磁场辅助激光熔覆铝基金属玻璃覆层

为提高铝合金的表面性能,采用磁场辅助激光熔覆的方法在5083铝合金表面制备了Al-Ni-Y-Co-La五元金属玻璃熔覆层,并对其进行组织成分及性能分析。实验结果表明：熔覆层主要由非晶相、α-Al相以及Al₄NiY等金属间化合物组成,旋转磁场的搅拌作用使熔覆层非晶相含量由10.2%提高到30.7%,且能够有效抑制多道搭接和多层堆积过程中重熔区晶粒的生长,细化了熔覆层晶粒组织,降低了残余应力,提高了显微硬度及韧性,使其平均显微硬度从278 HV_0.1提高至335 HV_0.1,且波动较小,平均抗拉强度为303 MPa,为基体拉伸件的110.2%,平均伸长率为6.79%,为基体的33.1%。     

Design of an innovative multi-stage forming process for a complex aeronautical thin-walled part with very small radii

In this paper, an aeronautical thin-walled part with a complex geometry which has several sharp bends and curvatures in different directions was investigated. This kind of part is difficult to be manufactured only in one stage. Therefore, an innovative multi-stage active hydroforming process assisted by the rigid forming method was designed. In addition, an optimized blank geometry is obtained. In fact, the main focused point of this paper is to propose a new small radius rounded corner forming technique and analyze the mechanism. Two kinds of forming modes of changing a big rounded corner into a small one, which are related to different tangential positions of the die in the process of calibration, are analyzed theoretically. Meanwhile, the stress and strain states of the deformation region are compared. The relationships between the minimum relative radii of rounded corners I and II in the first stage and the hydraulic pressure are calculated by the bending theory. Finally, the influences of the tensile-bulging effect and the interface condition of the double-layer sheet on the forming quality of the specimen are investigated. The achieved results can make a foundation for utilizing the proposed method in forming of thin-walled parts with very small radii.     

A new weighted mean temperature model in China

The Global Positioning System (GPS) has been applied in meteorology to monitor the change of Precipitable Water Vapor (PWV) in atmosphere, transformed from Zenith Wet Delay (ZWD). A key factor in converting the ZWD into the PWV is the weighted mean temperature ($T_m$), which has a direct impact on the accuracy of the transformation. A number of Bevis-type models, like $T_m-T_s$ and $T_m-T_s\text{,}{P}_s$ type models, have been developed by statistics approaches, and are not able to clearly depict the relationship between $T_m$ and the surface temperature, $T_s$. A new model for $T_m$, called weighted mean temperature norm model (abbreviated as norm model), is derived as a function of $T_s$, the lapse rate of temperature, δ, the tropopause height, $h_{\mathit{trop}}$, and the radiosonde station height, $h_s$. It is found that $T_m$ is better related to $T_s$ through an intermediate temperature. The small effects of lapse rate can be ignored and the tropopause height be obtained from an empirical model. Then the norm model is reduced to a simplified form, which causes fewer loss of accuracy and needs two inputs, $T_s$ and $h_s$. In site-specific fittings, the norm model performs much better, with RMS values reduced averagely by 0.45 K and the Mean of Absolute Differences (MAD) values by 0.2 K. The norm model is also found more appropriate than the linear models to fit $T_m$ in a large area, not only with the RMS value reduced from 4.3 K to 3.80 K, correlation coefficient $R^2$ increased from 0.84 to 0.88, and MAD decreased from 3.24 K to 2.90 K, but also with the distribution of simplified model values to be more reasonable. The RMS and MAD values of the differences between reference and computed PWVs are reduced by on average 16.3% and 14.27%, respectively, when using the new norm models instead of the linear model.     

考虑状态约束的弹性高超声速飞行器自适应饱和容错控制

针对弹性高超声速飞行器跟踪控制问题进行研究,主要考虑状态约束、输入饱和、执行器故障等约束条件.首先,将弹性模态、外界干扰和模型参数不确定性归结为一类带有未知上界的系统干扰.其次,根据被动容错思想,针对速度和高度子系统分别设计抗饱和自适应容错控制器,通过引入双曲正切函数和新型屏障李雅普诺夫函数分别处理了输入饱和与状态约束...     

基于SFEM的结构元件疲劳可靠性分析

将结构元件的弹性模量、泊松比、几何尺寸定义为随机场,并将随机场离散成随机变量,将抗拉强度定义为随机变量,采用Monte Carlo随机有限元法(MCSFEM),给出了元件危险点应力的随机分布。由危险点应力分布、材料的p-S-N曲线和Miner理论给出了概率名义应力法,计算常幅载荷下元件的寿命分布,并利用剩余寿命模型计算元件的可靠度。给出了两个算例,结果表明:计算结果与试验结果吻合良好。     

浅析高功率微波武器的研究与发展

随着外层空间日益军事化,作为反卫星武器的高功率微波武器的研究与发展备受关注,其军事价值日益显现.对高功率微波武器的作用效能及特点作了详细分析,重点评述了各主要军事强国在高功率微波武器方面的研究情况.最后分析了高功率微波武器的发展趋势.     

月球粉尘的研究现状

随着我国探月工程的开展,面临着月球粉尘危害性的问题,急需开展月球粉尘的研究。文章在调研的基础上,阐述了目前国外在月球粉尘方面的研究现状,主要是美国"阿波罗"计划中对月尘的特性、危害性、探测和防护方面的研究。     

基于群论的空间可展开结构自由度分析

为了开发构型新颖、生命力强、便于运输和储藏的空间可展开结构，使其满足所处环境的时间、空间等苛刻条件，适应特殊任务的实际需求，亟需开展空间可展开结构的自由度及折展性能分析。由于现有可展结构多具有一定的对称性，基于群论方法，从对称学角度解析结构可动的本质，提出判别对称体系可动性的充分条件。根据几何约束性质，运用矩阵理论和变分原理，推导了可展结构中典型构成单元的位移协调矩阵。利用对称子空间，推导了机构位移模态、自应力模态的对称表示，并以闭合环形可展开结构为研究对象，开展了结构自由度分析。研究工作有助于新型空间可展开结构的研发与设计，为可展结构及其衍生结构的进一步研究与应用提供了理论基础。     

和差通道相位差对差模跟踪接收机的影响分析

在数据中继卫星系统中,中低轨航天器常采用差模跟踪技术,完成对数据中继卫星的捕获跟踪,建立高速数据中继传输链路。文章根据某任务跟踪接收机实际设计参数,用Matlab／Simulink软件对和差通道相位差对跟踪性能的影响进行了仿真分析。     

甚高频数据链模式二通信协议栈一致性测试系统设计及验证

甚高频数据链模式二(VDLM2)通信协议是航空电信网(ATN)所支持的四种甚高频数据链模式之一,已被定为过渡时期ATN空地通信的主要方式,是目前应用最为广泛的甚高频数据链。本文以自主开发的甚高频模式二协议栈通信系统为被测系统,设计了一种与之适合的一致性测试系统,通过该测试系统对模式二协议栈进行了一致性测试。测试结果表明,测试系统可以很好地完成一致性测试的功能,并具有很强的扩展性,为系统性能进一步测试奠定了基础。