Página 18 dos resultados de 2122 itens digitais encontrados em 0.023 segundos

‣ A numerical framework for the direct simulation of solid-fluid systems

Cook, Benjamin Koger, 1965-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 136 p.; 18546802 bytes; 18546555 bytes; application/pdf; application/pdf
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Our understanding of solid-fluid dynamics has been severely limited by the nonexistence of a high-fidelity modeling capability for these multiphase systems. Continuum modeling approaches overlook the microscale solid-fluid interactions from which macroscopic system properties emerge, while experimental inquiries have been plagued by high costs and limited resolution. One promising numerical alternative is to simulate solid-fluid systems at the grain-scale, fully resolving the interaction of individual solid particles with other solid particles and the surrounding fluid. Until recently, the direct simulation of these systems has proven computationally intractable. In this thesis an accurate, efficient, and robust modeling capability for the direct simulation of solid-fluid systems is formulated and implemented. The coupled equations of motion governing both the fluid phase and the individual particles comprising the solid phase are solved using a highly efficient numerical scheme based on the discrete-element (DEM) and the lattice-Boltzmann (LB) methods. Particle forcing mechanisms represented in the model to at least the first order include dynamic fluid-induced forces, buoyancy forces, and intergranular forces from particle collisions...

‣ The valuation of construction companies

Sassine, Edmond, 1980-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 83 leaves; 3110268 bytes; 3110070 bytes; application/pdf; application/pdf
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The main objective of this thesis is to study the valuation of construction companies in mergers and acquisitions. The thesis is divided into three main parts; Mergers and Acquisitions, Valuation, and a Case Study. Mergers and acquisitions are at the forefront of discussions in the industry. This is in large part because of the way in which they characterize and contribute to the new economy; for the pressures that they impart on global competition and for their role in promoting globalization through the diminishing importance of traditional geographic boundaries. The number of studies in mergers and acquisitions in the construction industry are minimal when compared to other industries such as banking and telecommunications. Consequently, this first part identifies the general different types and reasons for mergers and acquisitions while attempting to tailor them to the needs of a construction company. The second part elaborates on the concept of valuation and on the different methodologies used by valuators when estimating the value of a construction company. The valuation approaches presented here can apply to all sizes and types of construction companies. Moreover, it is of fundamental importance that the valuator be familiar with the construction industry specifically as contractors typically retain the majority of their value in intangible assets. The theoretical concepts discussed in the first two parts of the thesis are then applied to a case study. The case study that will be discussed is the merger of HOCHTIEF AG with Turner Corporation.; (cont.) The M&A activity and diversification of businesses at HOCHTIEF AG is discussed...

‣ Moisture degradation in FRP bonded concrete systems : an interface fracture approach; Moisture degradation in fiber reinforced plastic bonded concrete systems

Au, Ching, 1977-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 254 leaves; 12930369 bytes; 12963835 bytes; application/pdf; application/pdf
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(cont.) characterization, and kink criterion implementation, form a synergistic analysis of the mechanistic debonding behavior affected by moisture. Results have shown that moisture affected debonding is a highly complex phenomenon that involves physical changes in the bond as well as in its constituent materials. In particular, moisture can initially enhance or reduce the interface fracture toughness, depending on the epoxy formulation being used. The toughness can, however, decrease by as much as 60% and become asymptotic upon reaching a certain moisture concentration threshold, which can be attained in as short as 2 weeks in case of peel fracture. While various debonding modes have been observed for dry specimens, epoxy/concrete interface separation, which has generally been considered an unlikely debonding mode, is observed consistently in all wet fracture specimens. Interface fracture analysis indicates that this newly discovered interfacial debonding mode is attributed to various interfacial material toughening or weakening mechanisms, and has also hinted on the possible interphase formation as a consequence of moisture diffusion. The new knowledge and results obtained from this research provide a basis for further analysis directions and for design of FRP bonded concrete systems against moisture affected debonding.; The objective of this research is to develop new mechanistic understanding of moisture affected debonding failures in carbon fiber-reinforced plastic (FRP) bonded concrete systems by means of an interface fracture approach. Central to the investigation is the use of interface fracture toughness as the quantification parameter...

