Bulletin of the American Physical Society
2018 Annual Meeting of the APS Four Corners Section
Volume 63, Number 16
Friday–Saturday, October 12–13, 2018; University of Utah, Salt Lake City, Utah
Session E01: Acoustics and Vibrations 2 |
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Chair: Tracianne Neilsen, Brigham Young University Room: JFB 101 |
Friday, October 12, 2018 1:30PM - 1:42PM |
E01.00001: Supersonic Acoustic Intensity for Sound Power Prediction Michael Rose, Scott Sommerfeldt, Jonathan Blotter The noise of some consumer products comes from their structural vibrations. The sound power can be predicted in early product design phases through finite element, boundary element, and statistical energy analysis methods. This is done by propagating the simulated surface pressure and velocity outwards and integrating the intensity over an enclosing surface in the far field. The radiated sound power of physical products can be validated by measuring the surface pressure or velocity and propagating outwards with near-field acoustical holography and again by integrating intensity in the far field. However, recent research using supersonic intensity (SSI) has sought to improve on these methods by implementing wavenumber truncation of the simulated or measured surface pressure and/or velocity and integrating on the surface of the structure with no need to propagate to the far field to obtain the radiated sound power. Unfortunately, SSI either overestimates or underestimates the sound power depending on the SSI method implemented and the frequency considered. This work presents an analysis of several SSI methods that have been proposed, identifies an SSI method that accurately calculates the radiated sound power, and gives supporting evidence for use of this method. |
Friday, October 12, 2018 1:42PM - 1:54PM |
E01.00002: Beamforming of crackle-related events in supersonic jet noise Aaron B Vaughn, Kent L Gee Crackle is an annoying component of supersonic jet noise. In the far field, crackle is related to the presence of acoustic shocks that develop due to nonlinear propagation, however, the intermittent source events that drive crackle generation are not well understood. This study investigates the apparent source locations of events related to crackle, which could include high-amplitude or steepened, shock-like waveforms. The measured data were obtained through ground-array measurements near a high-performance military aircraft, which was run at different engine powers. The apparent source regions corresponding to different event triggers, such as pressure amplitude, derivative amplitude, and spectral characteristics, are compared. The crackle-related event beamforming is also compared against trends of other jet noise metrics such as overall sound pressure level and derivative skewness. |
Friday, October 12, 2018 1:54PM - 2:06PM |
E01.00003: Comparing Clarinet Grunt and Squeak Notes to Transitions in Coupled Oscillators Cherise Cantrell, Joshua Vawdrey, Jeffrey O'Flynn, Bonnie Andersen Under certain circumstance, a clarinet can cause an undesired squeak or grunt note. A squeak note is the clarinet shifting to a higher register - a higher set of harmonics - while a grunt note is the clarinet shifting to a lower register. One might hypothesize that such changes occur naturally in the clarinet over time. Analysis of such transitions with waterfall plots reveals a similarity to transitions made with thermoacoustically-driven coupled oscillators. For coupled oscillators, transitions can occur when the resonance of one oscillator passes through that of the other. This suggests that the cause of the undesired transitions in the clarinet are the result of one resonance (possibly the reed, which is affected by the embouchure) passing through that of the resonance of the other (likely the bore) rather than the clarinet itself relaxing to a different register as a function of time. Various notes played on an artificially-blown clarinet are found to shift in seconds while others are found to play over a length of thirty seconds. This suggests that the reed-embouchure system has a factor in grunt and squeak notes. |
Friday, October 12, 2018 2:06PM - 2:18PM |
E01.00004: Preliminary results in developing an acoustic sound simulator Nathaniel Wells, Scott Sommerfeldt, Jonathan Blotter Noise, vibration and harshness (NVH) simulators are used in the automotive industry to help engineers diagnose and resolve sound quality issues during the development process. Transfer functions are measured between individual sound sources and the driver’s head using a prototype model or a model of a similar make. The transfer function is converted to an impulse response and convolved with a source signal to simulate what a driver hears. Filters are applied to the transfer function to simulate changes in the automobile. The development of heavy machinery would also benefit from an NVH simulator, but can have drastically different components and intended functions. A physics-based model would allow for unbuilt machinery to be tested in the design stage for sound quality. To begin to understand and implement this model, transfer functions were measured for some simple structures consisting of one to several members and used to generate a simulated signal. These signals were compared to the measured response of the system. Post-processing techniques were also investigated to improve the overall quality of the simulated response. |
