Combined beam elements for large dynamic motion of whipping pipes with fluid-structure interaction

Abstract

The paper gives comprehensive details of how a finite element computer code was developed to analyse the dynamic plastic collapse behaviour of a pipe undergoing large rotation with large strain during a pipe whip motion involving fluid-induced forces. A combined beam-type finite element model is developed which takes account of the elastic behaviour of the pipe structure and the localised plastic collapse of the section. The combined element is comprised of an elastic beam with non-linear inelastic (rotational) springs on either one or both of its ends. The rotational springs not only account for plasticity in the flexure behaviour of the pipe but also model the non-linear effect of the local plastic collapse of the pipe section due to large rotation about a plastic hinge. A numerical procedure uses the current deformed shape of the pipe to obtain the fluid reactions along the length of the pipe and estimates any reduction in the blowdown force due to flow area restrictin at the collapsed section. To validate the combined beam element for its application to the pipe whip problem with fluid structure interaction, details of the experimental tests and comparison with the finite element analysis is given.