Página 17 dos resultados de 2122 itens digitais encontrados em 0.072 segundos

‣ Development of technical bases for using infrared thermography for nondestructive evaluation of fiber reinforced polymer composites bonded to concrete

Starnes, Monica Anastasia
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 258 p.; 14980618 bytes; 14980417 bytes; application/pdf; application/pdf
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Fiber-reinforced polymer (FRP) composites, in the form of pultruded laminates or built-up woven fabrics, are being used widely to strengthen existing concrete and masonry structures. The success of these materials in performing their intended functions depends, to a large extent, on how well they are bonded to themselves and to the substrate. There is a need for an efficient and reliable method to detect and characterize defects at the substrate interface and within multi-ply systems. Infrared thermography is well suited for this purpose because it is inherently sensitive to the presence of near-surface defects and can interrogate large areas efficiently. Before infrared thermography can be developed into a standard methodology, however, an understanding is needed of the effects of testing parameters and different types of defects. This dissertation focuses on establishing the potential for quantitative infrared thermography, that is, not only detecting but also characterizing subsurface flaws. Numerical and experimental methods are used to investigate the effectiveness of infrared thermography to estimate the width of subsurface flaws in fiber-reinforced polymer laminates bonded to concrete. First, a dimensional analysis of a simplified case of one-dimensional heat diffusion in an infinite half space is performed to establish the parameters that affect the thermal response of the test object.; (cont.) The results from the dimensional analysis identified the factors that had to be investigated in the parametric study. Next...

‣ Analysis of optimum Lamb wave tuning

Shi, Yijun, 1970-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 251 p.; 15800871 bytes; 15800628 bytes; application/pdf; application/pdf
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Guided waves are of enormous interest in the nondestructive evaluation of thin-walled structures and layered media. Due to their dispersive and multi-modal nature, it is desirable to tune the waves by discriminating one mode from the others. The objectives of this thesis are (1) to develop schemes and procedures for Lamb wave tuning, (2) to develop tools for understanding and analyzing the mechanism of various tuning techniques, and (3) to provide suggestions and guidelines for selecting optimum tuning parameters. In order to remedy the inherent problems of traditional tuning techniques using angle wedge and comb transducers (such as the inability to tune the modes with low phase velocities, and the inability to control the propagation direction of tuned waves), a novel dynamic phase tuning concept using phased arrays is proposed. In this approach, the constructive interference of desired modes is achieved by properly adjusting the time delays. As an extension to this concept, the synthetic phase tuning (SPT) scheme is introduced, in which the tuning effect is achieved by constructing virtual waves. The effectiveness of SPT against other techniques is experimentally demonstrated, which shows its feasibility. To understand the mechanism of tuning...

‣ Generation of sand bars under surface waves

Hancock, Matthew James, 1975-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 282 p.; 7101999 bytes; 7162808 bytes; application/pdf; application/pdf
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(cont.) Experiments were performed in a large wave flume to validate the theory and to study additional aspects of sand bar evolution. The wave envelope and bar profile were recorded for low and high beach reflection, monochromatic and polychromatic waves, and several sediment grain sizes. In particular, sediment sorting was demonstrated under standing waves when the seabed consisted of initially well mixed sand of two grain sizes.; A quantitative theory is described for the evolution of sand bars under monochromatic surface water waves. By assuming the slopes of the waves and seabed are comparably gentle, an approximate evolution equation is found for the seabed elevation. The boundary layer structure is calculated by assuming a depth-linear or depth-independent time-invariant eddy viscosity. An empirical formula by Sleath (1978) is used to predict the bedload transport. A convective diffusion equation governs the suspended sediment transport (which includes the effects of wave-advection), and empirical formulae by Lee et al. (2004) and Wikramanayake & Madsen (1994) specify the time-varying concentration at the seabed. Effects of mean beach slope and narrow banded waves are also considered. The sand bar elevation is found to evolve according to a forced-diffusion equation...

‣ A fracture-based approach to understanding debonding in FRP bonded structural members

Güneş, Oğuz, 1971-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 254 leaves; 20979819 bytes; 21013195 bytes; application/pdf; application/pdf
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(cont.) members. The experimental program for RC beams involves qualitative and quantitative observation of the changes in the debonding behavior and load capacity of the beams with various configurations of shear and/or flexural strengthening and anchorage conditions in four evolutionary experimental stages involving both monotonic and cyclic loading. A dramatic improvement in the debonding behavior and performance of the beams was observed with shear strengthening and with providing anchorage. An innovative design methodology involving a fracture mechanics approach was developed to describe the system failure by means of a global failure criterion. Modeling and evaluation studies confirm the potential of fracture mechanics approach for analysis and design of FRP-RC and FRP-steel systems against debonding failures.; At the dawn of a new century, the need for repair and strengthening of existing structural systems that have become substandard due to various reasons has become one of the most important challenges regarding the sustainability of existing infrastructures worldwide. A relatively new class of materials, called the fiber reinforced plastic (FRP) composites, are widely recognized for their potential use in infrastructure rehabilitation and renewal that may contribute to meeting this challenge. Prerequisite to wide range use of these materials...

