Bulletin of the American Physical Society
2006 Four Corners Section of the APS Fall Meeting
Friday–Saturday, October 6–7, 2006; Logan, Utah
Session H3: Applied Physics and Spectroscopy |
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Chair: Charles Durfee, Colorado School of Mines Room: Eccles Conference Center Room 201/203 |
Saturday, October 7, 2006 8:30AM - 8:42AM |
H3.00001: Near-field mapping of pressure fields during active noise control of small axial cooling fans Benjamin Shafer, Cole Duke, Kent Gee In the past, tonal noise from small axial fans has been globally reduced using active noise control (ANC) with near-field error sensors placed according to a theoretical condition of minimized radiated power [K.L. Gee and S.D. Sommerfeldt, J. Acoust. Soc. Am. \textbf{115}, 228-236 (2004)]. The theoretical model, based on mutual coupling of point sources, showed that pressure nulls exist in the near field when the total radiated power is minimized. Error sensor placement at these locations should then optimize global ANC. This study comprises an experimental investigation in which the actual locations of these near-field pressure nulls have been measured over a two-dimensional grid with a linear array of microphones. The array consists of 25 quarter-inch microphones with half-inch spacing. This array has been used to map the radiated pressure field from a 60mm cooling fan during ANC, in addition to a benchmark case, where a small loudspeaker has been mounted in place of the fan. The experimental results are compared to the theoretical pressure null locations in order to determine the efficacy of the point source theoretical model. [Preview Abstract] |
Saturday, October 7, 2006 8:42AM - 8:54AM |
H3.00002: Use of near-field energy-based error signals for active control of free-field sound Ryan Chester, Timothy Leishman Practical efforts to actively control sound often require error sensors located in the acoustic or geometric near field of sound sources. Conventional pressure-based error sensors are highly sensitive to near-field position and other system parameters due to the spatial and spectral variation of the pressure field. Other acoustic quantities are less sensitive to spatial and spectral changes. This paper compares the potential, kinetic, and total energy density in the near field of sound source pairs. It also discusses the spatial and spectral variations of the aforementioned quantities. [Preview Abstract] |
Saturday, October 7, 2006 8:54AM - 9:06AM |
H3.00003: The Effects of Nonlinear Propagation on Acoustic Source Imaging in One-Dimension Micah Shepherd, Kent L. Gee The acoustics of finite-amplitude (nonlinear) sound sources, such as rockets and jets, are not well understood. Characterization of sound pressure amplitudes, aeroacoustic source locations and frequency dependence of these sources is needed to assess the impact of the acoustic field on the launch equipment and surrounding environment. Nonlinear propagation of high-amplitude sound is being studied to determine if a source-imaging method called near-field acoustical holography (NAH), which is based on linear assumptions, can be used to estimate the source information mentioned. A one-dimensional numerical algorithm is being used to linearly and nonlinearly propagate the radiation from a monofrequency source. NAH is used to reconstruct the source information from the simulated data and the error is determined in decibels. [Preview Abstract] |
Saturday, October 7, 2006 9:06AM - 9:18AM |
H3.00004: Aerodynamic and Propulsion Assisted Maneuvering for Waverider Vehicles Patrick Jolley Waveriders have long been sought after as the ideal space vehicle for space based aero assist maneuvers. Theoretically, waveriders can significantly increase gravity assist missions by performing an aero assist maneuver. These maneuvers are possible due to their high lift over drag ratio. However, implementing the theory is more difficult when considering the actual flight aerodynamics and heating problems that will be encountered. An aerodynamic database was generated using hypersonic incidence angle analysis tools with a viscous skin-drag correction. A performance analysis is performed and analyzes stagnation point heating, handling qualities, and controllability, etc. Finally, a simulation is being built to analyze various trajectories and possible mission scenarios. [Preview Abstract] |
Saturday, October 7, 2006 9:18AM - 9:30AM |
