半潛式浮式平台水動力試驗分析

Abstract

為確保浮動式平台於海上環境中的穩定性與安全性，準確地預測其運動響應是必要的。本研究透過模型試驗探討半潛式浮動平台的水動力特性。該浮台為國立臺灣大學團隊為5 MW風力發電機所設計，命名為TaidaFloat。實驗採用1/100的縮尺模型，垂直自由度透過自由衰減試驗進行分析，藉由量測運動振幅並求解運動方程式，可推算出自然頻率、附加質量及阻尼係數，並以不同初始振幅條件了解其對水動力係數的影響。由於未設置錨鍊系統，水平方向自由度的恢復力可忽略，故採用強制運動試驗，透過量測六軸力及傅立葉轉換方法獲取水動力係數，為釐清振幅及頻率對水動力係數之影響，試驗涵蓋多種振幅與頻率條件。實驗結果提供六個自由度中，關於附加質量及線性與二次阻尼係數的可靠數據。結果顯示，僅阻尼係數受振福及頻率影響，並呈現近似線性趨勢。此外，二次阻尼係數的影響大於線性阻尼係數，反映出阻尼受黏性效應影響顯著。

To ensure the stability and safety of floating platform, it is essential to accurately predict the motion responses under offshore conditions. This study investigates the hydrodynamic characteristics of a semi-submersible floating platform through model tests. The platform, designed by the National Taiwan University team for a 5 MW wind turbine, is named TaidaFloat. The experiments are conducted using a 1:100 scaled model. Free decay tests are carried out for vertical degrees of freedom (DOFs). By measuring motion amplitudes and solving the motion equations, the natural frequency, added mass, and damping coefficient are determined. Various loading conditions are applied to realize the effects of initial displacement on the hydrodynamic coefficients. Captive tests are performed for horizontal DOFs due to the negligible restoring forces in the absence of mooring. Hydrodynamic coefficients are obtained by measuring six-axis forces and applying Fourier transform analysis. A range of oscillation amplitudes and frequencies is tested to identify how these variables influence the hydrodynamic coefficients. The experimental results provide reliable data on the added mass and both linear and quadratic damping coefficients across all six DOFs. The results show that only the damping coefficients are affected by the oscillation amplitude and frequency, displaying an approximately linear trend. Moreover, the influence of the quadratic damping coefficient is greater than that of the linear damping coefficient, indicating a significant contribution of viscous damping.