Using a finite element method with Bloch-periodic boundary conditions, the sound absorption of anechoic coatings embedded with doubly periodic cavities and backed with periodically rib-stiffened plates is investigated, by researchers from the Institute of Acoustics of the Chinese Academy of Sciences recently.
During the past few decades, many mathematical models have been developed to study the sound absorptive performance of anechoic coatings.
The finite element method combined with Bloch’s theorem is usually used to investigate the sound reflection and insulation characteristics of anechoic coatings containing doubly periodic cavities.
In practice, the hull of vehicle (the structure underneath the anechoic coatings) has a significant effect on sound absorptive performance, especially at low frequencies. Therefore, it is reasonable to include the dynamics of the hull structure in the modeling. A typical hull structure consists of periodically rib-stiffened plates.
Although much attention has been devoted to the modeling of anechoic coatings, the prediction of absorptive performance of a fluid-loaded acoustic coating affixed to a rib-stiffened plate in three dimensions has not been reported in the literatures.
As a result, the sound absorption of anechoic coatings embedded with doubly periodic cavities and backed with periodically rib-stiffened plates is therefore investigated. The problem is solved by writing a finite element program using Bloch periodic boundary condition in three dimensions, and the mesh data are exported from ANSYS.
A simplified approach based on the finite element method and transfer impedance model is also introduced for a comparison. The results indicate that the increased mass resulting from the plate and ribs is essential for the sound absorption in the lower frequencies.
The shifting of the absorption peak could reach to one or two octave band depending on the increased mass of backing plates, and this is valuable for these efforts to achieve sound absorption especially in low frequency range.
The results also imply that the prediction of the main absorption performance of coated structures may be simplified by calculating an equivalent homogeneous coating layer affixed to the periodically rib-stiffened plate or even more complicated structures by the finite element method.
This method helps to capture the sound absorption features of anechoic coatings while at the same time reduce the calculation time dramatically in comparison with a full finite element method model.
Funding for the research came from NSFC Grant No. 11374326 and State Key Development Program for Basic Research of China (973 Program) Grant No. 2012CB720204.
References:
FU Xinyi, JIN Zhongkun, YIN Yao, LIU Bilong. Sound Absorption of a Rib-stiffened Plate Covered by Anechoic Coatings. The Journal of the Acoustical Society of America (Vol. 137, No. 3, pp. 1551–1556, March 2015).
Contact:
LIU Bilong
Key Laboratory of Noise and Vibration Research, Institute of Acoustics, Chinese Academy of Sciences, 100190 Beijing, China
Email: liubl@mail.ioa.ac.cn