基于声学超常材料的声能量调控研究
发布时间：2018-08-12 11:47
【摘要】：作为当前声学领域的热门课题,声学人工复合材料的设计和应用正受到广泛关注。声学人工复合材料一般具有特殊的人工结构,这些经过特殊设计的人工结构使其拥有了超越天然材料本身的超常物理性质,这为声学材料的研究开辟了新思路。声子晶体和声超构介质是声学人工复合材料研究领域中的两类典型,两者在尺度结构和物理机理上有所差别。声子晶体的研究更关注于对声波波动在其中传播过程的分析,因此对它的研究是多尺度的,既有布拉格散射型声子晶体,其工作声波波长与晶格常数相当,同时也有局域共振型声子晶体,其工作声波波长是晶格常数的上百倍。由于这类材料中存在声子带隙,其在高性能声学滤波和高精度隔振等方面有着潜在应用。相比之下,声超构介质更关注宏观尺度下人工微结构所表现出的等效声学参数。通过引入亚波长尺度的特殊微结构单元可以实现天然材料中不存在的超常物理性质,如零折射率、密度各向异性、负密度和负体模量等,这些超常的物理性质被应用于亚波长成像和声隐身等诸多领域。本文基于声子晶体和声超构介质这两种声学人工复合材料,通过理论计算和有限元数值分析相结合的方法对两种声能量调控方法的特性和机理进行了详细研究。主要涉及基于固-流超晶格结构的声能量透射增强研究和基于非均匀各向异性零密度超构介质的声能量流动控制研究。第一章绪论部分简要回顾了本文相关的声学人工复合材料的研究背景和研究进展,并概述了本文研究工作的主要内容。第二章作为对固-流超晶格结构的初步研究,其基于传递矩阵法,从理论上推导了全向入射条件下固-流超晶格结构的传递矩阵。在此理论的基础上,分别计算了无限周期和有限周期的固-流超晶格结构在全向入射条件下的能带结构和传输特性。计算结果证明了固-流超晶格结构的能带结构中低频声裂隙的存在。第三章中,研究了基于固-流超晶格结构的声能量透射增强问题。利用Green函数方法和传递矩阵方法分别得到固-流超晶格结构的表面模式色散曲线和相应的声能量透射系数曲线。结果表明,声能量透射增强现象是由固-流超晶格结构的特定表面声振动模式引起的,其透射系数要远高于普通通带的声能量透射系数。随后,为了进一步理解这种声能量透射增强效应的机理,使用有限元方法研究了不同入射条件下超晶格结构中的位移场分布。数值模拟结果证明,声能量透射增强效应可以归因于在超晶格表面激发出的表面声振动共振态。基于此效应设计的可调谐声耦合器件,可用于实时匹配两种声阻抗相差巨大的流体,实现声能量超常穿透。固-流结构为所设计的声耦合器件带来的实时可调性有效地弥补了声能量透射增强效应有限带宽的局限性。第四章中,研究了基于非均匀各向异性零密度超构介质的声能量流动控制问题。利用严格的声学理论分析,得到了非均匀各向异性零密度材料在正向入射条件下的等效密度和等效波长。进一步,结合理论计算和有限元数值模拟分析,证明了当声波在材料内以垂直于零密度的方向传播时,零密度分量会对非零密度分量施加一种强平均作用。随后,使用有限元法研究了该强平均效应作用下材料内部的声能量流动方式。借助于这种强平均效应,仅需通过设计非零密度分量的分布即可控制声能量在任意路径上流动。最后,讨论了非均匀各向异性零密度超构介质的具体物理实现方式。本章中所提出的利用非均匀各向异性零密度超构介质实现声能量流动任意控制,仅需简单地将流动路径上材料密度张量中的非零分量设计为较低值,有效地避免了利用变换声学理论所带来的极其复杂的各向异性和非均匀性。最后一章对全文主要工作做了总结,并展望未来的研究方向。
[Abstract]:As a hot topic in acoustics, the design and application of acoustical artificial composites have attracted much attention. Acoustical artificial composites usually have special artificial structures, which make them possess extraordinary physical properties beyond the natural materials themselves. This opens up the way for the study of acoustical materials. Phononic crystals and acoustic superstructure media are two typical types of acoustical artificial composites. They are different in scale structure and physical mechanism. The study of phononic crystals is more concerned with the analysis of the propagation process of acoustic wave in them. Therefore, the study of phononic crystals is multi-scale, including Prague scattering phononic crystals. Because of the existence of phonon band gaps in these materials, they have potential applications in high-performance acoustic filtering and high-precision vibration isolation. In contrast, acoustic superstructure media pay more attention to macro-scale. By introducing special microstructural units at sub-wavelength scale, supernormal physical properties, such as zero refractive index, density anisotropy, negative density and negative modulus, can be realized in natural materials. These supernormal physical properties are applied to sub-wavelength imaging and acoustic stealth. Fields. Based on phononic crystals and acoustic superstructure media, the characteristics and mechanism of the two acoustic energy modulation methods are studied in detail by means of theoretical calculation and finite element numerical analysis. In the first chapter, the background and research progress of the related acoustical artificial composites are briefly reviewed, and the main contents of the research work are summarized. In the second chapter, as a preliminary study of the structure of solid-fluid superlattices, the transfer matrix method is used. On the basis of this theory, the band structure and transmission characteristics of infinite-period and Finite-Period solid-flow superlattices under the condition of omnidirectional incidence are calculated respectively. In Chapter 3, the problem of sound energy transmission enhancement based on solid-fluid superlattices is studied. The surface mode dispersion curves and the corresponding sound energy transmission coefficient curves of solid-fluid superlattices are obtained by Green function method and transfer matrix method, respectively. In order to understand the mechanism of the enhancement effect of acoustic energy transmission, the finite element method was used to study the displacement field distribution in the superlattice structure under different incident conditions. A tunable acoustical coupler device based on this effect can be used to match two fluids with large acoustic impedance difference in real-time to achieve supernormal acoustic energy penetration. In Chapter 4, the control of acoustic energy flow in nonhomogeneous anisotropic zero-density superstructure media is studied. The equivalent density of nonhomogeneous anisotropic zero-density materials under forward incidence is obtained by using strict acoustic theory analysis. Furthermore, it is proved that the zero-density component exerts a strong average effect on the non-zero-density component when the sound wave propagates in the direction perpendicular to zero-density by combining theoretical calculation and finite element numerical simulation analysis. By means of this strong averaging effect, the flow of sound energy in any path can be controlled only by designing the distribution of non-zero-density components. Finally, the physical realization of inhomogeneous anisotropic zero-density superstructure media is discussed. In order to avoid the extremely complex anisotropy and inhomogeneity caused by the theory of transform acoustics, the non-zero component of the material density tensor in the flow path is simply designed as a lower value.
