Browsing by Subject "Winds -- Speed -- Measurement"
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Item A comparison of extreme wind events as sampled in the 2002 thunderstorm outflow experiment(Texas Tech University, 2003-08) Gast, Kirsten DeannNot availableItem Estimation of roughness lengths through gust factor analysis(Texas Tech University, 1999-08) Conder, Mark R.The aerodynamic roughness length is a parameter that quantifies the degree of friction that terrain elements have on the wind near the earth's surface. It is commonly used in the development of vertical profiles of the wind speed. However, uncertainty exists in the precision of current roughness length estimation schemes. A formula has been developed by Wieringa (1973) that calculates the roughness length from gust factors (ratio of the peak wind gust to the mean wind speed over a period). This method has an advantage in that it relies on readily available local wind data such as analog record charts found at the NWS. This study employed the Wieringa formula to evaluate its applicability and ease of use with a number of different types of wind records. First of all, the formula was applied to data collected at the Texas Tech Wind Engineering Research Field Laboratory (WERFL), where wind speed records are archived from five different vertical levels. Results indicated that both the gust factors and the roughness lengths obtained were higher than those from previous studies. Secondly, because both meteorologists and engineers are interested in vertical wind profiles in high winds, an attempt was made to obtain wind records from several hurricane passages. Four reliable hurricane wind records from anemometers located in the vicinity were acquired: Hurricane Bob (1991), Hurricane Iniki (1992), and two from Hurricane Bonnie (1998). The Wieringa formula requires specifications of the anemometry and since each record was produced by a different anemometer/recorder system, they provided a thorough assessment of the formula. Calculated roughness lengths were plotted and compared against the known topography of the site. The results showed a large variability according to the upstream fetch of the wind in the record. Another conclusion was that the gustiness of the wind during a hurricane is highly dependent upon the terrain and it is difficult to ascertain how turbulence caused by convection affects the gust factor and thus the roughness length.Item Hurricane Bonnie wind flow characteristics(Texas Tech University, 1999-12) Schroeder, John L.Whether convective influences result in localized areas of increased wind speeds and different turbulent structure than expected in a normal high wind situation has been debated for years. The question has been especially active concerning landfalling hurricanes. Given a lack of high-resolution wind speed data from within hurricanes necessary to resolve the debated questions, a field experiment was designed and conducted by Texas Tech University to acquire the necessary data. The Wind Engineering Mobile Instrumented Tower Experiment (WEMITE), the first successful field experiment to place a reinforced, self-powered, instrumented tower directly in the path of several hurricanes, successfully gathered high-resolution wind speed data from within Hurricane Bonnie as it made landfall near Cape Fear, North Carolina, on 26 August 1998, at 5:00 PM. These data are used to inspect the variations in turbulent characteristics of the wind during the passage of the storm. Specifically, turbulence intensities, integral scales, gust factors, and spectrograms are evaluated with respect to the surrounding meteorological events, such as the passage of rainbands. Comparisons are drawn between turbulence intensity and integral scale values present in Hurricane Bonnie, and those employed in the determination of the gust effect factor in ASCE 7-98. Wavelet analysis was also used to examine the incoherent model assumption employed in wind engineering.