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He, ZhengkaiStudy on the Vortex Wake of an Airfoil Equipped with Flexible Trailing Edge Fringes
Master of Science in Engineering (MSEgr), Wright State University, 2014, Mechanical Engineering
With the inspiration of owl’s silent flight, a traditional airfoil S833 equipped with flexible fringes on the trailing edge is investigated through numerical simulation and experiments in a wind tunnel. The newly constructed airfoil is modeled and numerically investigated. An incompressible, 2D and viscous flow solver in the Computational Fluid Dynamics (CFD) software FLUENT is utilized to conduct the numerical simulation on the vortex flow feature in the wake of the airfoil. A User Defined Function code was applied to generate the defined motion of flexible fringes. The effects of the flapping frequency of the fringe and the deformation pattern of the fringe are investigated in the parametric study. On the other hand, the airfoil model with the flexible fringe is manufactured for the experimental study. A digital Particle Image Velocimetry (PIV) system is employed to investigate the flow structure in the wake and the deformation of the flexible fringes. The motion of the trailing edge fringes is extracted from the experimental measurements as the input for CFD simulation. It has been found that the addition of the flexible fringe has a significant effect on the flow characteristics in the vortex wake downstream of the airfoil as well as the aerodynamic performance of the airfoil.

Committee:

Zifeng Yang, Ph.D (Advisor); Joseph Shang, Ph.D (Committee Member); Ha-Rok Bae, Ph.D (Committee Member)

Subjects:

Mechanical Engineering

Keywords:

Airfoil S833; Trailing Edge Fringe; Noise Reduction

Schmisseur, Brooke E.B.An Evaluation of Noise Reduction Effectiveness in Four Digital Hearing Aids
MA, University of Cincinnati, 2002, Allied Health Sciences : Communication Sciences and Disorders
Background noise can have a detrimental effect on the intelligibility of speech for all listeners. However, for individuals with a cochlear hearing loss, these effects can have even greater consequence. As persons with cochlear damage are unable to make use of the "dips" and spatial separation of noise, they may require a greater speech to noise ratio than a person with a normal, non-impaired cochlea. Professionals in the field of audiology attempt to assist an individual compensate for their hearing loss, and the difficulties associated with it, by providing the appropriate amplification, usually in the form of a hearing aid. A current methodology for manipulating the signal-to-noise (S/N) ratio that hearing aid manufacturers have developed is "noise reduction". The purpose of this study was to determine if there was a significant change in S/N ratio due to the internal noise reduction circuitry in four sample digital hearing aids, across five environmental noise conditions, and across the four sample digital hearing aids in conjunction with the five environmental noise conditions. Statistical analysis showed that for the sample the change in S/N ratio was significant at the 0.05 level of significance as an effect of the hearing aids. The analysis showed that for the sample the change in S/N ratio was not significant at the 0.05 level of significance across the five environmental noise conditions. The analysis showed that for the sample the change in S/N ratio was not significant at the 0.05 level of significance across the interaction of the four sample digital hearing aids in conjunction with the five environmental noise conditions.

Committee:

Dr. Donald Hayes (Advisor)

Subjects:

Health Sciences, Audiology

Keywords:

noise reduction; hearing aids

SUMME, LORI ANNNoise Reduction in Digital Hearing Aids Using Environmental Sounds
MA, University of Cincinnati, 2003, Allied Health Sciences : Communication Sciences and Disorders
Noise reduction in digital hearing aids is often tested using speech-weighted noise. Environmental sounds such as rain or an oscillating fan can also be used to determine the efficacy of noise reduction algorithms. The algorithms of four digital hearing aids were examined in the presence of five environmental sounds. Methods: Cool Edit 2000 was used to analyze the speech spectrum before and after noise reduction. The FAAF test was used as the speech sample. Recorded versions of a fan, a 727, ocean waves, rain, and a subway served as background sounds. The Natura, Signia, Lumina, and Danalogic hearing aids were used to compare noise reduction algorithms. Results: Noise reduction algorithms did not attenuate environmental sounds as well as they reportedly attenuated speech-weighted babble, in three of the four hearing aids tested. Only one hearing aid effectively attenuated the environmental sounds tested to an acceptable degree.

