Browsing by Subject "Winds"
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Item A stochastic model for purlin response(Texas Tech University, 2000-12) Zhou, NanTime series models can provide an economical computational technique for an engineer for modeling wind speed, wind-induced pressures, and the response of a structure (or one of its components) to wind loads. Time series models are compact; yet contain almost all of the information that is in the original data. When combined with functional relationships that link the model parameters to physical parameters, a general description of the process is provided. Autoregressive (AR) models are used in this thesis to characterize wind speed, wind-induced pressure, and associated wind-induced purlin displacement response data. The data used for the characterization was collected at the Texas Tech University's Wind Engineering Research Field Laboratory (WERFL). Autoregressive models of order 3 characterize the wind speed, wind-induced pressure, and purlin response adequately. The AR model parameters exhibit linear correlation of varying degree depending on the data type (e.g. wind speed, wind-induced pressure, or purlin response). This implies that by establishing a single model parameter, the complete model is specified. The relationships of the model parameters to physical parameters are explored. This investigation shows that the AR (3) model parameters for wind speed are closely related to the variance of the wind speed. Although not fully developed in this work, there appears to be a functional relationship between the models for wind speed, windinduced pressure, and the associated structural response of a member. Preliminary investigation indicates that this relationship is likely to be independent of the angle of attack. Further, the residuals of autoregressive models on both wind speed and purlin response can be reasonably characterized using the log-logistic distribution.Item An artificial neural network for wind-induced damage potential to nonengineered buildings(Texas Tech University, 1996-12) Sandri, PraveenExtreme winds such as hurricanes and tomadoes can be extremely destmctive and result in catastrophic property losses and loss of human lives. The need to predict damage and reduce loss of life and property is becoming more important with increasing urban sprawl. Artificial Neural Networks (ANNs) provide a novel approach for representing the wind-induced damage potential prediction model. Modeled loosely after the biological neural networks of the human brain, ANNs are generally used in situations where the interactions between the input and the output variable are too complicated for an analytical solution or where there is not suflficient understanding of the problem domain. Predicting wind-induced damage potential to nonengineered buildings is not a simple task because of the complexity of constmction and limited understanding of the wind efifects on buildings. This research concentrates on the investigation of the applicability of ANNs to wind-induced damage potential prediction and the corresponding implementation issues. Even after years of post disaster windstorm damage investigations consistent, complete and robust damage information is not available to train the ANN. Thus, synthetic data instead of observed building damage information is used. WIND-RITE*, a knowledge based expert system for grading individual buildings in windstorms is used to provide the necessary damage information for the synthetic data. This research shows that a feedforward multi-layer neural network with a modified backpropagation learning algorithm can be used effectively to model wind-induced damage potential predictions for nonengineered buildings. As few as four hundred building samples are suflficient to train the network to leam the underlying relationships between the features of the building and its corresponding building damage potential. During training the ANN model is able to leam the relationships between the input features and the resulting building damage grade eflfectively. It was also found that the ANN is able to predict reasonably for samples it has not seen before.Item Analysis of field data for wind profile(Texas Tech University, 1985-05) Khayrattee, Jaynool AbedeenOne of the principal loads acting on above-ground structures is that due to wind. In tall structures, say above 100 feet high, often the wind forces become the controlling factor in structural design. In such tall structures economy in design is achieved by a correct assessment of the wind profile (wind speed variation with height)- The wind forces acting on a structure are a function of the square of the wind speed. Therefore, a good knowledge of the wind profile which defines the variation of wind speed is essential for appropriate assessment of the wind forces. Among the variables for wind profile are the height above ground, the roughness of terrain, the intensity of wind speed and the averaging time of the mean wind speed.Item Collapsar accretion and the gamma-ray burst X-ray light curve(2010-05) Lindner, Christopher Carl; Milosavljević, Miloš; Bromm, Volker; Kumar, Pawan; Sneden, Christopher A.; Wheeler, John C.We present axisymmetric hydrodynamical simulations of the long-term accretion of a rotating gamma-ray burst progenitor star, a "collapsar," onto the central compact object, which we take to be a black hole. The simulations were carried out with the adaptive mesh refinement code FLASH in two spatial dimensions and with an explicit shear viscosity. The evolution of the central accretion rate exhibits phases reminiscent of the long GRB [gamma]-ray and X-ray light curve, which lends support to the proposal by Kumar et al. (2008a,b) that the luminosity is modulated by the central accretion rate. In the first "prompt" phase, the black hole acquires most of its final mass through supersonic quasiradial accretion occurring at a steady rate of [scientific symbols]. After a few tens of seconds, an accretion shock sweeps outward through the star. The formation and outward expansion of the accretion shock is accompanied with a sudden and rapid power-law decline in the central accretion rate Ṁ [proportional to] t⁻²̇⁸, which resembles the L[subscript