Estimation of hours per year when mean wind speed exceeds specified thresholds.
Abstract:ESDU 88038 provides an estimation method for use when meteorological records are inadequate to provide the data directly, or when they are not readily corrected for differences between the terrain at the site and at the measuring station, or when a rapid estimate of wind speed frequency of occurrence is required. It uses a theoretical approach, with some empirical factors, to relate the parameters of the Fisher-Tippett Type 1 extreme value distribution to the parameters of the parent Weibull cumulative distribution from which the number of hours when the mean wind speed exceeds specified thresholds can be calculated. In practice, the extreme value mode and dispersion parameters (or estimates) are more readily available for various regions of the world than the parent distribution data. The method may be used inversely, as illustrated in ESDU 87037, to estimate extreme wind speeds from relatively short records of the parent distribution. It applies to winds from any sector and to the case when all wind directions are combined. A method is also provided to estimate the proportion of hours in a year when the wind direction is in a particular 30 degree sector. Guidance is given on correction factors for changes from the conditions of the basic data in terrain roughness, height and simple topography. The method has been tested against data from 50 UK sites and is considered to be applicable to wind climates in middle to high latitudes. It has been tentatively extended to apply to a wind climate contributed by more than one mechanism (for example, frontal depressions and thunderstorms).
|Data Item ESDU 88038|