Algorithm And Implementation Of Nearfield Acoustical Holography In The Interior Sound Field

It is important to predict interior sound field in the domain of noise control, sound field analysis, etc. The principle, algorithm and implementation of nearfield acoustical holography in a cylindrical cavity with endcaps are conducted.Helmholtz integral equations involved in sound radiation are stated, and then the basic principle of nearfield acoustic holography (NAH) is analyzed, which deals with the inversion of the Helmholtz integral equations. For a sound field radiated from a plate, the sound field reconstruction is carried out by using FFT method. During the reconstruction process, the wraparound error and the selection of the filter functions are discussed.It is proved from the theory of sound field within a structural-acoustic coupled enclosure that NAH can be used to reconstruct the interior sound field. As one of the key techniques of the NAH, acquirement of the sound pressure on the holographic surface is also investigated in the paper.Computer simulations about the interior sound field reconstruction of the cylindrical cavity with endcaps are carried out in this thesis. Firstly, modal superposition approach is used to calculate the displacement of the cylindrical shell. Then, with the shell's vibration response, the interior sound field within the cylindrical shell is calculated by the modal superposition approach. After that, one cylindrical surface in the shell is selected as the holographic surface. Finally, the sound field reconstructed by NAH is compared with that calculated by acoustical modal superposition approach. In fact, the sound pressure of the selected surface is used as the holographic surface to reconstruct the interior sound field and the criterion of the sound pressure in comparison with the reconstructed results.It is concluded that, NAH can also be applied into the interior sound field, and the sound field reconstructed by NAH is consistent with the real sound field.