x] [proportional to] t⁻³ decline observed in the X-ray light curves. The collapsed, shock-heated stellar envelope settles into a thick, low-mass equatorial disk embedded within a massive, pressure-supported atmosphere. After a few hundred seconds, the inflow of low-angular-momentum material in the axial funnel reverses into an outflow from the thick disk. Meanwhile, the rapid decline of the accretion rate slows down, which is potentially suggestive of the "plateau" phase in the X-ray light curve. We complement our adiabatic simulations with an analytical model that takes into account the cooling by neutrino emission and estimate that the duration of the prompt phase can be ~ 20 s. The model suggests that the steep decline in GRB X-ray light curves is triggered by the circularization of the infalling stellar envelope at radii where the virial temperature is below 10¹⁰ K, such that neutrino cooling is inefficient and an outward expansion of the accretion shock becomes imminent; GRBs with longer prompt [gamma]-ray emission should have more slowly rotating envelopes.Item Direct measurement of wind loads on a low-rise test building(Texas Tech University, 1998-05) Bird, Mark WesleyWind loads on low-rise structures are studied in the field primarily so that the results obtained can be used to provide a base-line data set and to assist in wind tunnel studies. The objective of this work is to develop a means of directly measuring total wind loads in the field on a low-rise test building. This project is part of the Texas Tech University / Colorado State University Cooperative Program In Wind Engineering to study wind effects on low-rise buildings. The experimental facility utilized is the Wind Engineering Research Field Laboratory (WERFL) on the campus of Texas Tech University. This thesis contains development of an experimental procedure for directly measuring total wind-induced loads (total horizontal shear and uplift) on the 30 ft x 45 ft x 13 ft test building along with some preliminary results. These loads are measured by supporting the entire building on four load cells(one at each corner). The load cells were constructed in the laboratory to register force in the three orthogonal directions. Forces recorded by the load cells and pressures recorded at the 12 pressure taps (windward wall, roof and leeward wall) are used to measure wind-induced loads. Data utilized In this project is limited to records with winds normal to long axis of the building collected in February and March of 1995. A total of twelve 15-minute records are used in the analysis. Analysis of data indicates difficulty in obtaining a reference load (when wind Is zero). A procedure to overcome this difficulty is suggested. Preliminary results show that overall loads measured using the load cells are smaller than the ones obtained from the integration of pressure tap values. However, there is significant uncertainty and scatter in the results obtained from the load cells.Item Effects of mountainous terrain on hurricane boundary layer winds(Texas Tech University, 2000-08) Kasheta, Timothy E.Significant improvements in forecasting tropical systems have been made over the years by the development of more intricate, detailed numerical models. This study looks at the possibility of a simple, dry hurricane model being able to accurately predict hurricane winds over land. A strong emphasis has been placed on storm track and intensity forecast in past models, but the model being used in this study specifically looks at the boundary layer wind structure of a hurricane over mountainous terrain. The results of this model could help isolate the most extreme wind events over these areas resulting in increased readiness before the storm and faster damage control after. Several terrain features were used with the model to see the effects they produced on low-level windflow. Flat land, a circular mountain, an elongated mountain, and land data of the island of Taiwan were all used in this study. Changes in surface roughness, terrain height and size, and landfalling positions were all examined to see the effects on the wind profiles. Several features such as a lee-side flow and higher wind speeds over the mountain ridges were similar to other modeling studies using more advanced models. The increased resolution seen with this model showed higher detail in the wind vector patterns, especially over mountain peaks. This detail is further enhanced by using lower horizontal diffusion values and shows small features produced by the mountains that are not seen in other studies. Comparisons between the northern Taiwan landfalling experiment and the work of Wu et al. (1999), using the MM5 model to simulate typhoon Herb show these small features that are missed in the MM5 output. The highly resolved features seen in the wind pattern suggests that this model is more than sufficient for modeling boundary layer winds over mountainous terrain.Item Field measurements of wind pressures near wall corners of low-rise buildings(Texas Tech University, 2004-08) Martinez, Mark StevenAs flow approaches a bluff body with sharp edges and comers the flow separates. This leads to large fluctuating pressures, which during high winds cause cladding failure. This thesis investigates field measurements of fluctuating point pressures near the wall comer of a low-rise building. In order to better understand the wind pressures near the comer eleven records of field data were collected and validated for the case where the angle of attack of wind flow is normal to the long wall. Each run has 15-minute duration and the pressure coefficients are calculated using the mean wind speed at 13 feet. The pressure coefficients measured in the field are then compared to wind tunnel data from Colorado State University. The field-measured pressures were also compared to ASCE7-02 external wall pressuresItem 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 PBL mesoscale perturbations over the western United States during the summer months(Texas Tech University, 1997-05) Deighan, David R.The main objective of this research is to identify wind and geopotentialheight perturbations over the westem United States. The perturbations are fairly small and theorized as being generated over the plateau