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1
Goz, Caglayan. "Instream Flow Methodologies: Hydrological Environmental Flow Assessment In Pazarsuyu River". Master's thesis, METU, 2012. http://etd.lib.metu.edu.tr/upload/12615004/index.pdf.
Testo completoAbstract (sommario):
In Turkey with increasing energy demand by industrialization and urbanization, hydropower seemed to be the most environmental friendly and sustainable solution for
the problem. However, hydropower has also environmental effects especially when hydropower projects are numerous on a single river, and they use almost entire water in
the river. Environmental flow as a new term became popular in media with increased density of small hydropower projects in Turkey. It is the required flow in the part of diversion for Run-off River type of hydropower plant in order to protect health of the riverin other words, to balance components of the river, including physico-chemical quality standards, surface and groundwater, geomorphological dynamics, social, economic, cultural and landscape values. In this study, an analysis utilizing hydrological (desktop) environmental flow assessment methods is prepared for Turkey, focusing on the Pazarsuyu Basin as a case study, and the results are compared with the applications done by the Governmental Institutions. Moreover, insufficient applications with regard to environmental flow assessment are given and reasons for public concerns are pointed out due to small hydropower development in Turkey.
2
Peng, Yong. "Lattice Boltzmann simulations of environmental flow problems in shallow water flows". Thesis, University of Liverpool, 2012. http://livrepository.liverpool.ac.uk/8233/.
Testo completoAbstract (sommario):
The lattice Boltzmann method (LBM) proposed about decades ago has been developed and applied to simulate various complex fluids. It has become an alternative powerful method for computational fluid dynamics (CFD). Although most research on the LBM focuses on the Navier-Stokes equations, the method has also been developed to solve other flow equations such as the shallow water equations. In this thesis, the lattice Boltzmann models for the shallow water equations and solute transport equation have been improved and applied to different flows and environmental problems, including solute transport and morphological evolution. In this work, both the single-relaxation-time and multiple-relaxation-time models are used for shallow water equations (named LABSWE and LABSWEMRT, respectively), and the large eddy simulation is incorporated into the LABSWE (named LABSWETM) for turbulent flow. The capability of the LABSWETM was firstly tested by applying it to simulate free surface flows in rectangular basins with different length -width ratios, in which the characteristics of the asymmetrical flows were studied in details. The LABSWEMRT was then used to simulate the one- and two-dimensional shallow water flows over discontinuous beds. The weighted centred scheme for force term, together with the bed height for a bed slope, was incorporated into the model to improve the simulation of water flows over a discontinuous bed. The resistance stress was also included to investigate the effect of the local head loss caused by flows over a step. Thirdly, the LABSWEMRT was extended to simulate a moving body in shallow water. In order to deal with the moving boundaries, three different schemes with second-order accuracy were tested and compared for treating curved boundaries. An additional momentum term was added to reflect the interaction between the following fluid and the solid, and a refilled method was proposed to treat the wetted nodes moving out from the solid nodes. Fourthly, both LABSWE and LABSWEMRT were used to investigate solute transport in shallow water. The flows are solved using LABSWE and LABSWEMRT, and the advection-diffusion equation for solute transport was solved with a LBM-BGK model based on the D2Q5 lattice. Three cases: open channel flow with a side discharge, shallow recirculation flow and flow in a harbour, were simulated to verify the methods. In addition, the performance of LABSWEMRT and LABSWE were compared, and the results showed that the LABSWMRT has better stability and can be used for flow with high Reynolds number. Finally, the lattice Boltzmann method was used with the Euler-WENO scheme to simulate morphological evolution in shallow water. The flow fields were solved by the LABSWEMRT with the improved scheme for the force term, and the fifth order Euler-WENO scheme was used to solve the morphological equation to predict the morphological evolution caused by the bed-load transport.
3
Regnier, Eva Dorothy. "Discounted cash flow methods and environmental decisions". Diss., Georgia Institute of Technology, 2001. http://hdl.handle.net/1853/24544.
Testo completo
4
Petsul, Peter Haei. "Micro-flow injection analysis for environmental studies". Thesis, University of Hull, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.322521.
Testo completo
5
Durham, William McKinney. "Phytoplankton in flow". Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/70868.
Testo completoAbstract (sommario):
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2012.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 111-120).
Phytoplankton are small, unicellular organisms, which form the base of the marine food web and are cumulatively responsible for almost half the global production of oxygen. While phytoplankton live in an environment characterized by ubiquitous fluid motion, the impacts of hydrodynamic conditions on phytoplankton ecology remain poorly understood. In this thesis, we propose two novel biophysical mechanisms that rely on the interaction between phytoplankton motility and fluid shear and demonstrate how these mechanisms can drive thin phytoplankton layers and microscale cell aggregations. First, we consider 'thin phytoplankton layers', important hotspots of ecological activity that are found meters beneath the ocean surface and contain cell concentrations up to two orders of magnitude above ambient. While current interpretations of their formation favor abiotic processes, many phytoplankton species found in these layers are motile. We demonstrate that layers can form when the vertical migration of phytoplankton is disrupted by hydrodynamic shear. Using a combination of experiments, individual-based simulations, and continuum modeling, we show that this mechanism - which we call 'gyrotactic trapping' - is capable of triggering thin phytoplankton layers under hydrodynamic conditions typical of the environments that often harbor thin layers. Second, we explore the potential for turbulent shear to produce patchiness in the spatial distribution of motile phytoplankton. Field measurements have revealed that motile phytoplankton form aggregations at the smallest scales of marine turbulence - the Kolmogorov scale (typically millimeters to centimeters) - whereas non-motile cells do not. We propose a new mechanism for the formation of this small-scale patchiness based on the interplay of gyrotactic motility and turbulent shear. Contrary to intuition, turbulence does not stir a plankton suspension to homogeneity, but instead drives patchiness. Using an analytical model of vortical flow we show that motility can give rise to a striking array of patchiness regimes. We then test this mechanism using both laboratory experiments and isotropic turbulent flows generated via Direct Numerical Simulation. We find that motile phytoplankton cells rapidly form aggregations, whereas non-motile cells remain randomly distributed. In summary, this thesis demonstrates that microhydrodynamic conditions play a fundamental role in phytoplankton ecology and, as a consequence, can contribute to shape macroscale characteristics of the Ocean.
by William McKinney Durham.
Ph.D.
6
Cappiello, Alessandra 1972. "Modeling traffic flow emissions". Thesis, Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/84328.
Testo completo
7
Banijamali, Bahareh. "Development of a flow-condition-based interpolation 9-node element for incompressible flows". Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/34642.
Testo completoAbstract (sommario):
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2006.Includes bibliographical references.
The Navier-Stokes equations are widely used for the analysis of incompressible laminar flows. If the Reynolds number is increased to certain values, oscillations appear in the finite element solution of the Navier-Stokes equations. In order to solve for high Reynolds number flows and avoid the oscillations, one technique is to use the flow condition-based interpolation scheme (FCBI), which is a hybrid of the finite element and the finite volume methods and introduces some upwinding into the laminar Navier-Stokes equations by using the exact solution of the advection-diffusion equation in the trial functions in the advection term. The previous works on the FCBI procedure include the development of a 4-node element and a 9-node element consisting of four 4-node sub-elements. In this thesis, the stability, the accuracy and the rate of convergence of the already published FCBI schemes is studied. In addition, a new FCBI 9-node element is proposed that obtains more accurate solutions than the earlier proposed FCBI elements. The new 9-node element does not obtain the solution as accurate as the Galerkin 9-node elements but the solution is stable for much higher Reynolds numbers (than the Galerkin 9-node elements), and accurate enough to be used to find the structural responses in fluid flow structural interaction problems. The Cubic-Interpolated Pseudo-particle (CIP) scheme is a very stable finite difference technique that can solve generalized hyperbolic equations with 3rd order accuracy in space.
(cont.) In this thesis, in order to solve the Navier-Stokes equations, the CIP scheme is linked to the finite element method (CIP-FEM) and the FCBI scheme (CIP-FCBI). From the numerical results, the CIP-FEM and the CIP-FCBI methods appear to predict the solution more accurate than the traditional finite element method and t;he FCBI scheme. In order to obtain accurate solutions for high Reynolds number flows, we require a finer mesh for the finite element and the FCBI methods than for the CIP-FEM and the CIP-FCBI methods. Linking the CIP method to the finite element and the FCBI methods improves the accuracy for the velocities and the derivatives. In addition, when the flow is not at the steady state and the time dependent terms need to be included in the Navier-Stokes equations, or in the problems when the derivatives of the velocities need to be obtained to high accuracy, the CIP-FCBI method is more convenient than the FCBI scheme.
by Bahareh Banijamali.
Ph.D.
8
Schneur, Rina. "Scaling algorithms for multicommodity flow problems and network flow problems with side constraits". Thesis, Massachusetts Institute of Technology, 1991. http://hdl.handle.net/1721.1/13710.
Testo completo
9
Murphy, Enda. "Longitudinal dispersion in vegetated flow". Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/34603.
Testo completoAbstract (sommario):
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2006.Includes bibliographical references (p. 171-183).
Vegetation is ubiquitous in rivers, estuaries and wetlands, strongly influencing both water conveyance and mass transport. The plant canopy affects both mean and turbulent flow structure, and thus both advection and dispersion. Accurate prediction of the fate and transport of nutrients, microbes, dissolved oxygen and other scalars depends on our ability to quantify vegetative impacts. In this thesis, the focus is on longitudinal dispersion, which traditionally has been modeled by drawing analogy to rough boundary layers. This approach is inappropriate in many cases, as the vegetation provides a significant dead zone, which may trap scalars and augment dispersion. The dead zone process is not captured in the rough boundary model. This thesis describes a new theoretical model for longitudinal dispersion in a vegetated channel, which isolates three separate contributory processes. To evaluate the performance of the model, tracer experiments and velocity measurements were conducted in a laboratory flume. Results show that the mechanism of exchange between the free stream and the vegetated region is critical to the overall dispersion, and is primarily controlled by the canopy density.
(cont.) A numerical random walk particle-tracking model was developed to assess the uncertainty associated with the experimental data. Results suggest that the time scale required to obtain sound experimental data in tracer studies is longer than the commonly used Fickian time scale.
by Enda Murphy.
