Transient Response of Fluid Lines Including Frequency Modulated Inputs

In this paper, analytic descriptions for the step and impulse responses of the fluid in rigid cylindrical lines are obtained in the time domain. In all cases, the fluids considered are Newtonian liquids or perfect gases, with the effects of laminar viscous dissipation and heat transfer taken into account. In particular, a power series expansion is used to solve the partial differential equations of small amplitude signal propagation. With the advent of carrier techniques in fluid systems the study of the transmission of frequency-modulated signals in fluid-filled lines is needed. Recognizing this need, an analysis of the response of fluid-filled lines to a step modulation of carrier frequencies is presented. Experimental measurements of the step response of air filled lines are also given. An effect uncovered by the experimental work is the nonlinearity of the signals at signal amplitudes, unexpectedly as low as one percent of the mean pressure.