Bulletin of the American Physical Society
Joint Meeting of the Four Corners and Texas Sections of the American Physical Society
Volume 61, Number 15
Friday–Saturday, October 21–22, 2016; Las Cruces, New Mexico
Session J3: Acoustics |
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Chair: Jacob Urquidi, New Mexico State University Room: Meeting Room 2&3 |
Saturday, October 22, 2016 1:00PM - 1:24PM |
J3.00001: Near-field acoustical holography: Understanding sound generation from musical instruments to military aircraft Invited Speaker: Kent L. Gee Near-field acoustical holography (NAH), like its optical cousin, is a method by which measurements made along a two-dimensional surface are used to create a three-dimensional reconstruction. Its basic principles provide the physics student with a rich understanding of wave superposition and propagation, the Helmholtz equation, separable geometries, wavenumber spectra, and near-fields, i.e., evanescence. Implementing NAH requires an understanding of temporal and spatial Fourier transforms, signal-to-noise ratio, windows, filters, and other signal processing concepts. This paper introduces key concepts of NAH and explains its application to understanding sound radiation from the hammered dulcimer, the caj\'{o}n drum, and a military jet aircraft. [Preview Abstract] |
Saturday, October 22, 2016 1:24PM - 1:36PM |
J3.00002: Landau-Zener Transitions in Coupled Thermoacoustic Oscillators Stacks Aaron Horikami, Cicely Potter, Chit Kwok, Bonnie Andersen Landau-Zener transitions are characteristic in two level quantum systems and occur in many areas of physics and chemistry from ammonia masars to rapid adiabatic passage. Coupled pendulums, mass-spring systems, and RLC circuits are a few macroscopic analogs of coupled oscillators. A closed bottle-shaped acoustic resonator can result in coupled oscillations between the resonance of the neck and the cavity. Landau-Zener transitions occur between overtone modes as the cavity is lengthened such that its resonance passes through the resonance of the neck. The thermoacoustic stack is located in the neck and the length of the cavity can be varied with a piston. Previously, transitions were observed as the cavity was lengthened by hand. In this study the piston was controlled with a high level of accuracy with a translation stage. Four different neck-cavity combinations were tested using two neck lengths (3.8 cm and 5.8 cm, both with inner-diameters of 1.9 cm) and two cavity inner-diameters (4.8 cm and 9.5 cm). Mode transitions have been observed to occur repeatedly for a given input power at the same position within a standard deviation of 1.3 mm. The transition positions was also tested as a function of input power. For some input powers/positions, the temperature gradient fell below the critical temperature gradient, resulting in a loss of sound at those positions. [Preview Abstract] |
Saturday, October 22, 2016 1:36PM - 1:48PM |
J3.00003: Acoustic Frequency Splitting in Thermoacoustically Driven Coupled Oscillators with Fibrous Stacks Bonnie Andersen, Jacob Wright, Cory Heward, Emily Jensen, Justin Bridge Frequency splitting or level repulsion occurs near the point where the two resonant modes coupled oscillators intersect as one parameter is varied that allows the resonance of one to pass through the resonance of the other. A thermacoustic stack, which provides internal self-sustained oscillations, placed inside the neck of a closed bottle-shaped resonator can set up standing waves of the coupled neck-cavity system. A simplified model for using a fibrous stack is presented. A one dimensional wave equation with appropriately applied boundary conditions of the bottle system reveal the mode splitting between the neck and cavity modes. Thermoacoustic engines with bottle-shaped resonators were tested while varying one of three geometric parameters. All exhibit frequency splitting in good agreement with the model. Graphs of the solutions of the wave equation readily illustrate the mode splitting of the coupled oscillator system. [Preview Abstract] |
Saturday, October 22, 2016 1:48PM - 2:00PM |
J3.00004: Acoustic Study of Clarinet Voicing Stacks Chris Snellings, Mary Nelson, Jeff O'Flynn, Bonnie Andersen The clarinet functions as a stopped tube and therefore sounds the fundamental pitch, and overblows to the third and fifth harmonics. Learning to control these registers, or voicing the instrument, is an essential part of a clarinetist's education. By understanding how the clarinet couples to the overtones and whether the clarinet has an inherent ``memory'' for overtones, teachers can better instruct their students. In order to study the effects of overtones and voicing, data was collected for an advanced student just beginning to learn voicing. The duration she could maintain the sound coupled to the third partial without the benefit of the register key at the top of the tube to stabilize the sound was measured. By measuring duration and sound levels, the airflow affecting the coupling could be observed. As expected, the longer the fundamental wavelength was, the more energy it took to maintain coupling the third partial. An artificially blowing mechanism was then coupled to the clarinet to measure how a steady, unchanging stream of air affects coupling. [Preview Abstract] |
Saturday, October 22, 2016 2:00PM - 2:12PM |
J3.00005: Dynamical Systems Analysis of Thermoacoustics Stacks Robert Stoddard, Don McLaughlin, Bonnie Andersen Thermoacoutics is the science of interconversion between disorganized heat energy and organized sound energy. The effect was observed centuries ago with ceremonial rice cookers in China and may be easily observed by heating a wire mesh in a pipe. Time series gas pressures may be measured with a piezoelectric sensor embedded in the resonator of a thermoacoustic engine. The emergent resonant frequency of the sound produced depends on the working fluid and dimensions of the apparatus. A plot of time series data reveals an initial region of random pressure variation followed by a region of growing pressure amplitude together with interspersed regions of random and chaotic motion. Thermoacoustics has traditionally been modeled using fluid dynamics and acoustics theory. The purpose of the research reported here is to explore modeling thermoacoustics phenomena using the analysis tools of dynamical systems theory. This approach is capable of describing various regions of organized and disorganized behavior and produces mathematical models designed to describe observed data. The time series data suggest a sigmoid growth curve moderated by a periodic oscillation model. We have assumed a simple logistic growth curve having a single adjustable parameter (representing growth rate) multiplied by a simple sine curve having an observed resonant frequency of 2.28 kHz. It is found that a nonlinear least squares fit of the logistic/sine model parameters reproduces the observed behavior of the various regions reasonably well. [Preview Abstract] |
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