‣ Geotechnical characterization of sediments from Hydrate Ridge, Cascadia Continental Margin

Tan, Brian B. (Brian Bautista), 1979-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 264 p.; 9932975 bytes; 9932776 bytes; application/pdf; application/pdf
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Eight whole core sediment samples were obtained from ODP Site 1244, Hydrate Ridge, Cascadia Continental Margin with the goal of understanding the stress history, consolidation behavior and strength characteristics of the soil. A series of Constant Rate of Strain Consolidation (CRSC) and Ko- Consolidated Undrained triaxial (CKoU) tests were performed in order to study the behavior. In addition, Atterberg limits and x-ray diffraction were performed in order to better classify the material. One of the key issues regarding this soil is the level of disturbance imparted during sampling and transportation. Evidence of the disturbance are cracks and voids in x-rays, as well as highly rounded compression curves. Established soil quality criteria have shown the soil to have poor quality. A new criterion comparing the initial loading to the reload cycle shows that soil quality varies, but has no pattern with depth. Nonetheless, highly disturbed samples and trimmings from previous tests were resedimented to produce better quality specimens for consolidation and strength testing. Conventional application of the strain energy method yielded high preconsolidation pressures that indicate the soil is normal to overconsolidated (1

‣ A study of the Naval Construction Force project material supply chain; Sudy of the NCF project material supply chain

Stasick, Steven J. (Steven James), 1970-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 146 p.; 6644907 bytes; 6644714 bytes; application/pdf; application/pdf
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The Naval Construction Force (NCF) performs construction projects in all areas of the world during both peacetime and war. While some of these projects occur in populated areas where project materials are readily available, many of these projects occur in remote areas or war zones, where project materials must be procured from the United States or elsewhere and shipped to the unit performing the construction. The construction scopes also vary from projects as small as concrete sidewalks to projects as large as full utility system installations, or complete facility and base construction. As a result of the diverse locations and project types that the Naval Construction Force experiences, the logistics of providing project material and construction equipment to multiple global locations is a major challenge. The Naval Construction Force still experiences delays and inefficiencies in supplying construction materials to its various projects and units deployed throughout the world, which in turn reduces the overall productivity of the deployed Construction Battalions. This research explores the current supply chain that the NCF has in place for obtaining construction project materials. It also explores the latest initiatives in information technology and construction supply chain management that are being applied in the commercial sector.; (cont.) The two systems are compared to determine what private practices and technologies can be applied to the Navy system to make it more efficient. Since the Navy is restricted by Federal Acquisition Regulations...

‣ Parallel computation in efficient non-linear finite element analysis with applications to soft-ground tunneling project

Hsieh, Yo-Ming, 1973-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 381 p.; 15548917 bytes; 15548718 bytes; application/pdf; application/pdf
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Reliable prediction and control of ground movements represent an essential component of underground construction projects in congested urban environments, to mitigate against possible damage to adjacent structures and utilities. This research was motivated by the construction of a large underground cavern for the Rio Piedras station in San Juan, Puerto Rico. This project involved the construction of a large, horseshoe-shaped cavern (17m wide and 16m high) in weathered alluvial soils. The crown of the cavern is located less than 5.5m below existing buildings in a busy commercial district. Structural support for the cavern was provided by a series of 15 stacked drifts. These 3m square-section galleries were excavated mainly by hand and in-filled with concrete, while a compensation grouting system was designed to mitigate effects of excavation-induced ground movements on the overlying structures. Unexpectedly large settlements occurred during drift construction and overwhelmed the grouting system that was intended to compensate for tunnel-induced movements. Although two dimensional, non-linear finite element analyses of the stacked- drift construction suggest that movements exceeding 100mm can be expected, the 2-D representation of excavation and ground support is overly simplistic and represents a major source of uncertainty in these analyses. Massive computational efforts make more comprehensive 3-D models of the construction sequence completely impractical using existing finite element software with direct or iterative solver methods.; (cont.) This thesis develops...

