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
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Item Acoustic Black Hole with Functionally Graded Perforated Rings(2024) Petrover, Kayla; Baz, Amr; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This thesis investigates a novel class of acoustic black hole waveguides (ABH) that harnesses the functionality of an array of optimally designed Functionally Graded Perforated Rings (FGPR). Through this approach, the developed ABH exhibits inherent energy dissipation characteristics derived from the flow through the perforations, which enhances its acoustic absorption behavior, resulting in rapid attenuation of the propagating waves as it traverses the length of the waveguide. Furthermore, the proposed ABH structure facilitates the incorporation of additional porous absorbing layers sandwiching the rings to further enhance its absorption characteristics. Consequently, the operational mechanism of this new class of ABH waveguides diverges significantly from that of the conventional ABH waveguide, which generates the black hole effect by employing sequential solid-flat rings of decreasing inner radius to create the necessary virtual power law taper. Instead, the new class of ABH generates the black hole effect through reactive means rather than the effective dissipative means of the conventional ABH. Therefore, this thesis develops a transfer matrix modeling (TMM) approach and a finite element method (FEM) approach to model the absorption and reflection characteristics of the novel class of ABH, aiming to predict its behavior and, more importantly, demonstrate its merits as effective means for controlling sound propagation. The interior-point method for optimization was employed to select optimal geometric design parameters for the FGPR inside the proposed ABH. Accordingly, the ABH with FGPR is manufacturable, unlike the conventional, and its acoustic properties are tuned to minimize the reflection of incoming acoustic waves across the frequency range 0-5 kHz. This optimization process is then repeated for the ABH with FGPR sandwiched by absorbing layers. From the pool of optimal designs generated, those that offer manufacturing advantages are chosen for further testing and evaluation. Numerical simulations are conducted to showcase the advantages and behavior of the proposed ABH configurations. The predictions of the TMM and FEM are compared and validated against experimental results which are collected with the ACUPRO impedance tube. Furthermore, comparisons between the ABH with FGPR and conventional ABH are made to elucidate and distinguish their respective behaviors and underlying principles of operation.Item Efficient learning-based sound propagation for virtual and real-world audio processing applications(2024) Ratnarajah, Anton Jeran; Manocha, Dinesh; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Sound propagation is the process by which sound energy travels through a medium, such as air, to the surrounding environment as sound waves. The room impulse response (RIR) describes this process and is influenced by the positions of the source and listener, the room's geometry, and its materials. Physics-based acoustic simulators have been used for decades to compute accurate RIRs for specific acoustic environments. However, we have encountered limitations with existing acoustic simulators. For example, they require a 3D representation and detailed material knowledge of the environment. To address these limitations, we propose three novel solutions. First, we introduce a learning-based RIR generator that is two orders of magnitude faster than an interactive ray-tracing simulator. Our approach can be trained to input both statistical and traditional parameters directly, and it can generate both monaural and binaural RIRs for both reconstructed and synthetic 3D scenes. Our generated RIRs outperform interactive ray-tracing simulators in speech-processing applications, including Automatic Speech Recognition (ASR), Speech Enhancement, and Speech Separation, by 2.5%, 12%, and 48%, respectively. Secondly, we propose estimating RIRs from reverberant speech signals and visual cues in the absence of a 3D representation of the environment. By estimating RIRs from reverberant speech, we can augment training data to match test data, improving the word error rate of the ASR system. Our estimated RIRs achieve a 6.9% improvement over previous learning-based RIR estimators in real-world far-field ASR tasks. We demonstrate that our audio-visual RIR estimator aids tasks like visual acoustic matching, novel-view acoustic synthesis, and voice dubbing, validated through perceptual evaluation. Finally, we introduce IR-GAN to augment accurate RIRs using real RIRs. IR-GAN parametrically controls acoustic parameters learned from real RIRs to generate new RIRs that imitate different acoustic environments, outperforming Ray-tracing simulators on the Kaldi far-field ASR benchmark by 8.95%.Item Learning Autonomous Underwater Navigation with Bearing-Only Data(2024) Robertson, James; Duraiswami, Ramani; Electrical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Recent applications of deep reinforcement