Theses and Dissertations from UMD

Permanent URI for this communityhttp://hdl.handle.net/1903/2

New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM

More information is available at Theses and Dissertations at University of Maryland Libraries.

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Subject: search.filters.subject.Automotive engineering

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Now showing 1 - 5 of 5
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    INTELLIGENT INTERSECTION MANAGEMENT THROUGH GRADIENT-BASED MULTI-AGENT COORDINATION OF TRAFFIC LIGHTS AND VEHICLES
    (2021) Rodriguez, Manuel Aurelio; Fathy, Hosam K; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    This dissertation examines the problem of coordinating two different types of actors in a vehicular traffic network system, namely: the traffic lights and the connected and automated vehicles traversing the traffic network. The work is motivated by an extensive previous literature showing that traffic network synchronization has substantial potential throughput and fuel economy benefits. The literature presents many algorithms for synchronizing the traversal of intersections by connected and automated vehicles (CAVs), as well as the synchronization of traffic lights within a given network. However, the integrated solution of these two synchronization problems remains relatively unexplored. The main challenge of any algorithm proposed in this area consists of managing the trade-off between computational efficiency, communication requirements, and performance. This dissertation seeks to contribute to the list of proposed coordination strategies for CAVs and smart traffic lights by formulating a decentralized framework based on combining ideas from gradient-based multi-agent control, trajectory planning and control barrier functions. The overall proposed control framework consists of describing vehicles and traffic lights by an extra state that directly or indirectly represent its timing (i.e arrival time for the vehicles, and switching time for the traffic lights). This timing variable evolves according to a networked multi-agent system, where the planned timing of neighboring agents governs the evolution of the planned timing of the ego agent. The planned timing state is then translated into a control action for the agents (i.e. acceleration for the vehicles, switching actuation for the traffic lights), through trajectory planning and safety regulation. The proposed coordination framework (i) can coordinate both vehicles and traffic lights, (ii) scales efficiently to large numbers of vehicles and intersections, (iii) is computationally efficient, (iv) can work under different levels of connectivity assumptions and in the presence of human drivers, and (v) can allow for different types of coordination strategies encoded in the underlying ETFs.
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    Phase Change Materials for Vehicle and Electronic Transient Thermal Systems
    (2020) Jankowski, Nicholas Robert; McCluskey, F. Patrick; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Most vehicle operating environments are transient in nature, yet traditional subsystem thermal management addresses peak load conditions with steady-state designs. The large, overdesigned systems that result are increasingly unable to meet target system size, weight and power demands. Phase change thermal energy storage is a promising technique for buffering thermal transients while providing a functional thermal energy reservoir. Despite significant research over the half century, few phase change material (PCM) based solutions have transitioned out of the research laboratory. This work explores the state of phase change materials research for vehicle and electronics applications and develops design tool compatible modeling approaches for applying these materials to electronics packaging. This thesis begins with a comprehensive PCM review, including over 700 candidate materials across more than a dozen material classes, and follows with a thorough analysis of transient vehicle thermal systems. After identifying promising materials for each system with potential for improvement in emissions reduction, energy efficiency, or thermal protection, future material research recommendations are made including improved data collection, alternative metrics, and increased focus on metallic and solid-state PCMs for high-speed applications. Following the material and application review, the transient electronics heat transfer problem is specifically addressed. Electronics packages are shown using finite element based thermal circuits to exhibit both worsened response and extreme convective insensitivity under pulsed conditions. Both characteristics are quantified using analytical and numerical transfer function models, including both clarification of apparently nonphysical thermal capacitance and demonstration that the convective insensitivity can be quantified using a package thermal Elmore delay metric. Finally, in order to develop design level PCM models, an energy conservative polynomial smoothing function is developed for Enthalpy and Apparent Capacity Method phase change models. Two case studies using this approach examine the incorporation of PCMs into electronics packages: substrate integrated Thermal Buffer Heat Sinks using standard finite element modeling, and direct on-die PCM integration using a new phase change thermal circuit model. Both show effectiveness in buffering thermal transients, but the metallic phase change materials exhibit better performance with significant sub-millisecond temperature suppression, something improved cooling or package integration alone were unable to address.
