Transverse Vibrations of Bellows Expansion Joints

Abstract

<p>Bellows expansion joints are used in piping systems to absorb significant axial and/or transverse motions. Unfortunately, their flexibility also makes them susceptible to vibration. This thesis presents a detailed analysis of the transverse vibrations of single and double bellows expansion joints, including the effects of internal fluid.</p> <p>A differential equation of motion is developed which treats transverse bellows vibrations including the effects of fluid added mass, rotary inertia and internal pressure. The added mass is determined from potential flow theory and provided in the form of a mode dependent added mass coefficient. The equation of motion is solved for the first four transverse modes and comparison with experiments shows excellent agreement. The neglect of rotary inertia and the effect of convolution distortion on fluid added mass in the EJMA Standard makes the latter's predictions for natural frequency significantly higher than those measures, especially for transverse modes above the fundemental.</p> <p>The equation of motion is also solved approximately to provide an analytical expression for transverse natural frequncies. The results are presented in a form which makes hand calculations possible for the first four modes of single and double bellows expansion joints. Experiments in still fluid as well as flow-induced motion show excellent agreement with predicted frequncies.</p>