Bulletin of the American Physical Society
Annual Meeting of the Four Corners Section of the APS
Volume 57, Number 11
Friday–Saturday, October 26–27, 2012; Socorro, New Mexico
Session H3: Acoustics |
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Chair: David Hough, Trinity University Room: Macey Center Copper |
Saturday, October 27, 2012 10:12AM - 10:24AM |
H3.00001: High-Frequency Pulsed-Electro-Acoustic (PEA) Measurements for Mapping Charge Distribution Kristina Sorensen, Lee Pearson, J.R. Dennison, Timothy Doyle, Kent Hartley High-frequency pulsed-electro-acoustic (PEA) measurements are a non-destructive method used to investigate internal charge distributions in dielectric materials. This presentation discusses the theory and signal processing of simple PEA experiments and shows results of PEA measurements. PEA experiments involve a thin dielectric positioned between two conducting electrodes. A voltage signal on the two electrodes generates an electric field across the dielectric, which stimulates embedded charge and creates a pressure wave that propagates within the capacitor. A coupled acoustic sensor then measures the ensuing pressure pulse response. Spatial distributions of the charge profile are obtained from the resultant pressure waveform. Gaussian filters and other signal processing methods are used to increase the signal-to-noise ratio in this waveform. Estimates of the charge distribution inside the dielectric are extracted from this analysis. Our ultimate objective is to develop high resolution PEA methods to investigate in vacuo charge deposition in thin film polymeric, ceramic, or glass dielectric materials using medium to high energy (approximately 103 to 107 eV) electron beams. [Preview Abstract] |
Saturday, October 27, 2012 10:24AM - 10:36AM |
H3.00002: Geometric near-field characteristics of supersonic jets: Full and laboratory scales Jazz Myres, Shanell Reynolds, Tracianne Neilsen, Alan Wall, Kent Gee Sound pressure measurements were made in the geometric near field of a full-scale jet installed on a military aircraft. In this work, levels at 11.7 m (near the 42-ft foul line) are reported. Weighting curves that account for listener factors are applied to the overall sound pressure level, including A-weighting, C-weighting, and D-weighting. In addition, the effect of representative double hearing protection on A-weighted overall level is shown.A useful limited comparison is made between a laboratory-scale, Mach-2.0, unheated jet and the full-scale jet engine at the same scaled distance from the jet centerline. [Preview Abstract] |
Saturday, October 27, 2012 10:36AM - 10:48AM |
H3.00003: Bayesian analysis of equivalent sound sources for a military jet aircraft David Hart Radiated jet noise is believed to be generated by a mixture of fine-scale turbulent structures (FSS) and large-scale turbulent structures (LSS). In previous work, the noise from an F -22A Raptor has been modeled as two sets of monopole sources whose characteristics account for both FSS and LSS sound propagation [Morgan, J. Acoust. Soc. Am. \textbf{129}, 2442 (2011)]. The source parameters are manually adjusted until the calculations produce the measured field along a surface. Once this has been done, the equivalent source of monopoles can be used to further analyze the sound field around the jet. In order to automate this process, parameters are selected based on Bayesian methods that are implemented with simulated annealing and fast Gibbs sampler algorithms. This method yields the best fit parameters, and the sensitivity of the solution based on generated posterior probability distributions (PPD). For example, analysis has shown that the peak source region of the LSS is more important than the peak source region of the FSS. Further analysis of the generated PPD's will give greater insight into the nature of the radiated jet noise. [Preview Abstract] |
Saturday, October 27, 2012 10:48AM - 11:00AM |
H3.00004: Analysis of noise from reusable solid rocket motor firings Trevor W. Jerome, Kent L. Gee, Tracianne B. Neilsen As part of investigations into the design of next-generation launch vehicles, near and far-field data were collected during horizontal static firings of reusable solid rocket motors. Spatial variation of overall and one-third octave band pressure levels at sideline and polar arc arrays is analyzed. Spectra at individual microphone locations were analyzed. Positively-skewed pressure waveforms were observed in the probability density functions. Extreme skewness in the first-order estimate of the time derivative was found as a result of the presence of significant acoustic shocks. [Preview Abstract] |
