No description available.

The increasing congestion on the roads in the United States of America has become a topic of much interest among the transportation planners. There is a limit to which there can be building of new highways. Thus, the thrust for better utilization of the existing facilities is gaining ground. This research project is aimed at a solution to problems of increasing travel times due to congestion. A case study of the toll road (Route 44) in the tidewater region of Virginia has been made as an example of the common method of relieving congestion, ridesharing, which is being encouraged. The failure of the proper maintenance of the HOV lanes on the Route 44 leading to the subsequent rescinding of the same has been looked into. The use of DYNAMO programming was made in order to simulate the conditions on the toll road and to get an idea of the various alternatives which could be used to take care of the problem. On the basis of the simulations carried out, and taking into account the views held by the commuters who did not form a part of the ridesharing community, a method in which authorities could give an advantage as far as travel time is concerned, has been proposed. / Master of Science

A finite element model is developed for multiphase flow through soil involving three immiscible fluids: namely air, water, and an organic fluid. A variational method is employed for the finite element formulation corresponding to the coupled differential equations governing the flow of the three fluid phase porous medium system with constant air phase pressure. Constitutive relationships for fluid conductivities and saturations as functions of fluid pressures which may be calibrated from two-phase laboratory measurements, are employed in the finite element program. The solution procedure uses iteration by a modified Picard method to handle the nonlinear properties and the backward method for a stable time integration. Laboratory experiments involving soil columns initially saturated with water and displaced by p-cymene (benzene-derivative hydrocarbon) under constant pressure were simulated by the finite element model to validate the numerical model and formulation for constitutive properties. Transient water outflow predicted using independently measured capillary head-saturation data agreed well with observed outflow data. Two-dimensional simulations are presented for eleven hypothetical field cases involving introduction of an organic fluid near the soil surface due to leakage from an underground storage tank. The subsequent transport of the organic fluid in the variably saturated vadose and ground water zones is analysed. / Ph. D.

Macroscopic fundamental diagram is the concept of the highest importance in traffic flow theory used for development of network-wide control strategies. Previous studies showed that so called Arterial Fundamental Diagrams (AFDs) properly depict relationships between major macroscopic traffic variables on urban arterials. Most of these studies used detector’s occupancy as a surrogate measure to represent traffic density. Nevertheless, detector’s occupancy is not very often present in the field data. More frequently, field data from arterial streets provide performance metrics measured at the stop lines of traffic signals, which represent a hybrid of flow and occupancy. When such performance measures are used in lieu of density, the outcomes of the relationships between macroscopic fundamental variables can be confusing. This study investigates appropriateness of using degree of saturation, as a representative surrogate measure of traffic density, obtained from an adaptive traffic control system that utilizes stop-line detectors, for development of AFDs. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2016. / FAU Electronic Theses and Dissertations Collection

There are many options available when selecting a computational model for two-phase flows. It is important to understand all the features of the model selected, including when the model is appropriate and how using it may affect your results. This work examines how volume displacement effects in two-phase Eulerian-Lagrangian models manifest themselves. Some test cases are examined to determine what input these effects have on the flow, and if we can predict when they will become important. Bubble injection into a traveling vortex ring is studied in-depth, as it provides significant insight into the physics of these volume displacement effects. When a few bubbles are entrained into a traveling vortex ring, it has been shown that even at extremely low volume loadings, their presence can significantly affect the structure of the vortex core (Sridhar & Katz 1999). A typical Eulerian-Lagrangian point-particle model with two-way coupling for this dilute system, wherein the bubbles are assumed subgrid and momentum point-sources are used to model their effect on the flow, is shown to be unable to accurately capture the experimental trends of bubble settling location, bubble escape, and vortex distortion for a range of bubble parameters and vortex strengths. Accounting for fluid volume displacement due to bubble motion, using a model termed as volumetric coupling, experimental trends on vortex distortion and bubble settling location are well captured. The fluid displacement effects are studied by introducing the notion of a volume displacement force, the net force on the fluid due to volumetric coupling, which is found to be dominant even at the low volume loadings investigated here. A method of quantifying of these forces is derived and used to study the effects for a wide range of particle to fluid density ratios in Taylor-Green vortices. A simple modification to the standard point-particle Lagrangian approach is developed, wherein the interphase reaction source terms are consistently altered to account for the fluid displacement effects and reactions due to bubble accelerations. / Graduation date: 2013 / Access restricted to the OSU Community at author's request from Sept. 24, 2012 - Sept. 24, 2013