learning in controlling maritime autonomoussurface vessels have shown promise for integration into maritime transportation. These could have the potential to reduce at-sea incidents such as collisions and groundings which are majorly attributed to human error. With this in mind the goal of this work is to evaluate how well a similar deep reinforcement learning agent could perform the same task in submarines but using passive SONAR rather than the ranging data provided by active RADAR aboard surface vessels. A simulated submarine outfitted with a passive spherical, hull-mounted SONAR sensor is placed into contact scenarios under the control of a reinforcement learning agent and directed to make its way to a navigational waypoint while avoiding interfering surface vessels. In order to see how this best translates to lower power autonomous vessels (vice warship submarines), no estimation for the range of the surface vessels is maintained in order to cut down on computing requirements. Inspired by my time aboard U.S. Navy submarines, the agent is provided with simply the simulated passive SONAR data. I show that this agent is capable of navigating to a waypoint while avoiding crossing, overtaking, and head-on surface vessels and thus could provide a recommended course to a submarine contact management team in ample time since the maneuvers made by the agent are not instantaneous in contrast to the assumptions of traditional target tracking with bearing-only data. Additionally, an in-progress plugin for Epic Games’ Unreal Engine is presented with the ability to simulate underwater acoustics inside the 3D development software. Unreal Engine is a powerful 3D game engine that is incredibly flexible and capable of being integrated into many different forms of scientific research. This plugin could provide researchers with the ability to conduct useful simulations in intuitively designed 3D environments.Item The Natural Response of Uniform and Nonuniform Plates in Air and Partially Submerged in a Quiescent Water Body(2024) Fishman, Edwin Barry; Duncan, James; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The free vibration of three aluminum plates (.4 m wide, 1.08 m long) oriented horizontally is studied experimentally under two fluid conditions, one with the plate surrounded by air, called the Air case, and the other with the bottom plate surface in contact with a large undisturbed pool of water, called the Half-Wet case. Measurements of the out-of-plane deflection of the upper surfaces of the plates are made using cinematic Digital Image Correlation (DIC) over the center portion of the surface and optical tracking of the center point. Three plate geometries and boundary conditions are studied: A uniform plate with 6.35 mm thickness pinned at the two opposite narrow ends (designated UP), a uniform plate with 4.83 mm thickness simply supported at one narrow end and clamped at the opposite end (UC), and a stepped plate with thickness varying from 12.7 mm to 6.35 mm along its 1.08 m length pinned at two opposite narrow ends (SP). The plate's free response is induced using an impact hammer at three locations along the center-line of the plate. Video frames of the motion of the upper surface of the plate are collected from stereoscopic cameras and processed using DaVis-Strainmaster and MATLAB to extract full-field displacements as a function of time. Two-degree-of-freedom displacements of the plate center are also collected by tracking a target attached to the center of the plate's lower surface. Time and frequency response plots are presented for comparison between the Half-Wet and Air cases and analysis of their dynamics. It is found that the added mass of the water results in lower measured natural frequencies and modified mode shapes. In the Air case, these results are compared to mode shapes/frequencies produced in Creo Simulate and found to agree. Further experiments are discussed.Item Fish Bioacoustics: From Basic Science to Policy(2024) Colbert, Benjamin; Bailey, Helen R; Popper, Arthur N; Marine-Estuarine-Environmental Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Sound is critically important to fishes. Sound is used to communicate with conspecifics, to detect predators and prey, or to otherwise understand the world around them. Within this dissertation, I used a variety of methods to investigate multiple aspects of fish bioacoustics, including hearing, hearing in noise, the effects of anthropogenic sound, and the morphology of peripheral auditory structures.In Chapter 2, I reviewed international policy on the regulation of underwater sound and the effects of underwater sound on marine and aquatic habitats. I found that while there are increasing efforts to regulate underwater noise, the policy efforts are hampered by a lack of quantifiable metrics associated with impacts of anthropogenic sound in aquatic habitats and species. In Chapter 3, I measured auditory sensitivity of cyprinids using physiological methods. Auditory evoked potentials, a physiological measure of auditory sensitivity, have been used in previous studies to measure hearing sensitivity. However, while physiological methods have their place, they are