Modeling of Nonstationary Winds and Its Applications

Abstract

A model is proposed to represent nonstationary fluctuating winds based on the concept of instantaneous power spectrum representation and amplitude modulation to model the fluctuating winds with time-varying mean wind speed. This results in the nonstationary fluctuating winds at a point to be characterized by a power spectral density function with a frequency modulation; it is proposed and shown that the frequency modulation can be assigned based on a time transformation defined through a dimensionless distance traveled by the winds that is calculated using the mean wind speed. In essence, nonstationary fluctuating winds are obtained by mapping the stationary fluctuating winds through a nonlinear time transformation and by applying an amplitude modulation. The proposed model is employed to simulate nonstationary winds for parametric investigation of the peak displacement of linear and nonlinear inelastic single-degree-of-freedom systems. It is shown that a structure designed by neglecting ductility capacity and/or for stationary winds of 10 to 60 min has an unaccounted capacity to sustain nonstationary winds with a maximum mean wind speed that can be much greater than that for stationary winds. The use of the proposed model to represent the incoherent nonstationary fluctuating wind fields is also explored. An illustrative example focused on the fluctuating downburst winds at a few points within the downburst wind field is presented.