Theses and Dissertations from UMD

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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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    Semi-Active Magnetorheological Seat Suspensions for Enhanced Crashworthiness and Vibration Isolation of Rotorcraft Seats
    (2007-09-27) Hiemenz, Gregory J; Wereley, Norman M; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    This research focuses on the use of magnetorheological (MR) dampers for enhanced occupant protection during harsh vertical landings as well as isolation of the occupant from cockpit vibrations. The capabilities of the current state-of-the-art in helicopter crew seat energy absorption systems are highly limited because they cannot be optimally adapted to each individual crash scenario (i.e. variations in both occupant weight and crash load level). They also present an unnecessarily high risk of injury by not minimizing the load transmitted to the occupant during a crash. Additionally, current rotorcraft seats provide no means of isolating the occupant from harmful cockpit vibrations. The objective of this research was to investigate and demonstrate the feasibility and benefits of an MR-based suspension for rotorcraft seats. As such, this research began with an in-depth investigation into design feasibility. Three MR seat suspension design cases are investigated: 1) for only vibration isolation, 2) for adaptive occupant protection, and 3) for combined adaptive occupant protection and vibration isolation. It is shown that MR-based suspensions are feasible for each of these cases and the performance benefits and tradeoffs are discussed for each case. Next, to further illustrate the occupant protection benefits gained with an MR-based suspension, three control strategies were developed and performance metrics were compared. It was shown that MR dampers can be controlled such that they will automatically adapt to the crash load level as well as occupant weight. By using feedback of sensor signals, MR dampers were adjusted to utilize the full stroke capability of the seat suspension regardless crash level and occupant weight. The peak load transmitted to the occupant and the risk of spinal injury, therefore, was always minimized. Because this control significantly reduced or eliminated injury risk during less severe landings, it is a significant advance over the current state-of-the-art rotorcraft seat suspensions which can provide no better than 20% risk of occupant injury. Finally, an MR-based seat suspension designed solely for the purposes of vibration isolation was designed, analyzed, and experimentally demonstrated. MR dampers were integrated into the current crashworthy SH-60 crew seat with minimal weight impact such that the original crashworthy capabilities were maintained. Then, utilizing semi-active control, experimental vibration testing demonstrated that the system reduced vertical cockpit vibrations transmitted to the occupant by 76%. This is a significant advance over current state-of-the-art rotorcraft seats which provide no attenuation of cockpit vibrations.
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    Pedestrian-Vehicular Crashes: The Influence of Personal and Environmental Factors
    (2005-05-03) Burnier, Carolina Valdemarin; Clifton, Kelly J; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    This thesis examines the relationship between land use and pedestrian-vehicle crashes. Analysis focuses on how the pedestrian crashes vary by personal characteristics (age, sex, condition, and severity of injury) and physical characteristics of the crash area (location type, population density, land use, pedestrian activity, and demand). The data for this study are pedestrian- vehicle crashes in Baltimore City, MD occurring between 2000 and 2002, supplied by the State of Maryland Motor Vehicle Accident Report. The results from the analysis suggest that in general, there are significant effects of land use on pedestrian crashes and, more importantly, pedestrian exposure. When controlling for demand, urban downtown areas with high population and roadway densities and good commercial accessibility are found to have negative relationships to pedestrian exposure. The results may justify the promoting of denser urban neighborhood designs and advocate the need to guide safety policy investments to these urban areas with high pedestrian activity.