‣ Appropriate water treatment for the Nyanza Province of Kenya

Alekal, Pragnya Y. (Pragnya Yogesh), 1977-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 93 leaves; 6282758 bytes; 6293419 bytes; application/pdf; application/pdf
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In 2000 the Centers for Disease Control and Prevention (CDC) in conjunction with CARE International began working with several local non-governmental organizations (NGOs) in the Nyanza Province of Kenya to reduce the rate of waterborne diseases. In 2002, CDC partnered up with the Society for Women and AIDS in Kenya (SWAK), a local NGO, to implement safe water treatment in SWAK-affiliated communities. SWAK is seeking ways to improve and expand sales of safe water treatment products in all of its communities. The water treatment sales expansion study has two components: · A technical component that addresses the most appropriate treatment · A business component that addresses marketing and sales of the products. This study focuses on the technical component. Its purpose is to evaluate the most appropriate water treatment in SWAK communities in the Nyanza Province. Three water treatment products were assessed - WaterGuard®, PuR®, and an alternative naturally occurring coagulant made of seeds from the Moringa tree. WaterGuard® is a chlorine- based disinfectant; PuR® is a coagulant and chlorine-based disinfectant. Both are already being marketed by SWAK. Moringa trees are indigenous to the region. Research was conducted in the United States and Kenya from October to April 2005. Field evaluation in Nyanza during January consisted of surveys that addressed water treatment practices...

‣ High-speed rail commuting in the United States : a case study in California; HSR commuting in the United States

Kasuya, Shuichi, 1972-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 122 leaves; 7970817 bytes; 7986182 bytes; application/pdf; application/pdf
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High-speed rail (HSR) is primarily for intermediate distance intercity passenger travel. The concept of high-speed rail commuting is to provide short distance commuting transportation service on dedicated HSR, by sharing the same rolling stock and infrastructure. HSR commuting benefit all city commuters by relieving inner city traffic congestion as well as providing intercity service. HSR commuting also benefits its operators providing an additional financial resource. In the US, the rail is primarily for freight. Passengers usually take airlines and automobiles, but the congestion of airports and roads are increasing, which makes another transportation option necessary. Rail passenger transportation is less energy consuming and it is effective for the environment. For the sustainable development of many cities in the US, HSR is a potential option. From successful HSR examples in Japan, French, and Germany, the primary purpose of HSR is intermediate distance intercity passenger transportation, and dedicated tracks are necessary. In the US, there are no HSR by our definition, but there are still HSR transportation potential regional corridors in California, Texas, Florida, and other regions. There are several statewide HSR projects...

‣ Revenue management models in the manufacturing industry

Liu, Tieming, Ph. D. Massachusetts Institute of Technology
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 110 p.; 5024618 bytes; 5029174 bytes; application/pdf; application/pdf
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In recent years, many manufacturing companies have started exploring innovative revenue management technologies in an effort to improve their operations and ultimately their bottom lines. Methods such as differentiating customers based on their sensitivity to price and delays are employed by firms to increase their profits. These developments call for models that have the potential to radically improve supply chain efficiencies in much the same way that revenue management has changed the airline industry. In this dissertation, we study revenue management models where customers can be separated into different classes depending on their sensitivity to price, lead time, and service. Specifically, we focus on identifying effective models to coordinate production, inventory and admission controls in face of multiple classes of demand and time- varying parameters. We start with a single-class-customer problem with both backlogged and discretionary sales. Demand may be fulfilled no later than N periods with price discounts if the inventory is not available. If profitable, demand may be rejected even if the inventory is still available.; (cont.) For this problem we analyze the structure of the optimal policy and show that it is characterized by three state-independent control parameters: the produce-up-to level (S)...

‣ Development of a flow-condition-based interpolation 9-node element for incompressible flows

Banijamali, Bahareh
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 167 leaves; 6575290 bytes; 6584738 bytes; application/pdf; application/pdf
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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...