University of Macau / Faculty of Science and Technology / Department of Electromechanical Engineering

The prediction of moisture and contaminant transport through unsaturated soil to ground water is becoming increasingly important in the fields of hydrology, agriculture and environmental engineering. Computer aided simulation techniques enables one to conduct a series of systematic numerical experiments to analyze flow phenomenon in subsurface hydrology under various physical and chemical processes. The flow movement depends upon medium characteristics, initial and boundary conditions, which reflect, physical processes occurring below the ground. To understand the effects of physical process an efficient and accurate model is needed. Thus the model developed must be able to handle varied initial and boundary conditions. In this regard, infiltration into a very dry soil becomes a very important problem of study. Most of the earlier numerical models developed are concentrated on the development of an efficient algorithm or the modelling of a particular process which govern the flow in unsaturated or saturated-unsaturated homogeneous medium. Not much work has been done on the analysis of variably saturated flow in layered soil medium. Models to simulate unsaturated flow through dry soils, especially through layered soils with varied boundary conditions are very limited. Further, not much studies have been reported in the literature on the prediction of seepage face development and the phreatic surface movement in variably saturated media with layering. These aspects are very important in determining the flow field and the discharge from the domain. A detailed literature review covering above aspects has been made and is reported in this thesis. In the present work, two dimensional numerical models to predict the movement of wetting front in unsaturated domain and the movement of the phreatic surface in homogeneous and layered porous media under various initial and boundary conditions are developed based on finite difference and finite volume techniques. These models can handle flow in both rectangular flow domains and radial flow domains. The initial condition settings include the handling of very dry soil medium without any transformation of the governing equation, handling of infiltration and constant head conditions at the boundaries under steady state as well as transient scenarios. The models are also able to handle various soil moisture characteristics which depict the nonlinear behaviour between hydraulic conductivity, moisture content and pressure head in a soil media. A mixed form of the governing partial differential equation is used in the present study as it leads to better mass conservation. The finite difference model uses a central difference approximation for the space derivatives and an Eulerian backward difference approximation for the time derivative. The fully implicit formulation is solved iteratively using Strongly Implicit Procedure after making Picard approximation for the highly nonlinear coefficients. The process of infiltration into an initially dry soil leads to the development of a steep wetting front. As the finite volume technique is naturally an upwind method, it is expected to play a positive role in modelling such processes accurately. Hence, a finite volume model is also developed by approximating the convective part using a MUSCL approach and a fully implicit central difference method for the diffusive part of the governing equation. The models developed are validated using both experimental data and numerical solutions for problems reported in the literature. The validation problems cover a wide range of physical scenarios such as: infiltration into a very dry soil, infiltration into a dry soil column with gravity drainage, development of water table mound, steady state drainage in a sand filled wedge shaped tank with seepage face development and transient seepage face development in a rectangular domain. Five test problems are used for the validation of the models. The developed models perform very well for the test problems considered, indicating the models' capability in handling such situations. The results obtained by using the present models for simulating flow through highly unsaturated (very dry) soils show that the models perform very well when compared with models which use transformation techniques to handle such problems. The performance of the present models in comparison with the experimental data and numerical models available in the literature show the suitability of the present models in handling such situations. The present models are also used to analyse various types of unsaturated flow problems with varying initial and boundary conditions. The boundary conditions considered are no flow and /or free flow conditions along the left, right and bottom boundaries with infiltration condition along a part of the top boundary. For the various cases considered in the present study, infiltration rate varies from 5 cm/day to 50cm/day through an initially very dry soil of -15000 cm pressure head in homogeneous and layered soils. Different types of soil media considered vary from sandy loam, loam and clay with horizontal and vertical layering of these soils. A total number of 14 cases are analysed. The results are discussed in terms of pressure head variation in the flow domain along with moisture redistribution for all the cases under consideration. It is observed from these studies that the infiltration rate play an important role on the wetting front movement through layered soils depending on the type of layering and the boundary conditions considered. The soil properties of various layers affect the movement of wetting front by changing the direction of movement. Even though the wetting front movement is predominantly vertical, there is a tendency for the wetting front to move in the horizontal direction as it moves from a coarse soil to fine soil. It is also observed that the vertical layering of soils with different hydraulic conductivity helps in redirecting the flow towards the bottom boundary through the neighboring coarser layers. As finite volume method is more suitable for simulating sharp fronts, it is expected to perform better than finite difference method for simulating infiltration into very dry soils. So, a comparison is made between the performance of these two models by using the above test problems. It is observed from these studies that the performance of both the models are same except that the finite volume method takes much more CPU time than the finite difference model. Considering the type of problems tested, it is observed that for modelling unsaturated and saturated-unsaturated flows, finite difference method is better in comparison to finite volume method. It may be due to the predominant diffusive characteristics of the governing equation even while modelling flow through very dry soils. Proper estimation of the seepage height is an important aspect in finding the discharge through the porous medium. It is observed from the literature that the use of a saturated flow model in such situations can lead to an underestimation of the discharge through the porous medium. This effect is more important when dealing with small dimension problems. It is also observed that various parameters which govern the moisture movement through saturated-unsaturated regions affect proper estimation of the seepage face height and there by discharge. Various factors like effect of boundary conditions, type of soil layering, problem dimension and aspect ratio on seepage face development and the associated phreatic surface formation is studied in the present work. It is seen from the present study that the seepage face development is more in rectangular flow domain than in radial flow domain for both homogeneous and layered soils. It is also seen that the seepage face development in rectangular problems are more sensitive than radial flow problems for various factors considered. The seepage height is also influenced by the tail water level. It is seen from the present study that as the tail water level increases the seepage face reduces with no seepage face development for some of the cases studied. This influence is relatively less for radial flow problems. As the length of the domain increases the seepage height decreases. It is seen that for different cases with same horizontal dimension, as the height of the domain increases the seepage face height also increases. This phenomenon is observed for both homogeneous and layered soil medium. The influence of the aspect ratio, which is the ratio of the length to height of the domain indicate that as the aspect ratio increases the seepage height decreases. The type of the soil layering is observed to have a very strong influence on the seepage face development. The study for understanding the effect of soil layering on the development of seepage face and phreatic surface suggest that as the coarseness of the material increases, the phreatic surface become flatter and its steepness increases with the fineness of the soil. The present model is also used for studying the transient phreatic surface movement and the seepage face development. This is studied for homogeneous and layered rectangular soil medium. The present study is used to understand the effect of specific storage on the phreatic surface movement and the seepage face development. The studies indicate that the influence of specific storage on the seepage face development is insignificant in homogeneous soils with only very little effect in the early time for longer domains. It is also observed that the influence of the specific storage is significant in the case of layered soils. This effect depends on the type of layering and the problem dimension and is observed to have influence for relatively longer period. This observation suggests the importance of specific storage on transient seepage face development. When the specific storage effect is considered the drainage of the soil become faster resulting in a faster decline of the phreatic surface with time. The influence of specific storage is also studied considering the problem dimension effect. It is seen that as the aspect ratio increases, the effect of specific storage on the phreatic surface development decreases. The studies with change in the upstream boundary condition from a constant head to a no flow condition indicate that the effect of specific storage has no significant influence on the phreatic surface development for both homogeneous and layered soils.

