Study on Hydrodynamic Performance of a Breakwater-Integrated Oscillating Water Column Wave Energy Converter
| Autor: | Chun-Han Ko, 柯鈞瀚 |
|---|---|
| Rok vydání: | 2019 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 107 This study is aimed to investigate the hydrodynamic and aerodynamic performances of an innovative breakwater-integrated oscillating water column (OWC) wave energy converter. This innovative OWC device consists of an extra perforated wall in front of the typical OWC chamber, which can be integrated with a caisson breakwater for capturing efficiently the wave power. The characteristics of the flow behavior in the OWC chamber and the effect of structural geometry on the hydrodynamic efficiency of the device are investigated by adopting both numerical simulations and laboratory experiments. The CFD numerical model for solving this air-water and wave-structure interaction problems is based on the three-dimensional RANS equations and the RNG -ε turbulent closure model, from which the numerical simulations is implemented by the Flow-3D software. The numerical model is first validated by using previous PIV experimental results for a typical OWC chamber and the present experiments for the innovative OWC device. Then the numerical simulations considering full scale OWC model are implemented for exploring the water and air flow characteristics and the geometric effect on the hydrodynamic performance parameters, including the water column surface elevation, the differential air pressure in the chamber, the airflow rate through the orifice and the pneumatic power. Based on the numerical simulations and experimental investigation, it is found that the larger velocity of water flow and the corresponding vortices always occur near the lip of the front submerged wall, and the airflow forms a conical shape due to the circular orifice on the roof centre of chamber. The maximum positive and negative differential air pressures in the chamber occur at the instant as the mean water level of the oscillating water column commences upward and downward, respectively. The positive and negative differential air pressure inside the chamber induce the air to extrude and suck through the orifice. The effects of the chamber geometry including the chamber breadth, the open height of front submerged wall, the orifice size and porosity of the front perforated wall are discussed by simulations considering full scale model of the present OWC device. It is found that the following remarkable effects. (i) The maximum pneumatic efficiency could reach to about 84% under the resonant frequency condition and the optimized geometry. (ii) The resonant frequency condition decreases with the increase of the breadth of the OWC chamber. (iii) The smaller and larger entrances of the open submerged wall could not produce higher pneumatic power, which the optimum value is found as 0.6 times of the water depth. (iv) The smaller orifice area might induce the larger the airflow velocity across the orifice and the larger differential air pressure in the chamber, however it does not produce the larger the pneumatic power due to the lower airflow rate. The max hydrodynamic efficiency happened as the orifice area ratio is 0.7%. (v) The front perforated wall could influents the wave reflection coefficient and the dissipation of turbulent kinetic energy, and reaches the max hydrodynamic efficiency when the porosity is 25%. Finally, by the comparisons the hydrodynamic performance between present and typical OWC, it shows that the present OWC device has better performance for pneumatic power extraction and less wave pressure on the front submerged wall. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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