For the interior sound field formed by the complex vibrating structure,an identification approach of panel acoustic contribution based on equivalent source method(ESM)was presented.The normal velocity on the surface of vibrating structure was first reconstructed by using interior nearfield acoustic holography based on ESM and the prediction of whole interior enclosed sound field was realized.Then the sound pressure produced by each panel at the interested field point was respectively replaced by the radiated pressure of the enclosed interior sound field which is formed by the equivalent virtual sources located near the surface of the cavity.Combining with the reconstructed normal surface velocity,the acoustic contribution of each panel to any position in the cavity was obtained by transforming the complex enclosed non-free field into the simple interior free field.Numerical simulations and experiments are conducted,and the influences of the number of the equivalent sources and the distance between them and the reconstructed surface have been investigated.The results show that the proposed method is easier to be implemented with the same accuracy than the traditional analysis method.
To remove the scattering effect of the disturbing sound on the target source when implementing nearfield acoustic holography in a non-free field,a free field recovery technique based on the spherical wave superposition method is proposed.In the method,the sound field separation technique based on the spherical wave superposition method is first used to separate the incoming and outgoing fields,and a further step for separating the radiated and scattered fields is performed by utilizing the surface admittance of the target source as the boundary conc1ition.The technique makes it possible to correctly identify noise sources in a non-free sound feld.The basic principle of the technique is described firstly,a method for choosing the optimal number of spherical wave expansion terms is given,and two numerical simulations are used to demonstrate the validity of this technique.It is shown that,for the lower frequency,the scattering effect can be neglected,and the radiated field of the target source can be obtained by the sound field separation technique,however,as the increasing of the frequcncy,the scattering effcct cannot be neglected,and the frec field recovery technique has to be used to obtain the radiated field of the target source.
