Selected Publications
Sounds to Astound is an acoustics demonstration show, produced for the community twice yearly by the Brigham Young University Student Chapter of the Acoustical Society of America. The free, interactive demonstration show explores the science of sound for a target audience of fifth- to eighth-grade students. Introductory acoustics concepts, such as longitudinal wave motion, wave properties, propagation effects, and standing waves, are taught with live demonstrations, animations, and videos. The goal of this paper is to inspire and encourage readers in their outreach efforts by describing the purposes of Sounds to Astound and technical details of several entertaining and educational demonstrations. Lessons learned from a decade of these student-produced shows serve as an aid for future efforts and highlight the benefits of outreach efforts, particularly for the students involved.
On April 26, 2021 the Brigham Young University (BYU) acoustics research group made a number of acoustic noise measurements during the launch of a Delta IV Heavy rocket from Vandenberg Space Force Base in California. The sensors ranged in distance from 330 m to 19 km from the launch site. Some sensors were arranged in a rough arc of 1-2 km radius and others were placed along both an east-west line and a north-south line. This enabled the measurement of the distribution of the noise in the different directions and at different distances. Two of the sensors were 5-meter radius, 4-microphone intensity probes. Using these probes it was possible to track the trajectory of the rocket ascent; the acoustically traced trajectory agrees well with the trajectory data obtained from Vandenberg. The measurements showed that the peak directivity of the launch vehicle noise was at 70.4±2.1 degrees relative to the plume direction. The total acoustic power level was found to be 197 dB re 1 pW. This represents an acoustic radiation efficiency of about 0.3%, somewhat lower than is normally assumed.
One challenge with outdoor sonic boom measurements is making high-fidelity recordings during adverse weather conditions. This paper describes the deployment of a weather-robust measurement system as part of Brigham Young University’s (BYU) participation in the NASA Quiet Supersonic Flights 2018 (QSF18) test in Galveston, TX. BYU made measurements at four different stations across Galveston Island, representing different ambient environments: Scholes airport, a cemetery, a city park near a busy street, and a downtown Post Office parking lot. At each station, multiple measurements were made simultaneously using different data acquisition hardware and microphone types and configurations. The nearly collocated recordings allowed for the comparison of different measurement approaches in terms of practicality, instrumentation noise floor, measurement bandwidth, and wind noise reduction.
The 15 January 2022 climactic eruption of Hunga volcano, Tonga, produced an explosion in the atmosphere of a size that has not been documented in the modern geophysical record. The event generated a broad range of atmospheric waves observed globally by various ground-based and spaceborne instrumentation networks. Most prominent is the surface-guided Lamb wave (≲0.01 Hz), which we observed propagating for four (+three antipodal) passages around the Earth over six days. Based on Lamb wave amplitudes, the climactic Hunga explosion was comparable in size to that of the 1883 Krakatau eruption. The Hunga eruption produced remarkable globally-detected infrasound (0.01–20 Hz), long-range (~10,000 km) audible sound, and ionospheric perturbations. Seismometers worldwide recorded pure seismic and air-to-ground coupled waves. Air-to-sea coupling likely contributed to fast-arriving tsunamis. We highlight exceptional observations of the atmospheric waves.
The phase and amplitude gradient estimator (PAGE) method [Thomas, Christensen, and Gee, J. Acoust. Soc. Am. 137, 3366–3376 (2015)] has been developed as an alternative to the traditional p-p method for calculating energy-based acoustic measures such as active acoustic intensity. While this method shows many marked improvements over the traditional method, such as a wider valid frequency bandwidth for broadband sources, contaminating noise can lead to inaccurate results. Contaminating noise degrades performance for both the traditional and PAGE methods and causes probe microphone pairs to exhibit low coherence. When coherence is low, better estimates of the pressure magnitude and gradient can be obtained by using a coherence-based approach, which yields a more accurate intensity estimate. This coherence-based approach to the PAGE method, known as the CPAGE method, employs two main coherence-based adjustments. The pressure magnitude adjustment mitigates the negative impact of uncorrelated contaminating noise and improves intensity magnitude calculation. The phase gradient adjustment uses coherence as a weighting to calculate the phase gradient for the probe and improves primarily the calculation of intensity direction. Though requiring a greater computation time than the PAGE method, the CPAGE method is shown to improve intensity calculations, both in magnitude and direction.
This paper presents an analysis of acoustic radiation characteristics of a T-7A-installed F404 engine, as derived from far-field measurements. Radiated directivity at different engine conditions is compared with contemporary investigations into Mach wave radiation. The peak directivity angles observed in the far-field are used to evaluate appropriate values for the convective Mach number. It is shown that velocity from the convective Mach number is approximately 70% of the centerline jet velocity, agreeing with contemporary supersonic jet noise literature. Spatiospectral maps from far-field data indicate the presence of spatiospectral lobes, like those observed in the near field. These spatiospectral maps also illustrate interference nulls caused by ground reflection interference. A ground reflection model is used to attempt to correct these errors. Using these corrected data, the overall sound power level is calculated and is used to find the acoustic radiation efficiency, a value rarely calculated for jet engines. The F404 OAPWL is proportional to Uₑ⁸ subsonically, and Uₑ³ supersonically. The efficiency at afterburner exists between 0.5% and 0.8%, exhibiting similar acoustic efficiency trends as those seen in launch vehicles 50 years ago.