Active/passive control of sound radiation and power flow in fluid-loaded shells

Sound radiation and power flow of fluid-loaded shells are controlled using multiple stiffening rings treated with active/passive treatments. A finite element model is developed to study the fundamental phenomena governing the coupling between the shell, active/passive treatments and the fluid domain surrounding the shell. The geometry of the shell and the fluid domain allows the formulation of a harmonic-based model with uncoupled circumferential modes. The finite element model is used to predict the structural and acoustical behavior of the shell when both passive and active control techniques are applied to the stiffening rings. The numerical results obtained indicate that the active/passive hybrid treatment can significantly reduce the amplitude of vibration and the sound radiation into the fluid domain without substantially increasing the mass of the shell. The active/passive rings are found to be particularly effective in controlling the higher order lobar modes. The presented finite element model along with the power flow analysis provides an invaluable means for the design of quiet fluid-loaded shells.