‣ Natural attenuation of organophosphates in river systems: Chattahoochee River case study

Andrews, Matthew B. (Matthew Bryan), 1981-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 120, [2] p.; 5692829 bytes; 5692635 bytes; application/pdf; application/pdf
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Three organophosphoric acid triesters, tributyl phosphate (TBP), tris(2-chloroethyl) phosphate (TCEP), and tris(2-butoxyethyl) phosphate (TBEP) have been detected in surface waters across the world, primarily the result of sewage treatment plant discharge. Despite concentrations as low as a few parts per trillion, there is growing concern over the potential impact these compounds can have on human and environmental health. This study is an attempt to identify the presence of natural removal processes for these three organophosphoric acid triesters within the Chattahoochee River near Atlanta, Georgia, USA. Samples were collected during the month of January at various sites along the Chattahoochee River. They were subsequently analyzed for concentration of all three organophosphoric acid triesters. These concentrations were then implemented in the construction of mass balances with the intention of identifying a sink term for each compound. A separate set of samples were collected and analyzed at various times over a 24-hour period. These results were used to calculate a biodegradation rate for each organophosphoric acid triester within the Chattahoochee River. The results demonstrate that these three compounds are persistent in the Chattahoochee River over the course of one day. This conclusion is specific to the time of year and location of sampling. Despite findings of no significant natural attenuation...

‣ The Areal Reduction Factor (ARF) : a multifractal analysis; ARF : a multifractal analysis

Langousis, Andreas, 1981-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 117 leaves; 6755435 bytes; 6769826 bytes; application/pdf; application/pdf
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The Areal Reduction Factor (ARF) [eta] is a key parameter in the design for hydrologic extremes. For a basin of area A, [eta](A, D, 7) is the ratio between the area-average rainfall intensity over a duration D with return period T and the point rainfall intensity for the same D and T. Besides depending on A, D and possibly T, the ARF is affected by the shape of the basin and by a number of seasonal, climatic and topographic characteristics. Another factor on which ARF depends is the advection velocity, Vad, of the rainfall features. Commonly used formulas and charts for the ARF have been derived by smoothing or curve-fitting empirical ARFs extracted from raingauge network records. Here we derive some properties of the ARF under the assumption that space-time rainfall is exactly or approximately multifractal. We do so for various shapes of the rainfall collecting region and for Vad = 0 and Vad [not equal to] 0. When Vad = 0, a key parameter in the analysis is the ratio Ures = Vres/Ve between the "response velocity" Vres = L/D, where L is the maximum linear dimension of the region, and the "evolution velocity" Ve, = Le/De, where Le and De are the characteristic linear dimension and characteristic duration of organized rainfall features. The effect of Vad [not equal to] 0 depends on the shape of the region. For highly elongated basins...

‣ Service design for heavy demand corridors : limited-stop bus service

Schwarcz, Stacey
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 110, [5] leaves; 6434088 bytes; 6440895 bytes; application/pdf; application/pdf
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Many transit agencies run both limited-stop and local service along some of their heavy ridership corridors. The primary benefit of limited-stop bus service is higher speed which results in reduced running time and thus reduced travel time for passengers. This reduced travel time can improve the service quality for existing passengers and can increase ridership on the route and thus both passengers and the agency can benefit from limited- stop service. However, this strategy also results in increased access time, and in increased wait time for some passengers. This thesis develops a model to evaluate limited stop bus service and then applies the model to develop general design guidelines for limited-stop service. The model created evaluates a specific service configuration including both the local and limited-stop headways and stops. The model calculates travel times, and assigns existing demand to limited and local stops and to limited and local routes, based on minimum passenger (weighted) travel time. This assignment is applied at the origin-destination pair level. The model then calculates several measures of effectiveness, which are used to compare different configurations, including market share (local preferred, limited preferred...

