Bulletin of the American Physical Society
Annual Meeting of the Four Corners Section of the APS
Volume 59, Number 11
Friday–Saturday, October 17–18, 2014; Orem, Utah
Session I7: Acoustics II |
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Chair: Orest Symko, University of Utah Room: Science Building 074 |
Saturday, October 18, 2014 10:15AM - 10:39AM |
I7.00001: Active control of sound radiation from vibrating structures Invited Speaker: Scott D. Sommerfeldt Vibrating structures radiate sound that is often unwanted. However, because of the way structures and fluids couple, lower vibration levels do not necessarily result in lower radiated sound power. As a result, active control approaches that rely on simply minimizing the vibration of the structure are often either ineffective or inefficient. Ideally, an active control system designed for these applications would be sensitive to the radiation mechanisms that govern how efficiently the structure will radiate. An active control metric that shows significant correlation with radiated sound power has been developed and will be presented in this paper. The control metric is referred to as the weighted sum of spatial gradients (WSSG), and represents the metric that the active control system seeks to minimize. This paper will describe the sound-structure interaction problem and outline the WSSG metric that has been developed within that context. For a vibrating structure, the natural set of basis functions that describe acoustic radiation are referred to as radiation modes, and it will be shown that there are similarities between the most efficient radiation modes and the individual terms of the WSSG metric. The WSSG metric is a desirable control approach since it represents a localized point measurement, but yields global attenuation of the radiated acoustic sound power. This novel active control approach has been investigated for vibrating plates and cylindrical shells. Both computational and experimental results will be shown that demonstrate the effectiveness of the method for attenuating sound power radiated from these structures. [Preview Abstract] |
Saturday, October 18, 2014 10:39AM - 10:51AM |
I7.00002: A new method of estimating acoustic intensity applied to the sound field near a military jet aircraft Trevor Stout, Kent Gee, Tracianne Neilsen, Derek Thomas, Benjamin Christensen, Michael James Intensity probes are traditionally made up of closely-spaced microphones, with the finite-difference method used to approximate acoustic intensity. This approximation is not reliable approaching the Nyquist frequency limit determined by microphone spacing. However, the new phase and amplitude estimation (PAGE) method allows for accurate intensity approximation far above this limit. The PAGE method is applied to measurements from a three-dimensional intensity probe which took data to the sideline and aft of a tethered F-22A Raptor. It is shown that the PAGE method produces physically meaningful intensity approximations for frequencies up to about 6 kHz, while the finite-difference method is only reliable up to about 2 kHz. [Work supported by ONR]. [Preview Abstract] |
Saturday, October 18, 2014 10:51AM - 11:03AM |
I7.00003: Phased-array measurements of military jet noise Blaine Harker, Kent Gee, Tracianne Neilsen, Alan Wall, Michael James Beamforming techniques for aeroacoustics applications have undergone significant advances over the past decade to account for difficulties that arise when traditional methods are applied to distributed sources such as those found in jet noise. Nevertheless, successful source reconstructions depend on array geometry and the assumed source model. A deconvolution approach for the mapping of acoustic sources (DAMAS) is utilized to remove array effects seen in conventional beamforming and allows for improved interpretation of results. However, the distributed nature of the jet noise source, as well as large correlation lengths at low frequencies, can result in inaccurate source locations and/or amplitudes for both conventional beamforming and DAMAS. Results using DAMAS-C, an extension of DAMAS, indicate the degree of source correlation for distributed sources. The application of phased-array algorithms to ground array measurements of a full-scale tactical jet engine at military and afterburner engine conditions confirm the greater source correlation at low frequencies. These preliminary results represent the first implementation of DAMAS-C on full-scale jet noise data. [Preview Abstract] |
Saturday, October 18, 2014 11:03AM - 11:15AM |
I7.00004: Influence of source level, peak frequency, and atmospheric absorption on nonlinear propagation of rocket noise Michael Pearson, Kent Gee, Tracianne Neilsen, Brent Reichman, Michael James, Alexandria Salton Nonlinear propagation effects in rocket noise have been previously shown to be significant [M. B. Muhlestein et al. Proc. Mtgs. Acoust, (2013)]. This paper explores the influence of source level, peak frequency, and ambient atmospheric conditions on predictions of nonlinear propagation. An acoustic pressure waveform measured during a full-scale solid rocket motor firing is numerically propagated via generalized Burgers equation model for atmospheric conditions representative of plausible spaceport locations. Cases are explored where the overall sound pressure level and peak frequency has been scaled to model engines of different scale or thrust. The predicted power spectral densities and overall sound pressure levels, both flat and A-weighted, are compared for nonlinear and linear propagation for distances up to 30 km. The differences in overall level suggest that further research to appropriately include nonlinear effects in launch vehicle noise models is worthwhile. [Preview Abstract] |
Saturday, October 18, 2014 11:15AM - 11:27AM |
I7.00005: Comparison of nonlinear, geometric, and absorptive effects in high-amplitude jet noise Brent Reichman, Kent Gee, Tracianne Neilsen, Joseph Thaden In recent years, understanding of nonlinearity in noise from high-performance jet aircraft has increased, with successful modeling of nonlinear propagation in the far field. However, the importance and characteristics of nonlinearity in the near field are still debated. An ensemble-averaged, frequency-domain version of the Burgers equation can be rearranged in order to directly compare the effects of nonlinearity on the sound pressure level with the effects of atmospheric absorption and spreading on a decibel scale. Results from applying this analysis to F-22A data at various positions in the near field reveal that in the near field the nonlinear effects are of the same order of magnitude as spreading and that both of these effects are significantly greater than absorption in the area of maximum radiation. [Work supported by ONR and an ORISE fellowship through AFRL.] [Preview Abstract] |
Saturday, October 18, 2014 11:27AM - 11:39AM |
I7.00006: Determining Atmospheric Absorption for Jet Noise Analysis Joseph Thaden, Brent Reichman, Tracianne Neilsen, Kent Gee In high-amplitude noise propagation, as is the case with the military jet, nonlinear effects have to be taken into account. This paper will highlight and compare these nonlinear effects with those of geometric spreading and atmospheric absorption.~Extensive measurements were taken at Holloman Air Force Base, New Mexico during which one engine was cycled through four power settings while the other engine was set to idle. Measurements were conducted over five days during which atmospheric conditions changed significantly. Such changes in temperature, humidity, ambient pressure, and wind speed affect absorption and other important acoustic variables, such as speed of sound and density.~Although the changes were drastic over the course of a day, within a measurement period (typically 30 minutes), the changes are small enough that these variables can be treated as constants. [Preview Abstract] |
Saturday, October 18, 2014 11:39AM - 11:51AM |
I7.00007: Evidence of Mach-like Reflections From Exploding Balloons Kevin M. Leete, Jonathon R. Pendlebury, Sarah Young, Kent L. Gee, Tracianne B. Neilsen, Tadd T. Truscott The transition from regular to Mach reflections has been studied for large amplitude explosions like nuclear blasts, but little is understood about this transition from linear to nonlinear behavior for relatively weak shock waves where the acoustic Mach number is close to one. An experiment was performed at the Bonneville Salt Flats where large acetylene and oxygen filled balloons were exploded over a flat surface and the pressure waveform measured at different heights and distances from the explosion. From acoustic data and high speed footage that was taken of the explosions, strong preliminary evidence of the existence of Mach reflections was observed. [Preview Abstract] |
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