S.M.
10
Assemi, Shoeleh 1963. "Use of flow field-flow fractionation for the characterisation of humic substances". Monash University, Dept. of Chemistry, 2000. http://arrow.monash.edu.au/hdl/1959.1/9028.
Testo completo
11
Duteau, Michel. "Phosphorus removal in a vertical up-flow constructed wetland". Thesis, McGill University, 2013. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=119504.
Testo completoAbstract (sommario):
Accelerated eutrophication of freshwater ecosystems led by agricultural activities has raised concerns in Southern Quebec and other industrialized locales. Phosphorus being the main culprit, effort has been made to rationalize application and curtail exports of this nutrient with agricultural best management practices. Still, concentrations of phosphorus and nitrogen in typical tile drainage return flow wastewater exceeds the eutrophication-prevention criterion set by the Quebec Ministry of Environment (0.030 mg TP ∙L-1) and the ecosystem safeguard criterion suggested in the literature (1.10 mg TN ∙L-1), with cumulative loads becoming a major contributor to the poor quality of downstream aquatic ecosystems, especially when poorly diluted, as is the case with heavily drained agriculture-dominated watersheds.As a third line of defense in a best management practices package, constructed wetlands (CWs) for the interception of phosphorus are proposed. These wetlands can also mitigate nitrogen and contribute other ancillary benefits. They can be implemented at the mouth of tile drainage or at the confluence of a few outlets, i.e. drainage ditches or first order streams.The main phosphorus removal mechanisms in a CW are adsorption and precipitation with positively charged ions contained in the substrate (e.g., Ca2+, Fe3+, Al3+). Physico-chemical conditions prevailing in the system – especially redox potential – are major factors influencing these reactions. A sub-surface vertical up-flow system seems most appropriate, as it maximizes potential interaction of pollutant-charged water with the substrate constituents, allowing full radial contact and deterring preferential flow. These wetlands also are efficient longer into the cold season, given the underground nature of the flow. An experiment was conducted on McGill's CW research site, situated in Ste-Anne-de-Bellevue, Québec, so as to ascertain the efficiency of a vertical up-flow constructed wetland in treating tile drainage return flow wastewater. During 14 weeks, the capacity to remove the different forms of phosphorus was evaluated, as was the removal of nitrogen compounds. The effluent quality was also compared to the criteria. The wetland had a dimension of 9.15 m2 and the target flow rate was 1 L∙min-1, which is representative of a drainage system serving a 3 ha field in typical Southern Quebec conditions (wetland:watershed ratio: 0.03%; hydraulic loading rate: 0.16 m∙d-1; hydraulic retention time: 2.99 days). The target influent concentrations were 0.300 mg TP ∙L-1, and 10.00 mg TN ∙L-1, which – again – is typical of Southern Quebec tile drainage return flow. The wetland was efficient at removing 84% TP and 86% TN, but the treated wastewater was still above the criteria in 76% and 69% of the cases for TP and TN, respectively.Recommendation is made to supplement the wetland with a dedicated phosphorus-removal substrate so as to further enhance its performance, and to increase the wetland:watershed surface ratio to abate more nitrogen compounds. Community support is key to the implementation of agricultural best management practices. Hence, suggestion is made to include constructed wetlands in the set of initiatives that are financially aided through governmental programs, such as Prime-Vert of Québec.L'eutrophisation accélérée des écosystèmes aquatiques dû aux activités agricoles donne lieu à des inquiétudes tant dans le Québec méridional que dans d'autres pays industrialisés. Le phosphore étant le principal coupable, des efforts importants ont été consentis à la réduction des exportations de ce nutriment, avec l'instauration de pratiques de gestion agricole optimales. Néanmoins, les concentrations de phosphore et d'azote dans les eaux usées de retour de drainage agricole typiques sont encore au-dessus des critères pour la prévention de l'eutrophisation (0.030 mg TP ∙L-1) et de maintien de la santé des écosystèmes aquatiques (1.10 mg TN ∙L-1), la charge cumulative étant un contributeur majeur à la piètre qualité des écosystèmes aquatiques situés en aval, en particulier lorsque peu diluée, comme c'est le cas par exemple dans les bassins versants à dominante agricole où le drainage est fortement présent. À titre de troisième ligne de défense dans la série de pratiques de gestion agricole optimales, les marais filtrants ciblant l'interception du phosphore sont proposés. Ces marais peuvent également atténuer l'azote et apporter des bénéfices collatéraux. Ils peuvent être installés à l'embouchure de drains agricoles, ou bien à la confluence de plusieurs sorties, comme par exemple dans un fossé agricole ou un cours d'eau d'ordre un. Les deux principaux mécanismes d'enlèvement du phosphore sont l'adsorption et la précipitation avec des ions à charge positive qui sont contenus dans le substrat (e.g., Ca2+, Fe3+, Al3+). Les conditions physico-chimiques qui règnent dans le système – en particulier le potentiel d'oxydo-réduction – sont des facteurs importants pouvant influencer ces réactions. Le système à flux vertical ascendant sous-surfacique est celui qui semble le plus approprié, puisqu'il maximise les interactions entre l'eau chargée de polluants avec les constituants du substrat, permettant un plein contact radial et prévenant les flux préférentiels. Ce type de marais est aussi efficace plus longtemps pendant la saison froide, étant donné la nature sous-surfacique du flux. Une expérience a été menée au site de recherche de l'Université McGill, situé à Sainte-Anne-de-Bellevue, au Québec, afin de vérifier l'efficacité d'un marais à flux vertical ascendant pour traiter les eaux usées de retour de drainage agricole. Pendant quatorze semaines, la capacité d'enlèvement du phosphore sous ses différentes formes a été évaluée, de même que l'enlèvement des composés azotés. La qualité de l'effluent traité a aussi été comparée aux critères de qualité. Le marais avait une surface de 9.15 m2 et le débit cible était de 1 L ∙min-1, ce qui est représentatif d'un système de drainage desservant un champ de 3 ha dans les conditions typiques du Québec méridional (ratio bassin versant:marais filtrant : 0.03%; charge hydraulique : 0.16 m∙d-1; temps de rétention hydraulique : 2.99 jours). Les concentrations cibles dans l'affluent étaient de 0.300 mg TP ∙L-1 et 10.00 mg TN ∙L-1, ce qui – encore là – correspond à un retour de drainage agricole dans les conditions du Québec méridional. L'efficacité du marais est telle qu'un enlèvement de 84% du phosphore total et 86% de l'azote total a été observé, mais l'effluent traité outrepassait encore les critères dans 76% et 69% des cas pour ce qui est du phosphore total et de l'azote total, respectivement. Il est recommandé d'ajouter au marais un substrat dédié à l'enlèvement du phosphore, afin de renforcer la performance, ainsi que d'augmenter le ratio surfacique marais filtrant:bassin versant, afin de diminuer davantage les composés azotés. Le support par la communauté est un élément clé dans l'instauration de pratiques de gestion agricole optimales. Ainsi donc, il est suggéré d'inclure les marais filtrants dans l'ensemble d'initiatives qui sont financièrement appuyées par les programmes gouvernementaux, tels le programme Prime-Vert au Québec.
12
Aref, Lana A. 1971. "Flow and transport in wetland deposits". Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/9504.
Testo completoAbstract (sommario):
Thesis (Sc.D.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 1999.Includes bibliographical references.
At present, very little is known about the mechanisms that control flow and transport through wetland deposits. Therefore, the objective of this research was to investigate the factors that influenced flow in wetland soils. To accomplish this, Column Experiments, run on a specialized permeameter, were conducted on both re-sedimented and undisturbed wetland soil specimens. During these experiments, sodium chloride (NaCl) tracer was injected into the soil specimen, and its breakthrough was monitored concurrently with other parameters, such as flow velocity and hydraulic gradient. Subsequently, the breakthrough data collected during the Column Experiments were fit using both the One-Region and Two-Region transport models, and the fit results were analyzed and compared to the geotechnical data collected for the soil. The data collected during the experimental program indicate enormous complexity in the mechanisms controlling flow and transport through wetland soils. From their analysis the following observations were made: First, even though wetland soils are considered to be two-region soils, having both an effective and an immobile porosity, the One-Region model was able to describe Sodium Chloride breakthrough in the soil. This indicates that the NaCl tracer was not interacting with the immobile region of the specimen. Second, the results demonstrated that wetland soil hydraulic conductivity is highly variable and sensitive to volume of flow. In fact, hydraulic conductivity was seen to decrease irreversibly by up to 6% per pore volume of flow. It was also found that hydraulic conductivity was sensitive to increases in pore water salt concentration, and to the flushing out of salts from wetland specimens. Finally, it was observed that, for the most part, large changes in hydraulic conductivity did not correspond to changes in the specimen's effective pore size or pore distribution. In fact, unless salt concentrations were increased drastically, the effective pore space remained invariant over an order of magnitude change in soil hydraulic conductivity. This suggests that changes in soil hydraulic conductivity might be due to increases or decreases in the number of flow channel constrictions in a specimen. From the results of this research it is hypothesized that the number of flow channel constrictions increased when flow and a decrease in salt concentration mobilized organic and mineral particles, which collected and clogged narrow pore throats along the flow channels. It is also hypothesized that the number of flow channel constrictions decreased when increases in pore water salt concentration causect organic fibers along the flow channel walls to coil.
by Lana A. Aref.
Sc.D.
13
Lagerblad, Lovisa. "Assessment of environmental flow requirements in Buzi River basin, Mozambique". Thesis, Uppsala universitet, Institutionen för geovetenskaper, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-150870.
