The application of the FEM to determine the response of a pretorsioned pipe cluster to static or dynamic axial impact loading

Abstract

The FEM is employed to model the response behaviour of three identical thin tubes which are arranged so that the centres of their bases are positioned at the apices of an equilateral triangle. The effects of pretorsioning the cylinders and then applying static and dynamic loads are computed and presented. The cylinders in the model are firstly simultaneously subjected to an axial torque by the application of a uniformly distributed edge load at the upper circumference of each cylinder. The application of the torque to the system is implemented in the first solution step of the FEA in the absence of all other forces. The static or dynamic loads are applied in the second solution step. The static axial load is induced in the model by displacing the bases of the cylinders in the upward direction, while appropriately constraining their upper ends. For the application of the dynamic axial impact loading, a mass element is included in the model which is energised by an initial upward velocity. The subsequent load-deformation response modes are computed and discussed and compared with those obtained from a model which does not include pretorsioning. The system response modes, as revealed in this analysis, exhibit several novel features which have not been previously reported in the literature and which are the subject of close examination in this paper. Results are also presented from a more simplified model (using beam elements) of a three-legged platform subjected to similar loading conditions. In this case the load bearing characteristics of the system are shown to be dependent upon the angle that the legs make with the platform. The optimization of a system of this type, subject to these loading conditions, is discussed and demonstrated.