Ih J., Jeon I., Kim S.

In this paper, the vibro-acoustic source field of an engine is reconstructed from the measured pressure data of array microphones using the combined technique of equivalent source method (ESM) and inverse boundary element method (BEM). The engine structure is relatively large when the smallest wavelength of interest is considered. Accordingly, the number of boundary nodes for modeling the complicated engine geometry becomes very large. Because the precision of the holographic reconstruction depends on the number of field data, a number of pressure measurement are needed for applying the technique. In order to solve this problem, smaller number of measurement is made in the field than the number of boundary nodes: the other required field data is obtained by using the ESM employing a distribution of acoustic multipole and multi-order virtual sources inside the engine. After obtaining the sufficient field data, the vibro-acoustic source field of the engine surface is restored using the inverse BEM technique. The method was applied to a six-cylinder automotive engine and a satisfactory reconstruction result was obtained with an error less than about 20% when the frequency range of interest is spanned up to the third harmonics of firing frequencies.