Acoustic signature prediction of a combat vehicle using finite and boundary element methods

The acoustic signature, i.e., the tonal peaks of the radiated noise spectrum, is important to the detectability and survivability of a ground combat vehicle. In the low frequency range below 200 Hz, the structure-borne noise radiation of the vehicle caused by excitation from its track and suspension, can be simulated by numerical models. The numerical simulation provides useful guidance to minimize the detectability through design modifications and countermeasures. A full vehicle finite-element structural model of the M1 Abrams tank was built with approximately 7,000 elements. The dynamic modal frequency response was computed using MSC/NASTRANTM with simulated force/moment input from the track and suspension. The output surface vibration velocities were then mapped on to an acoustic boundary-element model with coarser mesh of approximately 2,000 elements. The radiated far-field acoustic pressure was then computed on a 30 meter radius hemisphere using COMET/AcousticsTM. The numerical results were able to predict the unique fundamental tonal frequencies and some of their amplitudes for different vehicle speeds with reasonable correlation to the test data.