【学位授予单位】：南京大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TB33
本文编号：2178962
[Abstract]:As a hot topic in acoustics, the design and application of acoustical artificial composites have attracted much attention. Acoustical artificial composites usually have special artificial structures, which make them possess extraordinary physical properties beyond the natural materials themselves. This opens up the way for the study of acoustical materials. Phononic crystals and acoustic superstructure media are two typical types of acoustical artificial composites. They are different in scale structure and physical mechanism. The study of phononic crystals is more concerned with the analysis of the propagation process of acoustic wave in them. Therefore, the study of phononic crystals is multi-scale, including Prague scattering phononic crystals. Because of the existence of phonon band gaps in these materials, they have potential applications in high-performance acoustic filtering and high-precision vibration isolation. In contrast, acoustic superstructure media pay more attention to macro-scale. By introducing special microstructural units at sub-wavelength scale, supernormal physical properties, such as zero refractive index, density anisotropy, negative density and negative modulus, can be realized in natural materials. These supernormal physical properties are applied to sub-wavelength imaging and acoustic stealth. Fields. Based on phononic crystals and acoustic superstructure media, the characteristics and mechanism of the two acoustic energy modulation methods are studied in detail by means of theoretical calculation and finite element numerical analysis. In the first chapter, the background and research progress of the related acoustical artificial composites are briefly reviewed, and the main contents of the research work are summarized. In the second chapter, as a preliminary study of the structure of solid-fluid superlattices, the transfer matrix method is used. On the basis of this theory, the band structure and transmission characteristics of infinite-period and Finite-Period solid-flow superlattices under the condition of omnidirectional incidence are calculated respectively. In Chapter 3, the problem of sound energy transmission enhancement based on solid-fluid superlattices is studied. The surface mode dispersion curves and the corresponding sound energy transmission coefficient curves of solid-fluid superlattices are obtained by Green function method and transfer matrix method, respectively. In order to understand the mechanism of the enhancement effect of acoustic energy transmission, the finite element method was used to study the displacement field distribution in the superlattice structure under different incident conditions. A tunable acoustical coupler device based on this effect can be used to match two fluids with large acoustic impedance difference in real-time to achieve supernormal acoustic energy penetration. In Chapter 4, the control of acoustic energy flow in nonhomogeneous anisotropic zero-density superstructure media is studied. The equivalent density of nonhomogeneous anisotropic zero-density materials under forward incidence is obtained by using strict acoustic theory analysis. Furthermore, it is proved that the zero-density component exerts a strong average effect on the non-zero-density component when the sound wave propagates in the direction perpendicular to zero-density by combining theoretical calculation and finite element numerical simulation analysis. By means of this strong averaging effect, the flow of sound energy in any path can be controlled only by designing the distribution of non-zero-density components. Finally, the physical realization of inhomogeneous anisotropic zero-density superstructure media is discussed. In order to avoid the extremely complex anisotropy and inhomogeneity caused by the theory of transform acoustics, the non-zero component of the material density tensor in the flow path is simply designed as a lower value.
【学位授予单位】：南京大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TB33
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