Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 61 for “"Broadband noise"”.
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Aerodynamic broadband noise from contra-rotating open rotors
… their introduction is their very high levels of noise emissions. There is therefore a need for schemes by which the noise from CRORs can be predicted and hence reduced. Nearly all of the research effort on the prediction and reduction of CROR noise has been so far focused on the tonal component, …
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Broadband Noise Prediction of an Axial Compressor Operating at Low Reynolds Number
… into the production and prediction of broadband noise in axial compressors operating at low Reynolds number. The low Reynolds number (chord based $Re_C \leq 5\times 10^4$) regime presents new flow physics by the large regions of laminar flow that are present in the compressor. As such …
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Modifications of Coherent Structures in Fan Blade Wakes for Broadband Noise Reduction
… experiments with a view to the likely effects on broadband aircraft engine interaction noise. Single and three-component hotwire velocity measurements were made downstream of the cascade for a chord Reynolds number of 390,000 and a Mach number of 0.07. Measurements of the two-point velocity …
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Numerical characterization of rotor broadband noise sources in a high bypass-ratio turbofan
Le rôle du bruit de rotor devient plus important avec des développements récents des turboréacteurs. Il peut se comparer avec le bruit de l'interaction rotor-stator à cause de l'augmentation du diamètre de rotor ainsi que de la vitesse en tête de la pale. Par contre, il n'y a pas beaucoup d'études …
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The perceived urgency and detection time of multi-tone and frequency-modulated warning signals in broadband noise
… interest were those settings with steady-state broadband machinery noise. Conditions included a loading task which presented additional attentional demands upon the subject during the signal detection task. Free-modulus magnitude estimation quantified the relationship between auditory signal …
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Use of fan rig data for the understanding and prediction of fan broadband noise and noise changes due to a variable area nozzle
… data for the understanding and prediction of fan broadband noise and noise<br/>changes due to a variable area nozzle<br/>As suggested by the title, fan rig noise measurements form an integral part of this thesis. The<br/>analysis of a database of rig noise measurements forms the first section of …
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Aerodynamic and Acoustic Modeling for eVTOL Rotor Noise Prediction
… Aeromechanics Rotorcraft Model (CHARM), tonal noise calculations using the acoustic solver PSU-WOPWOP, and broadband noise predictions from the UCD-QuietFly framework. Boundary-layer inputs traditionally obtained from the viscous-inviscid solver, XFOIL, were replaced with higher-fidelity …
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Numerical investigation of slat noise attenuation using acoustic liners
Noise generated by high-lift devices such as slats on a wing is a major contributor to the overall airframe noise during the landing approach of a commercial aircraft. In this work the concept of attenuating slat noise using absorptive acoustic liners in the slat/main element gap is explored using …
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Examining the Interaction Between Startle and Response Inhibition
… in the task: a startling stimulus (50 ms, 100 dB broadband noise) presented either alone or concurrently with a circle (Go or No- Go) stimulus; and, in the second study, a less intense prepulse stimulus (50ms, 75dB broadband noise) was either presented alone or 120 ms before a startling stimulus …
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Measurement and Prediction of Rotor Noise Sources for sUAS in Outdoor and Laboratory Environments
… comparison of aerodynamic performance and noise of eVTOL rotors operating in multiple facilities, and analysis of the noise associated with an outrunner brushless DC motor. Empirical and low-order models are used to predict aerodynamic performance, tonal noise, and broadband noise for …
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In-duct measurement techniques for the characterisation of broadband aeroengine noise
The focus of this thesis is the measurement of broadband fan noise, which due to reductions in tonal and jet noise, is now the dominant source at approach, and a major contributor at takeoff. This thesis proposes three new in-duct measurement techniques for the characterisation and measurement of …
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A Study of Narrowband Noise Characteristics Associated with Vortex Motion in High Temperature Superconductors
… To investigate their motion, voltage noise generated by moving vortices is studied for different material defect types using a nonequilibrium Metropolis Monte Carlo simulation. The current-voltage (I-V) characteristics obtained from the simulation for various vortex densities and …
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Advances in passive acoustic detection, localization, and tracking applied to unmanned underwater vehicles
… due to machinery vibration and cavitation noise. However, cavitation noise of UUVs is considerably quieter than ships and boats, making detection significantly more challenging. In this thesis, I demonstrated that it is possible to passively track a UUV from its highfrequency motor noise …
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Advances in Passive Acoustic Detection, Localization, and Tracking Applied to Unmanned Underwater Vehicles
… due to machinery vibration and cavitation noise. However, cavitation noise of UUVs is considerably quieter than ships and boats, making detection significantly more challenging. In this thesis, I demonstrated that it is possible to passively track a UUV from its high-frequency motor noise …
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Analysis of Two-point Turbulence Measurements for Aeroacoustics
… flows as it would be encountered by hypothetical noise producing blades passing through the flows. Two-point measurements taken in the first flow, a lifting wake from a rectangular NACA 0012 half wing, are used to calculate space-time correlation functions and 'pointwise' wave number frequency …
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Design optimization of acoustic metamaterials and phononic crystals with a time domain method
… material properties with a unit cell and the broadband noise reduction with periodic arrays of cylinders. The acoustic wave propagation problem is solved in the time-domain using a Streamline Upwind/Petrov Galerkin formulation. Topology parameterization is accomplished using the homogenization …
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Propeller Noise Prediction of an Urban Air Mobility Vehicle in Urban Environment
… significantly affect both performance and noise generation. Understanding these mechanisms is critical for developing quieter and more efficient eVTOL systems that meet future community noise and certification requirements. This dissertation focuses on the high-fidelity numerical …
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Analysis, Design and Performance Evaluation of Optical Fiber Spectrum-Sliced WDM Systems
… applications by utilizing spectral slices of a broadband noise source for the different data channels. The principal broadband noise source considered is the amplified spontaneous emission (ASE) noise from an optical amplifier. Each slice of the spectrum is actually a burst of noise that is …
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State space models for isolating neural oscillations
… power, effectively separating it from background broadband noise power. This approach provides a way of separating oscillations in the time domain and while also quantifying their structure efficiently with a small number of parameters.
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Implementation of Refractory Foam Technology for Silencing Small IC Engines
… in defense applications steadily increasing, noise reduction continues to play an important role in the world of aeronautics. With the ever increasing number of small UAV flight vehicle designs and their stringent weight requirements, acoustic solutions become progressively more complex. This …
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