| 摘要: | 本研究討論不同颱風風況與極限風況對於塔架所造成挫曲的影響，以及不同尺寸的裂縫失效評估。以NREL 5MW OWT風力機為分析模型，風況方面考量IEC61400-3之DLC6.1極限風況、中央氣象局所提供的的颱風資料，以及單一葉片節距角失控之狀況。分析方法整合了GH-Bladed、ANSYS及MATLAB軟體。
塔架的挫曲及裂縫失效之評估主要以Z軸應力大小作判斷。在不同高風速情況下，情況最大Z軸應力皆發生在塔架迎風面處。IEC61400-3規範的DLC6.1極限風況之Z軸應力明顯小於台灣颱風產生的值。規範中提及風況在沒有紊流強度的情況下可將原風速乘以1.4倍做分析設定，但本研究顯示後者的Z軸應力比前者大很多。在相同風速下，紊流度11%風況的Z軸應力大於紊流強度0%者海況方面，由於本研究的風速很大導致????,????對塔架應力的影響幾乎看不出來。
塔架屬於薄管結構，在高風速及機艙與葉片的高軸向負荷下，可能造成挫曲。本研究使用台灣颱風風況進行ANSYS非線性挫曲有限元素分析，模擬得到的挫曲係數遠大於臨界挫曲值1，顯示在正常待機的颱風風況下是不會發生挫曲。
在塔架裂縫方面，以S355鋼銲接結構的Haigh Diagram進行分析，在風速80 m/s時雖然有部分點落在線外，但作用次數需到達106次，故判定風力機使用期間不會因為颱風有疲勞裂縫起始。接著使用BS7910規範中的option 1方法進行裂縫失效評估。在30.2公尺處的塔架迎風面，當輪?風速70 m/s，裂縫深度20 mm，裂縫短長軸比(a/c)0.2時，會失效；當輪?風速80 m/s (紊流強度11%)及裂縫深度20 mm時，在所有a/c比值皆造成失效。而塔架外側在80 m/s (紊流強度11%)及裂縫深度20 mm時，在所有a/c比值皆時會發生失效。若有單一葉片節距角失控，則在風速30 m/s時，塔架就會失效。;This study investigates the effects of different typhoon wind conditions and extreme wind conditions on the buckling of tower structures, as well as the assessment of crack failures of different sizes. The NREL 5MW offshore wind turbine is used as the analysis model. Wind conditions considered include IEC 61400-3 DLC6.1 extreme wind conditions, typhoon data provided by the Central Weather Bureau, and scenarios of individual blade pitch angle loss of control. The analysis integrates GH-Bladed, ANSYS, and MATLAB software.
Evaluation of tower buckling and crack failures primarily focuses on the magnitude of Z-axis stress. Under various high wind speed conditions, maximum Z-axis stress occurs on the windward side of the tower structure. Z-axis stresses under IEC 61400-3 DLC6.1 conditions are significantly lower than those generated by Taiwan′s typhoons. The standard suggests analyzing wind conditions by multiplying the original wind speed by 1.4 in the absence of turbulence intensity, but this study demonstrates that the Z-axis stress in the latter case is much higher than in the former. At the same wind speed, the Z-axis stress under 11% turbulence intensity exceeds that under 0% turbulence intensity. Regarding sea conditions, the effects of significant wave height (????) and peak period (????) on tower stress are negligible due to the high wind speeds analyzed in this study.
Tower structures are characterized as thin-walled tubes, susceptible to buckling under high wind speeds and high axial loads from the nacelle and blades. Nonlinear buckling finite element analysis using Taiwan′s typhoon wind conditions in ANSYS shows buckling coefficients significantly greater than the critical buckling value of 1, indicating no buckling under normal typhoon conditions.
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Regarding tower crack assessment, Haigh Diagram analysis for welded S355 steel structures shows that although some points fall outside the line at a wind speed of 80 m/s, the number of cycles required for fatigue crack initiation is on the order of 106 cycles, indicating no fatigue crack initiation during the operational life of the wind turbine under typhoon conditions. Subsequent crack failure assessment using Option 1 of BS7910 standard indicates that at the windward side of the tower at 30.2 meters, a crack depth of 20 mm results in failure when the hub wind speed is 70 m/s. At 80 m/s hub wind speed (with 11% turbulence intensity) and a crack depth of 20 mm, failure occurs for all a/c ratios. Similarly, on the outer side of the tower at 80 m/s hub wind speed (with 11% turbulence intensity) and a crack depth of 20 mm, failure occurs for all a/c ratios. In the event of a single blade pitch angle loss of control, the tower fails at a wind speed of 30 m/s. |