‣ Reliability of corroded steel bridge girders; Reliability model for corroded steel bridge girders

Cordahi, Irene A
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 40 leaves; 2098489 bytes; 2100053 bytes; application/pdf; application/pdf
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Corrosion is one of the main causes of deterioration of bridges. Structures exposed to harsh environmental conditions are subjected to time-variant changes of their load-carrying capacity. Thus, there is a need for an evaluation to accurately assess the actual condition and predict the remaining life of a structure. System reliability can be used as an efficient tool in evaluation of existing structures. The traditional approach is based on the consideration of individual components rather than the system as a whole. However, it has been observed that the load-carrying capacity of the whole system often is much larger than what is determined by the design of components. Quantification of this difference is the scope of this study.; by Irene A. Cordahi.; Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2006.; Includes bibliographical references (leaves 39-40).

‣ Analysis of the diurnal behavior of Evaporative Fraction

Gentine, Pierre
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 160 leaves; 5805866 bytes; 5812566 bytes; application/pdf; application/pdf
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In this thesis, the diurnal behavior of Evaporative Fraction (EF) was examined. EF was shown to exhibit a typical concave-up shape, with a minimum usually reached in the middle of the day. The influence of the vegetation cover and the soil moisture conditions on EF diurnal shape was also investigated. We also checked the repercussion of a change in environmental conditions on EF. This study will finally allow a better understanding of EF and suggests some new methods to obtain a good estimate of EF and of evapotranspiration.; by Pierre Gentine.; Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2006.; Includes bibliographical references (leaves 153-160).

‣ Improving high-frequency bus service reliability through better scheduling

Fattouche, Grâce
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 135 p.
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Developing a schedule for high-frequency bus routes involves balancing the costs to the passengers in terms of passenger waiting time and in-vehicle time and the cost to the transit agency. Passengers are interested in short travel times and in short and reliable waiting times. In order to assess the trade-off between trip speed and reliability, transit planners need to follow a clear scheduling process; i.e., a series of steps the scheduler follows to create a schedule. This thesis develops a scheduling process based on a model which explicitly projects and evaluates the tradeoffs between overall travel time and reliability. The model uses Automatic Vehicle Location and Automatic Passenger Count data and is based on two critical hypotheses: (i) consecutive bus vehicle trips are independent and (ii) consecutive segment running times for a particular bus trips are independent. These two hypotheses will not be true in all cases but were shown to be true on the two CTA bus routes analyzed, 95E and 85. By simulating the running time distributions and headway variability of any proposed schedule, the model estimates the cost of the schedule for waiting passengers, onboard passengers and the transit agency.; (cont.) The scheduling process involves finding the time point schedule which minimizes the total cost with the help of the model. The scheduling process is applied to two CTA bus routes; Route 95E and 85. For each route...

‣ Development of the resource model for the Decision Aids for Tunneling (DAT)

Min, Sangyoon, 1973-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 353 p.
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The Decision Aids for Tunneling (DAT) are a computer based method with which distributions of tunnel construction time and cost as well as required and produced resources can be estimated considering uncertainties in geologic conditions, construction processes and resources. The results of the DAT in turn can be used for various decision making processes. Although the DAT included a resource management model, this was not at the same level as the other parts of the method. Hence, the main objectives of this research are to define the requirements for an adequate and comprehensive resource model for tunneling and develop a new resource model satisfying these new requirements. There are three major developments and contributions of the new resource models: 1. In order to have complete and accurate cost and time estimation, the new resource model can explicitly estimate the cost and time based on the actual amount of resources used for and produced from tunnel construction. 2. Resource scheduling and planning features have been implemented into the new resource model. This allows one to determine the optimal tunneling plan, which takes into account the technical precedence of the tunneling activities, the resource/space availability, the dynamic status of the process...

‣ Turbulent fluid jet excavation in cohesive soil : with particular application to jet grouting

Ho, Chu Eu
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 456 p.
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This thesis reviews the jet grouting methodology, and the current state of practice and research. Current methods of prediction of jet grout diameters are highly empirical and site specific, and do not take into account the jet hydrodynamics and soil properties explicitly. A rational model to describe the jet excavation mechanism for cohesive soil is presented in this thesis, with the aim of providing an improved prediction tool that can be used in jetting design. The model is based on the assumption that the velocity distribution in the cutting jet is equivalent to that of a free jet with boundaries corresponding to the dimensions of the cavity excavated in the ground. The shape of the cavity formed depends on the erosional properties of the soil and jet expansion is limited by the resistance at the jet-soil interface. It is hypothesized that the shape of the cavity excavated follows the locus of the jet radius satisfying the condition of constant wall shear stress. The model predicts that the limit of jet penetration is reached when the dynamic pressure at the jet tip becomes equal to the ultimate soil bearing resistance. The model was validated by laboratory jetting tests, using soil specimens manufactured from powdered kaolin clay...

