Determination of acoustic free sources in large cross-section ducts

Blocked forces are determined at the interface between source and receiver structures. Recent investigations have shown that these forces can be determined using inverse methods. Once determined, they can be used to drive simulation because they are independent of the receiver. This methodology has been primarily used for structural applications. This research demonstrates that a similar procedure can be used to determine acoustic free sources on a plane along the cross-section of a duct with the downstream portion of the duct serving as the receiver subsystem. This may be considered as a three-dimensional equivalent of source impedance and source strength. If a continuous source distribution is applied across the plane, these sources should be appropriate regardless of how the system is modified downstream so long as the upstream geometry is unchanged. The approach is first validated using acoustic finite element simulation. It is then demonstrated experimentally using a source room as the source component and an attached duct as the receiver component. Sources are determined along a cross-sectional plane within the duct. The downstream side of the duct is then modified, and it is shown that the acoustic free sources predict the downstream response successfully.