耦合BEM與CFD方法計算浮體式風機於規則波中運動之研究

A Coupled Blade Element Momentum - Computational Fluid Dynamics Model for Evaluating Floating Wind Turbine Motion Under Linear Waves

浮體式風機所搭配之浮體平台對其受風與波浪耦合作用下之運動程度扮演重要的角色，在離岸風場位址選擇受陸上地形及風切影響較小之浮體平台有利於減少風機之發電量損失。本研究以NREL 5MW風機當作目標風機，並分別搭配OC3-Hywind之Spar型浮體平台與OC4 DeepCwind之半潛型浮體平台為計算模擬之對象。研究方法為雷諾平均納維爾史托克（RANS）求解浮體平台受水動力作用之流場並選用適當的紊流模型及額外搭配BEM程式估算風機之氣動力性能。以BEM進行目標風機之氣動力性能計算結果與NREL公佈之資料相互驗證，轉子功率計算結果與資料趨勢相符，額定風速（11.4m/s）下之差異約為7.64%。BEM程式於縱搖運動下修正之計算結果顯示考慮真實風機之控制情形其平均功率會下降，且風機推力與功率變動週期與縱搖角速度週期相同，與參考文獻以RANS計算之結論相符。耦合BEM與CFD軟體計算浮體式風機於波高4m週期10s之規則波中進行縱搖運動之數值模擬，並比較Spar型與半潛型浮體式風機之實際發電平均功率耗損率以半潛型浮體式風機之耗損率較小，此結果與文獻亦相同，顯示耦合BEM與CFD軟體計算浮體式風機受風、波耦合作用下之可行性。藉由不同的波浪參數探討以發電量為目標時Spar型浮體式風機與半潛型浮體式風機之適用範圍，由數值模擬結果顯示當波浪週期小於8.4s之線性波，將選擇Spar型浮體式風機；當波浪週期大於10秒且波高5.2米以內的長浪條件，與波浪近似於靜水狀態，模擬結果發現半潛型浮體式風機因其較大的水線面積能提供穩定機制而不易晃動，故在平均功率上優於Spar型平台。 The offshore wind turbine will be influenced by the couple of aerodynamics and hydrodynamics. The selection of floating platform will directly affect the generating power of the wind turbine. The floating systems of the OC3-Hywind and the OC4 DeepCwind are adopted for computing in this paper. Through the Blade Element Momentum theory evaluate the power curve of NREL-5MW wind turbine and compare to the NREL data. It shows two of them have similar power curve, but they have about 7.64% difference in the rating velocity condition. When we consider the real wind turbine control system in the pitch motion, the average power is no longer that high anymore. Within the motion of turbine, it causes the power of turbine have the same period as the motion of turbine. In this paper, a coupling the Blade Element Momentum (BEM) method and computational Fluid Dynamics model (CFD) is used to evaluate two type of floating wind turbine, spar and semisubmersible wind turbine. Under the wave height 4m and period 10s, it shows that the semisubmersible type floating wind turbine has lower power loss than the spar type of wind turbine. This simulation results are verified with the results published in the references. According to this research results, it shows that a suitable wave condition can reduce the power loss for both of the floating wind turbine. If the wave period is less than 8.4s, so the spar type floating wind turbine is recommended. But if the wave period is larger than 10 s and the wave is just like calm sea state, the semisubmersible floating wind turbine will be better.