Applicability of Different Methods for Computing Wave Forces on Monopile Foundation of Offshore Wind Turbine

• Main Authors: Tzeng, Yu-An, 曾郁安
• Other Authors: Hsin, Ching-Yeh
• Format: Others
• Language: zh-TW
• Published: 2019
• Online Access: http://ndltd.ncl.edu.tw/handle/bqejm6

碩士 === 國立臺灣海洋大學 === 系統工程暨造船學系 === 107 === The wave load of an offshore wind turbine foundation is determined by water depth, waves, ocean currents and seabed geology, whether it is a monopile, tripod, jacket, or gravity type foundation. In this thesis, different computational methods are used to compute the wave load of the offshore wind turbine monopile foundation. Fifteen wave conditions are set by three periods and five wave heights which gradually increase from smaller wave heights to the wave heights of breaking wave, and the force per wave amplitude is defined as a comparison parameter. For the hydrodynamic analysis of the foundation, we use three methods to compute, they are Morison equation, potential flow program WAMIT, and the viscous flow RANS method. Morison equation and WAMIT can only be used for linear analysis, and the phenomenon of nonlinear waves cannot be shown. The viscous flow RANS method is applied by using the commercial software STAR-CCM+. Since the physics of viscous flow method is closer to the real physical phenomenon, it is possible to completely simulate linear and nonlinear forces with the method, but it takes a lot of computational time and cost to conduct. This thesis uses three methods and fifteen wave conditions to compute the force on monopile foundation. In addition to the comparison of the computational results of three methods, the results are also compared with the results of MacCamy and Fuchs method in the reference. The results show that in the case of non-breaking wave, the wave height and force relationship computed by the three methods generally grows linearly, while the force per wave amplitude decreases with the increase of the period, which is consistent with MacCamy and Fuchs. However, in the case of breaking waves, the force computed by the RANS method increases sharply, and the force per wave amplitude cannot be accurately observed due to the indeterminate nature of the position of the breaking point. After comparing the results, for the three methods applied in this thesis, each has its own advantages and limitations, so it is necessary to select different methods for different sea conditions.