【摘要】：作為當前聲學領域的熱門課題,聲學人工復合材料的設計和應用正受到廣泛關注。聲學人工復合材料一般具有特殊的人工結構,這些經(jīng)過特殊設計的人工結構使其擁有了超越天然材料本身的超常物理性質,這為聲學材料的研究開辟了新思路。聲子晶體和聲超構介質是聲學人工復合材料研究領域中的兩類典型,兩者在尺度結構和物理機理上有所差別。聲子晶體的研究更關注于對聲波波動在其中傳播過程的分析,因此對它的研究是多尺度的,既有布拉格散射型聲子晶體,其工作聲波波長與晶格常數(shù)相當,同時也有局域共振型聲子晶體,其工作聲波波長是晶格常數(shù)的上百倍。由于這類材料中存在聲子帶隙,其在高性能聲學濾波和高精度隔振等方面有著潛在應用。相比之下,聲超構介質更關注宏觀尺度下人工微結構所表現(xiàn)出的等效聲學參數(shù)。通過引入亞波長尺度的特殊微結構單元可以實現(xiàn)天然材料中不存在的超常物理性質,如零折射率、密度各向異性、負密度和負體模量等,這些超常的物理性質被應用于亞波長成像和聲隱身等諸多領域。本文基于聲子晶體和聲超構介質這兩種聲學人工復合材料,通過理論計算和有限元數(shù)值分析相結合的方法對兩種聲能量調控方法的特性和機理進行了詳細研究。主要涉及基于固-流超晶格結構的聲能量透射增強研究和基于非均勻各向異性零密度超構介質的聲能量流動控制研究。第一章緒論部分簡要回顧了本文相關的聲學人工復合材料的研究背景和研究進展,并概述了本文研究工作的主要內容。第二章作為對固-流超晶格結構的初步研究,其基于傳遞矩陣法,從理論上推導了全向入射條件下固-流超晶格結構的傳遞矩陣。在此理論的基礎上,分別計算了無限周期和有限周期的固-流超晶格結構在全向入射條件下的能帶結構和傳輸特性。計算結果證明了固-流超晶格結構的能帶結構中低頻聲裂隙的存在。第三章中,研究了基于固-流超晶格結構的聲能量透射增強問題。利用Green函數(shù)方法和傳遞矩陣方法分別得到固-流超晶格結構的表面模式色散曲線和相應的聲能量透射系數(shù)曲線。結果表明,聲能量透射增強現(xiàn)象是由固-流超晶格結構的特定表面聲振動模式引起的,其透射系數(shù)要遠高于普通通帶的聲能量透射系數(shù)。隨后,為了進一步理解這種聲能量透射增強效應的機理,使用有限元方法研究了不同入射條件下超晶格結構中的位移場分布。數(shù)值模擬結果證明,聲能量透射增強效應可以歸因于在超晶格表面激發(fā)出的表面聲振動共振態(tài)�；诖诵O計的可調諧聲耦合器件,可用于實時匹配兩種聲阻抗相差巨大的流體,實現(xiàn)聲能量超常穿透。固-流結構為所設計的聲耦合器件帶來的實時可調性有效地彌補了聲能量透射增強效應有限帶寬的局限性。第四章中,研究了基于非均勻各向異性零密度超構介質的聲能量流動控制問題。利用嚴格的聲學理論分析,得到了非均勻各向異性零密度材料在正向入射條件下的等效密度和等效波長。進一步,結合理論計算和有限元數(shù)值模擬分析,證明了當聲波在材料內以垂直于零密度的方向傳播時,零密度分量會對非零密度分量施加一種強平均作用。隨后,使用有限元法研究了該強平均效應作用下材料內部的聲能量流動方式。借助于這種強平均效應,僅需通過設計非零密度分量的分布即可控制聲能量在任意路徑上流動。最后,討論了非均勻各向異性零密度超構介質的具體物理實現(xiàn)方式。本章中所提出的利用非均勻各向異性零密度超構介質實現(xiàn)聲能量流動任意控制,僅需簡單地將流動路徑上材料密度張量中的非零分量設計為較低值,有效地避免了利用變換聲學理論所帶來的極其復雜的各向異性和非均勻性。最后一章對全文主要工作做了總結,并展望未來的研究方向。
[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.
【學位授予單位】：南京大學
【學位級別】：碩士
【學位授予年份】：2015
【分類號】：TB33

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