Browsing by Subject "Model"
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Item A Hydrological Model of Harrington Sound, Bermuda and its Surrounding Cave Systems(2013-04-23) Stoffer, Jonathan LHarrington Sound, located in east central Bermuda, is almost entirely enclosed by land except for a 26.4 m wide channel called Flatts Inlet. This limited connection to the open ocean restricts Harrington Sound?s tides, resulting in a near 3 hour delay and dampening the tidal range to 35% of those on the coast. By comparing the tidal amplitude and surface area of Harrington Sound, tidal exchange can be determined. Past research has shown Flatts Inlet only supplies the Sound with about half of its tidal water. The remaining tidal exchange enters and leaves the Sound either via groundwater influx through pores in the rock or through the traversable passageways of limestone cave systems in the land that encloses the Sound. The aim of this study was to model hydrodynamic tidal flux and current through marine caves into Harrington Sound. One of the goals of Bermuda?s cave habitat protection plan is to track tidal circulation of water through these cave systems. Information on such cave water transport would facilitate future pollution and nutrient exchange studies. This research was initiated during a six week trip to Bermuda by Jonathan Stoffer as he obtained tidal and water quality data from caves along the perimeter of Harrington Sound. Additional flow data was collected with instruments placed by local cave divers. A YSI 600XLM water quality sonde, Norteck Vector Current Meter, and an in-situ level Aqua TROLL were used to monitor tidal amplitude, periodicity, current velocity, and water quality in cave pools and submerged passages. Profiles of the top 1-2 meters of water at each pool were taken at 56 sites. Tidal gauges were placed in 27 major cave pools surrounding Harrington Sound, as well as Harrington Sound itself, for 48 hours, to monitor tidal propagation through the island. The vector current meter was placed for six weeks to measure water flow in and out of Harrington Sound in six cave passageways known to have high flow rates. The resulting data have been compared to atmospheric data obtained from the Bermuda Weather Service and analyzed using Microsoft Excel, MATLAB and ArcGIS. The final goal of this project was to create a hydrological model able to predict flow rate and water depth in Bermudian caves with water depth data from the ocean and Harrington Sound. In constructing a water budget for Harrington Sound, I was able to account for 72.3% of all tidal inflow and 43.3% of all tidal outflow from the Sound as passing through either Flatt?s Inlet or one of the six tested caves. In creating my tidal models, I was able to achieve an averaged sum of squared deviation (SSD) normalized against count ranging from 5.1x10^-4 to 8.4x10^-4 m^2. The flow model achieved a SSD of 3.8x10^-3 m^2. My data also suggest that exchange between Harrington Sound and other inland waters, through cave systems, does exist.Item A Parametric Model of the Portuguese Nau(2012-02-14) Cook, CharlesThis interdisciplinary research project combines the fields of nautical archaeology and computer visualization in order to create an interactive virtual reconstruction of a Portuguese nau. Information about the shipbuilding process is gathered from 16th and 17th century treaties by Fernando Oliveira and Joao Batista Lavanha, as well as from Dr. Filipe Castro (Texas A&M Department of Anthropology). Eight registered tonnage formulas from the 15th to 17th century are used to estimate the cargo capacity of the nau. Using this information, I develop an algorithm that creates a parametric computer model of a nau hull and calculates its registered tonnage. This parametric model allows the user to choose between the Oliveira and Lavanha hull shapes, adjust parameters to fine tune the hull shape further, and save the information about the hull shape for future editing. The eight registered tonnage estimates are compared to the volume of the parametric hull model below a generic waterline. The process I use to adapt the information provided by the two shipbuilding treatises into an algorithm determines the hull shape of a nau. This allows for projects in the future to introduce other shipbuilding approaches and information as it becomes available to this parametric model.Item An exploration of tensile fracture in a nonhomogeneous elastic material(2013-08) Pearce, Micah R.; Dwyer, Jerry F.; Barnard, Roger W.; Schovanec, Lawrence; Howle, Victoria E.The theoretical analysis of a mode I crack in functionally graded material is presented and the numerical values of the stresses and displacements are obtained for particular material parameters. Numerical results are obtained through inverse Mellin transforms. It was found that in most cases, the material inhomogeneity parameter had a greater effect on the stresses and displacements than did Poisson’s ratio. The energy release rate for the mode I and mode III cracks are analyzed and it was noted that under certain conditions the energy release rate vanishes.Item Characterizing the ultimate properties of triblock styrene-diene thermoplastic elastomers(2005-05) Zeng, Qiumei; Leggoe, Jeremy W.; Idesman, Alexander V.; McKenna, Gregory B.; Dai, Lenore L.Styrene-diene