摘要:
为评估覆盖层的吸声性能,研究黏弹层在无限大周期加肋双层板背衬下的声反射。首先通过弯曲波与Lamb波的比较,揭示了板近似理论不适用于黏弹性板的原因。为此采用(黏)弹性理论处理(黏)弹性板,而肋板的处理则采用板近似理论,并用Hull提出的方法解决肋板和平板的耦合问题,得到反射声场的解。与板近似理论计算加肋双层板声反射的结果进行比较验证了本文方法的正确性,对反射系数进行计算分析了背衬对声反射的影响,定义平均反射系数比较了不同覆盖层的性能。结果表明,频率较低时覆盖层无法有效抑制背衬的影响,板间流体层与双层板的耦合作用引起共振散射,肋板与双层板的耦合作用降低声反射。
Abstract:
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.Firstly,the reason why structural theories of plates are not,applicable to viscoelastic plates is explained through comparing flexural waves with Lamb waves.Therefore,(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 is solved by Hull's method.Solution of reflection field is obtained at last.The accuracy of present method is validated by comparing results of acoustic reflection from rib-stiffened double plates computed by structural theories of plates.The influence of a backing on acoustic reflection of the viscoelatic layer is analyzed by computing reflection coefficients.Performance of different viscoelastic materials are evaluated by defining the average reflection coefficients.The results show that,influence of a backing on acoustic reflection cannot be suppressed by viscoelastic materials in low frequencies.The resonance is introduced by coupling of the fluid layer and double plates.And ribs,which are coupled with double plates,mainly make acoustic reflection reduced.
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