LOCATION AND SIZING OF HOLES IN PIPES AND DUCT WALLS BY MEANS OF RESONANCE AND ANTI-RESONANCE SHIFTS

摘要

A technique recently used by the authors for the sizing and location of blockages in ducts has been successfully applied to the detection, location and sizing of small holes in duct walls. It is shown that when the blockage area function reconstruction process is applied using resonance and anti-resonance frequencies determined from a single measurement of sound pressure within a duct, the position of a hole in the duct wall is revealed as the beginning of an apparent gradual expansion emanating from an initial positive DC shift in the reconstructed blockage area function. Once the hole has been located, an impedance model of the duct incorporating the hole location and the measured wavenumber at the first order duct resonance allows the determination of the radius of the side hole from a simple quadratic equation. This hole sizing technique has also been successfully applied to thin slits in duct walls using an equivalent radius approach and shown to be highly accurate.