Practical requirements for modelling the dynamics of hydraulic pipelines

Abstract

Hydraulic pipeline dynamics play an important role in many real systems, for example in Diesel fuel injection, anti-skid braking, under-sea oil production and hydraulic control in general. When investigating the behaviour of such systems by simulation it is necessary to have suitable numerical models for the line. An excessively complicated model wastes computing time, but an inadequate one fails to predict the behaviour satisfactorily. A first step in deciding upon a suitable model is to look at the relationship between the frequency content of transient operations in the system and the natural frequencies of the lines. Rapid transients can be initiated by such things as valve operation, actuators reaching the end of their travel and cavitation and air release. A second important criterion is the amount of damping in the lines caused by fluid friction. This may be steady or frequency dependent friction in laminar or turbulent flow. On the one hand, increasing the complexity of the friction model employed makes the computations more involved. On the other hand, friction may limit the amount of higher frequency motion and consequently make the computations simpler. This paper examines the requirements for line models under different circumstances, and how these requirements can be met. Discussions are illustrated with results on practical systems. NOMENCLATURE Fluid Power. Edited by T. Maeda. (c) 1993 E & FN Spon. ISBN 0 419 19100 3.

The transmission line method for modelling laminar flow of liquid in pipelines

“…They may also be very inefficient. 12,13 The MA methods can be very accurate and are compatible with variable time-step solvers, but are only suitable for fixed parameters and linear behaviour. MA methods are not widely used at present for fluid lines in commercial simulation packages.…”

Modelling of transient flow in hydraulic pipelines

“…The number of terms, k, should be determined according to the relationship between the break frequency of the approximated weighting function and the frequency range of the system. This is discussed in reference (2).…”

“…The MS was received on 24 March 1997 and was accepted for publication on 5 August 1997. suitable technique for a particular application depends on a number of requirements (2). It must have sufficient steady state and dynamic accuracy.…”

Fluid power systems—some research issues

“…If the frequency content of a disturbance is suciently high to excite pipeline modes, system damping may limit the number of modes that need to be modelled accurately and the frequency dependence of¯uid friction is helpful in this respect. The limited bandwidth of other circuit components may also limit the upper frequency range needed to model the pipeline: Sanada et al [56] discuss these issues and show the eects of various simpli®cations.…”