Nonlinear pressure wave analysis by concentrated mass model (1st report, suggestion and validity verification of analytic model)

Pressure wave propagating in a tube often changes to shock wave because of nonlinear effect of fluid. Analyzing this phenomenon by the finite difference method requires high computation cost. In order to overcome the problem of computation cost, a concentrated mass model is proposed. This model consists of masses, connecting nonlinear springs, connecting dampers, and base support dampers. The characteristic of connecting nonlinear spring is derived from the condition of adiabatic change of fluid, and the equivalent mass and the equivalent damping coefficient of the base support damper are derived from the equation of motion of fluid in cylindrical tube. Pressure waves generated in a hydraulic oil tube, in a sound tube and in a plane-wave tube are analyzed numerically by using the proposed model in order to confirm the validity of the model. All numerical computational results agree very well with the experimental results carried out by Okamura, Saenger and Kamakura. Especially, the phenomena that the pressure wave with large amplitude propagating in the sound tube and in the plane tube change to shock wave are numerically reproduced. Therefore, it is concluded that the proposed model is valid for the numerical analysis of nonlinear pressure wave problem.