Time domain numerical modelling of guided wave excitation in fluid-filled pipes

Abstract

Acoustic waves have been widely used to inspect pipeline defects, including leakage, blockage and corrosion etc. The time-domain excitation of guided waves in the fluid/solid coupled pipeline system has rarely been studied theoretically. This requires the incorporation of a source term in the coupled system. This article introduces a finite element based numerical model to study the excitation of guided waves in the coupled system with a sound source either in the fluid or on the pipe wall. A compatible pair of time-domain Perfectly Matched Layers (PMLs) have been proposed to absorb pipe end reflections in the elastic wall and in the fluid respectively. These fluid/solid PML numerical formulations are coupled and the implementation of the coupling is introduced. The numerical model is validated against an enlarged model without PML, and excellent agreement has been achieved. The numerical model shows that the dominant excited wave mode is a fluid type wave mode when the sound source is a fluid source or a radial elastic line source. However, the dominant excited wave mode is a structure type wave mode when the sound source is an axial elastic line source. • A compatible pair of fluid and elastic PML formulations have been proposed. • A mixed displacement-strain un-split formulation is proposed in the elastic domain. • A mixed velocity potential-velocity un-split formulation is proposed in the fluid domain. • Fluid or radial elastic line source excites a fluid dominant wave mode in the low frequency range. • Axial elastic line source excites a structure dominant wave mode in the low frequency range.