‣ Novel monitoring system to diagnose rail track foundation problems

Aw, Eng Sew, 1978-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 177 p.
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A low cost, remote monitoring system has been developed to diagnose rail track subgrade failures. The portable monitoring system consists of five liquid vertical settlement probes, one piezometer, a small data acquisition system and laptop, and an Internet communication with remote control capabilities. The probes are designed to be small, easily installed (within railbeds using a one-man auger), easily manufactured, and low cost. The sensors and data acquisition have been rigorously tested and calibrated in the laboratory. The settlement probes and piezometer are sensitive to changes in the atmospheric pressure and temperature, and calibration curves have been obtained to correct for these effects. The settlement probes are further subjected to silicone oil density changes due to differential temperature between the atmosphere and the ground, and these effects are minimised by a proposed correction method. The prototype monitoring system was installed through a two phase installation exercise at the bridge approach site in FAST (Facility for Accelerated Service Testing) at Transportation Technology Centre Inc (TTCI), Pueblo, Colorado, USA. Since there are virtually no settlements at the stiff, sandy bridge approach site, the sensors are evaluated for ideal stability and robustness while being subjected to well-defined Heavy Axle Train (HAL) loadings. A detailed evaluation of the prototype system found that probes installed at depths 1.0 to 1.5m within the subgrade did not achieve satisfactory measurement stability (i.e. measurements have a spurious drift)...

‣ Water intrusion in underground structures

Nazarchuk, Alex
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 143 p.
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This thesis presents a study of the permissible groundwater infiltration rates in underground structures, the consequences of this leakage and the effectiveness of mitigation measures. Design guides and codes do not restrict, address or make clear recommendations for permissible inflows in underground space. Owners, with the help of engineers, typically make decisions based on costs or specifications from past projects without looking at consequences of excessive groundwater infiltration and mitigation costs. The Author has reviewed the published leakage rates for tunnels in comparison with current international standards. After examining over one-hundred case studies, the Author infers that water leakage is the principal damage causing degradation on tunnel linings. International standards for permissible leakage rates (transit tunnels) are consistent with class A definitions of CIRIA (1979) and are approximately 0.1-2 gpm/100,000 SF (0.05-1.2 Uday/SM). The most common cause of leakage (based on numerous case studies) in cast-in-place lining is due to cracks that develop from shrinkage of concrete during curing and to the inability of the structure to accommodate movements due to thermal changes. Individual sources of leakage may be allowable within the permissible rates...

‣ Simulating service reliability of a high frequency bus route using automatically collected data

Milkovits, Martin Nicholas
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 151 p.
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High frequency bus routes are subject to a variety of influences that can affect the quality of service provided to passengers. Since they have short headways and high passenger demand interaction between buses can easily develop, causing degradation in service reliability. This, in turn, can prompt service interventions to correct service reliability. Transit agencies are implementing new technology that provide rich data sets for analysis and are also experimenting with a variety of operating policies to improve service reliability. This research develops a simulation model of high frequency bus service in order to study the causes of service unreliability and strategies to alleviate it. The model is designed to be used in conjunction with data recorded by the Automatic Voice Annunciation System (AVAS), Automatic Passenger Counting (APC), and Automatic Fare Collection (AFC) systems and is calibrated to represent route 63, a key bus route in the Chicago Transit Authority (CTA) network The simulation model is first used to conduct a sensitivity analysis of the factors influencing reliability, such as passenger demand, terminal departure behavior, and unfilled trips. Next, several operating strategies, including terminal departure and timepoint holding for schedule or headway...

‣ Application of Smart Card fare payment data to bus network planning in London, UK

Seaborn, Catherine Whitney
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 141 p.
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This research contributes to an emerging body of literature on the application of smart card data to public transportation planning. It also addresses interchange planning, a key component of public transportation network planning that has lately received renewed interest as evidenced by planning literature on integrated and intermodal networks. The research objective of assessing the potential application of smart card data to bus network planning is met, first, by a review of existing data systems and the bus network planning approach at Transport for London (TfL). Then, three potential interchange combinations: bus-to underground, Underground-to-bus, and bus-to-bus are examined to gain an understanding of interchange behavior in London and to formulate recommendations for elapsed time thresholds to identify interchanges between journey stages for each passenger on the TfL network. Other TfL data are compared with the results of linking journey stages into complete journeys based on these elapsed time thresholds. Finally, the complete journey data are applied to bus network planning case studies that illustrate the value of new contextual and quantitative information that would be available to network planners using smart card data without necessitating additional data from other sources such as Automated Vehicle Locators or Automated Passenger Counters.; (cont) Recommended elapsed time thresholds for identifying interchanges across the London network are: 20 minutes for Underground-to-bus interchanges...

