Collective acoustic modes of a bubble plume.

We derive a simple formula for the lowest natural frequencies of an infinitely long bubble plume with arbitrary cross section. Expressions are derived in terms of bubble volume fraction and equivalent radius of the plume, and a criterion for the existence of collective modes is established. For the plume with the circular cross section, our analytical approach is validated with the results of previous studies and numerical solution.

Asymmetric sound scattering by gratings of monopolar and dipolar resonators in a viscoelastic materiala).

A self-consistent analytical model of a locally resonant coating exhibiting strong asymmetric wave scattering is presented. Gratings of resonant inclusions composed of cavities and hard particles embedded in a soft matrix are translated to the problem of sound scattering by monopolar and dipolar type resonators in a one-dimensional waveguide. Equations of motion for gratings of cavities and hard particles are developed that incorporate added mass, damping, and restoration forces to take into account multiple scattering effects.

Acoustic radiation from multilayered materials using the reciprocity principle.

Application of the reciprocity principle to evaluate the acoustic radiation from arbitrary multilayered fluid and solid materials is described. To include the effect of shear motion in surrounding media, including viscosity in a fluid, equations for the acoustic radiation from such materials under point force excitation are developed in terms of reflection and transmission coefficients for longitudinal and shear waves. Calculations for forcing on either side of the layered material and in arbitrary directions, and for any asymmetric layer arrangements, are conducted.

Scaling relations for sound scattering by a lattice of hard inclusions in a soft mediuma).

Soft elastic materials embedded with resonant inclusions are widely used as acoustic coatings for maritime applications. A versatile analytical framework for resonance scattering of sound waves in a soft material by a lattice of hard inclusions of complex shape is presented. Analogies from hydrodynamics and electrostatics are employed to derive universal scaling relations for a small number of well-known lumped parameters that map resonant scattering of a complex-shaped hard inclusion to that of a sphere.

Acoustic radiation from a cylindrical shell with a voided soft elastic coating.

An analytical framework for sound radiation from a fluid-loaded cylindrical shell covered with an acoustic coating is presented. The coating is composed of a soft elastic material embedded with a circumferential layer of equispaced voids. The layer of voids is modeled as an effective fluid medium sandwiched between two layers of the host material.