A new formulation for fluid–structure interaction in pipes conveying fluids using Mindlin shell element and 3-D acoustic fluid element

This paper explores the vibratory behavior of fluid-conveying flexible shells using a new generic finite element formulation employing the first-order shear deformation theory. The flexible tube conveying fluid is modeled using eight-noded curved Mindlin shell elements, which incorporate the effects such as shearing deformations and rotary inertia. The fluid is modeled using twenty noded isoparametric acoustic fluid elements. Solving the wave equation for an abstract scalar field velocity potential, we get the equations of motion for the fluid element. The energy transfer within the fluid and the shell is idealized with the pressure and velocity boundary conditions, which guarantees proper contact between the fluid and structure. The flexible tubes find various applications in medical as well as pharmaceutical industries. Flexible tubes demand minimal energy to excite. Hence, they can find applications in the flow measuring devices, which use vibration techniques. There is a difference in the fundamental frequencies of silicone tubes measured in the horizontal and vertical planes. This difference is due to the sagging of flexible pipes, which causes a beat phenomenon. A novel laser scanning technique is proposed to obtain the actual dimensions of flexible tubes when it sags due to gravity. This actual dimension is analyzed using the new formulation developed. The numerical results, with the actual dimensions measured using the scanning technique, give a good match with the experimental results.