‣ On-line calibration for dynamic traffic assignment

Antoniou, Constantinos
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 153 p.; 6855363 bytes; 6876045 bytes; application/pdf; application/pdf
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(cont.) application, the EKF has more desirable properties than the UKF. Furthermore, the Limiting EKF provides accuracy comparable to that of the best algorithm (EKF), but with computational complexity which is order(s) of magnitude lower than the other algorithms.; In this thesis, an on-line calibration approach for dynamic traffic assignment (DTA) that jointly estimates demand and supply parameters has been developed. The objective of on-line calibration is to introduce a systematic procedure that will use the available data to steer the model parameters to values closer to the realized ones. The approach is general and flexible and imposes no restrictions on the models, the parameters or the data that it can handle. The on-line calibration approach is formulated as a state-space model, comprising transition and measurement equations. A priori values provide direct measurements of the unknown parameters (such as origin-destination flows, segment capacities and traffic dynamics models' parameters), while surveillance information (for example, link counts, speeds and densities) is incorporated through indirect measurement equations. The state vector is defined in terms of deviations of the parameters and inputs that need to be calibrated from available estimates. Standard Kalman Filter theory does not apply to this formulation...

‣ Transition to smart card technology : how transit operators can encourage the take-up of smart card technology

Hong, Yi, S.M. Massachusetts Institute of Technology
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 184 p.
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This thesis explores and evaluates the essential strategies needed for transit agencies to switch from traditional fare collection systems to smart cards. More transit agencies today are investing in smart card technology as part of their new automated fare collection (AFC) systems. Although the benefits of switching to smart card systems have been well-researched and acknowledged by transit agencies, it is unclear how a transit agency should go about implementing a smart card system in order to achieve optimum customer acceptance and to reap maximum benefits from the system. Recent experience has shown that a range of implementation policy decisions can go a long way towards speeding or slowing down the adoption of the technology by customers. A case study approach is used here to identify and evaluate the effectiveness and impacts of policies used by five transit agencies that currently employ smart cards. These policies fall into two categories: 1) distribution, operational and usage policies, and 2) fare policies. Distribution, operational and usage policies must be designed to facilitate and enhance customer adoption of smart cards, especially in the case where alternative fare media will co-exist.; (cont.) Fare policies are designed to differentiate smart cards from other fare media through differential pricing strategies...

‣ Understanding the role of trading in water quality management : based on U.S. experience

Pharino, Chanathip
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 236 p.
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This research demonstrates an overview of the performance of water quality trading programs currently implemented within the U.S. The role of trading in water quality management is identified through systematical comparisons of all possible aspects related to trading process, structure, and scale of existing water quality trading programs. The role of trading focuses on the output of achieving standard ambient water quality and on increasing the flexibility of water quality management to enhance effectiveness and accommodate economic growth. The trading encourages independent polluters to make pollution control decisions that best suit their own situations. The trading reduces overall operating costs and distributes equity on water pollution control abatements between point sources and nonpoint sources. The achievement of each program is mainly affected by various factors that include (a) the flexibility of trading rules and water pollution regulations, (b) the polluters' obligation and financial ability to meet regulatory requirements, and (c) the localized characteristics of water pollution problems and diversity of polluters in a watershed. Any water quality trading framework should promote the principle of simplicity, reliability and minimal costs.; (cont.) The recommended approaches for improving program implementation are to (a) shift towards a cap-and-trade system; (b) allow the execution of a multi-party permit; (c) establish a statewide trading policy; (d) set up a hybrid system (between tradable permit and tax/rebate system); and (e) test the practicality of a program on a smaller scale before actual implementation at a larger scale.; by Chanathip Pharino.; Thesis (Ph. D.)--Massachusetts Institute of Technology...

