Design and Analysis of Buoy Geometries for Wave Energy Generator

Objectives/Methods: The main objective here is to make an optimum design of buoy. Wave power generation is one of the extensive research ﬁelds all over the world. The ocean waves are usually converted into electrical energy by a device called a wave energy converter (WEC). The electricity generated depends upon the intensity of the waves. In a traditional way, the motion of a buoy that occurred in a vertical direction due to waves in water, can be converted into current generation. Here, the numerical simulation using the Ansys tool is done to ﬁnd an optimum design of buoy shape to get maximum energy conversion. Findings: The simulations have shown that the drag force for the Oval shape is minimum 0.063 N and the ﬁrst mode of frequency for the Conical shape is minimum 165 Hz for Point-Absorber type Wave Energy Converter.


Introduction
The energy demand grew considerably and is even further increasing. Owing to depletion of fossil fuels and also the emissions caused by the fuels are the major hurdles for its use Thus, the demand for renewable energy sources is increasing. The renewable energy source is clean and available abundantly free of cost in nature. The various available renewable energy sources are wind energy, geothermal energy, solar photovoltaic and wave energy. The selection of renewable energy source varies from region to region (1) depending upon their availability. Ocean energy is consistently available energy with the highest energy density (2)(3)(4) throughout the year (5) . Wave energy has many advantages available for 24 hours. A number of wave energy devices are available and research is being done for its commercialization (6) . The wave energy can be converted into electrical energy by various methods as shown in Figure 1 below (7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20) .
https://www.indjst.org/ The point absorber is mostly used to harness wave energy. The multiple numbers of WEC (21) can be arranged in rows and columns to generate good amount of electrical energy. The WEC's are mainly classified as shown in following Figure 2 (6,22) . In the point absorber system in resonance with incident waves, the amplitude and speed increase and thus transfers the higher amount of energy (23,24) . Thus, wave energy must be considered a promising source of energy supply. There is a need to find out the suitable devices that are technically feasible and commercially available. The WEC devices that are available require a great deal of investigation in different areas like structural analysis (25) , fatigue analysis. This analysis can be done using the Ansys tool which mainly depends upon the wind system (26)(27)(28) .
The numerical analysis results obtained from the analysis will help to optimize (29)(30)(31)(32) the components, enhance the mechanical performance of the components and increase the efficiency of energy conversion. The performance of the buoy is also an important issue in the design of an oscillating buoy wave energy converter. The power output obtained from the buoy is the work with which the buoy has done to overcome the force produced by the system. The amount of work transferred by the buoy to the system is very important. The motion of the buoy depends mainly upon the waves induced.
Thus, this paper focuses on the design and analysis of buoy, from the structural point of view for various buoy geometries so that the efficiency of device also increases. https://www.indjst.org/

Forces Acting on Buoy
This is the case for the "buoy-type" or "point absorber" (33)(34)(35)(36) type of wave energy converter. The buoy will bob up and down on striking with the incoming waves. Whenever a crest of a wave hits the buoy, the buoy will travel up and when a trough comes, it will travel down. This linear movement of buoy is converted into electrical energy.
The various approaches to calculate the forces acting on wave given by Muetze (34,(37)(38)(39) , used are as shown in Figure 3.  The best element for meshing is the tetrahedral element as shown in Figure 5. Meshing parameters-Aspect ratio = 1.84, Jacobian 0.8, Element quality 0.88.  Figure 6 shows static pressure according to position and the velocity at different positions in the container as static pressure graph indicates at starting it has higher static pressure as we go forward in the tank pressure get reduced, exactly opposite to this as to go forward in the tank the velocity of the particle gets increased. https://www.indjst.org/  Figure 10 shows static pressure according to position and the velocity at different positions in the container as static pressure graph indicates at starting it has higher static pressure as we go forward in the tank pressure get reduced, exactly opposite to this as we go forward in the tank the velocity of the particle gets increased.  Figure 14 shows static pressure according to position and the velocity at different positions in the container. As the static pressure graph indicates at starting it has higher static pressure as we go forward in the tank pressure get reduced, exactly opposite to this as we go forward in the tank the velocity of the particle gets increased.

Conclusions
The commercial code in Finite element analysis is used to perform structural calculations to understand the behaviour of three different buoy geometries when subjected to wave forces. Based on the CFD readings given above, the drag force for the shapes in increasing order can be seen as follows: Oval Buoy → Conical Buoy → Spherical Buoy The drag force for the Oval shape is minimum 0.063 N for Point-Absorber type Wave Energy Converter. The first two modes of frequencies for all the shapes can be arranged in the increasing order as follows: Conical Buoy → Oval Buoy → Spherical Buoy The first mode of frequency for the Conical shape is minimum 165 Hz for Point-Absorber type Wave Energy Converter. Base on the above two analysis we can say that the oval shape or conical shape buoy are the best to get the optimum energy conversion. In future work, the performance will be verified in deep sea water with more depth.