triblock copolymers with polystyrene end blocks and polydiene midblock are an important group of thermoplastic elastomers (TPEs) and have been widely used in footwear, adhesives, automotive and the automotive industry. These materials exhibit a phase separated structure, with the polystyrene end blocks forming glassy domains distributed throughout the polydiene matrix. Styrenic TPEs have excellent mechanical properties comparable to those of vulcanized rubber, but can be processed like thermoplastics. The purpose of this research is to investigate the phenomena governing the failure process and ultimate properties in block-copolymer TPEs, and to propose a model to predict the theoretical strength of the materials. Styrene diene block copolymers were chosen as the model materials for this investigation since this class of TPE dominates commercial production of TPEs, and have simple, well characterized molecular structure, from which the properties of other block copolymer can be inferred. To support the development of the tensile strength model, uniaxial tensile test were performed for three commercial styrene-diene TPEs, polystyrene-polyisoprenepolystyrene (SIS) with 18 and 30 wt% polystyrene (PS) from Dexco Polymers and polystyrene-poly(ethylene-co-butylene)-polystyrene (SEBS) with 30 wt% PS from Kraton Polymers. Repeated loading tests confirmed that SIS with 18 wt% PS exhibited spherical morphology while the other two materials with 30 wt% PS exhibited continuous hard domains, as expected from the phase separation theory for block copolymers. The stress-extension curves for the second loading of SIS and SEBS with 30 wt% PS exhibit extensive stress softening, suggesting that the continuous domains break up progressively during deformation. The investigation on the influence of loading rate on tensile strength show that the tensile strength of SIS increase with increasing loading rate at low rates, eventually reaching a plateau or peak. The tensile strength of SEBS remained relatively constant over the entire loading rate range studied. The ultimate strain was found to be relatively independent of the loading rate. To investigate the fracture mechanism governing the ultimate properties of styrenediene TPEs, fractographic studies of the specimens broken during tensile testing were undertaken. SIS18 specimens were fond to contain gross processing flaws, as a result of the increased thickness of the specimens prepared for this material. The fracture surfaces of SIS30 specimens exhibited distinct rough and smooth regions, with the roughness of the surface decreasing with increasing strain rate. The fractures surfaces of the SEBS30 specimens indicated that failure in this material initiated at near surface flaws. The fracture surface in the initiation area was relatively smooth, becoming rough with the onset of rapid crack propagation (in a manner more akin to the behavior of glassy polymers than vulcanized elastomers). The appearance of the rapid crack propagation surface in this material was found to be unaffected by the loading rate. Based on the findings of the tensile test and fractographic investigations, it is apparent that flaws play a significant role in the fracture surface. In order to predict the ultimate strength of styrene-diene TPEs, it will be necessary to formulate models that account for the effects of flaws and the strength of the undamaged material adjacent to the flaws. In order to predict the effect of material parameters on the theoretical strength of undamaged material, a theoretical strength model has been proposed. The model takes into account the chain pullout and chain scission fracture mechanism expected to prevail at the molecular level. The theoretical strength is formulated as the maximum force the material can sustain per unit area based on the force supported by the glassy PS domains and the elastomeric mid-block chain sections intersecting a planar unit area. The strength contributed by the hard domains and elastomer matrix is related by the maximum force a chain can sustain without undergoing chain pullout or chain scission. The influence of degree of phase separation is also incorporated in the model. The model captures most features observed from experiment. Combined with the influence of flaws, the model is able to explain the different tensile strength behavior reported by different groups.Item Characterizing the ultimate properties of triblock styrene-diene thermoplastic elastomers(Texas Tech University, 2005-05) Zeng, Qiumei; Leggoe, Jeremy W.; Idesman, Alexander V.; McKenna, Gregory B.; Dai, Lenore L.Styrene-diene triblock copolymers with polystyrene end blocks and polydiene midblock are an important group of thermoplastic elastomers (TPEs) and have been widely used in footwear, adhesives, automotive and the automotive industry. These materials exhibit a phase separated structure, with the polystyrene end blocks forming glassy domains distributed throughout the polydiene matrix. Styrenic TPEs have excellent mechanical properties comparable to those of vulcanized rubber, but can be processed like thermoplastics. The purpose of this research is to investigate the phenomena governing the failure process and ultimate properties in block-copolymer TPEs, and to propose a model to predict the theoretical strength of