Axisymmetric vibrational power transmission in fluid filled pipes

Vibration of fluid-filled pipes represents an important problem in a variety of industries and fluid transportation networks. These pipes can be excited by a large number of possible sources related either to the structure or the internal fluid path. As vibrational energy propagates along a pipe system, it can subsequently excite other equipment attached to the structure, often causing unwanted disturbances in the structure or near the receiver. Therefore, it is of prime importance to be able to measure the energy flow going through the fluid and the shell material. Due to the fluid-shell coupling within the pipe, this can be difficult to achieve. For axisymmetric wave motion of the pipe, previous measurement techniques have been restricted to either measuring structure borne power in an empty pipe or fluid borne power. In the latter this was achieved by `drilling' holes into the pipe wall and inserting pressure transducers. Methods have been presented here for the practical non-intrusive measurement of axisymmetric vibrational power in pipes carrying both fluid and structure waves. This has been made possible with the use of a PVDF piezoelectric sensor. The PVDF sensor is wrapped around the periphery of the pipe (an integral number of turns) and detects axisymmetric n= 0 waves. The cross sensitivity of the PVDF sensor to the axisymmetric wave types n= 0, s= 2 and the n= 1 beam bending of a fluid filled pipe is examined both theoretically and experimentally. Expressions have been derived here using combinations of PVDF sensors and accelerometers on the surface of the pipe. In all four novel method for measuring longitudinal power transmission in the shell or in the contained fluid have been derived. This study includes experimental investigation of the methods derived. An examination into phase errors has highlighted several advantages in using these methods over traditional methods.(DX184258)