Periodically placed actuators are used to control the wave propagation and to localize the vibration and sound radiation of fluid-loaded shells. The filtering capabilities of the resulting periodic structure can be actively tuned by modifying the feedback control gain of the actuators thus allowing for controlling the spectral width and location of the stop and pass bands as well as introducing controlled aperiodicity in the structure.

A finite element model is developed to study the fundamental phenomena governing the coupling between the shell, actuators and the fluid domain surrounding the shell. The geometry of the shell and the fluid domain allows for the formulation of a harmonic-based model with uncoupled circumferential modes. The model is used to predict the pass and stop frequency bands for different proportional control gains and to evaluate the shell harmonic response and the sound radiation into the surrounding fluid. The obtained results indicate that the location and width of the stop bands as well as the attenuation characteristics of the shell can be modified by proper choice of the proportional control gain. Numerical simulations also demonstrate that the location of the stop bands can be identified from the frequency response function of the shell and from the sound intensity.

The tunable characteristics of the proposed active shells allow for the introduction of controlled aperiodicty through proper adjustments of the actuators’ feedback gains. Disorder in periodic structures typically extends the stopbands into adjacent propagation zones and, more importantly, localizes the vibration energy near the excitation source. Both structural response and sound radiation are evaluated for increasing levels of aperiodicity. The results presented demonstrate the effectiveness of the proposed concept as an effective means for controlling the attenuation characteristics of fluid-loaded shells and for confining both vibration and sound radiation near the excitation source. Also, the presented analysis provides an invaluable means for designing fluid-loaded shells, which are quiet over desired frequency bands and where the energy can be spatially confined in well-defined restricted areas.

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