This article is from the Acoustics FAQ, by Andrew Silverman with numerous contributions by others.
Structural acoustics is concerned with the coupled dynamic response of elastic structures in contact with non-flowing fluids. (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 air 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).
 
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