Active control of payload fairing interior noise using physics-based control laws

This paper presents results of an overview study that draws on active control technologies developed at the Naval Research Laboratory for submarine structural acoustics and aircraft interior noise problems and explores their use in reducing the interior acoustic levels inside rocket payload fairings. Research in controls at NRL includes wavenumber domain control, structural impedance control, and acoustic boundary control (ABC). ABC employs active blankets comprised of a collocated actuator and pressure-velocity sensor layers. A feedback controller is used to impose a spatially averaged local acoustic impedance at the structure-fluid boundary over the region that the blanket is attached. In the study reported here a high fidelity finite-elementinfinite-element model is used to conduct control simulations using active blankets. In this model, the main rocket body is modeled as a finite cylinder with an attached rib stiffened faking. The interior fluid is modeled with finite acoustic elements while the entire exterior fluid is modeled with finite and infinite acoustic elements. In order to better understand the physics of the problem and identify optimum physical control laws, we first conducted a study to uncover the relevant structural acoustics. Using this understanding, we use our numerical model and examine the performance of ABC active blankets as well as evaluate some simple anti-sound configurations.