To predict sound-absorbing performance of anechoic materials,the acoustic reflection problem of a viscoelastic layer backed with periodically rib-stiffened infinite double plates is studied in this paper.The reason wh...To predict sound-absorbing performance of anechoic materials,the acoustic reflection problem of a viscoelastic layer backed with periodically rib-stiffened infinite double plates is studied in this paper.The reason why structural theories of plates are not applicable to viscoelastic plates is explained through comparing dispersion and attenuation curves of flexural waves with those of Lamb waves.As a result,（visco-）elastic theory is adopted to deal with（visco-）elastic plates,and ribs are treated by structural theories of plates.The coupling between ribs and plates are solved by Hull＇s method,and solution of the reflected field is obtained.The accuracy of present method is validated by comparing with the results by the structural theories of plates.The influence of a backing on the acoustic reflection of the viscoelatic layer is analyzed by computing reflection coefficients.Performances of different viscoelastic materials are evaluated by the average reflection coefficients.The computational results show that,influence of a backing on the acoustic reflection cannot be suppressed by the viscoelastic materials in low frequencies.The resonance is determined by the coupling of the fluid layer and the double plates.And ribs,which are coupled with the double plates,mainly reduce the acoustic reflection.展开更多
The Lamb wave technique is used in the detection of internal defects in plates. The reflection of the Lamb wave at the free edge of the plate has been shown to be rather complicated. The reflected wave is usually comp...The Lamb wave technique is used in the detection of internal defects in plates. The reflection of the Lamb wave at the free edge of the plate has been shown to be rather complicated. The reflected wave is usually composed of infinite number of Lamb wave modes even in the case of incidence of one pure mode. The analysis of the reflection problem is complicated in nature as the orthogonality relations of the eigen modes of the Lamb wave concern both the stresses and displacements. We adopt the principle of the least squares as a new approach to simplify the analysis, in which the eigen-modes are taken as the trial function. It seems to be simple and effective. In most cases a good enough result can be obtained on using an 8- bit microcomputer. Here the coefficients of the various reflected modes are calculated, some interesting phenomena on the mode conversion are indicated and the conditions on the pure mode reflection are given.展开更多
基金supported by the Research Funds(9140A10040813CB04001)the Natural Science Foundation of Shandong Province(2013ZRF01039)
文摘To predict sound-absorbing performance of anechoic materials,the acoustic reflection problem of a viscoelastic layer backed with periodically rib-stiffened infinite double plates is studied in this paper.The reason why structural theories of plates are not applicable to viscoelastic plates is explained through comparing dispersion and attenuation curves of flexural waves with those of Lamb waves.As a result,（visco-）elastic theory is adopted to deal with（visco-）elastic plates,and ribs are treated by structural theories of plates.The coupling between ribs and plates are solved by Hull＇s method,and solution of the reflected field is obtained.The accuracy of present method is validated by comparing with the results by the structural theories of plates.The influence of a backing on the acoustic reflection of the viscoelatic layer is analyzed by computing reflection coefficients.Performances of different viscoelastic materials are evaluated by the average reflection coefficients.The computational results show that,influence of a backing on the acoustic reflection cannot be suppressed by the viscoelastic materials in low frequencies.The resonance is determined by the coupling of the fluid layer and the double plates.And ribs,which are coupled with the double plates,mainly reduce the acoustic reflection.
文摘The Lamb wave technique is used in the detection of internal defects in plates. The reflection of the Lamb wave at the free edge of the plate has been shown to be rather complicated. The reflected wave is usually composed of infinite number of Lamb wave modes even in the case of incidence of one pure mode. The analysis of the reflection problem is complicated in nature as the orthogonality relations of the eigen modes of the Lamb wave concern both the stresses and displacements. We adopt the principle of the least squares as a new approach to simplify the analysis, in which the eigen-modes are taken as the trial function. It seems to be simple and effective. In most cases a good enough result can be obtained on using an 8- bit microcomputer. Here the coefficients of the various reflected modes are calculated, some interesting phenomena on the mode conversion are indicated and the conditions on the pure mode reflection are given.
