A wave finite element approach for the vibroacoustic analysis of fluid-filled pipes with joints and defects

This paper investigates the wave propagation and time-domain behavior of fluid-filled pipes with joints and defects. Fluid-filled pipes represent elasto-acoustic waveguides, which can be modeled with the wave finite element method. Also, joints and defects represent coupling elements, with elastic and acoustic parts, which can be described from finite element-based scattering matrix models. To improve the computation of the scattering matrices, a Craig–Bampton reduction is proposed where the internal degrees of freedom of the elastic and acoustic parts are expressed from reduced bases of component modes. To address convergence issues of the Craig–Bampton method, the reduced bases of component modes can be enriched with static correction vectors to account for the fluid–structure coupling effect at the interface between the elastic and acoustic parts. Numerical experiments are carried out, which concern (i) two elasto-acoustic waveguides with a curved joint and a defect, and (ii) three elasto-acoustic waveguides with a T-shaped joint and a defect. In each case, the wave transmission/reflection coefficient about the joint are computed and discussed in detail. Also, time-domain responses are assessed to demonstrate the feasibility to detect a defect in a network of pipes with a joint from input wave packets of different frequencies. Results show that the influence of the fluid can strongly affect the pipe responses, and the detection of the defect.