Source Characterization using Inverse Numerical Acoustics based on Pellicular Modes

An inverse method is used to characterize radiating noise sources. Measurements of the sound pressure in the field are used to reconstruct the vibration on the surface of a vibrating structure. The basis functions for this inverse calculation are pellicular modes. These modes are calculated by assuming that there is a thin air envelope around the vibrating structure. The acoustic modes are calculated using this air envelope and the acoustic mode shapes are then assumed to be structural modes. Though not the actual structural modes, these modes are easily calculated and form convenient basis functions. This procedure is demonstrated on two examples. The first is a small electric motor and the second is a generator set. It is demonstrated that the procedure can be used to accurately characterize the sound radiation from a source.