可承静载且有5种动态零刚度变形模式的声学材料细结构的优化设计方法

During the past few years, the acoustic cloaking research has been stimulated or pushed forwards by an innovative design theory of electromagnetic wave cloaking. The basic principle underlying the innovative ideas is a so-called acoustic transformation method, in which the material parameters in the physical domain are defined by a spatial transformation. The latest researches show elastic materials with finite isotropic mass density and extreme anisotropic stiffness can also be used to design acoustic cloaking. However, the kind of elastic materials for acoustic cloaking has to possess extreme material elastic tensor matrix with rank one, in which case a structure made of the material will be an unstable structure with several degrees of movable freedoms, and it means that the kind of elastic materials cannot be used in practical engineering application. At present, how to design and manufacture the micro-structure of periodic composite materials, which satisfies the extreme material elastic properties and the practical demands of engineering application, is still an open problem and has not been solved yet. To meet the challenge, the project proposes a novel idea of elastic material properties, which defines a kind of new elastic material. And the main characteristic of the new material is that its elastic material properties are totally different under static or dynamic load conditions. In details, under the static load condition, the material behaves like the structural material and can bear certain loads with any stress states; while under the dynamic load condition such as acoustic wave propagation in the material, the material behaves like ideal pentamode material and has five independent easy deformation modes, which shows the new material possesses the extreme dynamic elastic material properties. For the sake of implementing the proposed idea of the new elastic material, a design method of periodic micro-structures of the material is also proposed and the micro-structure design scheme is constructed by using smart prestressed micro-structures.The quasi-zero dynamic stiffness of periodic micro-structures results from the singular geometry shape of prestressed micro-structures after the static load is applied. This project will research the design theory and method of acoustic cloaking material proposed here with static load bearing capacity and extreme dynamic material elastic properties, and some periodic smart prestressed micro-structures will be designed and presented. The new elastic material constructed here can be utilized to control the propagation trajectory of acoustic wave in practical engineering application according to designers' needs and also meet the demand of underwater acoustic cloaking for materials.

近年来，电磁隐身斗篷设计思想推动了声学隐身斗篷的研究，形成了声学隐身斗篷材料参数设计的变换声学方法。最新进展表明：具有标量质量密度的弹性材料，也可实现声学隐身斗篷设计，但其要求材料弹性张量的秩仅为一，该奇异性使设计斗篷必是有可动自由度的不稳定结构，无法承载也不能实际应用。目前如何设计制造具有这种极端材料特性且可实际应用的复合材料细结构，还是公开的未解决问题。对此，本申请提出一种新材料构思，将材料的静态和动态弹性特性分开考虑，要求材料静载下具有结构材料特征，可承任意静载；动载下表现为奇异的动态弹性特性，满足声波传播对斗篷材料的要求。并提出这种新材料的预应力智能周期细结构设计方案，该细结构利用静载作用后的奇异几何位型获得近零动刚度特性。这里将研究这种可承载并具极端动态弹性特性的声学隐身斗篷材料的优化设计方法。如成功，它可满足工程中控制声波传播路径的需要，特别是水下潜艇隐身对材料的要求。

本项目研究了应用五零能模式材料控制声波传播路径的坐标变换计算方法，构造了完整的计算列式，探讨了应用周期细结构设计五零能模式材料的方法，给出了保证五零能模式材料结构稳定的条件和策略。基于这些工作，撰写论文十余篇，其中发表13篇；培养研究生30多名，其中毕业23名；申请专利十余项，包括授权军工发明专利1项，授权发明专利5项，授权实用新型专利2项，在申请中国发明专利3项，国际发明专利处于PCT阶段3项等。.在项目实施的4年中，主要研究工作包括：①研究了五零能模式材料参数设计的坐标变换方法，构造了有效的迭代求解算法；②研究了五零能模式材料设计的非线性有限元计算中，系数函数的形式和参数对坐标变换的影响；③通过五零能模式材料结构的整体分析，研究了五零能模式材料结构稳定性条件，给出了通过施加预载荷以实现结构稳定的充分条件；④结合准静态分析和动态分析等多种方法，研究了五零能模式材料单胞构型的设计、分析、材料等效参数计算的方法；⑤构造了一种仅能传递膨胀波的五零能模式材料的单胞构型，研究了单胞结构参数对其声学特性的影响规律；⑥以一种典型的五零能模式材料单胞构型为对象，研究了周期结构准静态参数分析方法的适用条件；同时，研究了应用均匀化等效材料参数，分析梯度五零能模式材料波动问题的适应性。此外，为了进一步应用离散构件设计声学斗篷，探索了一维管道Webster方程的适用范围；并研究了三维嵌入薄膜型声学超材料的声学特性。.发明专利是本项目的主要成果，其中军工发明专利“********结构”、中国发明专利“一种三维声隐身斗篷结构”、“小型机械单元平面阵列的低频宽带多层吸声装置”和“以吸声材料单元弱弹性级联为周期结构设计层的低频宽带吸声装置”、以及国际发明专利“一种新型超薄声波阻抗变换器”、“宽带超薄声波扩散结构”和“控制声波传播路径的宽带超薄吸声隔声结构”等，兼具原理和技术的创新，既具有科学价值，也具有潜在的实用性。.