‣ Bus supervision deployment strategies for improved bus service reliability

Pangilinan, Christopher Allan
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 146 p.
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Bus service reliability has always been a top concern for transit agencies and their customers. Unfortunately, there are several factors detrimental to reliable bus service. Outside influences such as weather, traffic, and road construction can wreak havoc on even the best laid plans. Internally, poor planning, insufficient maintenance, and differing operator abilities can work to undermine bus service reliability. To help counteract these problems, transit agencies typically deploy a team of supervisors who are responsible for monitoring, maintaining, and restoring reliable service. To do their job effectively, supervisors require high levels of operational information and a reliable communications system. These resources, however, can vary in their availability and may not be at ideal levels. This research proposes a framework to aid in the planning of bus supervision deployment given different levels of information, communications, and personnel. The primary focus of the framework is the deployment of post, mobile, and control center supervisors given an agency's current level of information and communication resources. The application of the framework begins with a service reliability and supervision resource assessment.; (cont.) Based on these assessments...

‣ Design of a low cost bamboo footbridge

Laroque, Paul (Paul Vivien Marc)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 87 leaves
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Nowadays the construction business, more so than other industries, is responsible most of the environmental issues that our society encounters. Given the increasing concern our impact on the environment, the need for new sustainable materials is growing rapidly. Bamboo is a very promising green material with remarkable properties. It has been used as a structural material for centuries in China and in South America. However, it has not yet penetrated the European or the American construction market. Bamboo's exceptional strength and light weight renders it a sustainable alternative to other materials. The objective of this work is to use the results provided by recent studies of bamboo in order to generate a design of a low cost bridge made out of this material. The structure is designed for exclusive pedestrian usage. This affordable suspended footbridge could be used in developing countries or in emergency situations.; by Paul Laroque.; Thesis (M. Eng.)--Massachusetts Institute of Technology, Dept. of Civil and Environmental Engineering, 2007.; Includes bibliographical references (leaves 78-81).

‣ Hydroxyl radical production via the photo-Fenton reaction in natural waters

Southworth, Barbara A. (Barbara Anne), 1973-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 188 leaves; 5518688 bytes; 5518494 bytes; application/pdf; application/pdf
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This dissertation investigates the importance of photo-Fenton chemistry in natural waters. The Fenton reaction, H202 + Fe(ll) [right arrow] Fe(ll) + OH- + OH', can occur in sunlit waters because both H202 and Fe(ll) are photo-chemically produced. Photo-Fenton chemistry was investigated by irradiating model systems and natural water samples with simulated sunlight and measuring both H202 accumulation and OH' production in the presence and the absence of Fe reactions. Using these data, a model was developed to calculate the potential impact of the photo-Fenton reaction in sunlit natural waters. Throughout this work, a method based on the chemiluminescent reaction of an acridinium ester compound with the conjugate base of H202 was used to analyze H202. This method is sensitive, and has a greater dynamic range, greater selectivity, and fewer sources of interference than more commonly used methods. However, its behavior is not consistent with a simple reaction mechanism. The kinetics of the chemiluminescent reaction were investigated and a mechanism proposed that can explain its behavior, confirming the ability of this method to accurately measure H202, and suggesting ways to avoid potential problems with its application. The photo-Fenton reaction was studied in model systems consisting of a standard humic substance and amorphous iron oxide exposed to simulated sunlight. A probe method was adapted to allow low concentrations of OH' to be measured without otherwise influencing the chemical reactions occurring in experiments. The difference between measured H202 accumulation in the presence and absence of Fe in these systems was interpreted as the photo-loss of H202 by reaction with Fe(ll).; (cont.) Both this photo-loss...

‣ Off-line calibration of Dynamic Traffic Assignment models; Off-line calibration of DTA models

Balakrishna, Ramachandran, 1978-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 212 p.
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Advances in Intelligent Transportation Systems (ITS) have resulted in the deployment of surveillance systems that automatically collect and store extensive network-wide traffic data. Dynamic Traffic Assignment (DTA) models have also been developed for a variety of dynamic traffic management applications. Such models are designed to estimate and predict the evolution of congestion through detailed models and algorithms that capture travel demand, network supply and their complex interactions. The availability of rich time-varying traffic data spanning multiple days thus provides the opportunity to calibrate a DTA model's many inputs and parameters, so that its outputs reflect field conditions. The current state of the art of DTA model calibration is a sequential approach, in which supply model calibration (assuming known demand inputs) is followed by demand calibration with fixed supply parameters. In this thesis, we develop an off-line DTA model calibration methodology for the simultaneous estimation of all demand and supply inputs and parameters, using sensor data. We adopt a minimization formulation that can use any general traffic data, and present approaches to solve the complex, non-linear, stochastic optimization problem.; (cont.) Case studies with DynaMIT...