A quantitative understanding of ground water flow characteristics in unconfined aquifers is important because of the prevalence of abstraction from, and pollution of these systems. The current understanding of ground water flow in unconfined aquifers is limited because of the dominance of horizontal flow modelling strategies used to represent unconfined flow processes. The application of horizontal flow principles leads to an ignorance of seepage-face formation and can not predict the complicated three-dimensional nature of the ground water flow that dominates at the ground water-surface water interface. This study aims to address some of these deficiencies by exploring the true three-dimensional nature of ground water flow including the formation of seepage faces at the ground water-surface water interface using numerical and laboratory techniques. A finite element model for simulating two-dimensional (vertical) variably saturated flow is developed and benchmarked against standard laboratory and field-scale solutions. The numerical features of the finite element model are explored and compared to a simple finite difference formulation. The comparison demonstrates how finite element formulations lead to a broader spatial averaging of material properties and a different method for the representation of specified flux boundaries. A detailed comparison analysis indicates that these differences in the finite element solution lead to an improved approximation to the partial differential equation governing two-dimensional (vertical) variably saturated flow. A laboratory analysis of unconfined ground water flow and associated solute transport characteristics was performed. The analysis focused upon unconfined flow towards a pumping well. The laboratory observations were reliably reproduced using a three-dimensional (axi-symmetric), variably saturated ground water flow model. The model was benchmarked against the ground water flow characteristics such as the seepage-face height and total flow rate. In addition, the model was shown to reliably reproduce the solute transport features such as travel times and streamline distributions. This is the first time that a numerical model has been used to reliably reproduce the solute transport characteristics near a seepage-face boundary where the three-dimensional flow effects are prevalent. The ability to reliably predict solute transport patterns in the seepage-face zone is important since this region is known to support vital microbially facilitated reactions that control nutrient cycling and contaminant attenuation. The three-dimensional travel time distribution near the seepage-face was compared to that predicted using a horizontal flow modelling approach derived from the basic Dupuit-Forchheimer equations. The Dupuit-Forchheimer based model indicated that horizontal flow modelling would under-estimate the total residence time near a seepage-face boundary, thereby introducing a considerable source of error in a solute transport analysis. For this analysis, a new analytical solution for the steady travel time distribution in an unconfined aquifer subject to a single pumping well was derived. The analytical model has identified, for the first time in the hydrogeology literature, the use of the imaginary error function. The imaginary error function is a standard transcendental function and an infinite series approach to evaluate the function was successfully proposed. The two-dimensional (vertical) ground water flow model was extended to handle the case where the flow is driven by density gradients near the ground water-surface water interface. The unsteady, two-dimensional, Galerkin finite element model of density-dependent ground water flow in variably saturated porous media is rigorously presented and partially benchmarked under fully saturated (confined) conditions. The partial benchmarking involved reproducing solutions to the standard Henry salt-water intrusion and the Elder salt-convection problems. The model was used in a standard density-coupled and a new density-uncoupled mode to elucidate the worthiness of the Henry and Elder problems as benchmark standards. A comparison of the coupled and uncoupled solutions indicates that the Henry salt-water intrusion problem has limited worthiness as a benchmark as the patterns of ground water flow are relatively insensitive to density-coupled effects. Alternatively, the Elder problem is completely dependent upon a correct representation of the density-coupled flow and solute transport processes. The coupled versus uncoupled comparison is proposed as a new test of the worthiness of benchmark standards. The Henry salt-water intrusion problem was further analysed in an attempt to alleviate some of the difficulties associated with this benchmark problem. The numerical model was tested against a re-evaluated version of Henry's semi-analytical solution for the coupled solute concentration distribution. The numerical model was used to propose a modified version of the Henry problem where the importance of density-coupled processes was increased. The modified problem was shown to have an improved worthiness as compared to the standard solution. The numerical model results were benchmarked against a new set of semi-analytical results for the modified problem. Certain advantages in using the modified problem as a test case for benchmarking the results of a numerical model of density-dependent ground water flow are identified. A numerical investigation of the patterns of density-driven ground water flow at the ground water-surface water interface was undertaken. The numerical model is shown to produce grid-independent results for a finely discretised domain. The pattern of discharge is controlled, in part, by two parameters. One describes the recharge applied to the aquifer, and the second describes the magnitude of the density differences between the fresh recharging fluid and the saline receiving fluid. The influence of dense intrusions upon the formation of seepage-face boundaries at the ground water-surface water interface under steady-state conditions was also investigated. Dense intrusions are shown to dominate the pattern of ground water flow only under mild recharge conditions, while seepage faces dominate the outflow pattern under strong recharge conditions. Therefore, the formation of seepage-face boundaries and dense intrusions are unlikely to coincide under the conditions examined in this study.

