Browsing by Subject "Experimental"
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Item Analytical and Experimental Studies of Drag Embedment Anchors and Suction Caissons(2011-08-08) Beemer, RyanThe need for experimental and analytical modeling in the field of deep water offshore anchoring technologies is high. Suction caisson and drag embedment anchors (DEA) are common anchors used for mooring structures in deep water. The installation process of drag embedment anchors has been highly empirical, employing a trial and error methodology. In the past decade analytical methods have been derived for modeling DEA installation trajectories. However, obtaining calibration data for these models has not been economical. The development of a small scale experimental apparatus, known as the Laponite Tank, was developed for this thesis. The Laponite Tank provides a quick and economical means of measuring DEA trajectories, visually. The experimental data can then be used for calibrating models. The installation process of suctions caissons has benefited from from a more rational approach. Nevertheless, these methods require refinement and removal methodology requires development. In this thesis, an algorithm for modeling suction caisson installation in clay has been presented. An analytical method and modeling algorithm for removal processes of suction caissons in clay was also developed. The installation and removal models were calibrated to field data. These analytical and experimental studies can provide a better understanding of installation of drag embedment anchors and the installation and removal of suction caissons.Item Application of parametric sensitivity analysis to calcium handling in cardiac myocytes(Texas Tech University, 2003-08) Smith, Charles NHeart failure disease (HF) kills 220,000 people in America every year. HF is characterized by the ineffective handling of calcium ions by the mechanisms present in cardiac myocytes resulting in decreased contractile force in the heart. This inefficiency leads to necrosis of the myocardium, cardiac hypertrophy, and eventual death of the patient. The mechanisms affected include various ion channels and active transport mechanisms. Numerous technologies and techniques have been developed recently to apply genetic and pharmacological therapies to these cells. Unfortunately, there are a large number of target parameters that can be manipulated in the myocytes. Mathematical models have been developed that accurately reproduce the calcium mechanisms. These models are reproducible and rapidly evaluated on desktop computers using current mathematical software. Sensitivity analysis is useful in determining the best targets for manipulation by external sources in the hopes of restoring the proper calcium ion handling by ion channels and calcium transporters. Sensitivity analysis uses matrix algebra and calculus to determine the normalized response of a control variable to a change in a parameter. More specifically, this technique calculates the responses of all control variables to changes in all of the parameters individually. This generates a matrix of values that can easily be analyzed. This method will save valuable time and resources that would have been spent on performing multiple experiments or simulations to determine the best targets for manipulation. The cytosolic calcium concentration is targeted as it is directly related to the contractile force of the heart. Reduction of complex models is also possible using the results of sensitivity analysis. Rota et al. describe a method of normalizing fluxes and sensitivities against their greatest magnitude as a characteristic for suggesting unimportant fluxes and parameters. Two models are examined: the Tang-Othmer (T-0) model and the Winslow, Rice, and Jafri (WRJ) model. Both of these models seek to describe the handling of calcium ions within cardiac myocytes; however the level of their complexities differs greatly. The T-O model contains much fewer state variables, parameters, and fluxes than the WRJ model. The greater incorporation of states and the related parameters and fluxes leads the WRJ model to yield a much greater complexity than that presented with the T-O model. This complexity is magnified upon formation of the sensitivity matrices for these models, where the T-O model yields a fifty-five element matrix and the WRJ model yields 1,881 elements in its sensitivity matrix. The T-O model is used to develop the application method whereas the WRJ model is used to determine the best targets for manipulation and to illustrate the efficacy of model reduction. Sensitivity analysis upon the T-O model yields the sodium-calcium exchanger parameters and the sarcolemmal leak coefficient as the optimal targets for manipulation to restore proper cytosolic calcium concentration. The best targets for genetic or pharmacological manipulation according to the WRJ model are the Na+ and Ca2+ background currents, the maximum current for the sodium-potassium pump, and the half saturation constants for the sodium-potassium pump. These parameters are not present in the T-O