‣ Analysis of market characteristics for capesize bulk carriers

Hadjiyiannis, Nicholas
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 205 leaves
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Iron ore and coal play a key role in the global economy and their consumption per capita is indicative of a country's standard of living. Their vast majority is transported by sea, making many countries rely on the efficiency and cost of transportation by capes. The cape market has closely followed the dry bulk market since the introduction of capes in the late 1960s. It is highly cyclical, creating big investment opportunities with potential for high and fast returns. China's recent economic expansion has impacted capes in particular as they account for the vast majority of iron ore transportation. The rapid increase in demand combined with the short-run inelasticity of supply due to capacity constraints has led to a record-high market. This combined with lack of confidence has some very interesting implications. The price gap between newer and older vessels has narrowed significantly, while a modern cape is worth about 50% more than ordering a new building. Since 1986 when a 9-year-old cape was of scrap value, the market has moved to the opposite extreme with a 13-year-old cape worth as much as a newbuilding.; (cont.) The industry and its development is analyzed before focusing on the current market and its prospects. Extensive analysis is carried out on a wide range of factors contributing to the outcome of the market in terms of freight rates...

‣ Drive-access transit : a regional analytical framework

Sorensen, James B
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 131 p.; 8286926 bytes; 8304053 bytes; application/pdf; application/pdf
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A framework for analyzing drive-access transit at a regional level is developed in this research. This framework is intended primarily for in-house use by regional transit agencies, yet has implications for the regional community at large. This framework serves as a tool for understanding and communicating what drive-access transit is, its significance to the regional transportation system, and the behavior of regional drive-access transit users. This framework emphasizes the utilization of GIS technology for both the analysis and communication of information relating to drive-access transit. It also focuses scholarly attention on drive-access transit in general and on kiss-and-ride in particular. The framework is applied to the Boston Metropolitan Region as a primary case study. Data from a variety of regional sources are utilized. GIS technology is used to visualize drive-access transit's regional significance in terms of total ridership, mode share, and drive-access transit facilities' utilization rates. A sub-mode choice model and a station choice model are developed for both rapid transit and commuter rail drive-access transit users. These models depend on the CTPS Emme/2 network model and the MIT Boston Regional TransCAD network model for the rapid transit and commuter rail models...

‣ A transit route simulator for the evaluation of control strategies using automatically collected data

Moses, Isaac E
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 135 leaves; 6465924 bytes; 6473053 bytes; application/pdf; application/pdf
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This thesis develops and tests an extensible simulation model that uses automatically collected transit data to simulate transit route operations, demand, and control mechanisms. This model is motivated by the increasing availability of automatically collected transit data, which enables more detailed simulation and validation and also allows for advanced control strategies that can be evaluated using simulation. A framework is presented for using simulation to evaluate the improvement in service quality enabled by data. Most previous transit route simulation models included an explicit representation of traffic flow, which requires extra input data and introduces extra complexity. A detailed simulator design is presented that uses only transit-derived data to simulate vehicle and passenger movements and outputs a detailed log for flexibility of performance measurement. A case study of operations on the CTA's Route 9 Ashland was used to demonstrate and test the simulator. The simulator could be used to test alternative operator and supervisor behavior strategies and supervisor deployment schemes, as well as potential technological advances involving real-time data. Schedule, vehicle movement, terminal departure punctuality, passenger demand...

‣ The day activity schedule approach to travel demand analysis

Bowman, John L. (John Lawrence)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 185 p.; 657870 bytes; 657625 bytes; application/pdf; application/pdf
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This study develops a model of a person's day activity schedule that can be used to forecast urban travel demand. It is motivated by the notion that travel outcomes are part of an activity scheduling decision, and uses discrete choice models to address the basic modeling problem-capturing decision interactions among the many choice dimensions of the immense activity schedule choice set. An integrated system of choice models represents a person's day activity schedule as an activity pattern and a set of tours. A pattern model identifies purposes, priorities and structure of the day's activities and travel. Conditional tour models describe timing, location and access mode of on-tour activities. The system captures trade-offs people consider, when faced with space and time constraints, among patterns that can include at-home and on-tour activities, multiple tours and trip chaining. It captures sensitivity of pattern choice to activity and travel conditions through a measure of expected tour utility arising from the tour models. When travel and activity conditions change, the relative attractiveness of patterns changes because expected tour utility changes differently for different patterns. An empirical implementation of the model system for Portland...