[Truncated abstract] The lake boundaries are an important source of sediment, nutrients and chemicals. For life inside the lake, the exchange between the lake boundaries (littoral) and lake interior (pelagic) is of central importance to Limnology as the net flux of nutrients into the water column is both the driving force and limiting factor for most algae blooms found during the stratification period. Consequently, the understanding of the relevant processes defining such an exchange is a further step toward a sound basis for future decisions by lake managers in order to ensure high water quality. The objective of this research was to investigate the physical processes responsible for the exchange of water and particles between the lake boundaries and the lake interior. An integrated approach using field experiments and 3D modelling as applied to Lake Kinneret (Israel) is presented. The field data revealed large-scale metalimnion oscillations with amplitudes up to 10 m in response to westerly diurnal winds, the existence of a well-defined suspended particle intrusion into the metalimnion of the lake, characterized by high concentrations of organic matter, and a well-mixed benthic boundary layer (BBL). The changes in the thermal structure explained the observed vertical and horizontal movements of the suspended particle intrusion. The horizontal advective transport via the metalimnion, associated with the velocities induced by the basin-scale mode-two Poincare wave, controlled the exchange between the lake boundaries and lake interior on daily time scales. The observed BBL over the lake slope varied markedly with time and space. Detailed comparison of simulation results with field data revealed that the model captured the lake hydrodynamics for time scales from hours to days. The model could then be used to extract the residual motions in the various regions of the lake. The residual motions below the surface layer were predominantly forced by the basin-scale internal wave motions, but the residual motion in the surface layer was found to be very sensitive to the curl of the wind field. The residual circulation was responsible for redistributing mass throughout the lake basin on time scales from days to weeks. A clear connection of dynamics of the BBL with the large-scale features of the flow was addressed. The time history of the mixing in the BBL and the resulting cross-shore flux was shown to vary with the phase of the basin-scale internal waves.

