Browsing by Subject "Winds -- 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 A data collection and analysis system for wind measurements(Texas Tech University, 1973-08) Beauregard, Warner RayNot availableItem A digital instrumentation for an oscillatory anemometer(Texas Tech University, 1988-08) Musa, Philip FatingandaNot availableItem A full-scale investigation of roughness lengths in in homogeneous terrain and a comparison of wind prediction models for transitional flow regimes(Texas Tech University, 2004-05) Gardner, Anna G.Models for estimating the mean and gust wind speeds in the transitional flow regime are investigated and compared to full-scale measurements. Displacement heights and roughness lengths are also investigated for each data collection location. Roughness lengths are calculated from full-scale data using conservation of mass and turbulence intensity methods. These values are compared to wind tunnel, visual inspection and roughness element based methods. The displacement height is also estimated from conservation of mass and compared to roughness element based methods.Item Analysis of Data for the Response of Full-Scale Transmission Tower Systems to Real Winds(Texas Tech University, 1983-05) Jan, Con-linNot Available.Item Coastal boundary layer transition within tropical cyclones at landfall(Texas Tech University, 2004-05) Howard, James RobertHurricanes pose a great risk to life and property with their high winds, excessive rainfall, wave action, and storm surge. Predicting changes within hurricanes at and near the time of landfall requires an understanding of the dynamics that drive the boundary layer flow. Forecasters predict the timing, duration, and effects of the intense winds associated with a hurricane when it comes ashore, while emergency management officials call for public evacuations based upon these forecasts. One region where understanding the magnitude and structure of the wind is critical is within the surface layer just downstream of the coastline in the onshore flow. Within this region the flow begins to adjust to changes in surface triggered by its passage from the shallow coastal waters to the less homogeneous and rougher land. This adjustment may include a slowing of the mean wind with an increase in turbulence, both resulting from the increased friction of the man-made and natural terrain. Hurricane observing programs consisting of portable and mobile equipment and regional coastal mesoscale observing networks are leading to a better understanding of the processes involved with these flow modifications. The Texas Tech University Wind Engineering Mobile Instrumented Tower Experiment (WEMITE) continues to play a leading role in the observation and analysis of the boundary layer of tropical cyclones at landfall. In order to gain further insight into the characteristics of this coastal transition zone, experiments were planned utilizing portable in-situ and remote measuring devices to be placed within the onshore flow at landfall. Experiment plan designs along with results from these experiments ate discussed, including the analysis of a dataset collected by multiple institutions during the landfall of Hurricane Lili (2002) along the south-central Louisiana coast Investigation reveals the existence of frictionally-induced changes in the boundary layer downwind of the coastline within the right semicircle with respect to Lili's forward motion. In the outer reaches of Lili, these transitions appear similar to internal boundary layers produced by flow moving over an abrupt change in surface. The impact on the magnitude of the wind within this near-shore region is a reduction of 4-10% per 10 km distance from the coast up to 50 km inland for open terrain. Results of the study show this reduction to be an exponential function of distance from the coast which is dependent upon surface roughness. This rate of wind decay slows with farther progression inland and appears to be much faster than the rate found in soma modeling studies. In contrast near Lili's circulation center, little or no decrease in the magnitude of the mean wind was found for distances of up to 20 km inland.Item Dynamic gust response factors for transmission line structures(Texas Tech University, 1996-08) Shimpi, RajeshTransmission line structures are flexible, line-like, wind-sensitive structures used for distribution of electricity. Dynamic wind loads on these structures result from two components: wind loads on the tower and wind loads on the conductors. Various approaches are available for the calculation of the gust response factor. The Gust response factor (GRF) is the static equivalent of the dynamic loads acting on the transmission lines. The ASCE 7-95 Commentary Method (1995) has a procedure to evaluate the GRF based on the new 3-second gust wind speeds adopted in the code. This procedure is for general categories of structures. Davenport's model (1979) is tailored exclusively for transmission lines and is flexible with any averaging time. Simiu's model, which again is not developed for transmission line structures, uses graphs for the major part of the GRF calculations. In this study, Davenport's model is used as a reference model for the calculation of GRF and foundations of approaches put forward by ASCE 7-95 and Simiu are studied. All these methods are considered in evaluating the loads on representative transmission line systems using Static-Cast and Spun-Cast concrete poles. Sensitivity studies are carried out