JOURNAL OF SOUND AND VIBRATION Journal of Sound and Vibration 305 (2007) 689–702 Analysis of time harmonic wave propagation in an elastic layer under heavy fluid loading S.V. Sorokin Department of Mechanical Engineering, Aalborg University, Pontoppidanstraede 101, DK 9220 Aalborg, Denmark Received 21 July 2006; received in revised form 15 April 2007; accepted 19 April 2007 Available online 19 June 2007 Abstract This paper concerns assessment of the validity of elementary models of wave propagation in an isotropic elastic layer under heavy fluid loading as well as analysis of coupling effects due to uneven fluid loading. Dispersion curves, which describe propagation of dominantly flexural ‘in-phase’ waves and dominantly longitudinal ‘anti-phase’ waves in an elastic layer loaded by an acoustic medium at both sides, are compared with those obtained in the case of one-sided fluid loading. The latter are also compared with dispersion curves predicted by elementary theories of fluid-loaded plates. It is shown that the compressibility of the fluid dramatically extends the validity ranges of elementary theories and this phenomenon is explained. r 2007 Elsevier Ltd. All rights reserved. 1. Introduction Wave propagation in an elastic plate loaded by an acoustic medium on one side is a classical subject studied in many textbooks and research papers (for example, Refs. [1–4] and the literature cited there). In all these references, the waveguide properties of a plate are described in the framework of an elementary Kirchhoff theory. As it is very well known, this theory has a fairly narrow validity range in the case of vibrations in vacuum, which is, roughly speaking, limited by a cut-on frequency of the second flexural propagating wave (however, this wave is accurately described by Timoshenko theory). Therefore, in the case of heavy fluid loading of a plate the detailed analysis of its waveguide properties is usually performed for not too high frequencies (for a classical ‘steel-water’ pair, up to the coincidence frequency). Predictions for high frequencies (see Ref. [3]) obtained by use of this model might be regarded of theoretical rather than of practical value due to an anticipated breakdown of the approximate Kirchhoff plate model. One of the purposes of this paper is to show that analysis of propagation of a flexural wave in a plate under heavy fluid loading presented in, for example, Refs. [3,4] is valid in a very broad range of frequencies. A problem formulation that involves a plate theory (Kirchhoff, Timoshenko or sandwich) does not permit one to distinguish between one-sided and two-sided loading, because the plate equation contains as the loading term a pressure jump over its thickness, regardless of the actual distribution of normal forces at the surfaces of a plate. A problem formulation in the framework of the theory of elasticity is capable of taking into ARTICLE IN PRESS www.elsevier.com/locate/jsvi 0022-460X/$ - see front matter r 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.jsv.2007.04.028 E-mail address: svs@ime.aau.dk.