Vibro- Acoustic measurements and simulations of a rib-framed honeycomb core sandwich panel

Modes of resonance, mobilities, radiated sound, and sound power transmission loss have been measured and simulated for a rib-framed honeycomb core sandwich panel with carbon-fiber face sheets. The measured modal wavenumbers and resonance frequencies are used to confirm analytic estimates of the effective flexural sound speeds in the panel. The flexural wavespeeds are strongly affected by the honeycomb core shear properties, and become supersonic at about 700 Hz. The mode shapes of the panel section between the frames resemble those of simply supported plates. Numerical simulations of resonance frequencies made with a Finite Element (FE) model match measurements within 10%. The numerically extracted modes are used to compute point and surface averaged mobilities, which compare very well with those measured on the physical structure, and to infinite panel analytic calculations. The FE mobilities are then combined with an acoustic boundary element (BE) model to calculate radiated sound transfer functions which are further used to compute a virtual sound power transmission loss for acoustic diffuse field loading. The virtual transmission loss (VTL) calculations are within 3 dB of measurements made of the physical panel in NASA's Structural Acoustic Loads and Transmission (SALT) facility. Copyright