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 26 for “"tonal noise"”.
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The attenuation of flow-induced tonal noise using plasma actuators
The noise produced by low speed flows over cavities with and without plasma actuators were studied using experimental techniques. The acoustic and flow environments of open cavities with length-depth ratios of 0.5, 1.0, 2.0 and 3.0 have been investigated. Measurements using oil flow, particle …
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Blade tonal noise reduction using tail articulation at high Reynolds number
… is investigated as a means of reducing tonal noise due to the stator wake blade interaction in underwater vehicles. This work is experimental in nature and conducted in the closed channel water tunnel at Naval Undersea Warfare Center in Newport, Rhode Island. Tail articulation is carried …
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Numerical Investigation of Tonal Noise on a Transitional Airfoil under Varying Conditions
… for the generation of tones, but the selected tonal frequencies are governed not only by vortex shedding, but also through a feed-back loop that is determined, in addition to the flow instability, by the trailing-edge scattering and the receptivity mechanisms. The predicted tonal frequency …
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Generation of discrete frequency tones by the flow around an aerofoil
Tonal noise, the self-induced discrete frequency noise generated by aerofoils, is investigated. It is heard from an aerofoil placed in streams at low Mach number flows when inclined at a small angle to the stream. The tones are heard as a piercing whistle, commonly up to 30 dB above the background …
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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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Active Minimization of Acoustic Energy Density in a Mock Tractor Cab
<p>An active noise control (ANC) system has been applied to the problem of attenuating low-frequency tonal noise inside small enclosures. The intended target application of the system was the reduction of the engine firing frequency inside heavy equipment cabins. The ANC system was based on a …
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A New Multifunctional MEMS-Based Piezoresistive Pressure Sensor for Monitoring Static, Acoustic, and Turbulent Events in Underwater Applications
… states. Acoustic events (produced from tonal noise) reveal key behaviors in the frequency domain and possess strong alignment with published literature. The acoustic response addresses the underexplored research area of tonal noise in underwater settings. Lastly, behavior consistient …
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Active Flow Control For Reduction of Unsteady Stator-Rotor Interaction In a Turbofan Simulator
… advantage of active flow control. Significant tonal noise reductions in the far field are also obtained. The second control system involves using microphones as indirect wake sensors. The significance of these acoustic sensing approaches is to provide a practical TEB approach for realistic …
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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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Optimization of Active Noise Control for Small Axial Cooling Fans
Previous work has shown that active noise control is a feasible solution to attenuate tonal noise radiated by small axial cooling fans, such as those found in desktop computers. One such control system reduced noise levels of a baffled 80-mm fan in the free field with four small loudspeakers …
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Time average feedforward control techniques for time varying systems
… simply supported beam, and the control of inlet tonal noise radiated from a JT1SD-l turbofan engine.
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Acoustic and thermal packaging of small gas turbines for portable power
… that is required to attenuate the broadband and tonal noise of the high-speed turbomachinery. The challenge in the thermal management is the relatively large required cooling mass flow and the short flow mixing length, constrained by package size considerations. The objective is to conceive a …
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Towards a silent fan: an investigation of low-speed fan aeroacoustics
The noise (unwanted sound) from fans of all sizes, operating in close proximity to people, can be a design constraint due to annoyance or, in the worse cases, health damage. Of the total noise, aeroacoustic noise – produced by unsteadiness in the air – often represents a significant source and is …
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Large eddy simulation of acoustic propagation in turbulent flow through ducts and mufflers
… muffler. The improvement in the prediction of tonal noise and vortex shedding inside the chamber is highlighted in comparison to the RANS method. Further, the effect of forced pulsation on flow-acoustic is observed in regard to the shift in Strouhal number inside the simple expansion muffler. …
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Active structural acoustic control of aircraft interior flow noise via the use of active trim panels
Modem jet aircraft interior noise can be categorized into two main types: tonal noise caused by engine imbalance or blade passage, and mid frequency broadband noise resulting from turbulent flow. This project addresses aircraft interior flow noise caused by a flow separation over the crown of the …
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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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Prediction of Tonal Acoustic Radiation Due to Feedback-Loop Resonant Interactions in Transitional Airfoils
… surface integral methods to study the far-field noise propagation from the flow acoustic resonant interactions of the transitional airfoil. The Potential-Theoretic Method (PTM) as an advancement to traditional Kirchhoff methods is presented. The PTM eliminated the need to calculate the normal …
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A computational and experimental investigation into the aeroacoustics of low speed flows
The noise produced by low Mach number (M ? 0.4) laminar and turbulent flows is studied using computational and experimental techniques. The emphasis is on the development and application of numerical methods to further the understanding of noise generation and far field radiation. Numerical …
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Analysis and Synthesis of Aicraft Engine Fan Noise for Use in Psychoacoustic Studies
Community noise impact is an important factor in design of current generation aircraft, especially when considering projected trends in flight volume and urbanization. Simulation is a useful tool to evaluate the human annoyance response due to both current and proposed aircraft, and it has some …
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Prediction and control of sound propagation in turbofan engine bypass ducts
… means with which to suppress the rear fan noise. It is therefore important to make<br/>the best possible use of the available lined area by optimising the liner configuration. A set<br/>of analytic and numerical methods for predicting the liner attenuation performance have …
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