Trnasverse natural frequencies and flow-induced vibrations of double bellows expansion joints

摘要

This paper considers the transverse vibrations of fluid filled double bellows expansion joins. The bellows are modelled as a Timoshenko beam and the lfuid added mass includes rotary inertia and bellows convolution distortion effects. The natural frequencies are given in terms of a Ryaleigh quotient and both lateral and rocking modes of the pipe connecting the bellows units are considered. The theoretical predictions for the first six modes are compared with experiments in still air and water and the agreement is found to be very good. The flow-induced vibrations of the double bellows are then studied with the bellows downstream of a straight section of pipe and a 90 deg elbow. Strouhal numbers are computed for each of the flow excited mode resonances. The bellows natural frequencies are not affected by the flowing fluid but the presence of an immediate upstream elbow substantially reduces the flow velocity required to excite resonance.