×
Department Library

2020

David Franklin Van Komen (Masters Thesis, August 2020, Advisor: Traci Neilsen )

Abstract

[Abstract]

2019

Eric Lysenko (Senior Thesis, June 2019, Advisor: Traci Neilsen )

Abstract

Seismo-acoustic coupling occurs when seismic wave propagation creates air-borne acoustic signals. Research is ongoing to determine methods to distinguish between sound due to seismo-acoustic coupling and purely air-borne transmission. In a field experiment, we detonated 17-inch balloons filled with a stoichiometric oxy-acetylene mix placed both on and in the ground. We attempted to isolate ground-radiated waves by constructing a portable soundproof box to deaden air-borne sound waves. The box was constructed from mass-loaded vinyl, soundproofing composite board, liquid nails, and green glue. This design incorporated soundproofing through decoupling, absorption, and insulation techniques. Signals observed from a microphone placed in the box are compared with those obtained on microphones outside the box at various heights. The initial blast wave was not evident inside the box. However, the loudest sound measured in the box matches a subsequent portion of signals on microphones near the ground. Testing in a reverberation chamber is done to measure the insertion loss of the box. The insertion loss is applied to our signals from the balloons. Our results did not indicate the presence of coupled waves. However, ongoing research may suggest this as a viable technique for isolating ground-borne acoustic waves.

2018

David Van Komen (Senior Thesis, April 2018, Advisor: Traci Neilsen )

Abstract

An improved understanding of the sound generation of high-performance military aircraft is studied through beamforming. Conventional methods of beamforming, while powerful for localizing equivalent acoustics sources, are inadequate due to the complexities of jet noise. These complexities arise from the large, partially correlated source region, which violates the uncorrelated monopole assumption of conventional beamforming, and multiple types of noise sources, including directional and omnidirectional sources that vary with the aircraft’s operating power. These complexities require the utilization of advanced beamforming methods, such as the Hybrid Method and the Generalized Inverse method. The aim of this research is to apply advanced beamforming methods to the high-performance military aircraft jet noise to create frequency-dependent equivalent acoustic source distributions. These methods are applied to a ground-based array of 71 microphones that recorded noise from an F-35 aircraft. To investigate the multiple types of noise sources, the array is split into several subarrays that cover the sideline, maximum, and downstream regions of the noise. The advanced beamforming methods are applied to each of the subarrays at two different operating powers to investigate the different noise sources and how they change with operating powers. Subarray analysis on the F-35 engine noise yields equivalent sources for the different types of noise in overlapping regions.

Aaron Vaughn (Senior Thesis, April 2018, Advisor: Traci Neilsen )

Abstract

Jet noise has primarily been examined for laboratory-scale jets and only recently for full-scale jets. In this thesis, jet noise from a laboratory-scale Mach 1.8 jet and an F-35B high-performance military aircraft are observed and compared. Both contain turbulent mixing noise while only the full-scale jet contains broadband shock-associated noise (BBSAN). Previously developed empirical models for turbulent mixing noise were used to perform spectral decompositions. Similar angular trends for similarity spectra decompositions of the turbulent mixing noise exist across both sets of measurements. Full-scale BBSAN spatial trends are similar to laboratory-scale results from the literature for peak frequency but differ for peak level and spectral width. Similarity spectra decomposition is sufficient to match the spectra from the laboratory-scale jet while a three-way spectral decomposition including BBSAN is needed to fit the F-35B spectra. Discrepancies between fits and measured spectra exist for both jets at small inlet angles for high frequencies and at the region of maximum radiation for the F-35B. However, overall, the empirical models produce realistic representations of the measured spectra

2017

Adam Erickson (Capstone, January 2017, Advisor: Traci Neilsen )

Abstract

The most common challenge faced in architectural acoustics is designing a room with a proper reverberation time that will suit the purposes of the space. At the Center for Change located at 1790 N State St in Orem, Utah, a room known as the Dance Room exhibits an extraordinarily high reverberation time, making communication in the room extremely difficult. Using the EASERA system (Electronic and Acoustic System Evaluation and Response Analysis), as well as a starter pistol with multiple Larson Davis 824 sound level meters, measurements of the reverberation time were made in the room at the Center for Change on March 26th, 2016. Several possible solutions designed to lower the reverberation time were investigated and tested by constructing a computational model of the room using the Sabine equation as well as EASE software (Enhanced Acoustic Simulator for Engineers). Two solutions were chosen, and proposed in a written report to the Physical Facilities Manager at the center, Glenn Klemetson.