Committee:

Dr. Laura Kretschmer (Advisor)

Subjects:

Health Sciences, Audiology

Keywords:

noise reduction algorithms; digital hearing aids; environmental sounds

Tekgun, DidemAcoustic Noise and Vibration Reduction on Switched Reluctance Machines through Hole Placement in Stator/Rotor Laminations
Master of Science in Engineering, University of Akron, 2017, Electrical Engineering
Switched reluctance motors (SRMs) are used in numerous applications due to their simple and robust structure. In addition to being mechanically and thermally robust, features such as high torque density, efficiency, and reliability, coupled with their fault tolerant structure and low manufacturing cost make SRMs quite attractive. SRMs are double salient pole motors. The stator has simple concentrated excitation windings, and there is no winding or magnet on the rotor. Although SRMs have many features and advantages, large torque ripple, vibration, and acoustic noise are the major disadvantages of these machines. The vibration and acoustic noise of SRMs are mainly generated by the radial forces. The radial forces cause deformation on the stator yoke, which results in vibrations and consequently, frame deformation. When these vibrations resonate with the motor body’s natural frequencies, the amplitude of the oscillations and the deformations are intensified. Hence, the acoustic noise increases significantly. The vibration and acoustic noise of SRMs have been deeply investigated throughout the years, and various methods are reported based on modifications on the motor structure and motor control for reducing them. Since this thesis is focused on the acoustic noise reduction techniques from the design perspective, the acoustic noise and vibration mitigation techniques based on the motor structure modifications are investigated. Existing methods are focused on the radial force reduction, motor natural frequency manipulation, and stator damping effect improvement. Although, improving one of these factors also improves the others, most previous studies focus on a single factor. In this thesis, a new vibration and acoustic noise mitigation method is proposed. This method combines the radial force reduction and damping improvement on the stator. The radial force is reduced by introducing rectangular windows on the rotor and the stator poles, which result in a reduction on the stator deformation. In addition, damping elements that are diamond shaped air gaps are inserted into the stator back iron. The number, size, the distance between the elements, and the distance from the stator outer surface to the first air gap are adjusted to achieve the minimum stator deformation and consequently, the minimum acoustic noise. Analyses are performed with 2D/3D electromagnetic and mechanical finite element (FEAs) and vibration analyses tools, and the acoustic noise is reduced successfully.

Committee:

Yilmaz Sozer (Advisor); Malik Elbuluk (Committee Member); Alexis De Abreu Garcia (Committee Member)

Subjects:

Electrical Engineering

Keywords:

Switched reluctance machine, acoustic noise reduction, FEA

Tepvorachai, GornAn Evolutionary Platform for Retargetable Image and Signal Processing Applications
Doctor of Philosophy, Case Western Reserve University, 2008, Computer Engineering
In this thesis, we propose a cognitive information processing system (cognitive processing) on an evolutionary platform for retargetable applications such as facial image recognition, image feature extraction, evolvable filters, and environmental information tracking. Cognitive processing can process multiple-sensory information on an automated system such as an unmanned vehicle or a surveillance unit in a remote site to avoid harsh terrain. Evolutionary platform supports the ability to change information processing behavior to comply with ever changing environment in order to accomplish a mission objective. The cognitive processing model can overcome particular difficulties to traditional search, exploration, and engineering decision making applications. The proposed cognitive strategies emphasize the decomposition of multi-sensory information, the re-construction of internal representations, and the cognitive processing of combined information which yield sub-optimal solutions and indicate best local system direction. Several applications, such as facial image recognition and digital signal processing, are used to verify our models and compare them with other well-known approaches. The derived simulation and synthesized results show that the proposed cognitive processing model on evolutionary platform attains better performance than those of the conventional methods.

Committee:

Chris Papachristou, PhD (Committee Chair); Daniel Saab, PhD (Committee Member); Frank Merat, PhD (Committee Member); Vira Chankong, PhD (Committee Member); Frank Wolff, PhD (Committee Member)

Subjects:

Computer Science; Engineering

Keywords:

cognitive; processing; evolutionary; platform; retargetable; information; adaptive; neural network; neural net; filter; signal; image; signal cancellation; noise reduction; facial image; face; recognition; FPGA; application