Saturday, October 27, 2012 11:00AM - 11:12AM |
H3.00005: Dissonant Modes of Bottle-shaped Thermoacoustic Prime Movers Part 1: Mode Transitions with Varying Cavity Length Jacob Wright, Bonnie Andersen Dissonant overtones of closed bottle-shaped thermoacoustic prime movers are discussed. The resonator consists of two concentric cylinders with differing cross-sectional areas, closed at the outer ends. The condition for resonance results in a transcendental equation, which is solved numerically. The neck and cavity behave as coupled resonators, where the neck is a quarter-wave resonator and the cavity is a half-wave resonator. A variable cylindrical cavity with a sliding piston was constructed to study the nature of the device as the cavity length is varied. The stack is located in the neck region and the length and inner diameter of the neck are 5.39 and 1.91 cm, respectively. The inner diameter of the cavity is 4.76 cm and has a maximum length of 38 cm. The dominant mode of operation depends on the length of the cavity, favoring successively higher modes as the cavity length increases. The volume filling factor of the stack material was varied from 2 to 5{\%} to determine whether the amount of stack material affects the transitions. These filling factors were selected to yield hydraulic radii comparable to the thermal penetration depth for the highest and lowest possible fundamental frequencies of the system. The transition to higher modes occurs roughly where the higher mode overlaps with the fundamental frequency of the neck region, and is independent of the stack filling factor. With the given dimensions, three transitions to higher modes were observed, with frequencies consistent with the model. [Preview Abstract] |
Saturday, October 27, 2012 11:12AM - 11:24AM |
H3.00006: Dissonant Modes of Bottle-shaped Thermoacoustic Prime Movers Part 2: Hysteresis of Mode Transitions David Pease, Bonnie Andersen Transition regions to higher resonant modes of a bottle-shaped thermoacoustic prime mover (neck: 5.39 cm long, 1.91 cm ID; variable cavity with a sliding piston: up to 38 cm long, 4.76 ID) were studied. As the piston is extended, lengthening the cavity, starting from the neck, a transition of the dominant frequency from the fundamental to the first overtone occurs. However, when the length is then shortened, transition back to the first mode does occur at the same piston position, revealing hysteresis. Within the window of hysteresis for the cavity length, either state of the fundamental or first overtone is possible. Transition regions to higher modes continue as the length of the cavity is increased. The position and width of the hysteresis was studied for the first two transition regions as a function of input power and stack volume filling factor. Input powers studied were between 12.0 and 16.5 W and volume filling factors for the stack were about 3.0, 3.7 and 4.9{\%}. The transition regions occurred with cavity lengths between 12.6 and 14.0 cm for the first transition and between 25.0 and 27.8 cm for the second transition. Preliminary results indicate that the transition region occurs shallower in the cavity and the hysteresis widens as the input power is increased. The hysteresis is wider for the second transition region. Decreasing the stack mass causes an increase of the hysteresis width, but has no strong effect on the hysteresis depth. [Preview Abstract] |
Saturday, October 27, 2012 11:24AM - 11:36AM |
H3.00007: Radiation of Sawtooth Waves from the End of an Open Pipe Rachael Bakaitis, Josh Bodon, Kent Gee, Derek Thomas It is known, that because of nonlinear propagation distortion, a sinusoidal wave is transformed into a sawtooth-like wave as it travels through a pipe. It has been observed that the sawtooth wave, when measured immediately after it exits a pipe, has a form similar to a delta function. Currently this behavior is not understood, but has potential application to radiation of sound from brass instruments and rocket motors. Building on previous work in the 1970s by Blackstock and Wright, the purpose of the current research is to better understand the radiation of sawtooth waves from the open end of a circular pipe. Nonlinear propagation theory, the experimental apparatus and considerations, and some preliminary results are described. [Preview Abstract] |
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