model and have greater sensitivity magnitudes than those that carry over into the WRJ model. Model reduction by the method of Rota et al. reveals that the Tang-Othmer model is irreducible in its present state. The WRJ model was found to have no reducibility with regards to the number of fluxes in the model. However the integration of some sensitivities was unattainable, and some of these parameters may be found to be removable upon further analysis of the model once these sensitivities are obtained. Further integration methods will be attempted, such as the use of a hard-coded implicit integrator. Sensitivity analysis also revealed a crossover phenomenon in both models. This phenomenon describes the change in sign of a sensitivity of a state variable to a parameter during the course of a heartbeat. When this occurs the desired effect of manipulating the parameter yields the opposite effect upon the state variable. This phenomenon may generate interesting side effects that require further study. The results of sensitivity analysis provide future direction for physical experiments. These experiments will both confirm the calculated sensitivities, and investigate their application to failing myocytes. The crossover phenomenon will provide interesting avenues of research into the side-effects of parameter manipulation based on the magnitude and location in the cycle of the crossover. Model reduction may play a key role in simplifying models for easier computation and analysis.Item Computational fluid dynamics for LNG vapor dispersion modeling: a key parameters study(2009-05-15) Cormier, Benjamin RodolpheThe increased demand for liquefied natural gas (LNG) has led to the construction of several new LNG terminals in the United States (US) and around the world. To ensure the safety of the public, consequence modeling is used to estimate the exclusion distances. The purpose of having these exclusion distances is to protect the public from being reached by flammable vapors during a release. For LNG industry, the exclusion zones are determined by the half lower flammability limits (half LFL, 2.5% V/V). Since LNG vapors are heavier?than?air when released into atmosphere, it goes through stages, negative, neutral and positive buoyant effect. In this process, it may reach the half LFL. The primary objective of this dissertation is to advance the status of LNG vapor dispersion modeling, especially for complex scenarios (i.e. including obstacle effects). The most used software, box models, cannot assess these complex scenarios. Box models simulate the vapor in a free?obstacle environment. Due to the advancement in computing, this conservative approach has become questionable. New codes as computational fluid dynamics (CFD) have been proven viable and more efficient than box models. The use of such advance tool in consequence modeling requires the refinement of some of the parameters. In these dissertation, these parameters were identified and refine through a series of field tests at the Brayton Firefighter Training Field (BFTF) as part of the Texas A&M University System (TAMUS). A total of five tests contributed to this dissertation, which three of them were designed and executed by the LNG team of the Mary Kay O'Connor Process Safety Center (MKOPSC) and the financial support from BP Global SPU Gas (BP). The data collected were used as calibration for a commercial CFD code called CFX from ANSYS. Once the CFD code was tuned, it was used in a sensitivity analysis to assess the effects of parameters in the LFL distance and the concentration levels. The dissertation discusses also the validity range for the key parameters.Item Experimental investigation of the performance of a fully cooled gas turbine vane with and without mainstream flow and experimental analysis supporting the redesign of a wind tunnel test section(2013-12) Mosberg, Noah Avram; Bogard, David G.This study focused on experimentally determining the cooling performance of a fully cooled, scaled-up model of a C3X turbine vane. The primary objective was to determine the differences in overall effectiveness in the presence and absence of a hot mainstream flowing over the vane. Overall effectiveness was measured using a thermally scaled matched Biot number vane with an impingement plate providing the internal cooling. This is the first study focused on investigating the effect of removing the mainstream flow and comparing the contour and laterally-averaged effectiveness data in support of the development of an assembly line thermal testing method. It was found that the proposed method of factory floor testing of turbine component cooling performance did not provide comparable information to traditional overall effectiveness test methods. A second experiment was performed in which the effect of altering the angle of attack of a flow into a passive turbulence generator was investigated. Measurements in the approach flow were taken using a single wire hot-wire anemometer. This study was the first to investigate the effects such a setup would have on fluctuating flow quantitates such as turbulence intensity and