measuring the sensitivity of the ear rather than the entirety of the auditory pathway. Therefore, I further measured hearing sensitivity of goldfish using behavioral methods that encompass the full auditory pathway. I found that physiological methods tend to underestimate actual hearing sensitivity at frequencies less than 1000 Hz. In Chapter 4, I investigated cyprinid hearing in noise, using both physiological and behavioral measures. Critical ratios were measured for four species of carp and goldfish using auditory evoked potentials. Behavioral methods were also used to measure critical ratios for goldfish. These data represent the first measurements of critical ratios for carp and the first comparative analysis between critical ratios measured using both physiology and behavior. I found that critical ratios for carp increase by as much as 25 dB between 300 Hz and 1500 Hz. I also found that physiological methods likely overestimate actual critical ratios for fish. In Chapter 5, I used micro-computed tomography (micro-CT) and three dimensional geometric morphometrics to compare the peripheral auditory structures of three species of carp. Three dimensional models of the tripus ossicle, the posterior most Weberian ossicle, and the sagitta otolith were created and the shape of these structures for silver carp (Hypophthalmichthys molitrix), bighead carp (H. noblis), and grass carp (Ctenopharyngodon idella) quantified and contrasted. I found that the shape of the tripus differed between the Hypophthalmichthys genus (i.e., silver and bighead carp) and Ctenopharyngodon (grass carp), demonstrating a possible phylogenetic signal in the shape of the Weberian ossicles. In Chapter 6, I studied the response of wild oyster toadfish (Opsanus tau) to underwater radiated noise from boats. I used passive acoustic monitoring to record toadfish vocalizations and vessel passages in the Chesapeake Bay, U.S.A. The effect of acute vessel passage was determined by comparing the number of calls after a vessel had passed to a control period. The effect of both aggregate vessel passage over an hour and environmental variables were investigated using generalized additive mixed models. I found that there was no significant effect on toadfish call rates from acute vessel passage but when vessel generated sound was higher over an hour long period (i.e., aggregate effect), call rate declined.Item Shaping Sound: Engineering Adaptable Spaces(2023) Majka, Nicholas Charles; Bell, Matthew J; Architecture; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Music and architecture share a unique series of connections, not only in their terminology, rational fundamentals, and creative potential, but also in their special public-facing role in society. These two realms provide opportunities to deeply connect with the people who encounter them and unify groups under shared experiences. However, many projects that have attempted to blend music and architecture simply use sound as a design driver for architectural form, much to the degree that this thesis had originally intended. Instead, what if the architecture of a space could adapt itself to the performances taking place, and allow artists or performers to be themselves without feeling the need to bend their styles to conform to the venue. What if the venue could change and conform to the artist? This thesis aims to explore that possibility, and investigate how architectural solutions could alter a space through dynamics and materiality to better optimize the variety of genres that would exist there, allowing music and sound to perform at its best no matter what qualities of space are needed.Item NUMERICAL ACOUSTICS FOR PHYSICAL AND SIMULATED ENVIRONMENTS(2023) Kaneko, Shoken Eckhart; Duraiswami, Ramani; Gumerov, Nail A; Computer Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Computer modeling and numerical analysis of acoustical phenomena have important applications including manufacturing, audio technologies in immersive multimedia, and machine learning systems involving audio. The focus of the present dissertation is the exploration of numerical methods for modeling, simulating, synthesizing, estimating, processing, controlling, and analyzing acoustical phenomena in the physical world as well as its applications to the virtual world, i.e. immersive technologies for creating virtual, augmented, and extended realities.The dissertation is structured as follows. In chapter 1, I introduce some fundamentals and basic concepts of numerical acoustics and discuss existing practical problems in acoustics. In chapter 2 and chapter 3, I propose two novel techniques for three-dimensional sound field capturing end encoding for immersive audio applications, which are both based on (semi-)analytical cancellation of scattering caused by microphone arrays mounted on acoustic scatterers. In chapter 4 and chapter 5, I introduce a fast algorithm for synthesizing acoustic impulse responses in large-scale forests, and use it to predict the performance of acoustic wildlife monitoring systems based on large-scale distributed microphone arrays. In chapter 6, I propose a novel general-purpose individual-agnostic binaural localizer which