the materials. Styrene-diene block copolymers were chosen as the model materials for this investigation since this class of TPE dominates commercial production of TPEs, and have simple, well characterized molecular structure, from which the properties of other block copolymer can be inferred. To support the development of the tensile strength model, uniaxial tensile test were performed for three commercial styrene-diene TPEs, polystyrene-polyisoprenepolystyrene (SIS) with 18 and 30 wt% polystyrene (PS) from Dexco Polymers and polystyrene-poly(ethylene-co-butylene)-polystyrene (SEBS) with 30 wt% PS from Kraton Polymers. Repeated loading tests confirmed that SIS with 18 wt% PS exhibited spherical morphology while the other two materials with 30 wt% PS exhibited continuous hard domains, as expected from the phase separation theory for block copolymers. The stress-extension curves for the second loading of SIS and SEBS with 30 wt% PS exhibit extensive stress softening, suggesting that the continuous domains break up progressively during deformation. The investigation on the influence of loading rate on tensile strength show that the tensile strength of SIS increase with increasing loading rate at low rates, eventually reaching a plateau or peak. The tensile strength of SEBS remained relatively constant over the entire loading rate range studied. The ultimate strain was found to be relatively independent of the loading rate. To investigate the fracture mechanism governing the ultimate properties of styrenediene TPEs, fractographic studies of the specimens broken during tensile testing were undertaken. SIS18 specimens were fond to contain gross processing flaws, as a result of the increased thickness of the specimens prepared for this material. The fracture surfaces of SIS30 specimens exhibited distinct rough and smooth regions, with the roughness of the surface decreasing with increasing strain rate. The fractures surfaces of the SEBS30 specimens indicated that failure in this material initiated at near surface flaws. The fracture surface in the initiation area was relatively smooth, becoming rough with the onset of rapid crack propagation (in a manner more akin to the behavior of glassy polymers than vulcanized elastomers). The appearance of the rapid crack propagation surface in this material was found to be unaffected by the loading rate. Based on the findings of the tensile test and fractographic investigations, it is apparent that flaws play a significant role in the fracture surface. In order to predict the ultimate strength of styrene-diene TPEs, it will be necessary to formulate models that account for the effects of flaws and the strength of the undamaged material adjacent to the flaws. In order to predict the effect of material parameters on the theoretical strength of undamaged material, a theoretical strength model has been proposed. The model takes into account the chain pullout and chain scission fracture mechanism expected to prevail at the molecular level. The theoretical strength is formulated as the maximum force the material can sustain per unit area based on the force supported by the glassy PS domains and the elastomeric mid-block chain sections intersecting a planar unit area. The strength contributed by the hard domains and elastomer matrix is related by the maximum force a chain can sustain without undergoing chain pullout or chain scission. The influence of degree of phase separation is also incorporated in the model. The model captures most features observed from experiment. Combined with the influence of flaws, the model is able to explain the different tensile strength behavior reported by different groups.Item Drilling performance improvement : Brett and Millheim model adaptations for interaction effects and multiple learners(2012-08) Coddou, Ginny Anne; Groat, Charles G.; Jablonowski, Christopher J.This work reviews concepts in drilling-based learning curves and proposes modifications to the Brett and Millheim learning curve model to enable its use for multiple learners and to characterize interaction effects between learners. Enabling the model’s use for multiple learning scenarios at once improves modeling efficiency. Interaction effects are present when learners improve from their own experience and the experience of those in close proximity to them. Quantifying interaction effects leads to a more complete understanding of performance improvement and enables more effective forecasting of drilling resources and expenditure requirements.Item Dynamic subdivided relative humidity model of a polymer electrolyte membrane fuel cell(2013-05) Headley, Alexander John; Chen, Dongmei, Ph. D.The development of a control-oriented dynamic relative humidity model for a polymer electrolyte membrane (PEM) fuel cell stack is presented. This model is integrated with a first law based thermal model, which tracks energy flow within four defined control volumes in the fuel cell; the cathode channel, anode channel, coolant channel, and fuel cell stack body. Energy and mass conservation equations are developed for each control volume. On top of mass conservation, electro-drag and osmosis models were also implemented within the model to account for the major modes of vapor transfer through the membrane between the anode and cathode. Requisite alterations