Testo completoAbstract (sommario):
Rivers belong to the world’s most complex ecosystems but increasing demands for water are degrading rivers worldwide. The increase in human populations and activities has resulted in an intense and difficult conflict between the development of rivers as a natural resource and their function as living ecosystems. It is now widely recognized that a naturally variable flow regime is required to sustain freshwater ecosystems. Many countries that experience river degradation have started to implement environmental flows, i.e. the unallocated flow purposely preserved in a river. The objectives of this thesis are twofold. The first aim is to briefly describe the concept and science of environmental flows and the different methodologies for calculating environmental flows. This was done based on a literature review of the subject. The second aim is to present a case study calculating the environmental flow requirements. The case study was conducted through a field study in the Buzi River basin in Mozambique and the subsequent modeling of the environmental flow requirements. The literature study showed that not only the quantity of water is important; the timing and frequency of floods, droughts, low flows and high flows are very important as well. The literature study also showed that the advances in environmental flow science have been remarkable while the water policy and management has not been equally successful in implementing environmental flow standards. The calculation of environmental flow requirements was done with the Desktop Reserve Model developed in South Africa. The results indicated that to maintain the ecological status in the Buzi River at a largely natural condition (ecological category A) an average allocation of 57 % of mean annual runoff (MAR) is required. The present ecological status was determined in Revue River, which is one of the three major tributaries to Buzi River. To maintain the Revue River at its present ecological state requires an environmental flow between 23-37 % of MAR. The major environmental threats in Revue River are erosion and flow modification. The erosion is a consequence from artisanal gold mining, inadequate farming practices and deforestation. The flow alterations are caused by the large Chicamba Dam constructed for the generation of hydropower. One of the questions this thesis aimed to answer was if it was possible to set the present ecological state with a limited amount of data. This study showed that it could be possible but that the confidence level will be low. The relationships between ecological metrics and flow alterations must be investigated in detail for this region before environmental flow requirements can be successfully calculated and implemented.Floder hör till jordens mest komplexa och känsliga ekosystem, men ett ökat tryck på våra vattenresurser har försämrat situationen för många av världens floder. Befolkningsökningen och den globala utvecklingen har resulterat i en intensiv och komplicerad konflikt mellan utnyttjandet av floder som en naturresurs och bevarandet av deras funktion som unika ekosystem. Det är nu allmänt accepterat att den naturliga flödesvariabiliteten behövs för att bevara våra sötvattenekosystem. Flera länder där försämringen av floder är ett faktum har börjat införa miljöanpassade flöden, det vill säga vatten som medvetet tilldelas flodens ekosystem. Det finns två syften med det här examensarbetet. Det första är att genom en litteraturstudie beskriva miljöanpassade flöden och de modeller som används för att beräkna detta flöde. Det andra målet är att göra en fallstudie och beräkna det miljöanpassade flödet och bestämma den ekologiska statusen för Buzi floden i Moçambique. Litteraturstudien visade att det inte bara är kvantiteten av vatten som är viktigt; tidpunkt och återkomsten av översvämning, torka, lågflöden och högflöden är mycket viktiga om man vill efterlikna det naturliga flödet. Litteraturstudien visade även att framstegen i kunskapen om miljöanpassade flöden har varit stora medan vattenlagstiftningens anpassning och införandet av miljöanpassade flöden har varit svag i flera avseenden. Modellerandet gjordes med den sydafrikanska Desktop Reserve Model. Resultaten från modellen visade att för att bibehålla den ekologiska statusen för Buzi floden i ett nära naturligt stadium (ekologisk klass A) krävs en tilldelning på 57% av medelårsavrinningen. Den nuvarande ekologiska statusen bestämdes i Revue floden, som är en av tre huvudfloder i Buzi avrinningsområdet. För att behålla Revue floden i sitt nuvarande tillstånd skulle kräva ett miljöanpassat flöde på mellan 23-37% av medelårsavrinningen. De största ekologiska hoten i Revue floden visade studien var erosion och flödesförändringar. Erosionen är en konsekvens av guldutgrävning, jordbruk med fel teknik, och skogsavverkning. Flödesförändringarna härrör från den stora vattenkraftsstationen Chicamba Dam. En av frågorna den här studien syftade till att besvara var om det är möjligt att bestämma den nuvarande ekologiska statusen med en begränsad tillgång till data. Studien visade att det är möjligt men att osäkerhetsnivån i resultatet kommer att vara stort. Studien visade även att modellen Desktop Reserve Model kan användas för snabba beräkningar av det miljöanpassade flödet, men att mer utförliga studier som till exempel Building Block Methodology måste genomföras innan resultatet med säkerhet kan verifieras. Relationen mellan ekologiska förändringar och flödesvariationer måste utredas i detalj för studieområdet innan de miljöanpassade flödesbehoven kan bli implementerade med framgång.
14
Hayes, Michael F. (Michael Francis). "Stimulating In situ groudwater bioremidiation via sparging : gas flow, groundwater flow, and mass transfer in the biosparge zone". Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/38755.
Testo completo
15
Follett, Elizabeth (Elizabeth Marie). "Feedbacks between plants, flow, and particle fate". Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/104199.
Testo completoAbstract (sommario):
Thesis: Ph. D., Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, 2016.Cataloged from PDF version of thesis.
Includes bibliographical references.
Environmental flows carry a wide variety of particles that interact with vegetation. Vegetated canopies are anchored by sediment, release pollen and seeds to colonize new ground, rely on nutrients carried by sediment, and may be killed by disease spores. While the influence of vegetation on flow profiles has been investigated, the transport of particles within vegetated canopies remains poorly understood. In this thesis I present the results from laboratory experiments and numerical modeling that investigated particle fate and transport around emergent and submerged model vegetation canopies. The effect of canopy mediated flow on particle transport was explored in experimental studies using model vegetation. First, the flow diversion and extended wake region due to a circular patch of model reedy emergent vegetation resulted in regions of scour on the patch side and deposition in the patch wake, which are related to a non-dimensional flow blockage parameter. In-patch scour increased with turbulent kinetic energy levels, which were positively correlated to stem density. Second, within a long, submerged canopy, the capture of particles was reduced near the leading edge due to the presence of a vertical updraft. In the fully developed region, particle capture was increased for releases below the penetration of canopy scale vortices, and for particles with increased settling velocity. The impact of canopy flexibility on turbulence within the canopy was explored using a submerged canopy of model flexible vegetation. The drag reduction due to reconfiguration was described through a drag coefficient that decreased as a power-law function of velocity, with a negative exponent (Vogel number). Velocity measurements made within and above the canopy demonstrate that unsteady reconfiguration, responding to individual turbulent events, preferentially allows stronger sweeps to penetrate the canopy, enhancing the skewness. Next, spore escape was investigated across a range of canopy densities and particle settling velocities using a random displacement model (RDM) parameterized with an eddy diffusivity based on a simple set of physical parameters. This work filled a gap between field observations and traditional Lagrangian stochastic modeling, improving predictions of fungal spore escape to drive long range transport models. The effect of canopy and particle characteristics on the genotypic diversity of Zostera marina canopies was explored, pointing to the physical mechanisms governing successful pollination.
by Elizabeth M. Follett.
Ph. D.
16
Stolp, Bernard Jan. "Determining mean transit times of groundwater flow systems". Thesis, The University of Utah, 2014. http://pqdtopen.proquest.com/#viewpdf?dispub=3614458.
Testo completoAbstract (sommario):
Water is the elementary component of life on Earth, and quantifying this resource is critical to understanding ecosystem viability on planetary, continental, and local scales. In a simplified partition of the Earthfs freshwater resources, 75% is ice at the north and south poles, 25% is groundwater, and 0.01% exists in lakes and streams. Mean transit time is a robust description of groundwater volume within the discrete aquifers that together make up the 25% of Earthfs freshwater. Mean transit time can be estimated using environmental tracer concentrations in springs and gaining streams. That is because springs and streams are locations where groundwater flow paths naturally converge. Converging flowpaths create discharge that is a flow]weighted mixture of water from the contributing aquifer. The age of that flow-weighted mixture is a good measure of the mean transit time of water as it discharges from the contributing aquifer. Mean transit time can be directly used to estimate the volume of groundwater storage in the aquifer.
Although simple in principle, there are several important topics that need to be considered when collecting and dating a broad mixture of flow paths. They include 1) the necessity for a basic conceptual perception of the investigated aquifer, 2) the non-conservative aspect of most age-dating environmental tracers once exposed to the atmosphere, and 3) the importance of estimating a transit-time distribution. These specific topics are discussed in this dissertation.
17
Karhunen, A. (Antti). "Traffic Flow Garner -rajapinnan hyödyntäminen liikennevalojärjestelmän liikenneteknisessä seurannassa ja kehittämisessä". Master's thesis, University of Oulu, 2016. http://urn.fi/URN:NBN:fi:oulu-201604061380.