supports sound source localization from arbitrary directions without a priori knowledge of the process generating the binaural signal. In chapter 7 and chapter 8, I develop frameworks for regularized active sound control, using either point- or mode-control and using either distributed or local worn loudspeaker and microphone arrays with applications including speech privacy, personal active noise control, and local crosstalk cancellation with limited noise injection into the environment. In chapter 9, chapter 10 and chapter 11, three numerical methods for evaluating integrals arising in the (fast multipole accelerated) boundary element method are introduced. In chapter 9, a recursive algorithm is developed which allows efficient analytical evaluation of singular and nearly singular layer potential integrals arising in the boundary element method using flat high-order elements for Helmholtz and Laplace equations. In chapter 10, a differential geometry-based quadrature algorithm is developed which allows accurate evaluation of singular and nearly singular layer potential integrals arising in the boundary element method using smooth manifold boundary elements with constant densities for Helmholtz and Laplace equations. In chapter 11, an algorithm for efficient exact evaluation of integrals of regular solid harmonics over high-order boundary elements with simplex geometries is developed. In chapter 12, I discuss future research directions and conclude the dissertation.Item Aeroacoustic Implications of Installed Propeller Interactional Aerodynamics and Transient Propeller Motions(2023) Jayasundara, Dilhara; Baeder, James; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The emergence of advanced air mobility and sustainable aviation concepts have revived the interest in propeller-driven aircraft. A number of electric vertical take-off and landing (eVTOL) aircraft have been developed to cater to the demands of urban air mobility (UAM) and significant advancements have been made in unmanned aerial vehicles (UAV) equipped with vertical take-off and landing capabilities. However, the community acceptance of these new aircraft configurations highly depends on having a low noise footprint as they will operate in dense urban environments. Propeller noise is considered the major source of noise in these aircraft with the introduction of electric propulsion and it can significantly increase with the effects of installation and transient propeller motions. This study aims to comprehend the complex aerodynamic interactions within such aircraft that result from propeller installation and contribute to the generation of high noise levels. To understand the physics of propeller installation, a wingtip-mounted propeller was analyzed at several angles of attack using computational fluid dynamics (CFD) based on Reynolds-averaged Navier-Stokes (RANS) equations and computational aeroacoustics based on the Ffowcs Williams - Hawkings equation. The aeroacoustic implications of the propeller axis inclination and the propeller-wing aerodynamic interaction were studied in-depth. The propeller-wing interaction leads to a significant increase in propeller noise (~20 to 30 dB increase along the rotational axis) and causes the wing to generate a loading noise in the same order of magnitude as the propeller noise. To extrapolate the understanding of installation effects to a full aircraft, the aeroacoustic characteristics of a quadrotor biplane tailsitter were analyzed in both hover and forward flight focusing on the rotor-rotor and rotor-airframe aerodynamic interaction. The rotor-rotor interaction was found to be a significant source of loading noise in hover but having the fuselage as a physical barrier between the rotors largely reduces its effect. The airframe loading noise and rotor broadband noise are equally dominant as the rotor tonal noise when the aircraft is in forward flight. Moreover, the study evaluated the effectiveness of rotor synchrophasing in reducing the aircraft noise footprint and it showed promising results in hover, causing a reduction of aircraft noise by more than 10 dB. Furthermore, an efficient computational aeroacoustics framework was developed to facilitate the computations, ensuring optimal utilization of the computational resources. The CPU and GPU parallelization and other optimization techniques were able to achieve a 98% reduction in computation time for an isolated propeller case. This enabled the rapid aeroacoustic computations of periodic and non-periodic problems. This was used to analyze the aeroacoustics of an isolated propeller undergoing a transition from hover to forward flight. The aerodynamic and acoustic results of the unsteady case were compared with quasi-steady cases performed at intermediate tilt angles. The quasi-steady CFD simulations predicted the unsteady transition aeroacoustics with reasonable accuracy. A tilting quasi-steady approach was proposed to better capture the aerodynamics and acoustics of the unsteady transition.Item SURROGATE MODELING AND CHARACTERIZATION OF BLADE-WAKE INTERACTION NOISE FOR HOVERING SUAS ROTORS USING ARTIFICIAL NEURAL NETWORKS(2022) Thurman, Christopher; Baeder, James; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This