振动测试中低频失真放大问题的机理

针对振动环境试验和振动测量中低频失真放大现象的机理问题,应用MATLAB软件进行分析和仿真,在典型随机信号上叠加低频正弦信号或脉冲信号,复现了低频失真放大现象。通过试验对低频失真的物理机理进行了研究。分析和试验结果表明,测量信号中超低频成分与特定的谱分析方法共同作用,是出现低频失真放大的直接原因。测量电路虚接、电路连接松脱、测量超出传感器量程、被测结构或传感器松动、特殊结构单向脉冲等情况,是产生超低频信号并间接导致低频失真的物理原因。仿真与试验结果一致,证实了振动测试低频失真放大的机理。对该机理的认识有助于减少相关振动测量问题。     

尾翼展开部件测力天平技术研究

风洞是进行空气动力学研究与飞行器研制的最基本的实验设备,在风洞中进行尾翼展开部件测力实验是导弹风洞实验的一个重要部分,为型号设计提供可靠的气动数据.风洞测力实验是风洞中最基本的实验,而风洞天平是实验中最基本的装置.本文介绍了尾翼展开部件测力实验的小量程天平的研制,主要包括天平结构、量程、组桥方式及静校方法和校准公式;并介绍了实验采用的风洞和实验模型.经过试吹风检验和实验结果分析表明,实验数据合理可靠、对称性和重复性都较好,设计的天平符合要求,采用的组桥方式也是新颖独特,试验委托单位对最后的实验结果和试验效率作出了高度评价,满足了该型号的实验要求.     

Analytical determination of permeability of porous fibrous media with consideration of electrokinetic phenomena

Flow behavior in porous fibrous media with consideration of electrokinetic phenomena is investigated based on a linearized Poisson–Boltzmann equation and Navier–Stokes equation. An analytical solution of effective permeability of porous fibrous media as functions of porosity, dimensionless local averaging net charge density and dimensionless electric resistance number is derived in this paper. The influences of the electrokinetic phenomena can be measured by the dimensionless electric resistance number, which is proportional to the square of the liquid dielectric constant, the solid surface Zeta potential and inversely proportional to the liquid dynamic viscosity, electric conductivity and the square of the maximum pore radius. The analytical results show that when the dimensionless electric resistance number is small and the porosity is large, the dimensionless total flow rate shows a nearly uniform distribution. When the dimensionless electric resistance number is large, the resistant effects of the electrical double layer (EDL) become so significant that the superficial velocity decreases. The effective permeability of the porous fibrous media decreases correspondingly. Furthermore, the theoretical predicted effective permeability values are compared with experimental data, and good agreement is observed between the two. It shows that the mathematical model for the effective permeability of porous fibrous media with consideration of electrokinetic phenomena is satisfactory.     

3D打印技术及其军事应用发展动态

阐述了3D打印技术的基本概念与不同工艺采用的材料,对3D打印技术在航天航空、武器装备制造、消费电子产品等领域的发展概况进行了概述。同时,对3D打印设备的世界分布情况进行了统计,分别从武器装备受损部件修复和复杂结构部件生产两方面对3D打印技术在军事领域的应用进行了介绍。跟踪和梳理了国外3D打印技术的发展动态。     

多运动平台多传感器机动目标自适应跟踪

针对多运动平台多传感器背景下的机动目标跟踪问题,提出了模糊自适应无迹卡尔曼滤波(FUKF)算法,基于良好机动性描述的"当前统计"模型和良好非线性滤波能力的UKF(Unscented Kalman Filter),利用模糊推理技术实时自适应地调整系统噪声协方差矩阵,来提高对目标机动性的理解能力和跟踪精度.仿真实验表明该算法的有效性.     

规范形式LP问题的改进对偶单纯形法

通过分析对偶单纯形法迭代的实质，就所给LP问题的规范形式，不引进剩余变量而直接得出另一种改进的对偶单纯形法，使变量个数不增且运算规模缩小．     

基于复数小波变换的三维地形轮廓匹配算法

针对地形特征对方向选择具有差异性的特点，提出了一种新的三维地形轮廓匹配算法．利用复数小波变换的六个可分的正负方向频带，提取地形六个不同方向的特征信息．在不同尺度下，通过六个带通复值分量，实现了由粗到精的金字塔式分层匹配．最后，仿真结果表明，合理选取匹配策略后，该算法具有较强的鲁棒性和较好的快速性．     

The metallurgy,mechanics, modelling and assessment of dissimilar material brazed joints

At the heart of any procedure for modelling and assessing the design or failure of dissimilar material brazed joints there must be a basic understanding of the metallurgy and mechanics of the joint. This paper is about developing this understanding and addressing the issues faced with modelling and predicting failure in real dissimilar material brazed joints and the challenges still to be overcome in many cases. An understanding of the key metallurgical features of such joints in relation to finite element modelling is presented in addition to a study of the mechanics and stress state at an abrupt interface between two materials. A discussion is also presented on why elastic singularities do not exist based on a consideration of the assumption of an abrupt change in material properties and plasticity in the vicinity of the joint. In terms of modelling real dissimilar material brazed joints; there are several barriers to accurately capturing the stress state in the region of the joint and across the brazed layer and these are discussed in relation to a metallurgical study of a real dissimilar material brazed joint. However, this does not preclude using a simplified modelling approach with a representative braze layer in design and failure assessment away from the interface. In addition modelling strategies and techniques for assessing the various failure mechanisms of dissimilar material brazed joints are discussed. The findings from this paper are applicable to dissimilar material brazed joints found in a range of applications; however the references listed are primarily focussed on work in fusion research and development.     

Improving hole exit quality in rotary ultrasonic machining of ceramic matrix composites using a compound step-taper drill

Mechanical-machining-induced tearing defects at hole exits restrict the application of C/SiC composites. Rotary ultrasonic machining (RUM) is suitable for hole manufacture in brittle composites, providing reduced tearing size as compared with conventional grinding. Even so, substantial tearing defects at the hole exit remain with RUM. In this study, a novel compound step-taper diamond core drill for RUM of C/SiC was developed to further improve the hole exit quality. Contrastive machining tests were conducted to evaluate the effectiveness of the new type drill. Experimental results show that the compound drill can help reduce the tearing size by 30% on average. Results of variance analysis indicate that there is little dependency of tearing size on processing variables with the compound drill, whereas the common drill shows substantial dependence. Detailed observation of the thrust force reveals that the tearing size reduction using the compound drill is due to the reprocessing effects of its taper face. In the reprocessing process of the taper face, the thrust force gradually decreases at the hole exit. Increasing the ultrasonic amplitude can help further improve the hole exit quality when using our compound drill.     

Laser spot weld bonding of mild steel

Laser spot weld bonding (LSWB) is a new joining process, which combines laser spot welding with a layer of structural adhesive in a single joint. The purpose of this paper is to introduce a new LSWB process with a special pulsed laser. With this method, the impact of adhesive gas on molten pool is weakened, and the gas can exhaust from the gap of the metal sheets. The carbon decomposed from the adhesive diffuses into the molten pool and changes the microstructure of the weld joint. The joint is mainly composed of martensite and bainite, and twinned martensite is found in the interface between the adhesive layer and metal sheet. In tensile shear test, LSWB specimens give the highest energy absorption compared with laser spot welded samples and adhesive bonded samples.