Caleb Goates (Senior Thesis, April 2017, Advisor: Traci Neilsen )

Abstract

Acoustic beamforming uses recordings from a microphone array to find sound source locations. The response of a beamformer is limited by two requirements–the spatial Nyquist frequency on the high-frequency end and aperture requirements on the low-frequency end, which correspond respectively to the spacing of the microphones and the total length of the array. These limitations cause any array with a finite number of microphones to have a limited frequency bandwidth over which beamforming results are useful. This paper presents a method for overcoming the high-frequency limitation using phase unwrapping and array interpolation. This process can approximate the response of an array with many more microphones than are present by adding virtual microphone signals determined by interpolation. Experimental and numerical verifications of the method are presented. The method is found to octuple the bandwidth of the array when the source of interest is broadband.

2015

Jackson Farnsworth (Capstone, August 2015, Advisor: Traci Neilsen )

Abstract

The cymbal exhibits many interesting acoustic features as a percussive plate instrument. Experiments were conducted using a Scanning Laser Doppler Vibrometer (SLDV) in order to obtain frequency information about a driven cymbal. From the SLDV data, animations of the motion of the cymbal are made. Further scans showed the existence of sub-harmonics present in the resonance frequencies of the cymbal. A series of scans confirmed the appearance of sub-harmonics dependent on amplitude of driving voltage of the shaker connected to the cymbal.

Samuel Hord (Senior Thesis, April 2015, Advisor: Traci Neilsen )

Abstract

Ground reflections have a significant impact on the propagation of sound from a rocket firing. The impedance of the ground relies strongly on effective flow resistivity of the surface and determines the frequencies at which interference nulls occur. A softer ground, with lower effective flow resistivity, shifts the location of interference nulls to lower frequencies than expected for a harder ground. The difference in the spectral shapes from horizontal firings of GEM-60 rocket motors, over snowy and hard ground, clearly shows this effect and has been modeled. Different flow resistivity values yield reasonable comparisons to the results of horizontal GEM-60 test firings. A sensitivity analysis was performed to develop a method for obtaining reasonable flow resistivity values, with the results comparable to those supplied by the current literature.

Cameron Vongsawad (Capstone, April 2015, Advisor: Traci Neilsen )

Abstract

Science Technology Engineering and Math education is increasingly important in our world as we continue to build a highly technical global society. I have sought to prepare myself to be an effective physics teacher and STEM educator with every opportunity I have been given throughout my education. The redevelopment of both a local BYU acoustics outreach program as well as a national outreach program for the Acoustical Society of America is what I have accomplished. My work has given me a better understanding of the use of pedagogy in a variety of educational setting including teaching sound to the deaf and hard of hearing as well as the use of demonstrations in education. My work has focused on understanding Utah Core Curriculum and implementing those parts that revolve around acoustics specifically for middle, and high school aged students as well as the general public. This work has prepared me to be an effective educator as I go forth to serve in public education as a high school physics teacher.

2014

Zachary Anderson (Senior Thesis, April 2014, Advisor: Kent Gee, Traci Neilsen )

Abstract

Correlation analysis is useful in extracting spatiotemporal relationships between signals and can be used to examine features of jet noise for source properties. When applied to F-22 jet noise, maximum correlation coefficients show noticeable distinctions between near-field and downstream microphones; these distinctions become increasingly apparent in the spatial variation between short and long correlation lengths. Waveform width analysis complements the meaningfulness of our results. Finally, the calculation of phase speed clearly defines the relevant regions: a fine-scale upstream region, a large-scale downstream region, and a midway region that shares properties of fine-scale and large-scale noise. [Work supported by the Office of Naval Research.]

Jazmin Myres (Senior Thesis, April 2014, Advisor: Kent Gee, Traci Neilsen )

Abstract

In scan-based array measurements, stationary reference sensors are needed to temporally correlate the different measurement scans and produce coherent complex pressure fields that can be used to perform near-field acoustical holography (NAH). Because the number of references required increases with the number of subsources contributing to the sound field, an extended, partially correlated source (e.g., a turbulent jet) comprising many ill-defined sources can result in significantly increased measurement complexity and expense. Demonstrated here a is a new approach to creating spatiotemporally coherent pressures using self-referencing between overlapping measurement positions instead of separate reference channels. A laboratory experiment was designed and the data have been used to explore "stitching" together a complex pressure field. This experiment is described and the “stitching” method is detailed. To successfully execute the technique, unwrapping of intrascan phases is first accomplished with a two-dimensional phase unwrapping algorithm. Individual scan positions are then stitched together using median phase differences between multiple adjacent scans to create coherent planes of data. Amplitude-stitching is done by averaging across scans and preserving the integrated squared pressure across the overall aperture. The validity of this method is shown by showing that a consistent local coherence maintained through the stitching process. The technique is applied to jet noise, and the possibility of applying it to NAH is discussed. This technique provides direction for efficient experimental design for scan-based array measurements of extended sources.

