A finite element method for modelling the vibration of initially tensioned thin-walled orthotropic cylindrical tubes conveying fluids

This paper presents a method for the dynamic analysis of initially tensioned orthotropic thin-walled cylindrical tubes conveying steady fluid flow, based on Sanders' non-linear theory of thin shells and the classical potential flow theory. The method is relatively straightforward, using a hydrodynamic pressure formulation derived from the velocity potential, a dynamic coupling condition at the fluid-structure interface and two-noded frustum elements to assess the dynamic behaviour of these tube/fluid systems accurately. A non-linear strain-displacement relationship is also deployed to derive the geometric stiffness matrix due to the initial stresses and hydrostatic pressures. The equations of motion for the tube and fluid are solved by a finite element method, and this is validated by comparing the natural frequencies obtained with other published results. The influence of material properties, fluid flow velocities and initial axial tensions on the natural frequencies is then illustrated and discussed.