A Comparative Study of Discrete and Modal Approximation of Hydraulic Transmission Lines

Abstract

Analysis of dynamics of the fluid transmission line in the time domain requires considerable simplification of models which are used in the frequency domain. The paper compares the results of simulation of two such approximations. The first one is based on spatial discretization of a pipeline into segments with lumped parameters. Electro-hydraulic analogy is used for development of the model. The second approach is based on modal approximation. Each single-resonance mode of pipeline dynamics is described by the second order transfer function. Viscosity effect is described by the linear friction model. The bond graph technique is used in both cases for presentation of the model. Out of four causal possibilities, the case with mixed boundary conditions - flow rate and pressure as inputs is observed. The influence of the number of segments/modes and frequency of the input signal on the system response is analyzed.