Hsinping Pope (Capstone, August 2014, Advisor: Traci Neilsen )

Abstract

Similarity spectra for turbulent mixing noise obtained from matching the one-third-octave band and narrowband spectra measured near an F-22 are compared in this project in order to discover the differences between. The main finding in the research is that the resulting similarity spectra are different but not by a significant amount. This finding solidifies the correctness of the findings in a previous study by Dr. Neilsen. Such finding is beneficial for the investigation of new features in jet noise spectra discovered in a previous research done by Dr. Neilsen.

2013

David Hart (Senior Thesis, April 2013, Advisor: Traci Neilsen )

Abstract

The two-source model for jet noise holds that turbulent mixing noise in jets is generated by uncorrelated, fine-scale (FSS) and partially correlated, large-scale (LSS) turbulent structures [Tam et al., J. Fluid Mech. 615, 253-292, (2008)]. The noise from an F-22A Raptor is modeled with an equivalent source consisting of two line arrays of monopole sources. These arrays, one correlated and one uncorrelated, with Rayleigh-distributed amplitudes, account for both FSS and LSS sound propagation [J. Morgan et al., J. Acoust. Soc. Am. 129, 2442 (2011)]. The equivalent source parameters are selected based on a Bayesian optimization implemented with simulated annealing and fast Gibbs sampler algorithms. This method yields the best fit parameters, and the sensitivity of the solution is indicated by the estimated posterior probability distributions. This equivalent source model can generate results up to approximately 1 kHz and accurately predict both near-field and far-field measurements. Analysis of the resulting equivalent sources shows that the directional, correlated line array has a greater effect on the near-field sound. Additionally, the sensitivity of the model parameters appears to increase as the frequency increases. These and other findings give insight into the physical nature of the jet noise source.

Shanell Reynolds (Capstone, April 2013, Advisor: Kent Gee, Traci Neilsen )

Abstract

Aircraft maintenance workers can be exposed to high noise levels while working around military aircraft. Near-field measurements of an F-22 Raptor at different engine conditions provide information regarding the noise dosage experienced in the vicinity of the aircraft. Level weighting curves, which account for different aspects of hearing perception, have been applied to the overall sound pressure level data from locations where personnel might stand. Hearing protection attenuations are applied to the A-weighted overall sound pressure levels to determine the exposure levels while wearing properly inserted ear plugs and muffs. It is found that significant reduction is achieved by the required dual hearing protection used for this project. The dual hearing protection can provide around 40 dB of attenuation in the overall exposure level. These results can be used by the military to make informed decisions regarding acceptable exposure times for maintenance personnel.

Brace White (Capstone, April 2013, Advisor: Traci Neilsen )

Abstract

I built an open-closed tube demonstration under the direction of Dr. Neilsen and Dr. Gee. We used the structure to model brass instruments and to explore the changes in sound properties of tubes with the addition of a variety of bells. The project will be used in acoustics classes to help students visualize and better understand the associated principles.

2006

Bret Parker (Capstone, February 2006, Advisor: Traci Neilsen )

Abstract

The fluid model of reflectivity (FM) is a simple model in which both the water and the sediment are presumed to be fluids defined by three properties: compressional sound speed (c), attenuation (a) and density. The Biot-Stoll model is more complex and takes into account that the sediment is actually a mixture of grains and water. Recent work has been done to simplify the Biot-Stoll model by Kevin Williams. In the EFD model, Williams derives an effective density and bulk modulus from the Biot model by introducing a simplification to the frame parameters of the Biot-Stoll model. Effective Density and Fluid models were each coded into MatLab and plots of reflectivity versus angle were created for 5 different sediment types at frequencies ranging from 100 hertz to 1,000,000 hertz. Both models sufficiently show the general trends of the sound as it bounces off of the water-sediment interface. Sand has a critical angle where all the sound is completely reflected for all frequencies. Clay is just the opposite in that it has an angle of complete intromission (all sound is absorbed into the sediment. Silt and sitly-sand have both 100% reflection, for all high frequencies, and 100% intromission for low frequencies.