Research Papers on Wind Engineering - Softcover

Inhaltsangabe

Severe winds cause tremendous damage on structures. With the emergence of new generation tall structures which are remarkably flexible and low in damping the problem becomes more significant. Consequently, the effects of wind on structures are required to be considered more precisely than was previously required. Keeping above objective in mind the present study was undertaken to study the wind behavior.Wind Speed at any locality is extremely variable. For convenience its instantaneous magnitude can be resolved into Mean component and Gust, the fluctuating component around the Mean component. The Mean Velocity Component is assumed to result in Static Wind Pressure and corresponding steady deflection of the structure, where as the Gust component gives rise to dynamic amplification. However, work being presented here is for the Mean wind Component only. The data used in the present study pertains to meteorological measurements on a 120 m high tower carried out by micrometeorological laboratory at Tarapur. Wind Velocity observations recorded at different time can be considered as discrete values of the time series. These observations in time domain( Wind Velocity vs time) can be converted into frequency domain(Power Spectral Density vs Frequency) by discrete Fourier Transform(DFT) method. The Fourier Transform is obtained by using Fast Fourier Transform (FFT) algorithm given by Cooley et al.(1969). This technique was used in obtaining spectra for Mean Winds (in low frequency range).The Power Spectra obtained constitutes a frequency range from 0.00049 to 0.5 cycles/hour(c/h). The Power Spectrum was characterized by several major and minor peaks. The energy content in frequency range 0.00977 to 0.01075 c/h (corresponding to period of 4 days) showed slight peak at 6m height, however, the magnitude of peak rises at 120 m height. A spectral gap was observed until frequency 0.04201 c/h (corresponding to a period of 24 hours) at which major peak was observed. Similar peaks were also observed at 30 m and 120 m levels at frequency of 0.04250 c/h. A peak second in rank was observed at frequency of 0.08403 c/h (11.9 hours period). A third ranking peak was also noticed at frequency 0.12604 c/h (8 hours period). The results so obtained compare favourably with the results presented by the other authors.

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