| dc.description.abstract | 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. | en_US |