VALIDATION OF A NUMERICAL-METHOD FOR EXTRACTING LINER IMPEDANCE

We report the initial results of a test series to evaluate a method fo r extracting the normal incidence impedance of a locally reacting, aco ustically absorbing liner located on the lower wall of a duct in a gra zing incidence, multimodal, nonprogressive acoustic wave environment w ithout flow. This initial evaluation tests the method's ability to con verge to the known normal-incidence impedance of a solid steel plate, and to the normal-incidence impedance of an absorbing test specimen wh ose impedance has been measured In a conventional normal-incidence tub e. The method converges to the normal-incident impedance values and th us is an adequate tool for extracting the impedance of specimens in a grazing-incidence, multimodal, nonprogressive acoustic wave environmen t for a broad range of source frequencies.