Dynamic Response of Fluid Lines

The use of hydraulic transmission lines in automatic control, liquid-propellant rocket, and other systems requires accurate knowledge of their dynamic response. In this paper the effects of fluid viscosity and compressibility are included to derive transfer functions relating the pressure and velocity variables at the two cross sections of a line. The results of theoretical analysis are compared with experimental data obtained from frequency-response tests. The analysis includes the significant effect on the dynamic response caused by the natural frequency of vibration of the line in the longitudinal direction. It is shown that in small-diameter lines the viscous effects cannot be neglected. The theoretical analysis may be used to improve the performance of systems incorporating hydraulic networks.