Browsing by Subject "flow"
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Item BOD5 removal in subsurface flow constructed wetlands(Texas A&M University, 2005-08-29) Melton, Rebecca HobbsThe frequency of on-site systems for treatment of domestic wastewater is increasing with new residential development in both rural and low-density suburban areas. Subsurface flow constructed wetlands (SFCW) have emerged as a viable option to achieve advanced or secondary treatment of domestic wastewater. The pollutant removal efficiency in SFCW depends on design parameters. Many of these factors have been investigated while others such as aspect ratio, design of water inlet structure and method of dosing the wetland have yet to be fully examined. This study examined the effect of aspect ratio and header design on BOD5 removal efficiency as well as the impact of flow rate on flow distribution in a SFCW. An aspect ratio of 4:1 achieved 10% greater removal of organic matter than a 1:1 ratio. Tracer studies demonstrated that wetlands loaded at a constant rate of 3.8 L/min and 7.6 L/min experienced preferential flow. In addition, tracer studies showed wetlands with leaching chambers as headers failed to achieve equal flow distribution. An improvement in effluent water quality was achieved by replacing the leaching chamber for a perforated manifold as the inlet structure. This study demonstrated the importance of the careful selection of aspect ratio and means by which water is introduced to the wetland in the design of SFCW.Item Discontinuous Galerkin Finite Element Method for the Nonlinear Hyperbolic Problems with Entropy-Based Artificial Viscosity Stabilization(2012-07-16) Zingan, Valentin NikolaevichThis work develops a discontinuous Galerkin finite element discretization of non- linear hyperbolic conservation equations with efficient and robust high order stabilization built on an entropy-based artificial viscosity approximation. The solutions of equations are represented by elementwise polynomials of an arbitrary degree p > 0 which are continuous within each element but discontinuous on the boundaries. The discretization of equations in time is done by means of high order explicit Runge-Kutta methods identified with respective Butcher tableaux. To stabilize a numerical solution in the vicinity of shock waves and simultaneously preserve the smooth parts from smearing, we add some reasonable amount of artificial viscosity in accordance with the physical principle of entropy production in the interior of shock waves. The viscosity coefficient is proportional to the local size of the residual of an entropy equation and is bounded from above by the first-order artificial viscosity defined by a local wave speed. Since the residual of an entropy equation is supposed to be vanishingly small in smooth regions (of the order of the Local Truncation Error) and arbitrarily large in shocks, the entropy viscosity is almost zero everywhere except the shocks, where it reaches the first-order upper bound. One- and two-dimensional benchmark test cases are presented for nonlinear hyperbolic scalar conservation laws and the system of compressible Euler equations. These tests demonstrate the satisfactory stability properties of the method and optimal convergence rates as well. All numerical solutions to the test problems agree well with the reference solutions found in the literature. We conclude that the new method developed in the present work is a valuable alternative to currently existing techniques of viscous stabilization.Item Effectiveness of internet information for park, recreation and tourism practitioners(Texas A&M University, 2004-09-30) Patterson, Joni DeniseThis research is a four-step process. 1) Development of the Park, Recreation and Tourism (PRT) Planning Web site to meet the needs of rural communities, indicated through the Texas Community Futures Forum needs assessment process. 2) Evaluation of the PRT Planning Web site by experts in the field of PRT Sciences. 3) Inspect differences in the information needs and use between rural and urban PRT practitioners. 4) Examine factors contributing to the flow experience while utilizing the PRT Planning Web site. Evaluation information provided insight about strengths, weakness and modifications to be made to the PRT Planning site. Programming was reported as the service provided most by survey participants. Internet information is considered the most effective information resource, with suppliers/manufacturers and libraries being the least effective. When acquiring information on developing and providing PRT services, not knowing where to find information was the problem experienced most, while not understanding the information was the problem encountered the least. Marketing information was deemed the most useful type of information, and increasing community well being is the most important service benefit provided by respondents. No significant differences were reported between groups' perception of Internet information as the most effective information resource, intent to return to the PRT Planning Web site, or education levels. Significant differences were reported between groups' Internet connection speed, use of a dial-up modem, computer experience and Internet experience. Study findings also reported less computer and Internet experience for rural and small communities when compared to large and urban communities. In Skadberg's (2002) proposed model of flow in human-computer interaction, the factors that contribute to the flow experience are, experience, ease of use, response speed, interactivity, vividness, telepresence, knowledge of the information being presented, and challenge of the information being presented. Of these factors, experience was the only variable that did not show a significant or positive relationship with factors in the flow model. Increased learning and change in attitude and behavior are considered outcomes of achieving the flow state; both reflected a positive and significant relationship with the variable flow.Item Experiments to examine transplant procedures on the seagrass Halodule beaudettei(Texas A&M University, 2007-09-17) Land, Frederick JosephDuring the growing seasons of 1999 and 2000 five experiments were performed to test growth of the seagrass Halodule beaudettei (shoal-grass) in nursery pond conditions. Sediment oxidation state, sediment source, container type, flow regime, and light transmittance were tested to improve nursery pond cultivation techniques and to test assumptions about the decline of seagrasses in Galveston Bay, Texas. Oxidized and reduced sediments exhibited no statistical difference as mean percent change in the number of stems of shoal-grass, after 47 days. Sediment from three source locations, West Bay, East Beach Lagoons, and the experimental pond bottoms, showed no significant difference in the mean percent change in the number of stems of shoal-grass at 48 and 95 days. A statistical difference was seen in the container type experiment, trays versus pots, at 48 days where shoal-grass had double the number of stems produced in trays; however no significant difference was found at 93 days. A significant difference was found in the flow regime experiment, no-flow versus flow, at 47 