1.6. Main motivation for the current work 23
Figure 1.2: The Mutriku Wave Energy Plant (Courtesy Mustapa et al. [78]) has chosen to spend $9billion in the construction of a 2.5GW offshore wind farm in the country’s south west sea. The foundation for a wind turbine grows in size as the tower grows in height, and the rotor nackle grows in size as gross generation grows. The wave force has a significant impact on the substructures. As a result, reducing wave stresses on substructures is an essential aim. Using a structure with a porous surface is one option.
In 1970, the whole globe experienced a worldwide oil crisis. The notion of putting renewable energy to the forefront has gained attraction since then. Parallel to this, a significant amount of effort has been put into research and emerging activities such as solar, wind, and ocean energy. This progress has aided in the research of the current gap between renewable and non-renewable energy sources. It has recently been discovered that WEC (Wave Energy Converter) systems are more expensive than standard energy generated by coal power stations. However, the WEC’s charm may be boosted by com- bining it with other marine constructions like a breakwater pier or a jetty. The following are the results of combining a breakwater with a wave energy device over a stand-alone wave energy device (Mustapa et al., [78]):
1. Overtopping WEC-breakwater integration,
2. Oscillating water column and WEC-breakwater integration,
3. Piston-Type Porous Wave Energy Converter (PTPWEC) integration.
"The Mutriku Wave Energy Plant" (Figure 1.2), located in Mutriku on the northern coast of Spain between San Sebastian and Bilbao, and "Siadar Wave Energy Project" (Figure 1.3), located in Siadar Bay, Lewis, Scotland, are two identified current important projects in connection with breakwater integration. The semi-circular breakwater idea built in Miyazaki Port in Japan (Figure 1.4) is another porous breakwater project.
Wind farms may be installed in any large body of water, especially in the ocean on the continental shelf, to capture offshore wind power or wind energy. Wind energy may
1.6. Main motivation for the current work 25
Figure 1.3: Siadar Wave Energy Project (Courtesy [78])
Figure 1.4: Semi-circular breakwater concept at Miyazaki Port, Japan (Courtesy [78])
be transformed to electricity in a suitable manner. There are several wind energy power resources accessible across the globe. One such important wind energy resource is "Mar de Trafalgar" (Figure 1.4) in the sea, which runs south-west to the Gulf of Cadiz in Spain.
Multiple uses of a marine site via the co-location of such complementing activities would almost certainly result in more effective use of ocean space, which is good for nature.
The ideal method to investigate the economic benefits and efficient use of ocean space via multi-use and co-location is to start growing aquaculture inside the structure that serves as an ocean wind farm. The co-location of these two businesses, aquaculture and wind energy generation, will result in cost savings for both the public and commercial sectors.
The public advantages are attributable to the fact that such a shared structural layout does not have a detrimental impact on ecological services received from the ocean region, which would otherwise take up and exhaust more space. Cost reductions resulting from the pooling of infrastructure, logistical operations, and systems are the private advantages.
Buck and Langan [11] have discussed in great depth on such difficulties. Sarkar and Bora
[93] discussed the diffraction of linear water waves by a cylindrical storage tank whose inner part contained a cylindrical pile and the outer part contained a coaxial thin hollow porous cylinder in finite ocean depth.
A few features of the utilisation of multi-porosity structures as breakwaters appear important to be examined. It is a significant problem to build a breakwater that achieves optimal wave reflection, transmission, and high energy damping while using the least amount of construction material possible. Several research have been conducted on various kinds of coastal structures, and it has been shown that porous structures are the best for attenuating wave energy, which in turn regulates wave energy in the seaward and leeward open water zones. As a practical example, porous blocks were successfully used to control high wave attack in the Gudong and Zhuangxi Sea Dike in the Shengli Oilfield in China [124]. To protect against wave impact, perforated wall breakwaters were erected at Dieppe, France ([9]) and Dalian Chemical Production Terminal, China ([43]).
Furthermore, surface waves in reservoirs or lakes induced by landslides during earth- quakes have been studied using the thin porous-wavemaker hypothesis, which has con- siderable applications in the research of surface waves in these water bodies. Landslides produce water waves by moving vertically, at an angle, or horizontally, during the part of their journey. A vertical landslide was simulated by Noda [81] by using a two-dimensional box that fell to the bottom at the end of a semi-infinite canal. A porous box or wall would be more suitable when the majority mass of a landslide comprises of rocks and soils. Another conceivable use of the current approach is in the cases when the wave- maker is subjected to some type of structural limitation on the highest permitted force, and the wavemaker’s efficiency is of primary importance. As the porous-effect parameter grows, a porous wavemaker may be useful in lowering the overall load, which is followed by a drop in the wave amplitude. The thin plate inhibits the vertical motion of water oscillations so efficiently that it may significantly lower wave amplitudes. Wu et al. [112]
proposed an engineering application in which a horizontal plate might be connected to an existing seawall to lessen wave reflections. A pitching plate may be designed as part of a wave controller, according to Yip and Chwang [118]. They further investigated the hydrodynamic performance of a perforated wall breakwater with an internal horizontal plate (Yip and Chwang [119]).
After reviewing the preceding studies, it is clear that further substantial effort is re- quired to develop (i) a composite porous structure, (ii) thin porous structures, and (iii) flexible poro-elastic bodies. This sort of construction will aid in lowering the hydrody- namic effect on shoreline and structures that may be erected in the ocean for a variety of purposes. We address issues related to scattering and radiation using wave absorbing structures that also serve as wave energy devices in this context.
In this thesis, we are inspired to tackle the scattering and radiation issues in a two-layer fluid with different types of porous and flexible bodies in the presence of various types of
1.7. Outline of the thesis 27