for understanding the effects of different parameters in the Davenport and ASCE 7-95 methods and modifications are suggested in the ASCE 7-95 method.Item Flying debris behavior(Texas Tech University, 2003-05) Wang, KeyiBeside the building damage produced by direct wind force-either by overload caused by overstressing under peak load or fatigue damage under fluctuating loads of a lower level, a major cause of damage in severe windstorms is due to windborne debris. Penetration of the building envelope by windborne debris will lead to a change in the internal pressure which double the forces on the roof leeward and sidewalls. It also leads to a loss of building function by exposing the contents to subsequent weather damage. Wills et al. (2000) have develop a simple engineering model to describe the behavior of flying debris, which relates the flying behavior of debris to their size, shape, and density. The model classifies the debris into three categories: cube (3D), sheet (2D) and rod (1D). Two sets of tests following the philosophy of that engineering model were conducted in TTU wind tunnel. One set of experiments examined flight initiation wind speeds for sheet debris. Another set examined sheet debris flight behavior after takeoff. Both sets were tested for varying restraining forces. An electromagnet was used to control the restraining force. For the flight initiation tests, analysis of the results gave an average force coefficient Cp of 0.15. The restraining forces calculated from the engineering model (Wills et al., 2000) with CF of 0.15 agree well with the actual restraining force. For the flight behavior tests, a much more detailed observation was made than previous available (Wills et al., 2000). For each flight, relative flight speed Vd/Vw was plotted against flight time. An equation Vd/Vw = a * (1-e (1-1a/T' ) of the form was used to fit the relative flight speed variation with the flight time. For free-mounted sheets, a dimensionless figure, Vd/vwV,,vs. Pmt/(PaVw^2), was plotted. The figure shows that the relative maximum flight speed of sheet decreases with the increase of pmt/(paVw^2), and approaches a value of 0.5. Implying that the maximum speed an object can reach is approximately half of the prevailing mean wind speed. The result of sustained sheet flight tests shows that varying the restraining force does not change the maximum relative velocity for the same sheet..Item Multiscale study of a convectively driven high wind event(Texas Tech University, 2003-08) Midgley, Caleb JThe purpose of this study is to investigate a convectively-driven high wind event which affected the Texas Panhandle during the late afternoon/early evening hours of 30 May 2001. This storm was characterized by a feature referred to as a bow echo, a phenomenon that has typically been associated with straight-line winds. To accomplish the analysis, WSR-88D level II radar data from the Lubbock, Texas, radar site was used to diagnose storm structure based upon reflectivity and radial velocity data. Also, West Texas Mesonet data, along with the standard surface observing network, was obtained to identify storm-scale features in the low levels and investigate how these features may have affected the fransition from a supercellular convective mode to a linear bow echo mode. To complement the sparse upper-air network, an MM5 simulation was run for the event to diagnose features in the near-storm environment that may have had an organizing influence.Item The effects of stationarity on the pressure coefficients measured on a low-rise building(Texas Tech University, 2002-08) Whitworth, Mona RichardThe primary objective of this investigation is to establish whether or not nonstationarity has a significant effect on the pressures (and the resulting pressure coefficients) measured on the full-scale building at WERFL. Four flow regimes (stagnation, wake, separated and conical vortex) using three pressure taps located on the wall, the roof edge, and the roof comer were chosen for this investigation. Summary statistics from 15-minute duration runs collected in collection Modes 15, 28, 38, 48, 49, 50, 51, and 52 over a period of 10 years are used in this study. Four categories of stationarity were used for the analysis. Stationary Speed & Stationary Direction (SS), Nonstationary Speed and Stationary Direction (NS), Stationary Speed & Nonstationary Direction (SN), Nonstationary Speed and Nonstationary Direction (NN). The Kruskal-Wallis test on the Cp mean, rms, min and max pressure coefficients using the 4 stationarity categories were initially performed to establish a statistical significant difference in the Cp's associated with each of the stationarity categories. The Kruskal-Wallis test does not remove the effects of flow characteristics on the measured pressure coefficients. To remove the confounding effects of the flow turbulence parameters, the non parametric Friedman Test was used. Roughness length, zo, longitudinal turbulence Intensity lu, lateral turbulence Intensity L, and mean wind speed are used as blocking factors in the Friedman test. In general, stationarity of speed and direction was not significant when the effects of the flow characteristics are considered.Item The Utilization of Load and Resistance Statistics in a Wind Speed Assessment(Texas Tech University, 1983-05) Marshall, Timothy P.Not Available.Item Wind profile: estimation of displacement height and aerodynamic roughness(Texas Tech University, 1986-05) Abtew, WossenuNot available