Quantitative Schlieren Analysis of Acoustic Interaction with Submerged Plates
PENNSYLVANIA STATE UNIV UNIVERSITY PARK APPLIED RESEARCH LAB
Pagination or Media Count:
The transmission and radiation of sound from submerged plates are investigated by means of a quantitative Schlieren method which produces accurate visual representations of sound fields. The method is shown to have significant advantages over the usual time-consuming, point-by-point scans of acoustic fields. Previous investigations have shown the feasibility of quantizing Schlieren data, and this investigation demonstrates a dramatic improvement in the accuracy of that data, reducing the standard error to under one decibel which places the accuracy of the method on equal footing with other acoustic measurement systems. The further addition of stroboscopic techniques enables the resolution of individual acoustic waves and permitted the differentiation between standing waves and progressive waves. The low frequency resolution of the classical Schlieren system was also improved by nearly two orders of magnitude sound waves as low as 27 kHz were easily visualized. These improvements in the quantitative Schlieren system are demonstrated by a thorough study of transmission of sound through submerged metal plates over a study of transmission of sound through submerged metal plates over a frequency range extending from below to over one hundred times the classical coincidence frequency. Recent theoretical descriptions of the lowest order symmetrical Lamb mode are confirmed, and cancellation of modal pairs of Lamb waves with increasing frequency is observed.