to the thermal model as well as mass flow rate calculations are also discussed. Initially, the model utilized a single lumped control volume for the calculation of all values each channel (anode and cathode). This lumped value method is computationally inexpensive, and makes the model optimal for control design. However, investigation of the mass-based Biot number showed the need for greater granularity along the length of the channels to properly capture the relative humidity dynamics. In order to improve the resolution of the model, while still minimizing the computation expense, the model was subdivided into a series of lumped value models. The cathode channel was the point of focus as it is the major concern from a controls perspective. This method captures the proper trends found in far more complex CFD models, while still maintaining a quick calculation time. Different levels are subdivision (3 and 6 submodels) are investigated, and the differences discussed. Particularly, temperature range, relative humidity range, the effect on the modeled voltage, and calculation time are compared. This control-oriented model is low order and based on lumped parameters, which makes the computational expense low. Formulation of this model enables the development of control algorithms to achieve optimal thermal and water management.Item The effect of restrictive diffusion on hydrate growth(2016-05) Andris, Ryan Gerald; Daigle, Hugh; Mohanty, KishoreMethane hydrate is formed naturally in a number of geologic settings around the world. The most predominant methane hydrate reservoirs are found in shallow oceanic basins at low temperatures and high pressures. A widely observed phenomenon in these oceanic sequences is extensive fine-grained sediments containing little to no hydrate interbedded with highly saturated sand bodies (20-60%). At Walker Ridge Block 313 in the Gulf of Mexico, one particular coarse-grained bed (approximately 3m-thick) is estimated to have methane hydrate occupying as much as 60% of the available pore space surrounded by hydrate-free clay. Here, I develop a numerical model that simulates methane hydrate growth in shallow oceanic basins in order to test whether diffusive transport of methane is a viable transport mechanism for forming highly saturated sand layers. I conclude that methane diffusion is likely responsible for the key identifying features of hydrate formation in interbedded sands and shales (i.e. greater hydrate saturations at the sand boundaries surrounded by hydrate-free zones in the fine-grained matrix). In addition, I show that the key parameters affecting the hydrate saturation profile include the amount of available methane for hydrate growth, thickness of the sand layer, and the radius of the fine grained pore space. I also discuss the shortcomings of the developed model and what complexities need to be added to more accurately reproduce hydrate growth throughout intricate hydrogeologic systems.Item An efficient hybrid model reduction for use with the AMLS method for frequency response problems(2010-05) Li, Qinqin, 1980-; Bennighof, Jeffrey Kent, 1960-; Sirohi, JayantA hybrid model reduction for use with the automated multilevel substructuring (AMLS) method is presented for frequency response analysis of complex structures. Structure responses to harmonic excitations and quasi-static responses to dominant damping forces are included in a reduced approximation subspace. Both types of responses greatly increase the efficiency of the subspace for solving the frequency response problem (FRP) for systems with high modal density and structural damping, and provide a good preparation for future frequency-dependent problems. A distilled subspace assumed to provide accurate frequency responses is generated from the finite element (FE) models by using the AMLS method. Then, the hybrid model reduction method is used to reduce the distilled subspace into a small new subspace. Three types of vectors are used to construct this subspace. The first type is distilled subspace dynamic response vectors (DRVs), which are exact solutions in the distilled subspace at certain chosen frequencies, called the DRV frequencies. The second type is modal DRVs, which are inexpensive approximate solutions calculated in an eigenspace. The third type is damping deformation vectors (DDVs), which provide information about response of the structure to damping effects. As exact responses, the distilled subspace DRVs eliminate frequency response errors at the DRV frequencies, and improve the accuracy at nearby frequencies as well. A small number of DRV frequencies are chosen carefully to offer maximum benefit with minimal computational cost. The modal DRVs are approximated very inexpensively from a suitable eigenspace. Only the diagonal entries in the modal coefficient matrices are used, along with low-rank updates that improve the accuracy of the modal DRVs and are applied using the Sherman-Morrison-Woodbury formula. Because of their low cost, a large number of modal DRVs constitute the major part of the reduced subspace. A small number of DDVs represent response to provide damping with minimal computational cost. The dimension of the final subspace is minimized by removing any redundancy through a special implementation of the QR factorization. This method results