Vibration analysis of fluid filled pipework systems

Wang, Anbin (1999) Vibration analysis of fluid filled pipework systems. University of Southampton, Doctoral Thesis.

Abstract

In fluid filled pipework systems there is a need to predict the vibration transmission to the supports or end termination, arising from both variation inputs and fluid pressure inputs. If the vibration transmission was found to be excessive, steps could be taken to vary the stiffness and damping parameters to minimise the total power transmission from the pipe coupling points and the pipe outlet.

Pipework systems are quite complex and a few authors have attempted to model them using finite element models or the mobility method both using a modal superposition. The main difficulty is the complexity or overelaboration of these methods. The wave methods have also been used to model fluid filled pipes, but so far are restricted to a straight pipe. The objectives in this thesis are to investigate the theoretical analysis methods, and to develop a computer model for the prediction of the generation and propagation of the dynamic behaviour of three-dimensional complex fluid filled pipework systems.

The impedance matrix and transfer matrix methods within the framework of the power flow philosophy have been used to describe five wave types below the ring frequency, namely the three axisymmetric waves (compression and torsional waves in the pipe wall, plane wave in the fluid) and bending waves in two orthogonal axes. Fluid and wall waves are coupled in the radial direction and at discontinuities or pipe bends. The pipework system, described by a 14-element vector of vibration states at a point, is simplified to lumped mass, and stiffness elements for the pipe wall structure, with a longitudinal wave solution for the fluid elements within. The pipe wall elements are chosen to be sufficiently short which is satisfactory for the frequency region of interest. Allowance is made for the fluid loading to both the mass in the structural elements and the wavespeed in the fluid elements. The impedance or mobility of the pipework system is obtained by using the transfer matrix, and gives the transmitted force or power flow of general liquid-filled pipework systems to each point if necessary.

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