UMD Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/3
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 given thesis/dissertation in DRUM.
More information is available at Theses and Dissertations at University of Maryland Libraries.
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Item Aeroacoustic Analysis of Asymmetric Lift-Offset Helicopter in Forward Flight(2021) Arias, Paulo; Baeder, James; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In recent years, the University of Maryland has worked on an asymmetric lift-offset compound helicopter. The configuration consists of a single main rotor helicopter with the addition of two key ways to increase the forward speed: a stubbed wing on the retreating fuselage side, and a slowed down rotor. Experiments and simulations have shown that the novel concept provides improved thrust potential and lift-to-drag ratios in high-speed forward flight. This study aims to determine whether the asymmetric lift-offset configuration also provides aeroacoustic benefits in forward flight in addition to its aerodynamic advantages. The aerodynamic results from previous computational and experimental studies are recreated using the Mercury framework, in-house Computational Fluid Dynamics solver based on Reynolds-Averaged Navier-Stokes (RANS) coupled to a comprehensive rotor analysis for structural deformations and trim. The acoustic analysis is performed using an acoustic code based on the Ffowcs William-Hawkings equation to solve for the tonal noise propagating from the surfaces of the aircraft. The BPM model is used for broadband noise prediction. It was found that for an advance ratio of 0.5 the wing-lift offset configuration can produce 56.8% more thrust at the same collective angle without any penalties in total noise. When the configurations produce equal thrust it was found that the wing-lift offset case has a 4 dB reduction in maximum overall sound pressure level. At an advance ratio of 0.3 with trim for equivalentthrust between configurations, a 3 dB maximum OASPL reduction was obtained with the inclusion of the wing. The rotor of the wing-lift offset case was also slowed down while maintaining equal thrust to find a 6 dB reduction at an advance ratio of 0.55. Blade flap and lag bending moments near the root were also significantly reduced for the wing-lift offset configuration with equal thrust.Item RESPONSE CONTROL IN NONLINEAR SYSTEMS WITH NOISE(2019) Agarwal, Vipin Kumar; Balachandran, Balakumar; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Noise is unavoidable and/or present in a wide variety of engineering systems. Although considered to be undesirable from certain viewpoints, it can play a useful role in influencing the behavior of nonlinear mechanical and structural systems that have multiple solutions in the form of equilibrium points, periodic solutions, and aperiodic (including chaotic) solutions. The aim of this dissertation work is to discover clues related to noise enabled steering or control for engendering desirable changes in system behavior. A combination of experimental, analytical, and numerical studies have been undertaken on the following: i) shifting of jump-up and jump-down frequencies leading to an eventual collapse of hysteresis observed in the response of a nonlinear oscillator, ii) influence of noise on the chaotic response of a nonlinear system, and iii) noise-induced escape route from a chaotic-attractor. Furthermore, a combination of analytical and numerical studies have been undertaken to understand an extended Jeffcott rotor-stator system and the influence of noise on the system dynamics. Additionally, this dissertation includes work on partial control of chaotic systems under the influence of noise, wherein the trajectories are confined inside a particular region (chaotic attractor) despite the presence of white noise. Maintaining chaotic behavior in systems in the presence of an external disturbance may be desirable and important for the dynamics of certain systems. The proposed algorithm has been shown to be effective for systems with different dimensions. The dissertation outcomes provide answers to the following fundamental questions: i) how can noise influence the long-time responses of mechanical and structural systems and ii) how can noise be used to steer a system response to avoid an undesirable dynamical state. These answers can serve as an important foundation for many industrial applications (e.g., applications with rotor-stator systems) as well.Item Monitoring and Assessment of Residential Exposure to Noise Associated with Natural Gas Compressor Stations in West Virginia(2014) Boyle, Meleah; Sapkota, Amy R; Maryland Institute for Applied Environmental Health; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Noise is a growing concern for residents living near natural gas compressor stations. This study monitored and evaluated residential noise exposure associated with living near natural gas compressor stations in West Virginia. Short-term outdoor measurements (20 min) and medium-term (24-hour) indoor and outdoor measurements were collected at homes located near compressor stations. The average sound equivalent was calculated using logarithmic averages and stratified by distance from compressor station, time of day, and location. Average short-term noise levels were 61.43 dBA (45.3 to 76.1 dBA); average 24-hour noise levels were 60.20 dBA (35.3 to 94.8 dBA). Average noise levels at control homes were 51.40 dBA, with 45.02 dBA indoors and 54.03 dBA outdoors. Average noise levels at homes near compressor stations were 8.7 dBA higher, with a 16.25 dBA difference indoors and a 4.3 dBA difference outdoors. Results indicate that living near a natural gas compressor station may increase environmental noise exposure.Item Modern Warfare(2010) Hoffman, Joseph Daniel; Richardson, William C; Art; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Title of Document: Modern Warfare Joseph Daniel Hoffman, Master of Fine Arts, 2010 Directed By: Associate Professor Williams C. Richardson, Department of Fine Art This thesis discusses my use of sound as a sculptural object. I investigate the physical potential of sound as well as its use throughout art history. By exploring the distinction between sound, music, and noise I give context for my current body of work.