COMPARISON OF THE WEIBULL MODEL WITH MEASURED WIND SPEED DISTRIBUTIONS FOR STOCHASTIC WIND GENERATION

Authors: Van Donk, Simon; Wagner, Larry; Skidmore, Edward; Tatarko, John

Submitted to: Transactions of the ASAE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/12/2004
Publication Date: 3/4/2005
Citation: Van Donk, S.J., Wagner, L.E., Skidmore, E.L., Tatarko, J. 2005. Comparison of the Weibull Model with measured wind speed distributions for stochastic wind generation. Trans ASAE 48 (2):503-510.

Interpretive Summary: Wind is the principal driver of the Wind Erosion Prediction System (WEPS), which is a computer model for the simulation of wind erosion on agricultural fields. WEPS does not use 'real' measured wind data directly, but instead generates (simulates) wind. The objectives of this work were to improve this wind generation and to update the wind statistics used by the generator with statistics derived from more recent, quality controlled, data for the 48 contiguous states of the USA. A wind generator works with statistical wind speed distributions that are usually described by a model. The commonly used Weibull model did not describe the distributions well enough for application in wind erosion models. A more direct method stores wind speed distributions themselves instead of storing the Weibull parameters describing them. Wind speeds are then generated directly from the distributions. This direct method of wind speed generation reproduces wind speeds more accurately than the Weibull model, which is important for wind erosion prediction and may be important for other applications as well.

Technical Abstract: Wind is the principal driver of the Wind Erosion Prediction System (WEPS), which is a process-based computer model for the simulation of wind blown sediment loss from a field. WEPS generates wind using a stochastic wind generator. The objectives of this study were to improve the stochastic generation of wind speed and direction and to update the wind statistics used by the generator with statistics derived from more recent, quality controlled, data for the 48 contiguous states of the USA. Erosive wind power density (WPD) was chosen to evaluate how well wind is generated, since WPD is proportional to sediment transport by wind. The commonly used two-parameter Weibull model fitted many wind speed distributions reasonably well, but not well enough for application in wind erosion models. There were 168 out of the 331 windiest stations where WPD calculated from generated data deviated more than 20 percent from WPD calculated from measured data. Fitting the model to the high wind speeds only, with the expectation of a better curve fit, resulted in some generated wind speeds exceeding 100 m/s, which is unacceptable. A more direct method stores wind speed distributions themselves instead of storing the Weibull parameters describing them. Wind speeds are then generated directly from the distributions using linear interpolation between data points. This direct approach is robust and very closely reproduced WPD of the measured data. With this method, there were only 2 stations where WPD calculated from generated data deviated more than 20 percent from WPD calculated from measured data. The direct method of wind speed generation reproduces wind speeds more accurately than the Weibull model, which is important for wind erosion prediction and may be important for other applications as well.