Acoustical-based imaging techniques have found merit in determining the behavior of vibrating structures. These techniques are commonly used in numerous applications to obtain detailed noise source information and energy distributions on source surfaces. This thesis focuses on the continued development of the nearfield acoustic holography (NAH) approach. Conventional NAH consists of first capturing pressure data on a two-dimensional conformal measurement contour in the nearfield of the radiating source. These data are then propagated back to the vibrating structure to obtain the normal velocity profile on the source surface. With the source surface velocity profile known, the acoustic pressure, particle velocity, and intensity generated by the source can be reconstructed anywhere in space. The precision of source reconstruction is reliant upon accurate measurement of the pressure field at the hologram surface. For complex acoustic fields this requires fine spatial resolution and therefore demands large microphone arrays. In this thesis, a technique is developed for performing NAH using energy-based measurements. Recent advancements in the area of acoustic sensing technology have made particle velocity field information more readily available. Because energy-based measurements provide directional information about the field, a more accurate measurement of the pressure field is obtained. It is proposed that an energy-based system will significantly reduce the number of measurements required to perform NAH without sacrificing accuracy. Significantly reducing the number of measurements required to perform NAH will reduce the time, and therefore the expense, of using NAH as an analysis tool. Many potential applications exist for an improved NAH measurement method in the automobile and aerospace industries. These industries provide numerous large-scale applications where employing time-consuming scanning methods is not cost-effective. This is especially the case for airplane in-flight passenger noise tests, where the expense of operating the airplane is extremely high. Therefore, even a small savings in data acquisition time would be very beneficial.
| Identifer | oai:union.ndltd.org:BGMYU2/oai:scholarsarchive.byu.edu:etd-1324 |
| Date | 23 May 2005 |
| Creators | Harris, Michael C. |
| Publisher | BYU ScholarsArchive |
| Source Sets | Brigham Young University |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | Theses and Dissertations |
| Rights | http://lib.byu.edu/about/copyright/ |
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