Experimental Study of the Eigenfrequency Shift Mechanism in a Blocked Pipe System

Abstract

Eigenfrequency shift in a pipe with a blockage is investigated experimentally. The experimental test rig consists of a reservoir-pipe-valve (RPV) system that contains a single partial blockage. Blockages with different lengths are considered. The experiments confirm the existence of certain frequency bands where waves reflect strongly from the blockage and other bands where waves reflect weakly (Bragg-type resonance). These bands agree with the theoretically derived Bragg resonance condition. It is found that the values of the resonant frequencies are highly sensitive to the wave speed. For example, a 4% error in wave speed results in an error in the eigenfrequency estimates that increases almost linearly from approximately 4% for the first mode to 60% for the seventh mode. A direct and efficient approach is proposed for using the Bragg resonance condition to detect blockages in pipes.