in a much smaller new subspace than the one from traditional modal truncation while achieving the same FRP accuracy. Such an efficiency also establishes a good foundation for future application in frequency-dependent problems.Item Essays on Network Formation(2012-10-19) Mueller, William GrahamThis dissertation contains two essays which examine the roles that individual incentives, competition, and information play in network formation. In the first essay, I examine a model in which two competing groups offer different allocation rules that may depend on the network of connections among the individuals that make up each group. I assume the existence of a single divisible good, such as a monetary prize, which will be divided amongst the members of the winning network. The probability of winning the prize will depend on the network sizes. I examine two well-known allocation rules: the Myerson value and the egalitarian rule. I prove existence of equilibria and characterize the properties of the two networks. The implications of the equilibria networks for the outcome of the contest are discussed. I find that the winning probability of the network using the Myerson value has an upper bound very close to one half. There is no such upper bound for the network using the egalitarian rule. In my second essay, I examine a dynamic model of network formation in which individuals use reinforcement learning to choose their actions. Typically, economic models of network formation assume the entire network structure to be known to all individuals involved. The introduction of reinforcement learning allows us to relax this assumption. Through the use of a state-dependent reinforcement learning rule, one may allow for varying degrees of information available to the agents. Three informational settings are examined and I determine what networks, if any, each model may converge to in the limit. The long-run behavior of each model is examined through the use of simulations and compared to one another. I find that amount and type of information agents have access plays an important role in which networks emerge when there is no dominant strategy for the agents choosing links. If there is a dominant link choosing strategy, the most efficient network structure quickly emerges in each informational setting. Together, these essays investigate how information, incentives, and competition may affect network formation. Individual incentives in the presence of competition can create tension between an individual's social ties and the overall network size. Information plays a key role in the emergent network topologies when there are no dominate network building strategies.Item Experimentation and modeling of pulse sharpening and gyromagnetic precession within a nonlinear transmission line(2011-08) Vaselaar, Andrew; Bayne, Stephen B.; Mankowski, John J.A computer model is developed to predict the output of a NonLinear Transmission Line (NLTL) based upon an input pulse, material properties and physical dimensions. Additionally, a test bed is developed with the goal of validating the computer model with regards to its level of accuracy in comparison with a real world system. The test bed is also designed to provide the apparatus for evaluating ferrite materials for their performance characteristics as components for NLTL applications. The resulting model provides two computation algorithms that successfully simulate aspects of NLTL operation. They require further development to improve their computational algorithms and to take into account more material properties in order to serve as a better tool for design of NLTL systems. The NLTL testbed results in a working pulser and diagnostic system, however the NLTL suffers from high voltage breakdown that prevents it from functioning as designed.Item A fundamental approximation in MATLAB of the efficiency of an automotive differential in transmitting rotational kinetic energy(2012-05) Vaughn, James Roy; Matthews, Ronald D.; Bryant, Michael D.The VCOST budgeting tool uses a drive cycle simulator to improve fuel economy predictions for vehicle fleets. This drive cycle simulator needs to predict the efficiency of various components of the vehicle's powertrain including any differentials. Existing differential efficiency models either lack accuracy over the operating conditions considered or require too great an investment. A fundamental model for differential efficiency is a cost-effective solution for predicting the odd behaviors unique to a differential. The differential efficiency model itself combines the torque balance equation and the Navier-Stokes equations with models for gear pair, bearing, and seal efficiencies under a set of appropriate assumptions. Comparison of the model with existing data has shown that observable trends in differential efficiency are reproducible in some cases to within 10% of the accepted efficiency value over a range of torques and speeds that represents the operating conditions of the differential. Though the model is generally an improvement over existing curve fits, the potential exists for further improvement to the accuracy of the model. When the model performs correctly, it represents an immense savings over collecting data with comparable accuracy.Item G.R.A.C.E. satellite thermal model(2012-12) Jones, Fraser