major concerns in the design of marine infrastructures is the navigation safety adjacent to the breakwaters. In many cases, it is important to keep the amount of wave reflection in front of the breakwater to the minimal. The majority of the abovementioned breakwaters mainly serve as wave reflectors. It is hoped that the free surface semicircular breakwater considered for the present research would yield better performance characteristics by producing low reflection and desirable wave attenuation.

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