Testo completoAbstract (sommario):
Liikennevalot ovat keskeinen osa liikenneverkon toiminnallisuutta. Tällä hetkellä liikennevalojen liikenneteknisen toiminnan seurantaan ei ole olemassa erityisen hyviä laajoja alueita käsittäviä ja pitkäaikaiseen seurantaan soveltuvia työkaluja tai automatisoituja toimintoja. Liikennevalotietoja välittävä Dynniq:n kehittämä Traffic Flow Garner (TFG) -rajapinta antaa aivan uuden mahdollisuuden liikennevaloliittymien seurantaan. Sen välittämä yksityiskohtainen reaaliaikatieto sisältää opastinryhmien ja ilmaisimien tilatiedot sekä konfiguraatiotiedot, joista voidaan laskea useita sekä liikennevalojen että liikenteen toimivuuden tunnuslukuja. Tässä työssä tutkittiin liikenneteknisten tunnuslukujen laskentaa TFG-rajapinnan välittämästä tiedosta. Tarkempaan tarkasteluun valittiin kaksi Oulussa sijaitsevaa liikennevaloliittymää, joista toista tarkkailtiin myös maastossa. TFG-rajapinnan datasta laskettuja tunnuslukuja verrattiin maastossa havaittuun liikennetilanteeseen. Työssä tutkittiin seuraavia liikenneteknisiä tunnuslukuja: - Liikennemäärät - Ilmaisimen varausaste ja yhtäjaksoinen varausaika - Jonopituus - Maksimiodotusaika jonossa kiertoina (hetkellinen tarjonnan ja kysynnän suhde) - Kuormitusaste - Ohjausviive - Palvelutaso - Poistuminen läsnäoloilmaisimelta punaisen aikana - Vihreällä saapuvat ja liittymän läpäisevät ajoneuvot - Vihreän loppuminen kesken - Turha vihreä aika Rajapinnasta lasketut tunnusluvut vastasivat todellista liikennetilannetta hyvin. Kaistan ominaisvälityskyky vaikuttaa kuitenkin voimakkaasti useiden tunnuslukujen laskentaan. Se arvioitiin kaistoittain kaistatyypin mukaan aikaisempien tutkimusten perusteella. Kun kaistalla ei ollut väistettävää suojatietä, oli ominaisvälityskyvyn arviointi helpompaa ja tulokset parempia. Esimerkiksi minuuttikohtainen maksimijonopituus vastasi maastossa havaittua jonopituutta tällöin hyvin. Maksimijonopituus ei vastannut yhtä hyvin todellista, kun kaistalla oli väistettävä suojatie. Se oli kuitenkin oikeassa enimmäkseen oikeassa suuruusluokassa. Parhaiten hetkellistä toimivuutta kuvasivat jonopituus ja siitä johdettu maksimiodotusaika jonossa. Ne kuvaavat hyvin tienkäyttäjän kokemusta liikennetilanteesta ja liittymän toimivuudesta. 15 minuutin ja sitä pidempien tarkastelujaksojen toimivuutta kuvasivat parhaiten kuormitusaste, ohjausviive ja palvelutaso. Muiden tunnuslukujen avulla voidaan arvioida mm. vihreän aallon toimivuutta, vihreän pituuden riittävyyttä ja turhaa vihreää aikaa. Työssä määritettiin myös laskettujen tunnuslukujen tallentamista tietokantaan ja liikenneteknisen seurantajärjestelmän käyttöliittymän ominaisuuksia. Työn tulosten pohjalta on tarkoitus toteuttaa liikennevalojen liikennetekninen seurantajärjestelmä. Reaaliaikaisen liikenneteknisen seurannan myötä liikenteestä saadaan kattavaa laskennallista tietoa pistemäisten tai subjektiivisten havaintojen sijaan. Sen myötä muutokset liikennevalojen ohjauksessa perustuvat selvästi luotettavampaan näkemykseen liikenneverkon tilasta. Tienpitäjä voi laskettujen tunnuslukujen perusteella parantaa liikennevalojen ylläpidon tasoa ja myös todeta muutosten vaikutuksen. Lisäksi seurannassa voi olla automaattisia hälytyksiä poikkeuksellisista tilanteista, joiden havaitseminen muutoin olisi vaikeaa tai mahdotonta. Reaaliaikainen liikennetekninen seuranta mahdollistaa myös liikenteen reaaliaikaisen tilannekuvan tienpitäjälle ja sovellusten kautta myös suoraan tienkäyttäjälleTraffic signals are an essential part of the functionality of the traffic network. At the moment there are no especially good tools or automated functions for monitoring the performance of traffic signals in wide areas and for long periods of time. Traffic Flow Garner (TFG) is an interface developed by Dynniq that transmits traffic signal data. It gives a new opportunity to monitor signalled intersections. Its real time data includes the status of signal groups and detectors and configuration data of the intersection. Several performance measures of traffic signals and traffic can be calculated from the data. Calculation of performance measures was studied from the data transmitted by the TFG interface. Two signalled intersections in Oulu were chosen for closer examination. One of them was also monitored at the location. Performance measures calculated from the TFG data were compared with the observed situation at the location. The following performance measures were studied in this thesis: - Traffic volumes - Proportion of detector occupancy and continuous occupancy time - Queue length - Maximum waiting time in queue in cycles (the momentary relation of a supply and demand) - Volume to capacity ratio - Control delay - Level of service - Driving away from the presence of the stop bar detector during red - Proportion of vehicles that arrive and leave the intersection during green - Green ending too early - Unnecessary green time The calculated performance measures corresponded well to the perceived traffic situation. However, the saturation flow rate of the lane affects the calculation of several measures strongly. It was estimated according to the lane type based on earlier studies. When there was no pedestrian crossing to be yielded, estimation of the saturation flow rate was easier and the results were better. Then, for example, the maximum queue length per minute corresponded well to the queue length that was perceived at the location. The maximum queue length did not correspond equally well to the perceived when there was a pedestrian crossing had to be yielded. However, it was mostly in the correct order. Momentary performance was best described by queue length and maximum wait time in queue. They describe well how a road user experiences the traffic situation and performance of the intersection. Performance of periods of 15 minutes and longer was best described by volume to capacity ratio, control delay and level of service. Other measures may be used to estimate, among others, the functionality of the green wave, the adequacy of the green time and unnecessary green time. Properties of storing the calculated measures into a database and properties of the user interface of the traffic performance monitoring system were specified. A performance monitoring system of traffic signals is intended to be implemented based on the results of this thesis. With real-time performance monitoring of traffic signals comprehensive computational information could be obtained instead of spotty or subjective observations about the traffic. Thanks to it changes in programming of traffic signals could be based on a distinctly more reliable view on the state of the traffic network. The road administrator could improve the level of the maintenance of traffic signals based on the calculated measures. It is also possible to observe the effects of changes in programming. Furthermore, automatic alarms could be used for exceptional situations that would otherwise be difficult or impossible to notice. Real-time monitoring enables the road administrator and, through applications, road users to have real-time understanding about the traffic situation
18
Crouthamel, David Roger 1963. "In-situ flow testing of borehole plugs". Thesis, The University of Arizona, 1991. http://hdl.handle.net/10150/291331.
Testo completoAbstract (sommario):
A cement borehole plug and a crushed tuff/bentonite clay mixture borehole plug were tested insitu in highly welded tuff. The hydraulic performance of the cement plug was evaluated through steady-state and transient hydraulic tests with a hydraulic conductivity in the range of 10⁻¹⁰ cm/s. A crushed tuff/bentonite mixture plug was tested through a steady-state flow test with a measured hydraulic conductivity of 10⁻⁹ cm/s. The plug was installed in a fractured borehole which was grouted to reduce the overall rockmass permeability. Installation procedures were evaluated in the laboratory prior to field installation. Installation of the cement seal with a bailer indicated seal degradation with water present in the borehole. Degradation appeared as piping, both internal and along the interface, and mixing of the cement with the water. Tests on the mixture seal indicated the need for homogeneous placement and adequate compaction to resist internal water piping and channelling.
19
Autret, Arnaud. "Modular neural networks for analysis of flow cytometry data". Thesis, University of South Wales, 2003. https://pure.southwales.ac.uk/en/studentthesis/modular-neural-networks-for-analysis-of-flow-cytometry-data(49f3349b-e86a-4bfb-a689-c853323b6f2d).html.
Testo completoAbstract (sommario):
In predicting environmental hazards or estimating the impact of human activities on the marine ecosystem, scientists have multiplied the need for sample analysis. The classical microscopic approach is time consuming and wastes the talent and intellectual abilities of trained specialists. Therefore, scientists developed an automated optical tool, called a Flow Cytometer (FC), to analyse samples quickly and in large quantities. The flow cytometer has successfully been applied to real phytoplankton studies. However, analysis of the data extracted from samples is still required. Artificial Neural Networks (ANNs) are one of the tools applied to FC data analysis. Despite several successful applications, ANNs have not been widely adopted by the marine biologist community, as they can not possible to change the number of species in the classification problem without retraining of the full system from scratch. Training is time consuming and requires expertise in ANNs. Moreover, most ANN paradigms cannot cope effectively with unknown data, such as data coming from new phytoplankton species or from species outside the scope of the studies. This project developed a new ANN technique based on a modular architecture that removes the need for retraining and allows unknowns to be detected and rejected. Furthermore, the Support Vector Machine architecture is applied in this domain for the first time and compared against another ANN paradigm called Radial Basis Function Networks. The results show that the modular architecture is able to effectively deal with new data which can be incorporated into the ANN architecture without fully retraining the system.
20
Kassab, Bassam George 1968. "Flow of grains in channels : the granualr jump". Thesis, Massachusetts Institute of Technology, 1999. http://hdl.handle.net/1721.1/80916.
Testo completoAbstract (sommario):
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, February 2000.Includes bibliographical references (leaves 52-53).
by Bassam George Kassab.
S.M.
21
Zhang, Xin Ph D. Massachusetts Institute of Technology. "Modeling transient flow in intermittent water supply System". Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/111551.
Testo completoAbstract (sommario):
Thesis: S.M., Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, 2017.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 91-96).
Water distribution systems in cities throughout South Asia (and many other countries) only supply water on an intermittent basis (currently averaging less than 5hrs/day in most Indian cities). Intermittent Water Supply (IWS) creates inequities in water availability and carries public health risks associated with the ingress of contaminants from the surrounding ground through flaws in the aged piping systems. It is a major challenge to upgrade from intermittent to continuous water supply (CWS) as this involves an increase in the operating water pressures which promotes higher rates of leakage. There are currently no reliable computational models for characterizing the transient hydraulic behavior of IWS systems (including pipe filling and draining events) and hence, it is difficult to understand and control IWS systems. In a recent PhD thesis, Lieb (2015) developed an open-source code to solve the dynamics of IWS pipe networks through finite volume solution of the governing 1-D Saint Venant equations using the Preismann slot approximation. The current thesis extends and refines the algorithms proposed by Lieb to enable more robust simulations for pipe networks. Specific modification include algorithms for dry pipes and three-pipe junctions. The thesis proposes a new algorithm for representing the conservation of fluid mass, momentum and energy at a three-pipe junction which is validated by comparing computed loss coefficients with measured data reported in the literature. The research also validates predictions of mixed flow conditions (open-channel and pressured pipe flow conditions) with results from laboratory model tests. The proposed formulation has been applied to simulate a skeletonized pipe network (at a test site in Delhi), where simulations are compared with water pressures during intermittent water supply periods. The proposed analysis represents a first step towards comprehensive modeling of IWS that can be used to improve understanding and control of these systems and to manage the upgrading process for CWS operations.
by Xin Zhang.
S.M.
22
Essiam, Albert K. "Stochastic flow and transport through multifractal porous media". Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/84301.
Testo completoAbstract (sommario):
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2001.Includes bibliographical references.
