Acoustic transients from the impact force excitation of beams and wind chimes Free

A time dependent modal based approach is presented to address the structural acoustic transients resulting from the impact excitation of a beam or wind chime. The normal velocity of the structural element is first expressed as a space-time modal expansion using the in-vacuo normal modes as basis functions. A convolution integral equation approach is presented to determine the time dependent modal velocities where fluid loading is included via the use of self and mutual modal radiation impulse responses which provide modal coupling. The modal radiation impedances and impulse responses are obtained from the associated radiation resistances via the use of Hilbert and Fourier transform relationships. Time-dependent dipole modal distributions along the beam or wind chime are then used to determine the pressure field using a convolution integral approach with the modal velocities and modal space-time impulse responses which are simply related to the in-vacuo modes . Numerical results are presented to illustrate interesting coincidence effects in the transient acoustic far field from beams and wind chimes.