Black III; Howell, John R.I developed a thermal model of the Gravity Recovery and Climate Experiment satellite for the Center for Space Research to use in verifying their thermal models and for developing the next generation of satellites for their experiments. I chose COMSOL to model the satellite and used ProEngineer and 3Ds Max to generate the mesh from a .STEP file provided by DaimlerChrysler. I adjusted the model based on previous computer models and actual telemetry data from the GRACE satellite provided from 2002 through 2008. Using the model, I developed a sensitivity analysis of the satellites key thermal environment components and used that to recommend design changed for the next generation of satellites. Special attention should be given to redesigning the Star Camera Arrays and the heat transfer between the Main Equipment Platform and the Radiator.Item A generalized flow rate model for primary production and an analysis of gravity drainage through numerical simulation(2014-08) Vitter, Cameron Artigues; Balhoff, Matthew T.; Lake, Larry W.The age of “easy” oil has steadily declined through the years as many conventional land-based fields have been depleted to residual levels. Novel technologies, however, have reawakened old fields, allowing incremental oil to be added to their recoverable oil in place (ROIP). Underground Gravity Drainage (UGD), an example of one of these technologies, combines improved horizontal and deviated drilling technologies with the longstanding concept of gravity drainage. In this work, a better understanding of gravity drainage has been gained through (1) development of a numerical, three-dimensional, three-phase reservoir simulator (UT-EMPRES), (2) development of a universal, semi-empirical model of production rates through primary depletion, and (3) analysis of the important aspects of gravity drainage through simulation. UT-EMPRES is a new three-phase, finite-difference reservoir simulator, which utilizes a simple, easy-to-use Microsoft Excel interface to access MATLAB-programmed simulation code. This simulator produces nearly identical results to other well-established simulators, including UTCHEM and CMG. UT-EMPRES has some unique features, allows for easy post-processing in MATLAB, and has been utilized extensively in the other two areas of this thesis. The generalized flow rate model (GFRM) is a semi-empirical equation that is used to forecast the dynamic primary production rate of a reservoir with an arbitrary number of wells all operating at the same constant pressure condition. The model is an extension of the classic tank model, which is inherently a single flowing phase development. With the ability to make a priori predictions of production figures, users can screen various prospect assets on the basis of economic potential through optimization routines on the GFRM. Gravity drainage and its approximation through numerical simulation are analyzed. A sensitivity study was conducted on three-phase gravity drainage, leading to the conclusion that small changes in vertical permeability and portions of the relative permeability-saturation relationships can greatly affect production rates. Finally, two-phase (oil and air) and regions of three-phase (water, oil, air) flow simulations were found to exhibit exponential decline in phase production rates, which may enable the GFRM to be applicable to UGD-type processes.Item How information asymmetry affects contract design : paying for private firms with IOU's(2016-05) Jansen, Mark; Parrino, Robert, 1957-; Fracassi, Cesare; Almazan, Andres; Hartzell, Jay; Starks, Laura; Abrevaya, JasonThis dissertation examines a financing mechanism that is common in the acquisition of privately-held firms. Using a novel database of transactions in which the target firm is private, this paper shows that sellers receive a debt claim as a contingent payment for the firm that is being sold. The debt claim, which takes the form of seller financing, is secured by the assets of the target firm. I show that proxies for information asymmetry are correlated with the presence of seller financing as payment in the transaction. I also find that when the firm is more likely to have received a financial audit, the transaction is less likely to include seller financing. Since financial audits improve firm transparency, I interpret this as evidence that a reduction in information asymmetries between the parties of a acquisition affect the deal structure. A complementary explanation for the use of seller financing is related to capital constraints faced by buyers in the financing of the transaction. I present evidence that contract structures are affected by cross-sectional and time-series changes in the supply of local investment capital for buyouts. I find that seller financing is less common in areas in which locally informed capital is more abundant. I also find that transactions contain a lower percentage of seller financing in city-years in which Small Business Administration provides loan guarantees for the acquisition and expansion of firm’s loan guarantees are higher. The evidence suggests that seller financing is solving a contracting problem because it is unaffected by controls for local banking activity.Item Incoporating rubble mound jetties in elliptic harbor wave models(Texas A&M University, 