Stochastic theories of flow and transport in aquifers have relied on the linear perturbation approach that is accurate for flow fields with log-conductivity variance cr2 less than unity. Several studies have found that the linear perturbation ignores terms that have significant effects on the spectra of the hydraulic gradient VH and specific discharge q when (Y2 exceeds unity. In this thesis we study flow and transport when the hydraulic conductivity K is an isotropic lognormal multifractal field. Unlike the perturbation approach, results obtained are nonlinear even though several simplifying assumptions are made. The spectral density of F = in (K) for this type of field is SF (k) o kl-D where D is the space dimension. It is found that under this condition, the hydraulic gradient VH and specific discharge q are also multifractal; whose renormalization properties under space contraction involve random scaling and random rotation of the fields. Analytical expressions that are functions of D and the codimension parameter of F, CK 'are obtained for the renormalization properties and marginal distributions of VH and q . Because of the boundary conditions, the fields VH and q are anisotropic at large scales but become isotropic at very small scales. The mean specific flow decreases as the scaling range of F increases, at a rate that is dependent on D and CK. Flow simulations on a plane validate the analytical results. The multifractal properties of VH and q are used to derive their spectral density tensors, the macrodispersivities, and the effective conductivity of the medium. The spectra obtained account for the random rotation of the VH and q at smaller scales. Spectra for VH and q are anisotropic at large scales but become isotropic at small scales.
(cont.) The scale of isotropy depends on D and CK. The linear perturbation approach does not capture this important feature and further gives incorrect amplitudes and power decays of the spectral density tensors. Using the spectra of q the macrodispersivities are computed and compared with results from the linear perturbation approach. Reflecting the properties of the spectral density of q, the macrodispersivities for the nonlinear theory are isotropic at small travel distances and are anisotropic at large travel distances. In the ergodic case when the spatial averages of all fields of interest are close to their ensemble averages, it is found that our expression for effective conductivity Keff corresponds to a formula conjectured by Matheron [1967]. Using the scaling properties of the inverse of the velocity field (also known as slowness), we derive expressions for the first passage time distribution FPTD and mean plume concentration for transport in a multifractal K field. The theoretical results of FPTD for the nonlinear theory are fitted by regression methods to data from field experiments and from numerical simulations and compared with results from the continuous time random walk CTRW and two-phase transport model. Results of the nonlinear theory are found to be more suitable for predicting non-Fickian transport. The CTRW model is more suited for transport in statistically inhomogeneous media. Both the CTRW and two-phase models are suitable for modeling Fickian transport ...
by Albert Essiam.
Ph.D.
23
Cheng, Zhao 1969. "Flow problems in air venting and air sparging". Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/9593.
Testo completoAbstract (sommario):
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 1998.Includes bibliographical references.
Soil Vapor Extraction (SVE) and Air Sparging have been used for site remediation for about ten years, but most of the past designs are based on experiences and numerical models. Understanding toward the physical problems is far from complete, and some simplified assumptions used in those models may not be true. In this thesis, we focus our attention on the hydrodynamic problems in SVE and air sparging. In Chapter One some basic concepts related to the fl.ow problem in the porous media such as soil are introduced, and previous models for SVE and air sparging are reviewed in some detail. The SVE model is derived in Chapter Two. Specifically we examine the water table rise during SVE. In Chapter Three, A mathematical model for steady state air sparging is describe. Unlike previous models(Van Dijke et al, 1995), the air phase compressibility is accounted for. Numerical methods are used to solve the governing equations. Results are compared with two dimensional laboratory experiment(Ji et al, 1993) and field data(Lundegard, 1995). The most important parameter in air sparging system design is the Radius Of Influence(ROI) of the sparging well{McCray 1997). Computations are performed to reveal the relationship between ROI of a sparging well to other parameters such as air sparging pressure, well screen length, soil properties etc,. Air sparging is typically used in conjunction with a soil vapor extraction system to collect the volatilized compounds above the water table. The use of air sparging results in a net positive pressure in groundwater, and can lead to contaminant migration to previously uncontaminated areas. In Chapter Four, we discussed the coupling effects of SVE and air sparging system. Some interesting phenomena are revealed and discussed.
by Zhao Cheng.
S.M.
24
Hernandez-Ochoa, Abel F. "Conditioning nonlocal steady-state flow on hydraulic head and conductivity through geostatistical inversion". Diss., The University of Arizona, 2003. http://hdl.handle.net/10150/280279.
Testo completoAbstract (sommario):
Nonlocal moment equations allow one to render optimum predictions of flow in randomly heterogeneous media deterministically conditional on measured values of medium properties and to assess the corresponding predictive uncertainty. I present a geostatistical inverse algorithm for steady-state flow that makes it possible to further condition such predictions and assessments on measured values of hydraulic head and (or) flux. My algorithm is based on recursive finite-element approximations of exact first and second conditional moment equations. Computational efficiency is enhanced through the use of a direct sparse matrix solver. Hydraulic conductivity is parameterized via universal kriging based on unknown values at pilot points and (optionally) measured values at other discrete locations. Correlation among parameter estimates (or priors) is considered in the universal kriging equations. Optimum unbiased inverse estimates of natural log hydraulic conductivity, head and flux are obtained by minimizing a calibration criterion, composed of residuals of head or (and) flux and (possibly) log conductivity, using the Levenberg-Marquardt algorithm. Statistical parameters characterizing the natural variability of hydraulic conductivity can also be estimated using this algorithm. I illustrate the method for superimposed mean uniform and convergent flows in a bounded two-dimensional domain under various conditions for a range of parameters. My examples illustrate how conductivity and head data act separately or jointly to reduce parameter estimation errors and model predictive uncertainty. Over-parameterization is seen to create zones of high mean conductivity, in which flux prediction is more uncertain than is in other regions. It is found that a regular distribution of pilot points works better than does an irregular layout and that the number of pilot points should be as close as possible to the number of head data while maintaining parameters reasonably uncorrelated. Head and flux predictions are very satisfactory for cases with either log conductivity variance or integral scale between one and four, though prediction quality deteriorates with either larger variances or shorter integral scales. The method may perform satisfactorily in cases with no conductivity measurements and only a few head data.
25
Savoie, Courtney Beth Young. "Arsenic Mobility and Compositional Variability in High-Silica Ash Flow Tuffs". PDXScholar, 2013. https://pdxscholar.library.pdx.edu/open_access_etds/1012.
Testo completoAbstract (sommario):
Volcanic rocks typically have only low to moderate arsenic concentrations, none-the-less, elevated levels of arsenic in ground waters have been associated with pyroclastic and volcaniclastic rocks and sediments in many parts of the world. The potential for arsenic leaching from these deposits is particularly problematic as they often comprise important water-bearing units in volcanic terrains. However, the role that chemical and mineralogical variations play in controlling the occurrence and mobility of arsenic from pyroclastic rocks is largely unexplored.
This study uses chemical and X-ray diffraction data to characterize and classify 49 samples of ash-flow tuffs, and 11 samples of tuffaceous sediments. The samples exhibit a range of devitrification and chemical weathering. Total and partial digestion, and water extractions of samples are used to determine the total, environmentally available, and readily leachable fractions of arsenic present in all tuff samples. Leaching experiments were also performed with buffered solutions to determine the influence of elevated pH levels on arsenic mobility.
The 49 tuff samples have a mean arsenic content of 7.5 mg kg-1, a geometric mean arsenic content of 4.8 mg kg-1, a median arsenic content of 5.2 mg kg-1, and a maximum arsenic concentration of 81 mg kg-1. The mean and median values are 2.8 - 4.4x the average crustal abundance of 1.7 mg kg-1 (Wedepohl, 1995), and consistent with previously reported values for volcanic glasses and felsic volcanic rocks (Onishi and Sandell, 1955; Wedepohl, 1995), although the maximum arsenic content is higher than previously reported (e.g., Casentini et al., 2010; Fiantis et al., 2010; Nobel et al., 2004). In addition, the arsenic concentrations of tuffs were found to be highly heterogenous, both between and within individual units, and in some cases, individual outcrops.
Results of whole rock and leachate analyses indicate that there is no significant difference in the total arsenic content of tuffs as a result of devitrification or weathering, but both devitrified and weathered tuffs contain higher levels of environmentally available arsenic than unweathered glassy tuffs. Glassy tuffs did not produce any readily leachable arsenic, while individual devitrified and weathered tuffs both generated aqueous concentrations that exceeded regulatory limits after 18 hours. Leaching of weathered tuffs produced higher levels of arsenic at high (~9-11) pH than in tests conducted at circum-neutral pH. Devitrified and glassy tuffs showed no increase in leachable arsenic with increasing pH.
The results of this study indicate that devitrification and weathering processes determine the host phases, degree of adsorption, and overall mobility of arsenic from ash-flow tuffs. Tuffs that have undergone different types of alteration are likely to have different host phases of arsenic, and different mechanisms that mobilize arsenic into the environment. Potential host phases and mobility mechanisms are discussed, and a conceptual model of arsenic behavior in ash-flow tuffs is proposed.
26
Niu, Qian, e 牛倩. "An empirical study of environmental flow determination in Hong Kong streams". Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2009. http://hub.hku.hk/bib/B43224118.
Testo completo
27
Wang, Qiuchen, e Santiago Mompo. "Electric-road freight transport, Arlanda-Rosersberg logistic flow and environmental analysis". Thesis, KTH, Trafik och logistik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-149534.
