This paper addresses the multimodal acoustic wave propagation in elastic pipes which can carry multiphase fluids. The waveguide characteristics of circular fluid filled pipes and the influence of elasticity of the outer boundaries in relation to the compressibility of the filling liquid and the inner boundaries due to an additional fluid phase are discussed - in comparison to the assumption of rigid walls. As the main aspect for liquid monitoring systems the decrease of the sound velocity within the liquid below the bulk wave velocity is discussed in detail by numerical studies and empirical proofs. Further, it will be shown that an additional fluid phase causes a deterministic jumping of the wave modes and of the dispersion characteristics.
Wöckel, S., Steinmann, U., & Arndt, H. (2015). Low frequency guided wave transmission in water pipe systems. In Procedia Engineering (Vol. 120, pp. 1257–1260). Elsevier Ltd. https://doi.org/10.1016/j.proeng.2015.08.843