FRENZ, ERIC RNOISE SOURCE REDUCTION OF A HYDRAULIC ROAD SIMULATOR FOR USE AS A BSR EVAULATION PLATFORM
MS, University of Cincinnati, 2005, Engineering : Mechanical Engineering
The question was proposed: “Can a hydraulic road simulator be used, as is, for buzz, squeak and rattle (BSR) evaluation?” The road simulators, well known for durability testing, are used more and more for BSR noise evaluations and source identification. Since the systems are designed for durability testing, the acoustic impact on its test item was not a primary concern. As a result, it is necessary to determine if measurements of BSR events made inside a vehicle would be masked by the test system itself. There were three main questions investigated during the evaluation performed: What are the dominant sounds of a road simulator? Do the identified sounds affect an interior BSR evaluation of a luxury vehicle? What are the sources of the identified sounds? The road simulator system was tested at the University of Cincinnati Structural Dynamics Lab (UC-SDRL) facility with no modifications made to the environment or the test system. Baseline sound pressure measurements were made around the hydraulic actuators and inside a luxury class automobile under various configurations and excitations to determine the noise levels and frequency content of the system. The resulting noise levels inside the luxury vehicle were less than 40dB above 800 Hz for all configurations. Therefore, with no modifications, the road simulator can be used for end-of-line squeak and rattle testing in this configuration. Focusing on reducing actuator noise to improve the noise characteristics, acoustic intensity measurements were made on one of the actuators with the pump running to verify some of the known noise sources of the system. A number of the noise source frequencies were confirmed as well as their origin. The largest contributor of airborne noise in the system is the dither frequency of the servo valve. Based on the type and noise source of the road simulator, an acoustic enclosure would be effective at reducing the radiated noise levels. Two variations of an acoustic enclosure surrounding a hydraulic actuator were tested and proved to be effective in reducing the noise levels of the actuator.

Committee:

Dr. Randall Allemang (Advisor)

Subjects:

Engineering, Mechanical

Keywords:

Buzz; Squeak; Rattle; Noise Reduction; Road Simulator; BSR; Hydraulic

Harris, Christopher A.Acoustics and Fluid Dynamics Studies of High Speed Jet Noise Reduction Devices
MS, University of Cincinnati, 2009, Engineering : Aerospace Engineering
Jet noise reduction was investigated on a scale model turbofan exhaust simulator rig at a Reynold's Number O(10e6) through mean and time-resolved flow and aeroacoustic measurements. Various stream-wise vorticity production devices, including conventional and modified chevron nozzles and CVG's (Coupled Vortex Generators), were installed to increase turbulent shear layer mixing and ultimately reduce far-field radiated noise. Simplified flow simulations using a steady RANS k-epsilon turbulence model aid to elucidate the initial vortex development for several geometries. CVG's were installed in axisymmetric arrangements on both the core and fan streams of the exhaust simulator, and in the various boundary layers. Measurements of the nozzle boundary layer characteristics were performed using a total pressure probe on the baseline hardware to determine appropriate mean spatial scales, and to evaluate the boundary layer momentum thickness influence on noise for a coaxial, turbulent jet. LDV of two velocity components determined the turbulence properties in the jet at various locations in the initial mixing region and past the potential core. Acoustic far-field measurements showed that high levels of peak noise reduction were possible with added high-frequency energy. One purpose was to offer an explanation of this 'self' noise component and mixing mechanisms, in comparison with delta tabs which also incur high-frequency noise. With properly scaled geometry design, and installation configurations, the CVG's can achieve SPL peak noise reductions for essentially all directivity angles, with the addition of a high-frequency source that appears consistent with a self-noise induced dipole.

Committee:

Dr. Ephraim J. Gutmark (Committee Chair); Dr. Paul Orkwis (Committee Member); Dr. John Wojno (Committee Member); Dr. Steve Martens (Committee Member)

Subjects:

Acoustics; Aerospace Materials; Engineering; Experiments; Fluid Dynamics

Keywords:

jet; aeroacoustics; noise, reduction; suppression; vortex generators; vg; experimental

Fuller, Ryan MichaelAdaptive Noise Reduction Techniques for Airborne Acoustic Sensors
Master of Science in Engineering (MSEgr), Wright State University, 2012, Electrical Engineering
Ground and marine based acoustic arrays are currently employed in a variety of military and civilian applications for the purpose of locating and identifying sources of interest. An airborne acoustic array could perform an identical role, while providing the ability to cover a larger area and pursue a target. In order to implement such a system, steps must be taken to attenuate environmental noise that interferes with the signal of interest. In this thesis, we discuss the noise sources present in an airborne environment, present currently available methods for mitigation of these sources, and propose the use of adaptive noise cancellation techniques for removal of unwanted wind and engine noise. The least mean squares, affine projection, and extended recursive least squares algorithms are tested on recordings made aboard an airplane in-flight, and the results are presented. The algorithms provide upwards of 37dB of noise cancellation, and are able to filter the noise from a chirp with a signal to noise ratio of -20db with minimal mean square error. The experiment demonstrates that adaptive noise cancellation techniques are an effective method of suppressing unwanted acoustic noise in an airborne environment, but due to the complexity of the environment more sophisticated algorithms may be warranted.