Testo completoAbstract (sommario):
The expected economic and social growth, joint with the increase on the demand of services and goods that this will cause, will become an environmental problem (emissions and noise) as well as a logistical problem (congestion) that needs to be solved. The transport sector has to reduce drastically the use of fossil fuels and Sweden’s goal is to achieve a fossil independent vehicle fleet by 2030. It is expected that 2/3 of the traffic volume of trucks in Sweden will be performed along electrified roads. The most efficient way to achieve this is to use electricity and now that the technology to power trucks without the need of huge batteries has been tested and approved, is time to develop the infrastructure needed and study its impact in transportation and logistics. An electric road is planned to be operative around 2020 from Rosersberg logistics hub to Arlanda airport cargo city. The objective is to transfer goods from the logistic area to the freight terminal by the use of electric trucks. It will optimize the transit of logistics flow in the area, reduce emissions and release the traffic pressures on E4 at the same time. Arlanda airport used to have a restriction on the emission rate of all the companies operating inside Arlanda, the emissions of the trucks that drive the cargo outside Arlanda was also taken into account. This means that in order to be below the maximum levels, the high ground transport emissions limited the number of planes that could fly. Affecting therefore the capacity of handling bigger volumes and passengers. So in order to prevent this situation from happening again in the future (more environmental restrictions will appear) the best solution for all the parts involved is to give priority to sustainability in transport planning. The aim of this project is to come up with conclusions and forecasts of the whole transportation network according to the logistics needs, by analysing the economic, environmental and logistic impacts of using the El-road. The result expected is to provide a clearer overall picture of the logistic flows between Rosersberg, Arlanda Airport, Gavle container and nearby locations, such as Stockholm or Uppsala. As well as analyse the possible scenarios that might develop once the El-road is operating. Due to the nature of our data we decided to use qualitative and subjective methods rather than quantitative ones. AHP (Analytic Hierarchy Process, Saaty 1970), will enable us to derive ratio scales from paired comparisons by defining the different criteria (cost, time, operations and sustainability) and assigning values to their respective sub criteria. These values will be assigned by each of the companies working inside Arlanda, since the goal is to define the best possible scenario for them in the future. The other method we will use is the decision tree analysis, this model of decisions and possible consequences that can occur will show a graph of all the variables that must be taken into account while defining the issues that will lead to one scenario or another. We consider it the best method to analyse and show how many facts can affect the final scenario outcome of this project.
28
Niu, Qian. "An empirical study of environmental flow determination in Hong Kong streams". Click to view the E-thesis via HKUTO, 2009. http://sunzi.lib.hku.hk/hkuto/record/B43224118.
Testo completo
29
Barbour, Emily. "Quantitative modelling for assessing system trade-offs in environmental flow management". Phd thesis, Canberra, ACT : The Australian National University, 2015. http://hdl.handle.net/1885/109583.
Testo completoAbstract (sommario):
This research aims to better enable the management of environmental flows through exploring the opportunities and challenges in using quantitative models for decision making. It examines the development and application of ecological response models, river system models, and multi-objective optimisation for improved ecological outcomes and the identification of trade-offs. In doing so, the thesis endeavours to capture a deeper and more holistic understanding of uncertainty in the application of quantitative models, to assist in making more informed decisions in water resource management. The thesis includes three main components. Firstly, an ecological response model is developed to advance previous methods by: (1) adopting a systems approach to representing water availability for floodplain vegetation, considering rainfall and groundwater in addition to riverine flooding; (2) including antecedent conditions in estimating current ecological condition; and (3) including uncertainty in modelling ecological response through the use of upper and lower prediction bounds and multiple conceptual models derived through expert elicitation. Secondly, the ecological response model is evaluated using sensitivity and uncertainty analysis. Global sensitivity analysis was used to identify model components that are both uncertain and have critical impact on results, and demonstrated that conceptualisation of ecological response had the greatest impact on predicted ecological condition. A novel application of Bayesian analysis was then used to evaluate different expert derived models against observed data, considering multiple sources of uncertainty. The analysis demonstrates a number of remaining challenges in modelling ecological systems, where model performance depends upon assumptions that are highly uncertain. The third and final component evaluates opportunities and challenges in using multi-objective optimisation, to assist in water resource management and the improvement of ecological outcomes. This component begins with a synthesis of previous studies drawing upon literature from hydrology, ecology, optimisation and decision science, and identifies a number of strategies for improvement. The synthesis is followed by a case study on the Lachlan catchment of the Murray-Darling Basin, Australia. The case study uses multi-objective optimisation to explore different environmental flow rules using a river system model combined with the expert-based ecological models. In doing so, it addresses the challenges of objective setting and problem framing in the context of significant uncertainty. The case study evaluates results generated using the optimisation framework in terms of likely actual decision outcomes. The research identifies a need to revisit fundamental questions regarding system understanding and objective framing in the light of rapidly improving computational capacity and sophistication. This is particularly relevant in the case of ecological management, where objectives form an interplay between ecological science and social values. Modelling tools provide valuable pathways to system learning and communication, yet a deeper understanding and evaluation of model behaviour in the context of actual decisions is needed. The methods presented in this thesis aim to provide a step toward addressing the challenges of working with uncertain information, incomplete knowledge, and integration across multiple disciplines within a decision-making environment. Through the methods developed here, the research seeks to advance the science of model development and application.
30
Jacobs, Bruce Lee. "Effective properties of multiphase flow in heterogeneous porous media". Thesis, Massachusetts Institute of Technology, 1998. http://hdl.handle.net/1721.1/9697.
Testo completoAbstract (sommario):
Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, February 1999.Includes bibliographical references (leaves 218-224).
The impact of heterogeneity on multiphase fl.ow is explored using a spectral perturbation technique employing a stationary, stochastic representation of the spatial variability of soil properties. A derivation of the system's effective properties - nonwetting phase moisture content, capillary pressure, normalized saturation and permeability - was developed which is not specific as to the form of the permeability dependence on saturation or capillary pressure. This lack of specificity enables evaluation and comparison of effective properties with differing characterization forms. Conventional characterization techniques are employed to parameterize the saturation, capillary pressure, relative permeability relationships and applied to the Cape Cod and Borden aquifers. An approximate solution for the characteristic width of a dense nonaqueous phase liquid (DNAPL) plume or air sparging contributing area is derived to evaluate the sensitivity of system behavior to properties of input processes. Anisotropy is predicted for uniform, vertical flow in the Borden Aquifer consistent with both prior experimental observations and Monte Carlo simulations. Increases of the mean capillary pressure (increasing nonwetting phase saturation) is accompanied by reductions in nonwetting phase anisotropy. Similar levels of anisotropy are not found in the case of the Cape Cod aquifer; the difference is attributed largely to the mean value of the log of the characteristic pressure which is shown to control the rate of return to asymptotic permeability and hence system uniformity. A positive relation between anisotropy and interfacial tension was observed, consistent with prior numerical simulations. Positive dependence of lateral spreading on input fl.ow rate is predicted for Cape Cod Aquifer with reverse response at Borden Aquifer due to capillary pressure dependent anisotropy of Borden Aquifer. The effective permeability for horizontal fl.ow with core scale heterogeneity was found to be velocity dependent with features qualitatively similar to experimental observations and numerical experiments. Application of Leverett scaling as generally implemented in Monte Carlo simulations under represents aquifer hetero geneity and for the Borden Aquifer, van Genuchten characterization reduces system anisotropy by several orders of magnitude. Anisotropy of the effective properties proved to be less sensitive to Leverett scaling if the Brooks-Corey characterization was used due to insensitivity in this case to the variance of the slope parameter.
by Bruce L. Jacobs.
Ph.D.
31
Kelly, Anna C. "Finite element modeling of flow through ceramic pot filters". Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/82817.
Testo completoAbstract (sommario):
Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2013.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 54-55).
Pure Home Water (PHW) is an organization based in Tamale, Ghana that manufactures and distributes ceramic water filters. While many ceramic filter factories manufacture flowerpot-shaped filters, PHW has transitioned from the flowerpot shape, to a paraboloid shape, and finally to a hemispheric filter shape. The PHW factory conducts flow-rate testing as part of their quality control process and has documented a wide range of flow rates for the hemispheric filter as compared to the global standard. This thesis uses finite-element groundwater-flow modeling software to develop models of flow through three different ceramic filter shapes: flowerpot, paraboloid, and hemispheric filters. A sensitivity analysis was then conducted for each filter shape by simulating flow through the filter for a range of hydraulic conductivities. It was found that the hemispheric filter shape produces a higher flow rate than the flowerpot filter for a given hydraulic conductivity, and that the flow rate through the hemispheric filter is more sensitive to changes in hydraulic conductivity.
by Anna C. Kelly.
M.Eng.
32
Ley, J. D. "An environmental and material flow analysis of the UK steel construction sector". Thesis, Cardiff University, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.504959.
Testo completo
33
Bohner, Richard H. Jr. "Definition of the mean environmental steering flow for TCM-90 tropical cyclones". Thesis, Monterey, California. Naval Postgraduate School, 1992. http://hdl.handle.net/10945/23615.
Testo completoAbstract (sommario):
Approved for public release; distribution is unlimitedA definition for the environmental steering flow in the vicinity of the TCM-90 tropical cyclones is sought by low-pass filtering the Naval Operational Global Atmospheric Prediction System deep-layer mean u- and v- velocity and geopotential height fields. One-dimensional and two-dimensional Fourier decompositions in a limited region (120(o) long) and in a global region are compared with six wavenumber low-pass filters (1-6, 1-9,...,1-21). The measure of goodness of the environmental steering flow interpolated to the storm position was to determine the minimum standard deviation of the propagation vector (defined as difference between storm motion and the steering estimate) for all six storms and the ensemble. The best results were found for either the limited and global region one-dimensional Fourier analyses of the u and v wind fields with a low-pass filter that included only wavenumbers 1 -15. The sic TCM-90 tropical cyclones were subsequently analyzed using this definition of the steering flow to estimate the propagation vectors and to examine the linear shear and relative vorticity gradients of the environmental flow. Except for early stages of storms in low latitude, the low-pass filtered analyses provided steering vectors consistent with the changing translation directions. However, the translation speeds tended to exceed the storm motion and lead to more westward propagation vectors than expected. These propagation vectors tended to be almost perpendicular to the absolute vorticity gradient vector.
34
Zhang, Zhuqing. "No-flow underfill materials for environment sensitive flip-chip process". Thesis, Georgia Institute of Technology, 2001. http://hdl.handle.net/1853/19084.
Testo completo
35
Galloni, Susanna. "Regional flow model of west Cape Cod and optimization analysis". Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/43925.
Testo completo
36
Grier, Nathaniel J. (Nathaniel Jedidiah) 1978. "Improved methods for solving traffic flow problems in dynamic networks". Thesis, Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/84805.
Testo completo
37
Barrantes, Analía Inés. "Turbulent boundary layer flow over two-dimensional bottom roughness elements". Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/42585.
Testo completo
38
Tse, Rosanna. "A critical assessment of two phase flow characterization of soil". Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/28178.