integral length scale rather than simply the mean quantities. It was found that both the downstream turbulence intensity and the turbulence integral length scale increase monotonically with approach flow incidence angle at a specified distance downstream of the turbulence generator.Item An experimental test of collegiate drinking norms(2011-05) Patel, Amee Bipin; Fromme, Kim; Beevers, Christopher G.; Beretvas, Susan N.; Josephs, Robert A.; Markman, Arthur B.Social norms play a pivotal role in both explaining the development and maintenance of collegiate alcohol use and creating prevention and intervention programs targeted at reducing heavy drinking. By theoretically functioning as a model of normative and popular behavior, descriptive and injunctive norms are consistently associated with college drinking. In the current study, we endeavored to test the mechanisms through which social norms influence drinking by experimentally manipulating normative beliefs. Participants (N = 181) were assigned to one of nine conditions in a 3 (descriptive norms (DN): positive, negative, none) x 3 (injunctive norms (IN): positive, negative, none) experimental design. Norms exposure occurred within a series of three same-gender Internet-based chat room sessions. The norms manipulation was partially successful in creating groups with distinct normative beliefs, with the no norms groups failing to maintain a neutral norm for both descriptive and injunctive norms. Consequently, no descriptive norms groups were combined with positive descriptive norms groups and no injunctive norms groups were combined with negative injunctive norms groups, resulting in a 2 (DN: positive, negative) x 2 (IN: positive, negative) design for analyses. Overall findings for type (DN, IN) and valence (positive, negative) of norms indicated that participants globally reduced descriptive norms and drinking from pre-chat room to post-chat room, regardless of the type or valence of the manipulation, indicating that there were no experimental effects by condition. Whereas drinking appeared to stabilize at post-chat room, descriptive norms continued to decrease by three-month follow-up. Injunctive norms and personal attitudes about alcohol use also decreased by three-month follow-up. Although we were unsuccessful in changing normative beliefs in expected directions, these findings have important implications for college prevention and intervention programs for reducing drinking. The lack of experimental effects suggested that changing norms may be more complex than previously hypothesized and that changes in norms may not result in changes in drinking, which is the purported mechanism of change in norms-based interventions. These results further suggested that continued research is necessary to provide empirical support for a causal link between norms and drinking and that alternative explanations for the association between norms and drinking need to be considered.Item Experimentally determined external heat transfer coefficient of a turbine airfoil design at varying incidence angles(2015-05) Packard, Gavin Ray; Bogard, David G.; Hall, Mathew JPredicting and measuring external heat transfer coefficients of hot gas path turbine components are important tools for gas turbine designers. Inlet temperatures often exceed the melting temperature of the materials used in such components, requiring protective measures such as thermal barrier coatings or film-cooling to prevent component failure. The external heat transfer coefficients can be used to design for the thermal loading that will ultimately lead to such failures. Modern engine designers use computational codes to predict the conditions of the hot gas components during engine operation. Before these codes can be relied upon as accurate, they must first be verified with experimental measurements. However, measuring the heat transfer coefficients can be a difficult process, especially on an actual engine component, due to the extreme temperatures and inaccessibility. As such, low speed, low temperature wind tunnels are often used to simulate a scaled version of turbine components to collect experimental data to assist in validating computational codes. This thesis details the construction of scaled up turbine airfoils to collect such data. It also provides data covering the generation of turbulence using an array of vertical rods upstream of a linear cascade in a low speed wind tunnel at off-normal incidence flow angles.Item Fatigue behavior of post-installed shear connectors used to strengthen continuous non-composite steel bridge girders(2016-08) Ghiami Azad, Amir Reza; Engelhardt, Michael D.; Williamson, Eric B., 1968-; Helwig, Todd A; Jirsa, James O; Taleff, Eric MMany older bridges in Texas are constructed with floor systems consisting of a concrete slab over steel girders. A potentially economical means of strengthening these floor systems is to connect the existing concrete slab and steel girders using post-installed shear connectors to change the behavior of the beam from non-composite to partially-composite. Since fatigue is one of the main