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摘要
Using wind-speed records from mobile weather stations deployed in tropical cyclones making landfall along the United States coastline over the period 1998-2008, an analysis was made of the gust factors observed in near-neutral conditions by station site and wind direction. The dataset used contained a total of 56 individual station site/wind-direction combinations representative of a wide variety of terrain conditions, ranging from open water to urban exposures. Consideration of the peak gust measured along a given axis, together with the associated components measured simultaneously along the other two axes, showed that peak along-wind gusts are primarily associated with vertical velocities in air moving towards the surface, while peak downwards and upwards vertical gusts are associated with along-wind velocity components that are respectively larger and smaller than the mean along-wind velocity. This behaviour is directly related to the value of the primary component of the surface shear stress in the coordinate system used for the analysis, which involves the product of the along-wind and vertical velocity components and which must be negative in the surface layer. Grouping the mean gust-factor curves for each velocity component into bins based on the turbulence intensity showed that the individual curves in a given bin could not all be considered to be drawn from the same underlying parent distribution, an observation that was confirmed by statistical testing. A quantitative exploration of the effects of upstream terrain variations on the observed gust factors for a selected number of sites suggested that the gust factors and other flow parameters, such as the turbulence intensity, are heavily influenced by the upstream terrain at many of the station sites considered.
- 出版日期2015-4
