Optimization for Hydrodynamic Performances of Flapper Wave Energy Converters

• Main Authors: Chang, Yu-Chi, 張育齊
• Other Authors: Chow, Yi-Chih
• Format: Others
• Language: zh-TW
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/49250019712916755865

博士 === 國立臺灣海洋大學 === 系統工程暨造船學系 === 104 === Wave energy as a major type of renewable energy from the ocean has considerable potential to be exploited. Therefore, so many kinds of wave energy converter (WEC) have been conceptually proposed for different applications in recent years. This thesis studies the bottom-hinged flap-type WEC, which can be folded to submerge to avoid impacts of huge waves caused by the extreme weathers of Taiwan like typhoons, aiming to maximize its energy capture for the application in the sea area around Taiwan with relatively low wave resources. This thesis combines the 2-D analytical theory and 3-D numerical simulations (WEC-Sim) to elucidate how the hydrodynamic characteristics affect the capture factor (CF) of the bottom-hinged flap-type WEC, along with conducting experiments to validate the predicted trends. The wave-energy-capturing performance of the bottom-hinged flap-type WEC can be attributed to three important parameters: the (moment of) inertia and restoring moment of the flap body, the damping of the power take-off (PTO) and the ratio of the flap body’s geometry and the incident wavelength (L). Derived from the 2-D analytical theory, several important design principles are obtained, including the impedance cancelling involving the restoring moment and inertia effects, the impedance matching between the PTO’s damping effect and the wave radiation effect, and the negligibility of the influence of the wave variability on the bottom-hinged flap-type WEC’s performance under the costal-water condition for irregular waves. After that, we are able to optimize the geometry of the flap body based on the characteristic wavelengths in the northeast of Taiwan (the test site of the National Taiwan Ocean University) using WEC-Sim. WEC-Sim simulations for different widths (B) and thicknesses (d) of the flap body show that the maximum CF can be as high as about 0.8 with B/L around 1/3 (B ranging from 21m to 23m) at an appropriate PTO’s damping coefficient. The comparisons between the 3-D simulation and 2-D analytical results indicate that the wave diffraction effect is a key factor to the trend of CF. The issues of the size minimization of the bottom-hinged flap-type WEC and the measurements of wave radiation/diffraction effects in the flow field around the WEC can be further addressed in the future.