concerns in designing bridges, investigating the fatigue properties of these post-installed shear connectors becomes crucial. Results from direct-shear testing show that post-installed shear connectors have a better fatigue life compared to conventional welded shear studs. However, based on currently available data from direct-shear tests, fatigue life of post-installed shear connectors is still inadequate for economical retrofit in some cases. Furthermore, it is unclear if direct-shear tests provide an appropriate means of evaluating fatigue performance. The objective of this dissertation is to develop new and more accurate approaches for evaluating the fatigue characteristics of post-installed shear connectors. This objective is addressed through large-scale beam fatigue tests and computational studies. The focus of the work is on evaluating fatigue life of shear connectors based on both slip and stress demands.Item Florence(2015-05) Kuntz, Caleb Brandon; Raval, P. J. (Paul James); Rifkin, Edwin; Spiro, EllenFlorence is an 8-minute narrative film about an adolescent girl with a spectrum of Asperger's Syndrome that is medically misdiagnosed and prescribed psychotropic medication. The following report gives and account of the conception, pre-production, production and post-production phases of the film's realization. The lessons learned through both successes and failures will be considered as well as the future life of the project.Item Superposition in the leading edge region of a film cooled gas turbine vane(2013-12) Anderson, Joshua Brian; Bogard, David G.The leading edge of a turbine vane is subject to some of the highest temperature loading within an engine, and an accurate understanding of leading edge film coolant behavior is essential to efficient engine design. Although there have been many investigations of the adiabatic effectiveness for showerhead film cooling within the leading edge region, there have been no previous studies in which individual rows of the showerhead were tested with the explicit intent of validating superposition models. For the current investigation, a series of adiabatic effectiveness experiments were performed with a five-row showerhead, wherein each row of holes was operated in isolation. This allowed evaluation of superposition on both the suction side of the vane, which was moderately convex, and the pressure side of the vane, which was mildly concave. Superposition was found to accurately predict performance on the suction side of the vane at lower momentum flux ratios, but not for higher momentum flux ratios. On the pressure side of the vane, the superposition predictions were consistently lower than measured values, with significant under-prediction of adiabatic effectiveness occurring at the higher mass flow rates. Possible reasons for the under-prediction of effectiveness by the superposition model are presented.Item When will states talk? Predicting the initiation of conflict management in interstate crises(Texas A&M University, 2006-10-30) Bragg, Belinda LesleyThis research addresses the question of why some crises between states are resolved through negotiated agreements while others result in continued conflict or escalate to war. The model deviates from previous approaches to the study of conflict management in four key ways: 1) management is treated as a conflict strategy rather than an outcome; 2) costs, rather than calculation of the relative benefits of conflict over management, motivate the initiation of conflict management; 3) the conceptualization of costs is broadened to incorporate subjective factors; and 4) issue salience is proposed to determine the threshold at which an actor??????s preference for conflict over management changes. The central question this conceptualization raises, therefore, is what factors influence actors?????? strategy choices during a crisis. The theory proposes that, when it comes to the initiation of conflict management, it is costs that dominate the decision process. Or as Jackman (1993) so succinctly puts it; ??????for those confronted with a very restricted range of available alternatives extending from horrendous to merely awful, minimizing pain is the same as maximizing utility??????. Both experimental and statistical methodologies are used to test the hypotheses derived from the theory. Original experimental data were collected from experiments run on undergraduate students at Texas A&M University. For the statistical analysis a data set of interstate crises and negotiation behavior was compiled using data from the SHERFACS and International Crisis Behavior data sets and data collected specifically for this research. This multi-method approach was chosen because of the nature of the questions being examined and in order to minimize the limitations of the individual methodologies. The experimental tests demonstrate that the expectations of the model are supported in the controlled environment of the experiment. The results from the empirical analysis were, within the restrictions of the data, consistent with both theoretical expectations and the experimental results.