Friday, October 12, 2018 2:18PM - 2:30PM |
E01.00005: Comparing two inverse array methods for source reconstructions of noise radiated from a high-performance jet aircraft Jacob Alexander Ward, Kevin M Leete, Kent L Gee, David F Van Komen, Tracianne B Neilsen, Alan T Wall, J. Micah Downing, Michael M James, Blaine Harker Because direct flow measurements of tactical aircraft jet engines are not currently possible, acoustic source characteristics are instead inferred from array processing. This paper compares two array processing methods using the same array data from a high-performance military aircraft. Hybrid beamforming (HBF) and multisource statistically-optimized near-field acoustical holography (M-SONAH) have both been used previously for frequency-dependent jet noise source characterization, but are compared here for the same input data. A 71-element linear array of equally spaced microphones was placed approximately parallel to the shear layer covering a distance of 32 meters. Complex pressures obtained from this array served as the input to both methods. Favorable agreement in terms of maximum source location, source shape, and source extent was seen between the two methods' respective results. While the methods continue to have their relative strengths and reasons for use, this favorable agreement indicates that an improved understanding of military jet noise sources has been achieved. |
Friday, October 12, 2018 2:30PM - 2:42PM |
E01.00006: Clustering analysis of inputs to a geospatial model of outdoor ambient sound Brooks A Butler, Katrina L Pedersen, Kent L Gee, Mark Transtrum, Casie Gaza Outdoor ambient acoustical environments may be predicted through supervised machine learning using geospatial features as inputs. However, collecting sufficient training data is an expensive process, particularly when attempting to improve the accuracy of models based on supervised learning methods over large, geospatially diverse regions. Unsupervised machine learning methods, such as K-Means clustering analysis, enable a statistical comparison between the geospatial diversity represented in the current training dataset versus the predictor locations. In this case, the geospatial features that represent the regions of western North Carolina and Utah have been simultaneously clustered to examine the common clusters between the two locations. Initial results show that most geospatial clusters group themselves according to a relatively small number of prominent geospatial features, and that Utah requires appreciably more clusters to represent its geospace. Additionally, the training dataset has a relatively low geospatial diversity because most of the current training data sites reside in a small number of clusters. This analysis informs a choice of new site locations for data acquisition that maximize the statistical similarity of the training and input datasets. |
Friday, October 12, 2018 2:42PM - 2:54PM |
E01.00007: Charging Effects of High Voltage Probe Pulse on Pulsed Electroacoustic Measurements Zachary John Gibson, JR Dennison, Lee Pearson, Erick Griffiths, Anthony Pearson Under certain circumstances, charging near the sample-electrode interface is seen with Pulsed Electroacoustic (PEA) measurements. The effects of the amplitude, width, and repetition rate of the pulsed high voltage probe, with and without the presence of a high voltage DC bias, on the presence and magnitude of charge build up in the sample are studied. PEA measurements are arguably the most promising of several methods to measure spatial distributions and time evolution of embedded charge. The PEA method works by applying an electric field to a charged layer within a dielectric with a pulsed high voltage probe. This produces a force on the embedded charge, creating a pressure wave that can then be detected by a piezoelectric transducer. Measurements of spatial distributions of charge within polymethylmethacrylate (PMMA) were acquired using PEA measurements. Measurements of 250 µm thick sheets of PMMA using pulsed voltages with 5 Hz repetition rate, varying between 0.5 – 5 ns pulse width and 1000 – 2000 V pulse amplitude with and without 8 kV high voltage DC biasing (~30 kV/mm) were shown to affect charging at the interfaces. |
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