Approximate Solutions for Acoustic Radiation Problems: A Critical Appraisal of the Method of Comparative Sources

Radiation and scattering from vibrating bodies can be expressed by a source system that is placed inside the radiator and whose source strengths are determined appropriately. The Method of Comparative Sources (MCS) provides an estimate of these source strengths from the nearfield data. In the present article, the MCS is reviewed by applying it to cylinders with elliptical cross-section for which exact solutions of the sound field are available. Solutions for different, more and less efficiently radiating velocity distributions are compared to results obtained with the MCS, using various source systems and different weighting functions. It is demonstrated that, contrary to current assumptions, the error in the surface velocity approximation is generally not proportional to the error in the radiated sound power. Furthermore, the method provides an adequate prediction of the radiated sound power only for efficient radiators. Inefficient radiators are not handled well with the MCS. Finally it is shown, that the incorporation of certain weighting functions will further improve the MCS.