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|Title : ON THE MOST LIKELY EOG AMPLITUDES
Authors : Gunner Chr. Larsen and Kurt S. Hansen
For most structures exposed to wind loading, extreme response is associated with extreme wind
speeds. However for wind turbines - especially for pitch regulated wind turbines - the design driving thrust loading is
often associated with severe wind gust situations occurring during normal operation, and these are thus related to the
mean wind speed regime [5m/s; 25m/s]. Based on knowledge on the load response characteristic of the wind turbine
(in terms of aerodynamics and pitch action) it is possible to identify a general critical mean gust shape that may
potentially result in ultimate thrust loading. In the IEC 61400-1 design code, this particular load case is defined as
Extreme Operational Gust (EOG). The code prescribes the gust shape, extend and magnitude for recurrence periods 1
year and 50 years, respectively.
In a recent cogent study, based on wavelet filtering combined with extreme statistics, the most likely extreme
amplitudes of wind speed gusts (with shapes and time scales identical to those specified for the EOG load case in the
IEC-61400 code) has been assessed. The estimated extreme gust amplitudes from the analysis shows substantial
qualitative and quantitative differences compared to the specifications in the most recent IEC-61400 code revision.
Assuming the mean wind speed to be Rayleigh distributed (as specified in the code) and adopting the conjecture that
wind speed gust amplitudes scale directly with the turbulence standard deviation, the EOG amplitudes have been
estimated for the 3 WTGS classes combined with the 3 turbulence classes prescribed in the IEC-61400 code. The
estimation is performed for recurrence periods 1 year and 50 years, respectively, and the estimated amplitudes are
finally synthesised into a simple algebraic expression.
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