2007-09-17) Zhang, JianfengSimulation models based on the elliptic mild or steep slope wave equation are frequently used to estimate wave properties needed for the engineering calculations of harbors. To increase the practical applicability of such models, a method is developed to include the effects of rubble mound structures that may be present along the sides of entrance channels into harbors. The results of this method are found to match those of other mathematical models (i.e. parabolic approximation & three-dimensional solution) under appropriate conditions, but they also deviate from results of parabolic approximations in some cases because dissipation can create angular scattering. Comparison with hydraulic model data also shows that this approach is useful for designing pocket wave absorbers that are used to reduce wave heights in entrance channels.Item Investigating Rainwater Harvesting as a Stormwater Best Management Practice and as a Function of Irrigation Water Use(2012-02-14) Shannak, Sa'D Abdel-HalimStormwater runoff has negative impacts on water resources, human health and environment. In this research the effectiveness of Rain Water Harvesting (RWH) systems is examined as a stormwater Best Management Practice (BMP). Time-based, evapotranspiration-based, and soil moisture-based irrigation scheduling methods in conjunction with RWH and a control site without RWH were simulated to determine the effect of RWH as a BMP on a single-family residence scale. The effects of each irrigation scheduling method on minimizing water runoff leaving the plots and potable water input for irrigation were compared. The scenario that reflects urban development was simulated and compared to other RWH-irrigation scheduling systems by a control treatment without a RWH component. Four soil types (sand, sandy loam, loamy sand, silty clay) and four cistern sizes (208L, 416L, 624L, 833L) were evaluated in the urban development scenario. To achieve the purpose of this study; a model was developed to simulate daily water balance for the three treatments. Irrigation volumes and water runoff were compared for four soil types and four cistern sizes. Comparisons between total volumes of water runoff were estimated by utilizing different soil types, while comparisons between total potable water used for irrigation were estimated by utilizing different irrigation scheduling methods. This research showed that both Curve Number method and Mass-Balance method resulted in the greatest volumes of water runoff predicted for Silty Clay soil and the least volumes of water runoff predicted for Sand soil. Moreover, increasing cistern sizes resulted in reducing total water runoff and potable water used for irrigation, although not at a statistically significant level. Control treatment that does not utilize a cistern had the greatest volumes of predicted supplemental water among all soil types utilized, while Soil Moisture-based treatment on average had the least volume of predicted supplemental water.Item Investigation of analytical models incorporating geomechanical effects on production performance of hydraulically and naturally fractured unconventional reservoirs(2014-08) Aybar, Umut; Sepehrnoori, Kamy, 1951-; Patzek, Tadeusz W.Petroleum and Geosystems EngineeringItem Model and analysis: Diabetes and obesity(2007-12) Al-Hashmi, Sam; Martin, Clyde F.; Drager, Lance D.The thesis is a further revision of a mathematical model based upon Sorensen’s progress and Alvehag’s modification under Dr Clyde Martin. The intention of the model is to address the aspect of regulating glucose concentration with in the body from a control theory point of view. The chosen method of simulation is based upon the pharmacokinetic approach; and our revision main aspect is to address the effect free fatty acid (FFA) in the blood. This is a necessary step since the primary role of the model is to establish a mathematical model simulating the behavior of a type II diabetic patient. Type II diabetes can be classified into categories; such early stages of type II diabetes and fully developed type II diabetes. The thesis emphasis on the affect of insulin resistance by including a sub-model of adipose tissue; hence creating a further understanding to the behavior of a healthy human body under induced insulin resistance, or obese individuals, or early stages of a type II diabetic patient. The thesis remains lacking the ability to simulate the unique behavior of impaired insulin secretion. Further research is needed to be able to fully simulate the response of early stages type II diabetic patients and follow the progress into a fully type II diabetic patients.Item Modeling and simulation of a high pressure hydrogen storage tank with dynamic wall(Texas Tech University, 2005-12) Cumalioglu, Ilgaz; Ertas, Atila; Ekwaro-Osire, Stephen; Ma, Yanzhang; Maxwell, Timothy T.Hydrogen storage is one of the divisions of hydrogen powered vehicles technology. To increase performances of high pressure hydrogen storage tanks, a multilayered design is proposed featuring the dynamic wall capable of absorbing hydrogen. Modeling and parametric study have been done to extract information on required mechanical and physical properties of the wall. Parameters and system constraints have been defined, relations are found and discussed.