region in the western U.S. by low-Ievel circulations. The circulations exist on the plateau due to the temperature contrasts between the elevated terrain of the plateau and lower terrain adjacent to the plateau. Sixty-six cases included in the data set are separated into four categories; well-defined and not well-defined perturbations at 00 UTC and 12 UTC. Mean conditions of lapse rates, temperatures and geopotential heights are computed and analyzed for each category to propose possible locations of and conditions most likely to produce perturbations. The possible effect of perturbations on moist-convection coverage is also analyzed. Surface data from various observation stations in the westem U.S. has been collected for the sixty-six cases and employed to compute an average coverage of moist-convection for the included states. Comparisons are made in the magnitude of coverage values between states and in coverage values between categories for each state. Finally, the Rapid City Flood is examined to detect possible influence of perturbations on conditions leading to the flood event. Rainfall of up to 300 mm was observed during a four-hour period from 00 UTC to 04 UTC on 10 Jime 1972 along the eastem slopes of the Black Hills in southwestem South Dakota. Geopotential-height data is analyzed for three days previous to the flood event and the day of the flood event.Item Process-based aerodynamic roughness model for evaporation predictions from free water surfaces(Texas Tech University, 1998-12) Darwish, MukaddesThe process of evaporation is a complex phenomenon, which includes physical processes in several areas of physics. Accurate estimation of evaporation is important for designing and planning projects in which a water balance is key factor as well as for conservation of water. Although considerable progress has been made in understanding and measuring evaporation, the methods used in the past have serious short-comings measuring evaporation and thus developing more accurate measurements and predictions is needed. One approach to the prediction of evaporation from free water surfaces is through the use of the Borrelli-Sharif combination method which requires standard meteorological data. However, accuracy of the resulting estimation is dependent upon the interaction of wind profile and the determination of aerodynamic roughness, ZQ. It is evident that evaporation rate is influenced by the mean and turbulent flow properties near the surface of a given body of water. If the aerodynamic roughness can be estimated for the water surface, then the accuracy of predicting evaporation from that free-water surface will be greatly improved. In this study a formula is proposed for determining the aerodynamic surface roughness parameter for free water surfaces. The model is process based using the energy -transfer theory describing the reaction between wind and water surface. Wind is the main force, which causes the waves on water surfaces. Surface roughness of water is directly influenced by the velocity of the wind. The equation developed in this study predicts the wave height as a function of wind speed, and then surface roughness as a function of the wave height. This model expands the overall accuracy of evaporation prediction from free water surfacesItem Re-design of a drive system for a low-speed wind tunnel(Texas Tech University, 1998-05) Walker, Todd D.The Thermal Systems Lab at the Texas Tech University Mechanical Engineering Department has an instructional wind tunnel. An improvement was made to the drive system of the tunnel so that the average test section velocity would increase. This involved the design and manufacture of a 2 ft. diameter fan as well as some modifications to the tunnel. The results were a 21% increase in the efficiency of the drive system and a 19 mph increase in the test section velocity.Item Surface layer characteristics of thunderstorm outflow(Texas Tech University, 1997-12) Weinbeck, Stephen W.The objective of this study is to define the turbulent characteristics of thunderstorm outflow winds in the surface layer. Thunderstorms are one of the most common types of severe weather, and the climatological record for many stations shows many extreme wind events can be identified as having been generated by thunderstorms. However, until recently it has proved difficult to separate which high wind events are caused by thunderstorm outflows, and which are generated by typical extratropical low-pressure systems. The advent of the Doppler weather radar and the deployment of a national network of these radars across the continental United States provides a powerful new tool for the classification and analysis of thunderstorm outflow events. Studies have shown that in many locations the strongest winds on record are generated by thunderstorms (Twisdale and Vickery, 1992, 1995). In many cases, these straight-line winds can cause damage similar to that caused by tornadoes. Besides causing structural damage near the surface, the lifting of less dense ambient air by thunderstorm winds can be the focusing and/or riggering mechanism for further thunderstorm development to occur. It is the modification of the environment surrounding the storm, and the localized nature of the outflow and cloud system that has made the investigation and forecasting of thunderstorms difficult. It is possible to be very near a severe thunderstorm and yet not feel the effects of the rain, hail, or outflow winds. In many cases the thunderstorms are not captured by the surface observation network that the National Weather Service (NWS) has set up to observe weather systems that occur on much larger scale.Item Vertical axis wind turbine wake velocity measurements and comparison with analysis(Texas Tech University, 1981-05) Sun, HuanmingMean velocity measurements were performed in the wake behind a Darrieus Turbine. In this experiment the turbine was towed through a tank filled with water. Reynolds' number scaling was used to relate the operation in water to that in air. The results were compared with predictions from the momentum and vortex models developed by previous workers. In addition, some data from a full scale rotor obtained by other workers are presented and compared with analytical results.