15 MW半潛式浮式風機拖航數值模擬及繫纜長期疲勞分析

Abstract

本研究針對半潛式浮式風機進行兩種數值模擬分析：拖航性能評估與繫纜疲勞分析。所有模擬皆以整合 IEA 15 MW 風機之臺大浮台為基礎。水動力模擬方面，分別採用基於勢流理論的ANSYS AQWA與考慮黏性效應的STAR-CCM+ 進行模擬，並透過 OrcaFlex 求解時域運動方程式，以獲得浮台運動響應與纜繩張力變化。環境載荷條件假設風、波浪與海流同向，風與波浪分別使用 API 風譜與 JONSWAP 波譜加以描述。拖航模擬設置拖航速度為 3 節，考量三種不同吃水與兩種風向條件。繫纜疲勞分析部分，以 3×3 繫纜系統為基礎，考慮四種風浪入射方向與三種繫纜直徑。模擬結果顯示，在建議的拖航海況條件下，浮台初始穩定性良好，並符合相關設計規範；拖纜張力顯著低於材料斷裂強度，而機艙處最大加速度及浮台最大傾斜角均未超出設計容許範圍，顯示浮台於拖航階段具備充分安全性。另一方面，在新竹外海長期運轉情況下，繫纜直徑對疲勞性能具顯著影響。直徑為0.165 m與0.18 m的繫纜於多數風浪方向下無法滿足疲勞設計準則，尤以H_P方法評估時最為明顯；僅有0.20 m直徑之繫纜可在所有方向與所有分析方法下滿足疲勞容許標準。

This study conducts two numerical analyses on a semi-submersible floating offshore wind turbine system: towing performance and mooring line fatigue analysis. All simulations are based on the TaidaFloat platform integrated with the IEA 15 MW wind turbine. Hydrodynamic modeling is performed using ANSYS AQWA, based on potential flow theory, and STAR-CCM+, which incorporates viscous effects. The time-domain dynamic responses, including platform motions and mooring tensions, are solved using OrcaFlex. Wind, wave, and current directions are assumed to be collinear in all simulations, with wind and wave spectra defined according to the API wind spectrum and the JONSWAP wave spectrum, respectively. The towing analysis assumes a towing speed of 3 knots and considers three different draft conditions and two wind directions. For the fatigue analysis, a 3×3 mooring configuration is adopted, with simulations conducted under four wind directions and three mooring line diameters. Simulation results indicate that under the recommended towing sea state, the platform exhibits sufficient initial stability and satisfies all design criteria. The maximum towline tension remains well below the minimum break load, and both the nacelle acceleration and platform inclination angle stay within allowable limits, confirming the safety during towing. For long-term operational condition at the Hsinchu offshore site, mooring line diameter significantly influences fatigue performance. Mooring lines with diameters of 0.165 m and 0.18 m fail to meet fatigue design requirements under most wind directions, particularly when evaluated using the H_P method. Among all configurations, only the 0.20 m diameter mooring line satisfies the fatigue criteria under all environmental directions and analysis methods.