D K Longmore

A finite Element Model of Hydraulic Pipelines Using an Optimized Interlacing Grid System

Simulation of flow and pressure variations in fluid pipelines using finite difference and finite element models can give unrealistic results, corresponding to errors in natural frequencies. A novel finite element model of hydraulic pipelines has been developed, using an interlacing grid system. The grid spacing is non-uniform and is optimized, using a genetic algorithm, to make some or all of the undamped natural frequencies of the model as close as possible to exact theoretical ones for a uniform pipe with the extreme boundary conditions of either constant pressure or no flow. Inaccuracies in the highest natural frequencies may be acceptable because of the effect of frequency-dependent friction and limited system frequency response. The optimized model gives accurate results in time domain simulation, and it allows variable properties and a variable integration step to be readily accommodated.

Modelling of transient flow in hydraulic pipelines

Abstract This paper describes a method of modelling time-varying flow in hydraulic pipelines which may be incorporated into time domain simulations of hydraulic systems operating with variable time steps. A previously reported finite element method is extended. New approximations to frequency-dependent friction for laminar and turbulent flow are presented. These are applicable to this finite element method as well as the method of characteristics and finite difference methods. Simulation results are compared against theory and excellent agreement is found.

Measurement of the longitudinal transmission characteristics of fluid-filled hoses:

Abstract Flexible hoses used within a hydraulic circuit can reduce the levels of both pressure fluctuations and structural vibration. An important application is in automotive power steering where tubular inserts and restrictors are often used inside a hose to enhance the reduction of pressure ripple. The performance of a hose assembly in the frequency domain is usually specified by an impedance matrix relating pressure and flow ripple at the ends. However, these quantities are coupled to fluctuating axial tension and motion of the hose walls and it is desirable to have a 4 × 4 impedance matrix relating the complex amplitudes of all these quantities. A convenient method of experimentally measuring this matrix is presented. As well as allowing investigation of the main structural and fluid transmission from the hose assembly to the subsequent pipework, the 4 × 4 impedance matrix provides a way of obtaining the dynamic properties of hose walls under realistic conditions for use in further studies.

Theoretical analysis of pressure and flow ripple in flexible hoses containing tuners

Abstract In automotive power steering systems it is common practice to include highly expandible hoses containing tubular inserts, referred to as tuners, to minimize the pump-generated pressure ripple. A theoretical model of a flexible hose containing a tuner is described, which can be used to compute the fluid-borne noise characteristics of complete systems. Excellent agreement with experimental measurements is obtained. Leakage through the tuner wall is shown to have a strong effect on the results. With the common type of spiral wound tuner, most of the damping present is obtained from this leakage and from energy loss in the hose wall, and for low-viscosity fluids it may be acceptable to ignore the effect of fluid viscosity.