Structural and internal acoustic response of cylinders with applications to rocket payload fairings

In this work the internal acoustic response of a closed simply-supported (SS) cylinder actuated by piezoelectric (PZT) actuators is presented. A research-grade SS cylinder is created and the modal properties are analyzed experimentally. The experimental modal properties are compared to finite element analysis (FEA) and to results predicted by Love shell theory. The experimental results indicate that the created cylinder has dynamic properties that are similar to the analytical and FEA results.;The validated model is used to extrapolate results for a SS cylinder that emulates a Minotaur payload fairing. The internal cylinder acoustic levels are investigated for PZT actuation between 35 and 400 Hz. It is found that changes in cylinder parameters (stiffness and material density) do not have a large effect on the magnitude of the structural response. Likewise the interior acoustic response is not greatly affected by changes to the cylinder parameters. As the applied voltage increases linearly, the internal sound pressure level (SPL) varies logarithmically. This behavior is a limiting factor in using a PZT actuator to generate high internal SPLs. Significant reductions in the structural response due to increased damping do not equate to similar reductions in the acoustic SPLs for the cylinder. The sound levels at the acoustic resonant frequencies are essentially unaffected by the significant increase in structural damping while the acoustic levels at the structural resonant frequencies are mildly reduced. The interior acoustic response of the cylinder is dominated by the acoustic modes and therefore significant reductions in the overall interior acoustic levels will not be achieved if only the structural resonances are controlled.;The model indicates that the maximum acoustic levels generated by the baseline PZT actuator are sufficient at the higher frequency range but are not commensurate with the levels found in a typical fairing in the lower frequency range (below ∼200 Hz). Since the baseline actuator's applied voltage can not be increased, additional actuators are required in order to increase the response of the cylinder at some of the lower frequencies. The results of this work indicate that PZT actuators do not have the authority to control the payload fairing internal acoustics below ∼100 Hz. (Abstract shortened by UMI.).