VISCOSITY-INDUCED ATTENUATION OF LONGITUDINAL GUIDED-WAVES IN FLUID-LOADED RODS

The main goal of this paper is to extend the analytical treatment of l ongitudinal wave propagation along the fiber direction of multilayered coaxial fibers to immersion in a viscous fluid. The viscous fluid is modeled as a hypothetical isotropic solid having rigidity c(44) = -i o mega eta, where eta denotes the viscosity of the fluid and omega is th e angular frequency, i.e., the vorticity mode associated with the visc osity of the fluid is formally described as the shear mode in the hypo thetical solid. Among other interesting phenomena, the analytical resu lts revealed the presence of a sharp minimum in the viscosity-induced attenuation of the lowest-order longitudinal mode of thin rods. This m inimum occurs at a particular frequency when the otherwise elliptical polarization of the surface vibration becomes linearly polarized in th e radial direction. Generally, the experimental results on immersed an d fluid-covered wires and fibers showed good agreement with the analyt ical predictions. In particular, the existence of the theoretically pr edicted minimum in the attenuation spectrum of the lowest-order longit udinal mode was verified. (C) 1996 Acoustical Society of America.