FIELD MEASUREMENT ON POWER SPECTRA AND COHERENCE CHARACTERISTICS OF NEAR-GROUND WIND IN SHANGHAI COASTAL AREA

The wind characteristics of typhoon ‘Meari’ and monsoons, such as power spectra and coherence functions, are analyzed and compared with each other on the basis of the measured data that were recorded at the height of 10m, 20m, 30m, and 40m respectively, above the ground in Pudong coastal area, Shanghai. The results show that the power spectra of fluctuating wind speeds of typhoon ‘Meari’ are significantly different from those of the monsoons. The slope rates of spectra decrease gradually with the increasement of the frequency, and accord with the -5/3 law in the inertia sub-range during ‘Meari’. However, the slope rates accord with the -5/3 law in the whole frequency range for the monsoons. The observed wind spectra are generally in agreement with the Von-Karman spectrum. Based on the expression form of the Von-Karman model, the fitting spectrum equations for measured data are presented, whose overall errors are reduced by about 15%, compared with Von-Karman spectrum. The decay factors of coherence functions of fluctuating wind speeds decrease with the increasement of wind speed during typhoon 'Meari' and monsoons, and the mean longitudinal value of those are 7.5 and 18.6, respectively.