In practical acoustic measurement for large cylindrical surfaces, it is difficult to keep conformal and coaxial between the holographic surface and the reconstruction surface. To overcome this problem, a combined sound field reconstruction method using non-conformal plane measurement is proposed in this paper. Based on the sound pressure measured on the holographic plane, the combined method first reconstructs the sound field on the cylindrical conformal surface using statistically optimal planar near-field acoustic holography, and then reconstructs the sound field on the cylindrical reconstruction surface using statistically optimal cylindrical near-field acoustic holography. And a least square optimization method is proposed to determine the optimal position of the conformal surface. In addition, to overcome ill-posed problems, an error reduction method combining truncated singular value decomposition and Tikhonov regularization is proposed. Finally, the proposed method is applied to a test bed, and the accuracy and robustness of the sound field reconstruction for large cylindrical surfaces are obviously improved, which can provide reliable evidences for noise monitoring and control of mechanical systems.
In practical acoustical measurement for large cones, maintaining coaxial and conformal between the holographic surface and reconstructed surface is usually tedious. To overcome this flaw, a conical near-field acoustic holography (NAH) based on cylindrical wave function of variable radius and nonconformal plane measurement is proposed in this paper. First, cylindrical wave function of variable radius (VR)–based modified statistically optimal cylindrical NAH (SOCNAH) method, entitled VR-SOCNAH, is proposed, which is more applicable to conical surfaces. Second, with the measured sound pressure data on the holographic plane, sound pressure on the conical conformal surface is first reconstructed using statistically optimal planar NAH (SOPNAH), and sound pressure on the reconstructed surface is then reconstructed using VR-SOCNAH. Third, fixed and variable radius measurement methods are comparatively studied, and the former is adopted. Furthermore, a measurement parameter optimization method based on orthogonal experiment is proposed to determine appropriate value ranges. Finally, the proposed NAH is applied to a test bed, and the robustness and accuracy of sound field reconstruction for large cones are significantly enhanced, which provides reliable scientific basis and engineering guidance for noise monitoring and control of mechanical equipment.
For the sound field reconstruction of non-cylindrical rotative surfaces, current near-field acoustic holography (NAH) methods have relatively poor applicability and low accuracy. To overcome the problem, a combined sound field reconstruction method is proposed. First, an improved multipoint Helmholtz equation least square (HELS) method is proposed, which is more applicable to reconstruct the sound field with an aspect ratio larger than 1. Second, based on single criterion traversing method (SCTM), an improved double criterion traversing method (DCTM) is proposed to determine the optimal truncation order, and reduce the reconstruction error of multipoint HELS. Third, with the sound pressure measured on the holographic surface, the sound pressure on the transitional surface is reconstructed using statistically optimal cylindrical near-field acoustic holography (SOCNAH), and the sound pressure on the reconstruction surface is reconstructed using multipoint HELS. Finally, typical numerical case studies and experimental studies on a test bed are carried out, which validate that the combined method can obviously improve the accuracy and robustness of sound field reconstruction for non-cylindrical rotative surfaces, and thus provide reliable evidences for noise monitoring and control of mechanical systems.
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