Testo completo
39
Pokhrel, Sajjan. "Computational Modeling of A Williams Cross Flow Turbine". Wright State University / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=wright1515428122798392.
Testo completo
40
Little, Stephen Nicholas. "The flow behaviour of non-Newtonian sludges". Thesis, University of Greenwich, 1998. http://gala.gre.ac.uk/6228/.
Testo completoAbstract (sommario):
A large body of data is analysed of the flow of concentrated sewage sludge through straight pipes. Mathematical models are obtained of the laminar and turbulent flow of each main category of sewage sludge. The sludges are modelled as time-independent, non-Newtonian relations between shear stress, rate of shearing strain, and solids concentration. Due to the inhomogeneity of sewage sludge, error analysis becomes pivotal to the data analysis, and options are examined for reducing the error of each model with one or more user-fitted parameters. Parameter estimation is discussed for viscous, time-independent, non-Newtonian, laminar and turbulent flow models. Due to extensive requirements of the data analysis, the parameter estimation methods are robust, and generally suitable for any shear flow relation. The difficulties of estimating parameters of shear flow models from pipe flow data are addressed. Numerical algorithms are presented for modelling the flow of time-independent, non-Newtonian, viscous fluids through a straight pipe. Laminar, critical and turbulent flow algorithms are developed to offer predictions such as pressure gradient, mean cross-sectional velocity, and the velocity distribution. To handle the requirements of the data analysis, the algorithms impose few restrictions on the type of shear flow relation, the flow velocity, and the pipe diameter. Suitable pipe flow equations are chosen, and are manipulated mathematically into forms that would yield robust and efficient schemes. The appropriate use of numerical methods for the algorithms is investigated. Mathematical models of sludge are for use by the sewage industry to give an idea of the flow behaviour of sludges for any relevant application. The parameter estimation techniques and pipe flow algorithms are not constrained to any particular pipe, fluid or flow conditions, so they would be useful for any relevant application.
41
Hogge, Joshua Ryan. "Achieving Uniform Flow Distribution in Compact Irrigation Splitter Boxes with High Flow Rates". DigitalCommons@USU, 2016. https://digitalcommons.usu.edu/etd/4630.
Testo completoAbstract (sommario):
In many irrigation systems and networks, there are multiple water users and shareholders who take their water from different locations along a single canal or pipeline. Often, irrigation splitter boxes are used to divert water to multiple shareholders from a single location. The splitter boxes, which can be small and compact, are generally installed at different locations along a piped irrigation supply line. The purpose of a splitter box is to split a specific amount of water so that each user receives their allotted portion, regardless of the flow rate in the system.
Each splitter box usually includes two compartments, separated by a wall that acts as a weir for the water to flow over. The water in the supply pipe enters the box and fills the upstream compartment until it spills over the weir. As water flows over the weir, it is separated by vertical dividers. Each divider is positioned to split a certain percentage of the total flow to one of the outlet pipes, which carry the water to various destinations. In general, splitter boxes perform very well at lower flow rates. However, if high flow rates are present in the box, due to under-design of the box or for any reason, the water surface becomes turbulent and the flow profile over the weir becomes disturbed and nonuniform. Because of these conditions, the flow becomes unevenly distributed and an accurate flow split cannot be achieved.
This study focuses on developing a solution that can be installed in flow splitter boxes to effectively dissipate energy and uniformly distribute the flow across the length of the weir during times of high flow rates.
42
Whitley, Annie R. "Method Development for Detecting and Characterizing Manufactured Silver Nanoparticles in Soil Pore Water Using Asymmetrical Flow Field-Flow Fractionation". UKnowledge, 2012. http://uknowledge.uky.edu/pss_etds/9.
Testo completoAbstract (sommario):
Recent advances in nanotechnology have led to the production of materials with nanoscale dimensions (nm) and properties distinctly different from their bulk (>100 nm) counterparts. With increased use, it is inevitable that nanomaterials will accumulate in the environment and there is concern that the novel properties of nanomaterials could result in detrimental environmental and human health effects. In particular, there has been concern recently regarding the use of silver (Ag) based nanomaterials as antimicrobial agents in consumer and medical products. Current regulations dealing with the discharge of metals into the environment are based on total concentrations with no consideration for the form (e.g., ionic, nanoparticle, colloid) which can largely determine toxicity. Methods for the identification and characterization of nanoparticulates within complex matrices are lacking and the development of robust methods for this purpose are considered a high priority research area. This research focuses on the development and application of a novel method for characterizing Ag manufactured nanoparticles (MNPs) within terrestrial environments, in particular in soil pore water, with applications relevant to other metal MNPs as well. The method was then applied to understand the dynamics and behavior of Ag MNPs in soil and soil amended with sewage sludge biosolids.
43
Gassiat, Claire. "Simulating regional groundwater flow in layered, faulted sedimentary basins: implications for groundwater age and shale gas". Thesis, McGill University, 2013. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=119745.
Testo completoAbstract (sommario):
Groundwater plays an important role in a wide range of geologic processes. Sedimentary basins are heterogeneous, layered and faulted which strongly impacts regional groundwater flow. An important concern is how anthropogenic alterations such as groundwater or shale gas development affect these complex systems. Heterogeneities are likely to impact groundwater age and affect geologic processes that depend on groundwater or solute fluxes. They may also enhance long term contamination of shallow aquifers from the fracturing of the target shale unit, as contaminants may migrate from the shale to shallow aquifers through preferential pathways such as faults. We use numerical modelling to study the effect of a layered system on distribution of groundwater age in a regional groundwater basin and the impact of hydraulic fracturing in a generic faulted sedimentary basin on potential contamination of a shallow aquifer. First, we show that high age zones with predictable locations occur in layered geologic systems across a wide range of hydraulic gradients, basin geometries and permeabilities. The zones of older groundwater result from two mechanisms: low groundwater velocities in the low permeability layer; and the rejuvenation of the groundwater through mixing of different flow paths near discharge zones. Second, we show that hydraulic fracturing leads to the transport of contaminants along the fault and long-term contamination of a shallow aquifer in some specific, realistic cases. The location of the hydro-fractured zone relative to the fault zone and the top of the shale is the most critical factor controlling contaminant transport potential.L'eau souterraine joue un rôle déterminant dans de nombreux processus géologiques. Les bassins sédimentaires comportent des hétérogénéités, des couches sédimentaires ainsi que des failles géologiques, qui ont un impact important sur l'écoulement régional de l'eau souterraine. Une question essentielle est de comprendre comment les altérations anthropiques, comme l'extraction d'eau souterraine ou de gaz de schiste, affectent ces systèmes complexes. Les hétérogénéités peuvent probablement avoir un impact sur l'âge de l'eau souterraine et affecter les processus géologiques qui dépendent des flux d'eau souterraine ou de solutés. Elles peuvent aussi favoriser la contamination à long terme des nappes phréatiques par la fracturation hydraulique d'une formation de schiste, en permettant aux contaminants de migrer du schiste vers les nappes phréatiques peu profondes le long de chemins préférentiels comme les failles géologiques. Nous modélisons l'écoulement régional d'eau souterraine afin d'étudier l'effet d'un système à couches multiples sur la distribution de l'âge de l'eau souterraine, ainsi que l'impact de la fracturation hydraulique sur la contamination potentielle d'une nappe phréatique superficielle par migration le long d'une faille géologique. Premièrement, nous montrons que des zones de grands âges, dont la localisation est prévisible, se forment dans des systèmes géologiques à couche multiples pour de nombreux gradients hydrauliques, géométries et perméabilités. La formation de zones comportant de l'eau souterraine est due aux faibles vitesses de l'eau souterraine dans la couche peu perméable, ainsi qu'au rajeunissement de l'eau souterraine par mixage d'eaux issues de différentes trajectoires à proximité des zones de décharge. Deuxièmement, nous montrons que la fracturation hydraulique entraine le transport de contaminants le long de la faille géologique et la contamination à long terme d'une nappe phréatique superficielle dans certains cas réalistes. La localisation de la zone de fracturation par rapport à la faille géologique et à l'interface supérieure de la formation de schiste sont des facteurs critiques qui contrôlent le potentiel de transport de contaminants.
44
Kondziolka, John M. (John Michael). "Feedbacks between flow, vegetation, deposition, and the implications for landscape development". Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/90051.
Testo completoAbstract (sommario):
Thesis: S.M., Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, 2014.Cataloged from PDF version of thesis.
Includes bibliographical references.
Flow and sedimentation around patches of vegetation are important to landscape evolution, and a better understanding of these processes would facilitate more effective river restoration and wetlands engineering. In wetlands and channels, patches of vegetation are rarely isolated and neighboring patches influence one another during their development. This patch-to-patch interaction, and its influence on landscape evolution, was examined through laboratory experiment and numerical modeling. In an experimental study, an adjacent pair of emergent vegetation patches were modeled by circular arrays of cylinders. The flow and deposition patterns behind the pair of patches were measured for two stem densities and for different patch separations (gap widths). For all gap widths (A), the velocity on the centerline between the patches (Uc) was elevated to a peak velocity Umax that persisted over a distance L. Although Umax was not a function of [delta], L decreased with decreasing [delta]. Beyond Lj, the patch wakes merged, and Uc decayed to a minimum at a distance Lm. The merging of wakes and associated velocity minimum produced a local maximum in deposition downstream from and on the centerline between the patches. If this secondary region of enhanced deposition promotes new vegetation growth, the increased drag on the centerline could slow velocity between the upstream patch pair, leading to conditions favorable to their merger. The patch-scale interactions documented in the lab were incorporated into a model of vegetation evolution. The initial flow field was solved using a porous media formulation for hydraulic resistance, and the velocity in wake regions was adjusted to match the wake structure measured in the laboratory study. Vegetation growth was added based on a probabilistic growth function linked to the velocity field. The simulations explored the influence of initial plant density (ID) and threshold velocity (TV, the velocity above which no plants can grow) on landscape evolution. Three types of stable landforms occurred: full vegetation coverage, channeled, and sparse. Full vegetation coverage was achieved for ID >/_ 5% when wakes were included, whereas simulations that excluded the influence of wakes rarely reached full coverage. The model highlights the role of flow diversion into bare regions (channels) in the promotion of growth within vegetated regions.
by John M. Kondziolka.
