Acoustics becomes a concern when the coupling between a fluid and a structure becomes significant enough to cause high levels of noise, severe structural vibrations, or fatigue problems. ATA is experienced in providing acoustic analysis and test services over a large range of applications. This includes the prediction of liftoff and ascent fluctuating pressures, analytic modeling of coupled fluid-structure systems, and testing to measure load cases and correlate analytic models.
Prediction of Fluctuating Pressures
ATA has provided estimates of fluctuating pressure levels during liftoff and ascent for a variety of launch vehicles including Space Exploration’s Falcon 1 and NASA’s Ares I. These load cases are critical to the successful design and eventual launch of the launch vehicle. Liftoff levels are estimated using augmented NASA standards, and ascent levels are predicted using empirically-based methods based on over 30 years of wind tunnel and flight data.
Analytic Modeling of Coupled Fluid-Structure Systems
ATA has extensive experience with the construction and use of analytic models to represent coupled fluid-structure systems. These models are then used to predict the response of structural components (acceleration, stress, strain) and/or the sound pressure level response for internal cavities or external locations. The modeling methods that ATA uses include statistical energy analysis (SEA), the boundary element method (BEM), the finite element method (FEA), and hybrid models which can combine the best characteristics of SEA, BEM, and FEA.
SEA has traditionally been used in applications where the response at high frequencies is of primary interest. ATA has used SEA to provide zonal and sub-zonal vibration environments for component manufacturers, to predict interior noise levels, to track the power flow paths through the system so that design changes can be properly targeted, and to quickly conduct design trade studies. Successful SEA projects include NASA’s Orion spacecraft, the presidential helicopter, and small commuter aircraft.
BEM is typically used at lower frequencies, explicitly modeling the fluid-structure interaction and is a more accurate modeling method than the so-called “patch” method, which makes inaccurate assumptions about the spatial correlation of the fluctuation pressures. ATA’s experience with BEM includes the recovery of acceleration, stress, and strain responses in a variety of structures. ATA has also successfully correlated structural responses to test data from reverberant chamber acoustic testing.
Measurement and Prediction of Jet Noise
ATA has developed innovative methods of measuring, interpreting, and extrapolating jet noise using an automated scanning acoustic holography system. This system allows for the collection of essentially infinite spatial resolution data over a surface allowing characterization of the noise from high-speed jets and other sources. We have also developed analytical methods that allow projection of these near-field noise measurements to the far-field.