撞击载荷下Nomex蜂窝夹芯梁的变形模式研究

本文研究了Nomex蜂窝夹芯结构在不同冲量下的变形模式和失效模式.实验采用子弹撞击的加载方式,对Nomex蜂窝夹芯梁施加大小不同的冲量,使用激光位移传感器测量每个试件后蒙皮的变形位移.分析了同芯层厚度,不同蒙皮厚度的Nomex蜂窝夹芯梁在不同冲量作用下抵抗变形的能力,以及冲量大小与蒙皮厚度对夹芯梁抵抗撞击能力的影响,计算分析了蒙皮与芯层的吸能性.实验结果表明:增加蒙皮的厚度能够改善夹芯梁在撞击荷载下抵抗变形的能力,在撞击过程中芯层吸收了50％左右的能量,且冲量越大,芯层吸收的能量越多.     

Existence and multiplicity of positive solutions for an elastic beam equation

This paper investigates the boundary value problem for elastic beam equation of the form

广义静态梁方程非负解的存在性

运用Leray—Schauder拓扑理论,证明了广义静态梁方程和静态梁方程非负解的存在性,仅要求非线性项f在原点的某个邻域满足一定的符号条件,突破了以往对非线性项f的增长性限制．所获结果对工程设计具有重要的理论意义和实用价值．     

On the formation of gap solitons in nonlinear electromagnetic metamaterials

A nonlinear (Kerr‐type) electromagnetic metamaterial, characterized by a double‐Lorentz model of its frequency‐dependent linear effective dielectric permittivity and magnetic permeability, is considered. The formation of gap solitons in the low‐ and high‐frequency band gaps of this metamaterial is investigated analytically. Evolution equations governing the gap solitons, of the form of a nonlinear Klein‐Gordon and a nonlinear Schrödinger equation, are obtained, and the structure of their solutions is discussed.     

Restricted thresholding: recovering smoothness and preserving edges

Restricted non linear approximation is a generalization of the N‐term approximation in which a measure on the index set of the approximants controls the type, instead of the number, of elements in the approximation. Thresholding is a well‐known type of non linear approximation. We relate a generalized upper and lower Temlyakov property with the decreasing rate of the thresholding approximation. This relation is in the form of a characterization through some general discrete Lorentz spaces. Thus, not only we recover some results in the literature but find new ones. As an application of these results, we compress and reduce noise of some images with wavelets and shearlets and show, at least empirically, that the L²‐norm is not necessarily the best norm to measure the approximation error.     

Imbert–Fedorov shifts of a Gaussian beam reflected from uniaxially anisotropic chiral media

We study the Imbert–Fedorov (IF) shifts of a reflected Gaussian beam from uniaxially anisotropic chiral media (UACM), where the chirality appears only in one direction and the host medium is a uniaxial crystal or an electric plasma. The numerical results are presented for three kinds of UACM, respectively. It is found that the IF shifts are closely related to the propagation properties of the two eigenwaves in the UACM. In general, when either of the eigenwaves is totally reflected, the IF shifts can change abruptly near the critical angle. The cross-polarized reflection coefficient has a greater effect on the spatial IF (SIF) shift than on the angular IF (AIF) shift, and the sign of the AIF shift depends mainly on that of the difference between the co-polarized reflectivity. By designing artificially the electromagnetic parameters of the UACM, we can control the IF shifts and acquire their more abundant properties.     

基于多元高斯声束模型的圆柱体超声检测声场仿真

为了提高圆柱体缺陷检测的准确性,需了解其超声声场分布。针对圆柱体实际检测的要求,本文采用超声水浸检测法。通过多元高斯声束模型分别模拟了实心圆柱体及空心圆柱体中的辐射声场,计算仿真了垂直入射与倾斜入射至圆柱体时的声场,实现了检测声场的可视化。通过计算得出仿真结构与实际理论相符,表明本论文的方法能够应用在圆柱体结构超声声场仿真中。     

强非局域非线性介质中强光导引的弱光呼吸子传输规律研究

研究了强光导引的弱光呼吸子传输问题. 尽管弱光本身的非线性效应可以忽略, 但强光通过强非局域非线性效应会对弱光形成约束并与弱光本身的衍射效应达到动态平衡, 从而形成呼吸子. 得到了弱光呼吸子的解析表达式, 在此基础上分析了其束宽的呼吸演化规律, 并对弱光呼吸子整体轨迹的形状、方位、旋向等性质进行了系统的研究.     

一种全光开关及任意比能量输出光分束器的设计

基于光子晶体非线性Kerr效应设计了一种结构简单的任意比能量输出光分束器, 通过控制抽运光的强度来控制端口能量输出比. 该结构还可以实现控制光传输的动态开关作用, 并且具有插入损耗低、无串扰、信号光的开/关两个状态下的透射率相差非常大的特点, 因此该光开关具有很高的开关比. 关键词： 全光开关 光分束器 非线性Kerr效应 光子晶体     

用于矢量水听器的低频高灵敏度层合梁加速度传感器

压电加速度传感器是同振型矢量水听器的核心部件。为了满足低频高灵敏度矢量水听器的应用需求,提出并研究一种具有层合梁结构的低频高灵敏度加速度传感器。结合弹性力学和压电方程推导层合梁加速度传感器的加速度灵敏度解析解表达式,通过有限元仿真对层合梁加速度传感器尺寸进行优化,给出优化后的尺寸范围。从优化的尺寸范围中选取两种不同尺寸进行加速度传感器振动特性的仿真分析及实物制作(其中压电材料为PZT-5)与性能测试。仿真与测试结果均表明,相比已有的同尺寸金属梁加速度传感器,层合梁加速度传感器可以有效降低谐振频率并提升加速度灵敏度。当压电层厚度为0.5 mm时,加速度灵敏度最大提升3.9 dB,谐振频率下降23%。测试结果与理论分析相符。