使用半潛式臺大浮台之15MW浮式風機系統考慮3×2與3×3繫纜設計於新竹外海場址一般運轉與極限海況性能研究

Abstract

本研究使用半潛式臺大浮台搭載IEA 15MW 風機與3×2、3×3懸垂式繫纜佈置的浮式風機系統，預測新竹外海海氣象條件下一般、高波海況及考慮50年迴歸週期極端海況下的運動響應與功率性能。本研究使用JONSWAP波譜描述新竹外海波況，除考慮固定風速外，一般與高波海況下亦使用API風譜描述風速變化情形，極端海況下則以颱風陣風模型加以描述。本研究使用ANSYS-AQWA與STAR-CCM+預測水動力特性，接著以OrcaFlex求解運動方程式，預測風機系統的性能。由於波浪主要起因於風，因此假定風向與波向一致。本研究探討七組風向、四組流向、三種海況條件與兩種繫纜設計，共計一百六十八組分析案例。風機系統運動響應、風機功率與繫纜受力的平均值與標準差，在一般與高波海況下受到流向影響較不明顯，極端海況下流向影響則較為顯著，三種海況下風向造成的影響皆十分明顯。風速變化對運動響應與繫纜張力的平均值影響不大，對標準差影響較大。與固定風速條件比較，使用API風譜風機功率輸出約減少1%至3%。使用3×2繫纜風機功率於一般海況下皆高於14.14 MW，高波海況下皆高於14.53 MW；使用3×3繫纜風機功率於一般海況下皆高於14.47 MW，高波海況下皆高於14.65 MW。3×2及3×3繫纜佈置最大縱搖角度於一般海況下分別為5.59°與5.48°，高波海況下分別為1.50°與1.49°，極限海況下分別為10.81°與9.73°；最大位移於一般海況下分別為12.59 m與7.67 m，高波海況下分別為7.98 m 與 3.79 m，極限海況下分別為15.87 m與14.56 m; 最大繫纜張力於一般海況下分別為斷裂負荷的37.3% 與14.8%，高波海況下分別為斷裂負荷的16.0% 與11.2%，極端海況下分別為斷裂負荷的95.7% 與44.8%，風機系統使用3×3 繫纜佈置的運動較為穩定且纜繩安全係數較高。根據浮式風機在一般運轉與極端海況下的運轉安全性要求，對於本研究的目標風機系統建議使用3×3繫纜設計。

The study aims to predict the behavior of a floating offshore wind turbine (FOWT) system equipped with a semi-submersible Taida platform and an IEA 15 MW wind turbine under different metocean conditions in the Hsinchu offshore area where the performance of the FOWT system with 3×2 and 3×3 mooring designs is compared as well as three metocean conditions, i.e., common wave (CW), high wave (HW), and extreme wave (EW), are considered. The JONSWAP spectrum is utilized to describe the irregular wave in the Hsinchu offshore area. In addition to the constant wind speed, API spectrum is used under the CW and HW conditions to describe the wind speed variation, and the transient typhoon profile is employed to describe the extreme gust under the EW condition based on 50-year return period. The hydrodynamic properties are predicted via ANSYS-AQWA and STAR-CCM+, and the motion response, mooring line tension and aerodynamic of the FOWT system are solved via OrcaFlex. As waves are mainly driven by winds, the wind and wave direction are assumed to be identical. With seven wind and wave directions, four current directions, and two mooring line designs, a total of 168 cases is investigated in this study. The results show that the mean value and standard deviation of the motion response, generator power, and mooring line tension are sensitive to wind (wave) directions, but insensitive to the current direction under the CW and HW conditions, while under the EW condition, the current and wind and wave direction both pose a significant impact on the mean value and standard deviation of the motion response. The wind speed variation slightly impacts the mean value, but can significantly influence on the standard deviation of the motion response and mooring line tension. The API spectrum leads to a 1% to 3% reduction of generator power. The powers of 14.14 MW and 14.53 MW are guaranteed under the CW and HW conditions when a 3×2 mooring design is employed; 14.47 MW and 14.65 MW are guaranteed under the CW and HW conditions when a 3×3 mooring design is employed. The maximum pitch angle is 5.59° and 5.48° under the CW condition, 1.50° and 1.49° under the HW condition, and 10.81° and 9.73° under the EW condition; the maximum offset is 12.59 m and 7.67 m under the CW condition, 7.98 m and 3.79 m under the HW condition, and 15.89 m and 14.55 m under the EW condition; the maximum mooring line tension reach 37.3% and 14.8% of the MBL under the CW condition, 16.0% and 11.2% under the HW condition, 95.7% and 44.8% under the EW condition, respectively. The 3×3 mooring design shows a lower offset and a greater safety factor. According to the safety requirements of operating a FOWT system under the normal operating and extreme wave condition, a 3×3 mooring design is recommended for the investigated FOWT system.