黏性效應對於半潛式浮式風機系統性能的影響

Abstract

本研究探討流體黏性對半潛式浮式風機系統性能的影響，分析三種半潛式浮 式風機系統(圓碟型、駁船型及圓柱型)在四種系統佈置方向(15°、45°、75°及 105°)下的性能表現，模擬場址為新竹外海，模擬條件包括額定風速條件(RC)、50 年回歸期風速條件(50C)及長期條件(LTC)。三種半潛式浮式風機皆為 35875 噸，搭 載 SNL 13.2 MW 風機，使用 3×3 繫纜系統。ANSYS AQWA 用於預測忽略流體黏 性的水動力特性，STAR-CCM+用於預測考慮黏性效應的水動力特性，ORCAFLEX 用於預測繫纜受力和葉片空氣動力，以及求解運動方程式獲得運動響應、發電機功 率及纜繩張力。假設波向和風向相同，風和浪分別以 API 風譜及 JONSWAP 波譜 描述，預測 RC(示性波高 1.7m、零上切週期 5.5s)、50C(示性波高 12.72m、零 上切週期 8.83s)及 LTC 在四個風向(45°、135°、225°及 315°)下浮式風機各項性 能，其中長期條件是基於新竹外海 2015 至 2021 年的統計結果。本研究結果顯示， 圓碟型浮式風機在 RC 下的最大傾角及平均傾角超過限制值，駁船型在 50C 下的 最大偏移量及纜繩張力超過限制值。圓柱型浮式風機在系統佈置為 105°時為最佳 設計，發電機容量因子 0.446，九條纜繩最大損傷為限制損傷的 26.97%。流體黏性 對性能標準差影響最大，對性能平均值影響最小。流體黏性對發電機容量因子影響 極小，最大差異僅 0.227%，駁船型浮式風機容量因子最大，圓柱型次之，圓碟型 最小，分別為理論容量因子的 98.08%、95.98%及 94.58%。流體黏性對纜繩疲勞損 傷影響顯著，差異在-35.70%至-63.42%之間，九條纜繩最大損傷以駁船型浮式風機 最小，圓柱型次之，圓碟型最大，分別為限制損傷量的 17.14%、26.97%及 97.47%。

This study investigates the impact of fluid viscosity on the performance of semi- submersible floating offshore wind turbine (FOWT) systems. Three types of semi- submersible floating platform (disk-, barge-, and column-type) are investigated in the Hsinchu offshore area under four system arrangement directions (15°, 45°, 75°, and 105°) and three simulation conditions: rated wind speed (RC), 50-year return period wind speed (50C), and long-term (LTC). The studied FOWTs all have a mass of 35,875 ton, a 3×3 mooring system, and an SNL 13.2-MW wind turbine. The hydrodynamic properties without fluid viscosity are predicted using AQWA based on potential flow theory, while the hydrodynamic properties considering viscous effects are predicted using STAR- CCM+. ORCAFLEX is employed to predict the mooring system forces and blade aerodynamics of the FOWT system and to solve the motion equations for obtaining the motion response, generator power, and mooring line tension. Assuming that the waves align with the wind direction, the wind and waves are described using the API wind spectrum and JONSWAP wave spectrum, respectively. Predictions are made for the performance evaluation of the FOWT system using a significant wave height of 1.7 m and a zero-up-crossing period of 5.5 s in the RC scenario, a significant wave height of 12.72 m and a zero-up-crossing period of 8.83 s in the 50C scenario, and four wind directions (45°, 135°, 225°, and 315°) in the LTC scenario. The LTC scenario is analyzed based on the statistical results from the Hsinchu offshore area from 2015 to 2021. The results indicate that the disk-type FOWT exceeds tilt angle limits under RC scenario. Under 50C scenario, the barge-type FOWT exceeds limits for maximum offset and mooring line tension. The column-type FOWT, with a system arrangement of 105°, is identified as the optimal design, where its capacity factor is 0.446 and the maximum damage is 26.97% of the allowable damage. The effect of viscosity is most pronounced on the standard deviation of performance metrics, particularly affecting the disk-type FOWT under RC scenario and the barge-type the under 50C scenario. The capacity factor is limited affected by viscosity, with a maximum difference of only 0.227% . The barge-type FOWT has the highest capacity factor (98.08%), followed by the column-type (95.98%) and disk-type ones (94.58%). The viscosity significantly impacts mooring line fatigue damage, with differences ranging from - 35.70% to -63.42%. The barge-type FOWT shows the least damage, followed by the column-type and disk-type ones, with damages of 17.14%, 26.97%, and 97.47% of the allowable damage, respectively.