ASA 129th Meeting - Washington, DC - 1995 May 30 .. Jun 06

1pNS4. Near-field acoustic holography for enclosures with unknown Green's functions.

Kelly Q. Kay

Virginia Polytech. Inst. & State Univ.---Virginia Consortium of Eng. and Sci. Universities, 2713-D Magruder Blvd., Hampton, VA 23666

Chris R. Fuller

Virginia Polytech. Inst. and State Univ., Blacksburg, VA 24061

Karen H. Lyle

U.S. Army Vehicle Structures Directorate, NASA Langley Res. Ctr., Hampton, VA 23681

A method for predicting the acoustic field in acoustically complex cavities is developed based upon current near-field acoustic holography (NAH) techniques. Current NAH methods make use of analytical Green's functions to generate predictions of global acoustic fields. For this reason, NAH is easily applied to generate predictions in free fields, and in cavities with simple geometries and uniform boundary impedances. For acoustically complex cavities, however, the absence of a known analytical Green's function, renders current NAH methods either not solvable, or in cases where approximate Green's functions are used, not accurate. The method requires no prior knowledge of the acoustically complex cavity's Green's function. As well, no approximations about the boundary conditions are required. Instead, the method takes advantage of the discrete nature of NAH predictions, in conjunction with an initial measurement of a cavities acoustic pressure field, to generate a cavity specific discrete Green's function. Computational and experimental results will be presented along with a detailed explanation of the method. [Work supported by NASA Langley Research Center.]