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    MODEL-BASED SYSTEMS ENGINEERING APPLIED TO THE TRAJECTORY PLANNING FOR AUTONOMOUS VEHICLES
    (2018) Bansal, Siddharth; Baras, John S.; Systems Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Passing maneuver is a complex driving maneuver and it becomes more challenging in oncoming traffic. In this study, a passing scenario with three vehicles is considered where car 1, an Autonomous Vehicle (AV), is moving behind car 2 in the same lane. The third vehicle is part of the oncoming traffic in the adjacent lane. The primary goal is to model and evaluate a measurement-based decision-making strategy for the AV satisfying driving safety constraints. This strategy is based on the optimal control with the objective to performing the passing maneuver safely. To evaluate the efficiency of the decision-making strategy – probability of safely completing passing maneuver, a model of the system was developed considering all three cars as point-masses. Two binary variables, each representing the collaborative nature of the cars 2 and 3, were defined. These variables show if the two vehicles will collaborate with the AV when they find out about its intention to overtake. Lastly, a sensitivity study and trade-off study are done to determine optimal design parameters for AV’s measurement system and decision-making strategy.
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    CHARACTERIZING THE QUASI-STATIC AND DYNAMIC RESPONSE OF A NON-CONTACT MAGNETO-ELASTIC TORQUE SENSOR
    (2017) Muller, Brooks Richard; Flatau, Alison; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Advances in the development of rolled-sheet magnetostrictive materials led to testing of a prototype wireless magneto-elastic torque (WiMET) sensor using the iron alloy Galfenol. As torque was applied to a shaft, stress-induced changes in the magnetic state of Galfenol that was bonded to the shaft were proportional to the applied torque. Building on that work, this thesis investigates strategies to improve both repeatability and the signal to noise ratio of WiMET sensor output. Multi-physics models of WiMET stress and magnetic states under applied torques are used to improve understanding of sensor operation. Testing to validate simulations is performed using Galfenol and Alfenol, a newer rolled-sheet alloy, for torsional loads of 0 – 200 in-lb, and under quasi-static and dynamic (0 – 2000 RPM) loading conditions. The experimental results presented support the potential of WiMET sensor use for dynamic torque measurement and health monitoring of drive train systems.
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    TRANSIENT PERFORMANCE EVALUATION OF AUTOMOTIVE SECONDARY LOOP SYSTEMS
    (2012) Eisele, Magnus; Radermacher, Reinhard; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Automotive air-conditioning is a high impact technology where improvements in energy consumption and environmental performance can make a significant difference in fuel efficiency and comfort. The mandatory phase out of R134a as refrigerant in the European Union has set the stage for new systems and alternative refrigerants. While some of these refrigerants, such as R152a or R290, have a low Global Warming Potential, their flammability requires secondary loop systems to be used. The added thermal mass of such systems may increase power consumption and delay cool down while benefitting thermal comfort during start/stop operation. The recent revival of electric vehicles, as well as the associated focus on air-conditioning energy consumption, provides new challenges and opportunities. This research focuses on the performance evaluation of refrigerants R152a and R290 during transient operation in secondary loop systems, quantification of thermal storage benefits for start/stop operation, and investigation of energy saving potentials in electric vehicles through the use of advanced air-conditioning system controls and cabin preconditioning. A test facility was built to dynamically test secondary loop systems over a wide range of pull down conditions and drive cycles using a passenger cabin model and associated controls. It was shown that R290 is a viable alternative in secondary loop systems and system performance may be on par or better compared to R134a direct expansion systems. The preservation of cooling capacity and thermal comfort during off-cycle periods were quantified for a secondary loop system, as well as a combined ice storage system. System efficiency increases with longer off-cycle periods compared to direct expansion systems. Advanced compressor control strategies and the use of cabin preconditioning can make use of this characteristic and improve energy efficiency by more than 50%. Ice storage may be used in combination with cabin preconditioning to preserve comfort for an extended driving time with reduced use of the vapor compression cycle. A Modelica model of the secondary loop system was developed and validated with experimental data. The model enables dynamic simulation of pull-down and drive cycle scenarios and was used to study the effects of coolant volume and coolant concentration on transient performance.