Committee:

Brian Rigling, PhD (Committee Chair); Kefu Xue, PhD (Committee Member); Fred Garber, PhD (Committee Member)

Subjects:

Acoustics; Aerospace Engineering; Applied Mathematics; Electrical Engineering; Engineering; Remote Sensing

Keywords:

Adaptive Noise Cancellation; Adaptive Algorithms; Acoustic Sensors; Acoustic Eavesdropping; UAV; Unmanned Aerial Vehicle; Active Noise Reduction; Remote Sensing; Signal Processing; Acoustics

Mustafa, MansoorInvestigation into Offset Streams for Jet Noise Reduction
Master of Science, The Ohio State University, 2015, Aero/Astro Engineering
This effort investigates the near field behavior of two ideally-expanded subsonic dual-stream jets. One case implements a traditional symmetric, concentric dual-stream nozzle configuration while the other imposes an asymmetric, eccentric layout to model the behavior of an offset stream. The essence of an offset stream is to force an uneven azimuthal distribution of the secondary coflow and create an outside stream that varies in thickness. Past studies have shown a benefit in acoustic propagation in the direction of the thickest coflow and the present work further analyzes this phenomenon. A LES (Large Eddy Simulation) approach is implemented to run the simulations for both cases and a number of qualitative and quantitative analyses tools are used for post-processing. A reduction in the noise levels for the lower, thicker side of the eccentric nozzle is observed in comparison to the baseline concentric case. Examination of the mean flow behavior shows a shorter, thinner primary potential core for the offset case and a faster axial velocity decay rate. The asymmetric distribution of the coflow causes varying velocity profiles in the radial direction for the top and bottom regions and consequently produces unique flow features on either side. Lower levels of shear stress and slower decay rates lead to less turbulence production on the lower side of the eccentric nozzle. An investigation into the flow structures reveals lower vorticity and weaker convective structures on the bottom which influences propagation in that direction. Two-point correlation analysis reveals the presence of smaller turbulence scales in the lower, thicker portion of the eccentric case. This is further confirmed by an Empirical Mode Decomposition (EMD) study that shows lower frequency ranges dominate the concentric near field in comparison to the eccentric. The combination of these unique features demonstrate the principles behind the acoustic benefit of implementing offset stream flows in dual-stream nozzle configurations.

Committee:

Datta Gaitonde (Advisor); Mei Zhuang (Committee Member)

Subjects:

Aerospace Engineering

Keywords:

offset; noise reduction; jets; aerospace; aerodynamics; LES; computational simulation; jet noise; eccentric; concentric; dual-stream; nozzle

Palaniappan, PrashanthDe-noising of Real-time Dynamic Magnetic Resonance Images by the Combined Application of Karhunen-Loeve Transform (KLT) and Wavelet Filtering
Master of Science, The Ohio State University, 2013, Electrical and Computer Engineering
A hybrid filtering method called Karhunen Loeve Transform-Wavelet (KW) filtering is presented to de-noise dynamic cardiac magnetic resonance images that simultaneously takes advantage of the intrinsic spatial and temporal redundancies of real-time cardiac cine. This new image filtering technique combines two well-established methods: temporal Karhunen-Loeve transform (KLT) and spatial adaptive wavelet filtering. KW filtering has four steps: 1. Apply KLT along the temporal direction, generating a series of “eigenimages”. Because of the high temporal correlations, most of the energy is concentrated into a few eigenimages. 2. Marcenko-Pastur (MP) law is used to identify and discard the noise-only eigenimages; 3. 2-D spatial wavelet filter with adaptive threshold is applied to each eigenimage. An adaptive threshold is used to define the wavelet filter strength for each of the eigenimages based on the noise variance and standard deviation of the signal, resulting in stronger filtering of the eigenimages that primarily contain noise. 4. Apply the inverse KLT to the filtered eigenimages to generate a new series of cine images with reduced image noise. KW filter was compared with 2 other filters – Spatial Wavelet filter and Temporal KLT filter in terms of SNR gain and edge sharpness. For four volunteer data acquired using rate 5 acceleration, KW filter showed an SNR gain of 98%. For a matched value of SNR gain between KW filter, Wavelet filter and KLT filter, KW filter preserved 93.83% of original image sharpness while Wavelet filter and KLT filter preserved 82.23% and 88.05% respectively.

Committee:

Orlando P. Simonetti (Advisor); Yuan F. Zheng (Committee Member); Yu Ding (Committee Member)

Subjects:

Electrical Engineering

Keywords:

Noise reduction; SNR; Image Processing; MRI