The Influence of Spectrum Functions and Filters on Crossing Frequency of Atmospheric Turbulence

Abstract

Abstract In the recent past, for estimation of fatigue life of structural components in a turbulent atmosphere, the along-wind crossing frequency of the wind speed has been computed using a variety of filters, spectrum functions and procedures. This has led to some discrepancies in the predicted frequencies of crossing. The present work, assuming stationary Gaussian processes in strong winds and Rician theory, investigates the effect on the crossing frequency of different spectrum functions and filters by systematically mixing the Von Karman and Kaimal spectrum functions with four filters: ideal band-pass, ideal low-pass, “quadratic-type” (nc2+n2)−1 and the “sinetype” sin2(αn)/(αn)2. Except for the quadratic-type, when the difference is about 17% at high frequency and declines to zero at low frequency, the influence of spectrum functions is very small. The filters have a much greater effect. The predicted crossing frequency varies by as much as 50% among the low-pass filters, and ideal one decade wide ban...