work illustrates the use of artificial neural network modeling to study and characterize broadband blade-wake interaction noise from hovering sUAS rotors subject to varying airfoil geometries, rotor geometries, and operating conditions. Design of Experiments was used to create input feature spaces over 9 input features: the number of rotor blades, rotor size, rotor speed, the amount of blade twist, blade taper ratio, tip chord length, collective pitch, airfoil camber, and airfoil thickness. A high-fidelity strategy was then implemented at the discrete data points defined by the designed input feature spaces to design airfoils and rotor blades, predict the unsteady rotor aerodynamics and aeroacoustics, and isolate the blade-wake interaction noise from the acoustic broadband noise, which was then used for prediction model training and validation. An artificial neural network tool was developed and implemented into NASA's ANOPP2 code and was used to identify an optimal prediction model for the nonlinear functional relationship between the 9 input features and blade-wake interaction noise. This optimal artificial neural network was then validated over test data, and exhibited prediction accuracy over 91% for data previously unseen by the model. First- and second-order sensitivity analyses were then conducted using the developed artificial neural network tool and it was seen that input features which serve to directly modify the thrust coefficient, such as airfoil camber and collective pitch, had a dominant effect over blade-wake interaction noise, followed by second-order interaction effects related to the mean rotor solidity. The optimal prediction model along with aerodynamic simulations were used to further study the effect of varying input features on blade-wake interaction noise and three types of blade-wake interaction noise were identified. Blade-wake interaction noise caused by impingement of the turbulence entrained in a tip vortex on the leading edge of a subsequent rotor blade showed to be the most prominent type of blade-wake interaction noise, exhibiting an acoustic contribution upward of 7 dB. Blade-wake interaction noise caused by a direct impingement of a tip vortex on the leading edge of a subsequent rotor blade had the second largest acoustic significance, exhibiting roughly 6 dB of broadband noise. The third, and least significant type of blade-wake interaction noise was shown to be caused by impingement of a blade-wake sheet on the mid-span of a subsequent rotor. This last type of blade-wake interaction noise was seen to only occur in the turbulent-wake operating state and possibly mild vertical descent conditions, and had approximately a 2.5 dB acoustic contribution.Item PASSIVE AND ACTIVE GRADED-INDEX ACOUSTIC METAMATERIALS: SPATIAL AND FREQUENCY DOMAIN MULTIPLEXING(2022) Yazdkhasti, Amirhossein; Yu, Miao; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Acoustic metamaterials, similar to their electromagnetic counterparts, are artificial subwavelength materials designed to manipulate sound waves. By tailoring the material's effective properties such as bulk modulus, mass density, and reflective index, these materials can be designed to achieve unprecedented acoustic waves control and realize functional devices of novel properties. Specifically, high-refractive-index acoustic metamaterials have an effective refractive index much larger than air, enabling wave compression in space and a strong concentration of wave energy. Another type of acoustic metamaterials closely related to high-index acoustic metamaterials is graded-index metamaterials, which can be obtained by gradually varying material compositions or geometry over a volume of high-index acoustic metamaterials.The overall goal of this dissertation is to achieve a fundamental understanding of passive and active graded-index acoustic metamaterials for spatial and frequency domain multiplexing and explore their applications in far-field acoustic imaging and sonar systems. Three research thrusts have been pursued. In the first thrust, the spatial domain multiplexing of passive graded-index acoustic metamaterials has been investigated for enhancing far-field acoustic imaging. An array of passive graded-index acoustic metamaterials has been designed and developed to achieve a far-field acoustic imaging system. Parametric studies have been carried out to facilitate the performance optimization of the imaging system. The performance of the metamaterial-based imaging system has been investigated and compared to the scenario without the metamaterials. In the second thrust, frequency-domain multiplexing with active graded-index acoustic metamaterials has been investigated. An active graded-index metamaterial system with a number of active unit cells has been designed and fabricated. A fundamental understanding of the frequency multiplexing properties of the metamaterials has been developed through numerical and experimental studies. In the third thrust, the capabilities of an acoustic sensing system with active graded-index metamaterials as an emitter for shape, size, and surface classification have been explored.