S.M.
45
Luhar, Mitul. "Analytical and experimental studies of plant-flow interaction at multiple scales". Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/78142.
Testo completoAbstract (sommario):
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2012.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 163-171).
Across scales ranging from individual blades to river reaches, the interaction between water flow and vegetation has important ecological and engineering implications. At the reach-scale, vegetation is often the largest source of hydraulic resistance. Based on a simple momentum balance, we show that the resistance produced by vegetation depends primarily on the fraction of the channel cross-section blocked by vegetation. For the same blockage, the specific distribution of vegetation also plays a role; a large number of small patches generates more resistance than a single large patch. At the patch-scale, velocity and turbulence levels within the canopy set water renewal and sediment resuspension. We consider both steady currents and wave-induced flows. For steady flows, the flow structure is significantly affected by canopy density. We define sparse and dense canopies based on the relative contribution of turbulent stress and canopy drag to the momentum balance. Within sparse canopies, velocity and turbulent stress remain elevated and the rate of sediment suspension is comparable to that in unvegetated regions. Within dense canopies, velocity and turbulent stress are reduced by canopy drag, and the rate of sediment resuspension is lower. Unlike steady flows, wave-induced oscillatory flows are not significantly damped within vegetated canopies. Further, our laboratory and field measurements show that, despite being driven by a purely oscillatory flow, a mean current in the direction of wave propagation is generated within the canopy. This mean current is forced by a wave stress, similar to the streaming observed in wave boundary layers. At the blade-scale, plant-flow interaction sets posture and drag. Through laboratory experiments and numerical simulations, we show that posture is set by a balance between the hydrodynamic forcing and the restoring forces due to blade stiffness and buoyancy. When the hydrodynamic forcing is small compared to the restoring forces, the blades remain upright in flow and a standard quadratic law predicts the relationship between drag and velocity. When the hydrodynamic forcing exceeds the restoring forces, the blades are pushed over in steady flow, and move with oscillatory flow. For this limit, we develop new scaling laws that link drag with velocity.
by Mitul Luhar.
Ph.D.
46
VecchiarelliI, Alessandra. "Further development and application of GEOFRAC flow to a geothermal reservoir". Thesis, Massachusetts Institute of Technology, 2015. http://hdl.handle.net/1721.1/97979.
Testo completoAbstract (sommario):
Thesis: Civ. E., Massachusetts Institute of Technology, Department of Civil and Environmental Engineering, 2015.Cataloged from PDF version of thesis. Page 174 blank.
Includes bibliographical references (pages 169-173).
GEOFRAC is a three-dimensional, geology-based, geometric-mechanical, hierarchical, stochastic model of natural rock fracture systems. The main characteristic of GEOFRAC is that is based on statistical input representing fracture patterns in the field in form of the fracture intensity P₃₂ (fracture area per volume) and the best estimate fracture size E(A). Recent developments in GEOFRAC allow the user to calculate the flow in a fractured medium. For this purpose the fractures are modeled as parallel plates and the flow rate can be calculated using the Poisseuille equation. This thesis explores the possibility of the application of GEOFRAC to model a geothermal reservoir. After modeling the fracture flow system of the reservoir, it is possible to obtain the flow rate in production. A parametric study was conducted in order to check the sensitivity of the output of the model and to explain how aperture, width and rotation (orientation distribution) of the fractures influence the resulting flow rate in the production well. A case study is also presented in this thesis in order to confirm the applicability of GEOFRAC to a real case. GEOFRAC is a structured MATLAB code composed of more than 100 functions. Examples on how to obtain P3 2 and E(A) from fracture trace lengths on outcrops are presented in the Appendix 1. A GUI was created in order to make GEOFRAC more accessible to the users. It should also be kept in mind that future improvements are the keys for a powerful tool that will let GEOFRAC to be used to optimize the location of the injection and production well in a geothermal system.
by Alessandra VecchiarelliI.
Civ. E.
47
Zhang, Xueyan Ph D. Massachusetts Institute of Technology. "Mechanics of exchange flow between open water and an aquatic canopy". Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/62392.
Testo completoAbstract (sommario):
Thesis (Ph. D. in Environmental Fluid Mechanics)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2010.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 121-126).
The presence of aquatic vegetation is a common feature in shallow water systems. It alters the dynamics of the system by producing additional drag and by generating differential heating between regions of vegetation and open water through the shading it provides. The differential heating creates density differences that drive flow between vegetated and open regions. This thesis presents a series of experiments that explored the magnitude and structure of these exchange flows for different forcing and vegetation distributions. The first project considers emergent vegetation with flow forced by a constant density difference. After a short inertial period, the discharge is controlled by the vegetative drag, and the current entering the vegetation, as well as the total discharge, decrease with time. The toe velocity of the current moving into the open region is controlled only by inertia and is constant in time. The second project considers emergent vegetation with a temporally increasing density difference, which was generated by a constant heat input. In the vegetated region, both the buoyancy and vegetative drag experienced by the intruding current increase linearly in time, offsetting on another and resulting in a current velocity moving into the vegetation that is constant in time. The thickness of this intruding layer is set by the length scale of light penetration. The third project considers a mat of floating vegetation whose roots penetrate a fraction of the water depth. The flow was driven by a constant density difference (constant g'). The flow entering the vegetated side bifurcates, with some flow moving through the root layer and the remaining flow displaced downward beneath this layer. The fraction of flow going through and beneath the root layer is allocated such that the conversion from potential energy to kinetic energy is maximized in the system. Finally, this work shows that thermally-driven exchange flow can flush a significant portion of a vegetated sidearm during a diurnal cycle and thus can play a crucial role in the mass balance and distribution in a natural water body.
by Xueyan Zhang.
Ph.D.in Environmental Fluid Mechanics
48
Paonessa, Michael E. (Michael Edward) 1979. "A model for predicting air flow during in-situ air sparging". Thesis, Massachusetts Institute of Technology, 2003. http://hdl.handle.net/1721.1/85753.
Testo completo
49
Zong, Lijun. "Interactions among flow, sediment deposition and aquatic vegetation in a channel". Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/70770.
Testo completoAbstract (sommario):
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2011.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 69-72).
Aquatic vegetation is commonly present in rivers in many forms. This thesis consists of two studies, which examine the flow structure around a patch of emergent, rigid vegetation in a laboratory channel. The vegetation patch is represented by an array of circular cylinders in a staggered arrangement. The first study investigates flow structure and deposition pattern associated with a long patch of vegetation located at the sidewall of a channel (i.e. a partially vegetated channel). Along the flow-parallel edge of the patch, a shear layer is formed due to the velocity difference between the open region and the vegetated region. Coherent vortices are formed via Kelvin-Helmholtz stability in the shear layer, which also induces an edge wave. Both the energetic vortices and the edge wave enhance the lateral mass transport. Particles were introduced to the flow in order to observe the patterns of net deposition within and around the patch. There are two sources of particle flux to the patch: the advection of particles across the upstream leading edge and the lateral dispersion of particles from the adjacent open channel. The relative contribution of these two supplies determines the spatial pattern of net deposition in the patch. A simple model was developed to find the empirical value of the lateral dispersion coefficient. Longitudinal and lateral length scales were found to determine the region where particles cannot be delivered and the net deposition is limited by particle-supply. In the second study, a circular patch of emergent model vegetation located in the middle of the channel was examined. Its diameter was smaller than the channel width. Velocity measurements and flow visualization were conducted to study the turbulent wake behind the patch. Compared to the wake behind a solid obstruction, the wake behind a patch of vegetation (i.e. a porous obstruction) is different. Because of its porosity, some of the flow can pass through the patch, so that directly downstream of the patch there is a region of steady stream-wise velocity with no transverse velocity. This region is called the steady wake and it is also observed from the flow visualization. Unlike the wake behind a solid obstruction, the formation of a von-Karman vortex street behind a porous obstruction is delayed until the end of the steady wake region. As the stem density decreases (i.e. the patch becomes sparser), the velocity deficit in the steady wake region decreases and the length of the steady wake increase.
by Lijun Zong.
S.M.
50
Wang, Mingyu. "Discrete fracture fluid flow modeling and field applications in fractured rocks". Diss., The University of Arizona, 2000. http://hdl.handle.net/10150/284182.
Testo completoAbstract (sommario):
Fluid flow modeling in fractured rocks is a complicated and important research and application topic in many fields such as geological, hydrogeological, environmental and petroleum engineering. Commonly used methods based on equivalent continuum assumption for fluid flow modeling can generally be applied directly to the porous geological media, but have limited applicability when the geological medium is dominated by fractures. It often happens that only limited time, cost, hydrogeological data and computer resources are available in solving a practical problem of the fluid flow modeling in fractured rocks. Therefore, it is a challenge, but necessary, to investigate the hydraulic behaviors and propose new approaches, procedures, and methodologies to build a reliable fluid flow model for fractured rocks with limited available related data. The general concepts on fluid flow modeling in fractured rocks are introduced firstly and the different ways to treat major and minor fractures in 2-D and 3-D discrete fracture fluid flow modeling are propounded. The author has investigated the relations between the hydraulic behaviors and fracture geometry parameters and found out the effect of fracture parameters on the Representative Elementary Volume (REV) for the fracture systems with statistically distributed fracture geometry parameters including the size, orientation and location. Further, a systemic procedure for fluid flow modeling in fractured rocks in two-dimensional domain is suggested and demonstrated through a 2-D case study for groundwater resources evaluation. Six 3-D conceptual linear pipe discrete fracture fluid flow models which focus on the utilization of fracture information are proposed to simulate packer or pumping tests conducted in fractured rock masses. These models can reflect channel flow in fractures, simplify and minimize the complexity of fluid flow in fractures, save computer resources and increase the possibility to solve a field problem at large scales, and implement a discrete fracture fluid flow model easily. Finally, the author has developed a practicable systemic approach to determine the REV for hydraulic properties and then the hydraulic conductivity tensor for the REV in fractured rocks using single well packer test results. These procedures are illustrated through a 3-D case study by implementing the proposed fluid flow models.