‣ Simulation of filtration for suspension transport in porous media

Kim, Yun Sung, 1974-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 308 p.; 14644532 bytes; 14685932 bytes; application/pdf; application/pdf
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This thesis describes the development and application of a novel method for analyzing the filtration of particles transported through a granular porous medium. The proposed analysis considers the deposition of particles through discrete simulations of particle-laden flow in a cylindrical model pore. The pore model assumes that particles collect, mound up and ultimately clog the pore under the action of hydrodynamic and gravitational forces. By simulating particle deposition processes at the pore scale, the current analyses provide a more realistic physical framework for interpreting filtration experiments than conventional continuum models that implicitly assume length scales much larger than the pores. A detailed parametric study has established relationships between the collection efficiency, mound height and deposit depth as functions of the model pore dimensions, orientation (relative to the gravitational field) and particle settling velocity for injection at constant flow rate. The results showed that the maximum mound height and deposit depth can be correlated with the pressure difference necessary to maintain flow through the model pore. A quasi one-dimensional network 'bubble' model (Datta and Redner, 1998) was developed to simulate 1-D suspension transport problems. The bubble model comprises a serial linkage of bundles of cylindrical bonds with shared nodes at each end. Bubble model simulations include distribution functions for the pore dimensions. Filtration in an individual bond is characterized by correlations from the model pore simulations.; The bubble model has been applied to interpret filtration data from two sets of column experiments: acrylic particle transport through glass beads by Yoon et al. (2004)...

‣ Temperature analysis for lake Yojoa, Honduras

Chokshi, Mira (Mira K.)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 115 p.; 21424512 bytes; 21424051 bytes; application/pdf; application/pdf
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Lake Yojoa is the largest freshwater lake in Honduras, located in the central west region of the country (1405' N, 88° W). The lake has a surface area of 82 km2, a maximum depth of 26 m. and an average depth of 16 m. The locals believe that the anthropogenic activities around the lake for the past 25 years have impacted the water quality of the lake. Temperature analysis of the lake helps to understand the seasonal changes in the thermal structure of the lake, and it also indicates the seasonal changes in the water quality of the lake. The lake is marginally stratified most of the year, with a maximum difference of 4°C between the water surface and the lake bottom. The temporal changes in the thermal structure of the lake are studied using the lake stability analysis and a temperature model CE-THERM. The two analyses confirm that the lake overturns once a year. However, they differ on the onset of the overturn event and the seasonal changes in the stratification depth. The stability analysis indicates an overturn in November and for some years less stable lake conditions in June. The CE-THERM model was run for year 2005 and it indicates a possible overturn in June, and the lake remaining mixed until December.; (cont.) Further analysis using additional data is recommended to improve the temperature model predictions. Higher wind speeds...

‣ Encouraging low-impact-development stormwater-management practices / Assabet River Watershed sub-basin case study

Brown, James E. (James Edward), 1969-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 95 leaves; 6775893 bytes; 6786815 bytes; application/pdf; application/pdf
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Regulatory codes and ordinances create a framework that guide stormwater management decision processes. These regulations are designed to protect the health and safety of the public and to preserve the natural integrity of the environment. Using a case-study approach in Acton, Massachusetts, a two-part examination is performed. The first is a comprehensive review of Acton's developmental code and ordinances. The second part of the study is a site redevelopment design using LID technologies for site-level stormwater management. To facilitate the regulatory review, a code and ordinance worksheet (COW) developed by The Center for Watershed Protection (CWP) was used to evaluate Acton's regulations against the CWP's twenty-two model development principles. Acton's score was then compared to previously completed worksheets from eighteen other eastern seaboard communities. The Discovery Museums, a children's museum in Acton, was chosen for the site redevelopment. The museum expressed a desire to remove an existing parking area and reconfigure another lot to absorb the displaced spaces. The EPA's Low-Impact Development Design Strategies manual was used to guide the museum site planning and design development. The design evaluation included comprehensive hydrologic and water quality analyses to determine pre- and post- development performance. The results of the regulatory review demonstrate that Acton's existing developmental codes and ordinances do not presently encourage LID practices and have only a 62% agreement with the CWP model development principles. The museum site redevelopment design proves that site-level stormwater management technologies can be incorporated into the site landscape and be used to return the site's hydrologic volume...