Orientador: Janito Vaqueiro Ferreira / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-24T20:08:14Z (GMT). No. of bitstreams: 1 MartinezRicardo_DianaMarcela_M.pdf: 3485991 bytes, checksum: 9bd64ce80b2e1c25ed98644d4f52fd64 (MD5) Previous issue date: 2014 / Resumo: Este trabalho tem como objetivo desenvolver um processo de identificação da vazão de gás em um dos equipamentos usados na indústria petrolífera, às bombas centrífugas submersas (BCS) em regime de escoamento multifásico. Estas bombas apresentam falhas frequentes prematuras quando a vazão de gás é alta, as quais ocorrem por falta de informação do tipo de escoamento bifásico presente na bomba no tempo de operação. Por isto estudos de identificação experimental são requeridos nesta área. Neste contexto a presente pesquisa tem seu foco na obtenção de modelos mediante dados experimentais, recompilados diretamente da resposta do sistema que descrevem o comportamento da vazão de gás na planta de interesse, como: vibração, vazão, elevação entre outros. Estes modelos estão baseados na identificação não paramétrica e no algoritmo de aprendizagem de Máquina de Vetores de Suporte (SVM), onde os parâmetros ocultos da máquina de aprendizagem serão obtidos mediante algoritmos genéticos, visando obter modelos mais representativos / Abstract: This work develops a process to identify the flow of gas in one of the equipment used in the oil industry, the electric submersible pump (EPS) under multiphase flow. These pumps feature frequent premature failures when the gas flow is high. That occurs due to lack of information on the type of two ¿ phase flow in the pump in operation time. Experimental studies for this identification are required in this area. In this context, the present research focuses on obtaining models by experimental data collected directly from the system response which describes the behavior of the gas flow on the system of interest such as: vibration, fluid, elevation etc. These models are based on nonparametric identification and in learning algorithm support vector machine (SVM), where the hidden parameters of the learning machine will be obtained by genetic algorithms in order to obtain more representative models / Mestrado / Mecanica dos Sólidos e Projeto Mecanico / Mestra em Engenharia Mecânica