【作者】 邵颖；

【导师】 赵社戌；

【作者基本信息】 上海交通大学 ， 固体力学， 2007， 硕士

【摘要】 将潜水体覆盖上粘弹性材料,可以提高其对外界声波的吸收,降低反射,从而提高其声学隐密性。为了研究满足耐高静水压并且具有良好的低频宽带吸声性能的消声结构,本文应用有限元方法研究了含非均匀介质层的复合薄层结构中的低频(0-2000Hz)声反射特性,其中橡胶中周期分布有多孔介质体和重核,构成非均匀介质层。文中将流体等效处理为(粘)弹性体;对多孔介质,提出在薄层、低频下忽略其骨架的运动,由Biot理论获得退化的孔中流体的基本方程,之后也将其等效处理为(粘)弹性体;对于重核则将其处理为刚性体。利用Galerkin方法建立了有限元格式,进行了大量的数值计算,分别研究了非均匀层中多孔介质、重核的材料参数和结构的变化对声反射特性的影响;同时也计算了双胞元结构下多孔介质和重核相互作用下的声传播特性。结果表明,均匀的橡胶层中引入周期性分布的多孔介质和重核来改善结构的吸声性能是有效可行的途径,并且为实际吸声结构的优化和设计提供了重要的参考依据。更多还原

【Abstract】 In order to increase the absorption of the sound waves, submarines are often covered with viscoelastic layers. In this paper, the finite element method is applied to analyze the sound characteristics of thin layered acoustic structures, containing fluid layer, elastic layer and viscoelastic layer with periodic porous medium, at low frequency (0-2000Hz). It is considered that the fluid can be modeled as a viscoelastic medium with equivalent Lame constants. In addition, for thin layer at low frequencies, the porous frame may be assumed as motionless. In this case, the reduced control equation of pore fluid in porous material is obtained by Biot’s theory. Similarly, the pore fluid is also equivalent to a viscoelastic medium. The finite element formulation is derived by using the Galerkin technique. Influences of material constants and the structure both of the porous medium and the heavy particles on reflection characteristics of the structure is analyzed. In addition, we also considered the corporate influences of the porous medium and the heavy particles through the double cell structure. The results show that existence of the inhomogeneous medium layer has obvious effect on the reflection coefficient of the structure at lower frequency. This research provides important reference for the practical engineering.更多还原