H3.00005: Flush Air Data Sensing System for Trans-Atmospheric Vehicles Joel Ellsworth With the emergence of multiple companies attempting to tap the space tourism market, as well as NASA's return to the moon initiative, an inexpensive but reliable means of determining wind relative vehicle attitude is becoming a necessity. The traditional means of obtaining air data (altitude, Mach number, angles of attack and sideslip) using fixed pitot probes and directional flow vanes is not viable for collecting data on high supersonic and hypersonic vehicles, due to the high temperatures and dynamic pressures. The solution is to use a matrix of flush mounted pressure ports on the vehicle nose or on an outboard wing leading edge. Since the ports will be located behind a detached shock wave at supersonic velocities, the temperatures will remain substantially lower. A Flush Air Data Sensing (FADS) system can also be used for subsonic conditions, although it must be calibrated for the effects of the vehicle geometry. The physics of air behavior and the mathematics of the solution algorithm will be presented. Several relevant examples of planned vehicles will be presented. [Preview Abstract] |
Saturday, October 7, 2006 9:30AM - 9:42AM |
H3.00006: Conical soft x-ray Von Hamos spectrometer Matthew Harrison, John E. Ellsworth, Alexander Shevelko, Larry V. Knight The soft x-ray spectroscopy group has designed and implemented a unique form of the Von Hamos spectrometer. Von Hamos spectrometers are used to provide spectral information of laser produced plasmas, and commonly have a detector placed perpendicular to the focusing plane. Such a set up provides a large spectral range at high resolution, but does not allow for absolute intensity information. This new design places our CCD detector parallel to the focusing plane, allowing for the absolute calibration of the plasma source. [Preview Abstract] |
Saturday, October 7, 2006 9:42AM - 9:54AM |
H3.00007: Conical Reflection in Direct Simulation Monte Carlo Andrew Sampson, Adam Payne, William Somers, Ross Spencer Fenix is a particle-in-cell simulation, using a Direct Simulation Monte Carlo method, and is aimed to improve the accuracy of Inductively Coupled Plasma Mass Spectrometry (ICP-MS). It currently focuses on the ICP-MS first expansion region through a supersonic nozzle in cylindrical symmetry. Due to increased complexity in Fenix, it has become necessary to solve the general conical surface reflection problem. The previous method, the new solution, and results from the enhanced simulation will be presented. [Preview Abstract] |
Saturday, October 7, 2006 9:54AM - 10:06AM |
H3.00008: Increasing Diagnostics Resolution in a Monte Carlo Simulation of an ICP-MS Adam Payne, Andrew Sampson, William Somers, Ross Spencer An implementation of the Direct Simulation Monte Carlo Method has been used to model the physical behavior of plasma gas in an Inductively Coupled Plasma mass spectrometer as it expands supersonically through a nozzle. As the simulation proceeds, data is taken over prescribed cells and then averaged to determine steady state physical properties such as temperature, density, and velocity. Special attention is given to plasma flow through the nozzle. Results from multiple simulations which show high resolution images of the plasma properties inside the nozzle are presented. [Preview Abstract] |
Saturday, October 7, 2006 10:06AM - 10:18AM |
H3.00009: Supersonic Nozzle Flow Using DSMC William Somers, Adam Payne, Andrew Sampson, Ross Spencer Fenix is a particle-in-cell Direct Simulation Monte Carlo (DSMC) computer simulation which models gas flow through an inductively coupled plasma mass spectrometer (ICP-MS). Particular attention is given to a nozzle region in the ICP-MS where gasses moving through a steep pressure gradient undergo a supersonic transition, expanding into a near vacuum environment. The physical behavior of the gasses in the nozzle region are closely studied, including interaction with the thermalized nozzle, incompressibility of the gas, and flow fields near the nozzle. Fenix has recently reached a stage of completion allowing our research group to produce pressure, temperature and velocity flow data for various regions in the ICP-MS. It is now necessary to verify the algorithms used in Fenix, and to check our work against other methods. Grahame Bird, one of the foremost experts in DSMC simulations, has made available to the public a general DSMC simulation which may be used to model the ICP-MS. Bird's simulation will be used to corroborate the data produced by Fenix, and the images of flow conditions for each method will be presented and compared. [Preview Abstract] |
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