Use of Lower Harmonics of Pressure Oscillations for Blockage Detection in Liquid Pipelines

The transfer matrix method was applied to detect partial blockages in liquid pipelines using the first four harmonics of the pressure oscillations produced by sinusoidal opening and closing of a downstream valve. Unlike most available methods, which use a large number of harmonics to analyze the pattern of the frequency response diagram, this study uses only the first few harmonics to investigate the effect of a partial blockage on the amplitude of pressure head oscillations. A relationship between the relative blockage location and the amplitude of the pressure head oscillation was determined for each lower harmonic in the steady-oscillatory flow. The effect of steady and unsteady friction is discussed. The results of the current approach are compared with those obtained in the time domain by using the method of characteristics and with the experimental data reported in the literature; there is a satisfactory agreement.