days in the mean percent change of shoal-grass with double the number of stems produced in the flow regime. Significant differences were observed between the low light and high light treatments with shoal-grass, widgeongrass (Ruppia maritima), star grass (Halophila engelmannii), and turtlegrass (Thalassia testudinum), with survival and growth occurring in the high light treatment and decline and death occurring in the low light treatment. The importance of reduced sediment may have been overstated in the past as sediment reduction occurs rapidly with submersion. It appears that while West Bay sediment did not have a deleterious effect on shoal-grass, West Bay simulated light conditions did. Container type seems to be important at first but not so much in the long term. Some flow, water movement, or current appears to be important.Item Flow assurance and multiphase pumping(2009-05-15) Nikhar, Hemant G.A robust understanding and planning of production enhancement and flow assurance is required as petroleum E&P activities are targeting deepwaters and long distances. Different flow assurance issues and their solutions are put together in this work. The use of multiphase pumps as a flow assurance solution is emphasized. Multiphase pumping aids flow assurance in different ways. However, the problem causing most concern is sand erosion. This work involved a detection-based sand monitoring method. Our objectives are to investigate the reliability of an acoustic sand detector and analyze the feasibility of gel injection as a method to mitigate sand erosion. Use of a sand detector coupled with twin-screw pumps is studied under varying flow conditions. The feasibility of gel injection to reduce slip and transport produced solids through twin-screw pump is investigated. A unique full-scale laboratory with multiphase pumps was utilized to carry out the experimental tests. The test results indicate that acoustic sand detection works in a narrow window around the calibration signature. An empirical correlation for predicting the twin-screw pump performance with viscous fluids was developed. It shows good agreement in the practical operational limits ? 50% to 100% speed. The results indicate that viscous gel injection should be an effective erosion mitigation approach as it reduces slip, the principle cause of erosive wear. To correlate the performance of viscous fluid injection to hydroabrasive wear, further experimental investigation is needed.Item Interactive eshopping experience: an empirical investigation(Texas A&M University, 2005-02-17) Mahfouz, Ahmed Yousry MohamedUtilizing an experimental design, the study investigates the effects of eshopping behavior (experiential, utilitarian, or mixed) and interactivity level (low or high) on the consequences of eshopping (site attitude and future purchase intentions), as mediated by eshopping experience (sensory, affective, and cognitive) and flow experience (control, attention focus, and cognitive enjoyment). Structural equation modeling was used for data analysis. Eshopping behavior had a weak negative effect, and interactivity level had a weak positive effect, on eshopping experience. Experiential eshopping behavior decreased eshopping experience more than mixed or utilitarian eshopping behavior did. The latter two behaviors were not significantly different from each other in terms of eshopping experience. High interactivity level web sites increased eshopping experience more than low interactivity level sites did. Interactivity level had a weak negative effect on flow's control dimension and a moderate positive effect on flow's cognitive enjoyment component. High interactivity level sites moderately increased cognitive enjoyment more than low interactivity level sites did. Eshopping experience strongly and positively influenced flow experience in terms of control and cognitive enjoyment, and moderately impacted attention focus. Cognitive enjoyment had a strong positive effect on site attitude and future purchase intentions. However, control and attention focus did not significantly affect future purchase intentions. The study found an indirect effect of eshopping behavior on site attitude, instead of the traditional effect of attitude on behavior based on the theory of reasoned action and technology acceptance model. The results of the pilot study (N = 105) were consistent with the final study (N = 310). The study attempts to add to the small base of existing studies that examine eshopping experience and flow theory in an ecommerce setting (Novak et al. 2003; Skadberg and Kimmel 2004). The present study contributes to the online consumer behavior literature by utilizing flow theory and investigating the mediating effects of eshopping experience and flow experience on the consequences of eshopping. The findings should help inform web site design, facilitating the creation of sites which are more responsive to users by providing interactive features and understanding eshopping behaviors which users exhibit.Item Lymphatic Functional Adaptations to Prolonged Changes in Mechanical Stimuli(2013-03-21) Nguyen, Tam LFluid drainage via the lymphatics prevents swelling due to excess fluid in interstitial space. Since interstitial fluid volume can vary dramatically, the function of lymphangions are rather dynamic so that they can contend with the wide ranges of lymph flow and pressure. Sharing with blood vessels an acute sensitivity to mechanical stresses, lymphangions could be expected to be similarly sensitive to prolonged changes in transmural pressure and flow. The purpose of this research was to quantify the adaptation of lymphangions to prolonged alterations in lymph hydrodynamics and to investigate how adaptation of individual lymphangions acts together within a network to affect the regulation of lymph flow. In project I, bovine postnodal mesenteric lymphatic vessels were partially occluded for three days, which divided the vessel into two segments. Both segments, therefore, were exposed to the same flow but different transmural pressures. In project II, an isometric preparation was employed to study developed wall tension in lymphangions exposed to mesenteric venous hypertension. In project III, an analytical model of a symmetrical lymphatic network was developed to investigate how its pressure-flow relationship emerges from the complex interaction of its pumping lymphangions. Results from this research indicate that lymphangions become stronger pumps when exposed to prolonged increases in transmural pressure, but exposure to prolonged venous hypertension attenuates lymphangion pumping. The main mechanism for lymphangion adaptation is the alteration of preload-dependent maximal tension developed by lymphatic muscle. Lower cytosolic Ca2+ concentration is likely to be the underlying cause for weaker developed tension. The analytical model suggests that the ratio of lymphangion systolic contractility to diastolic stiffness results in a differential response of lymph flow to changes in inlet and outlet pressures. This differential sensitivity to inlet and outlet pressures allows homeostatic responses to both microvascular and venous hypertension, and provides a framework for interpreting the functional implications of chronic lymphangion adaption.