Errors in th e simulation of pressure transients in a hydraulic system

The describing dynamic equations for pressure transients in a closed pipe are non-linear partial differential equations. No closed form of solution exists and, consequently, simulation techniques must be used to effect a solution. The partial differential equations must be discretised, at least to ordinary differential equations using a finite difference scheme. It is shown in the paper that finite differencing introduces a source of error into the simulation. The errors takes the form of different frequencies of a disturbance being propagated through the finite difference scheme with a shift in phase and attenuation from the true solution. It is shown that, for a linear system, the distortion can be quantified. Errors can be minimised by a correct choice of the number of discrete segments. A simple example of a non-linear system is included to illustrate the technique.