Structural acoustics is concerned with the coupled dynamic response of elastic structures in contact with non-flowing fluids into which vibrations or sound is consequentially emitted. Conversely, sound in the fluid can excite vibrations in the structure.
The fluid, although non-flowing, undergoes small-amplitude vibration relative to some equilibrium position.) For heavy fluids like water, the coupling is two-way, since the structural response is influenced by the fluid response, and vice versa. For lighter fluids like air, the coupling may be either one-way (where the structural vibration affects the fluid response, but not vice versa) or two-way (as occurs, for example, in the violin.
Structural acoustics problems of interest involving water include the vibration of submerged structures, acoustic radiation from mechanically excited, submerged, elastic structures; acoustic scattering from submerged, elastic structures (e.g., sonar echoes); acoustic cavity analysis; and dynamics of fluid-filled elastic piping systems. These problems are of interest for both time-harmonic (sinusoidal) and general time-dependent (transient) excitations. Water hammer in pipes can be thought of as a transient structural acoustics problem.
Structural acoustics problems of interest involving the air medium include determining and reducing noise levels in automobile and airplane cabins.
Reference (for simple geometry problems): “Sound, Structures, and Their Interaction,” Second Edition, by M.C. Junger and D. Feit, MIT Press, Cambridge, Mass (1986).