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An analysis of damaged wind turbines by Typhoon Maemi in 2003

This paper examines the damages of all six operating wind turbines on Miyakojima Island by Typhoon Maemi on September 11, 2003.

ABSTRACT

This paper reports damages of wind turbines on Miyakojima Island by Typhoon Maemi on September 11, 2003. Maemi struck the island with an average wind speed of 38.4m/s and a maximum gust of 74.1m/s, recorded at Miyakojima meteorological station. All six wind turbines operated by Okinawa Electric Power Company were extensively damaged. Two Micon M750/400kW turbines collapsed by the buckling of the towers and one Enercon E40/500kW turbine turned over due to the destruction of the foundation. For the other three, the blades were broken and the nacelle cover was damaged. From wind tunnel test and numerical simulation, the maximum wind speed was estimated to be approximately 60m/s and the maximum gust to be 90m/s at the turbine sites. The maximum bending moment of the destructed foundation was larger than the ultimate bending moment because only one blade was feathering. The maximum bending moment of the collapsed towers were larger than the ultimate bending moment because of undesirable slippage of locked yaw while the maximum bending moment of the survived tower was lower than the ultimate bending moment. 

CONCLUSIONS

In this study, field investigation was conducted to clarify the damage of wind turbines located on Miyakojima Island caused by typhoon Maemi in 2003. Maximum wind speed and the maximum gust were estimated by wind tunnel test and numerical simulation. FEM simulation and wind response analysis were performed to evaluate the ultimate bending moment and maximum bending moment acting on the turbine towers and the foundation. Following conclusions were obtained.

(1) Typhoon Maemi struck Miyakojima Island with a central pressure 912hPa. An average wind speed of 38.4m/s and a maximum gust of 74.1m/s were recorded at Miyakojima meteorological station, which was the seventh largest in history. The observed wind direction showed a sudden change in wind direction of 120°. 

(2) All the wind turbines on the island manufactured by Micon, Enercon and Vestas were extensively damaged. Three of six turbines collapsed and the other three suffered destructive damage, whose blades were broken or the nacelle cover drooped. 

(3) From wind tunnel test and numerical simulation, the maximum wind speed was estimated to be approximately 60m/s and the maximum gust to be 90m/s at the turbine sites. 

(4) The maximum bending moment of the foundation of Nanamata wind turbine No.1 was larger than the ultimate bending moment causing the destruction of the foundation. 

(5) The reason for the buckling and the collapse of the tower of Karimata wind turbines No.3 and 5 is that the maximum bending moment of the towers were larger than the ultimate bending moment. The maximum bending moment of wind turbine No. 4 was lower than the ultimate bending moment. This is why the wind turbine No.3 and No.5 were buckled and collapsed, but wind turbine No. 4 survived during the typhoon. 

(6) Following points were learned and should be useful in wind turbine design in the future: a) the locked yaw can be slipped undesirably; b) the tenacity of the foundation is very low causing the easy destruction; c) some tower have its most weak part at its entrance door, which might cause undesired buckle and collapse of the tower. 

In Japan external force is strong, so it is necessary to evaluate the ultimate strength of the turbine in design process and it is important that the manufacturers provide data needed to perform structural analysis and wind resistant design. 

Turbine-damage-maemi-typhone-analysis_thumb
Turbine Damage Maemi Typhone Analysis

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Source: http://windeng.t.u-tokyo.ac...

SEP 12 2005
http://www.windaction.org/posts/43220-an-analysis-of-damaged-wind-turbines-by-typhoon-maemi-in-2003
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