Time-domain analysis of the energy exchange between structural vibrations and acoustic radiation using near-field acoustical holography measurements

Abstract

The vibrational energy in a structure and the radiated acoustic energy are analyzed in the time domain using data from near-field acoustical holography measurements. A signal processing method is described that uses data from a single broadband acoustical holography measurement to determine the structural and acoustic responses for synthetic forces different from the original measurement force. The processing is based on the assumption that the measured acoustic pressure and particle velocity are related to the drive force by a linear shift invariant transfer function. Finite time length synthetic forces are examined for measurements from a fluid-loaded, point-driven, finite cylindrical shell. Comparisons of the amount of energy input to the structure by the driver, the energy injected into the fluid near field, and the energy radiated to the fluid far field show large amounts of energy that enter the fluid near field while the drive force is on, but then re-enter the structure where it is damped once the drive force is turned off. We are also able to see the rate that energy radiates to the acoustic far field and the areas of the structure which contribute most significantly to the far-field radiation. Results show that approximately 50% of the far-field energy is radiated during the active time of a transient driving force.