红外频率选择表面特性的数值分析

在微波频段,频率选择表面中的金属部分通常被认为是完全电导体,但是在红外波段,金属通常具有有限大的色散的复值电导率.因此首先建立了包含有金属色散电磁性质的材料模型,即金属部分被看作具有合适介电常数的介质层,然后采用时域有限差分法研究它在红外波段的特性并给出了场更新方程.最后与文献的结果进行对比,验证了方法的有效性,并研究了不同金属种类对红外频率选择表面谱域性质的影响.     

一种星载固态功率放大器用400W二次电源设计

为了满足导航卫星系统对于固态功率放大器大功率、高可靠性、轻量化的需求,文章采用移相全桥同步整流变换电路加反激变换电路匹配的拓扑方案,设计了一种星载L频段固态放大器用400W二次电源,并详细给出了二次电源拓扑结构及设计原理分析。文章重点对变压器热耗进行分析,为了更好地进行变压器散热设计,该方案创新性采用灌封主功率变压器散热方案,灌封变压器的温度从104℃降低为85.5℃,散热相比有明显改善。同时给出了实物环路测试、电性能指标对比测试以及热平衡与热仿真对比测试,电源效率92.8%,环路的相位裕量42°,增益裕度26dB。测试结果表明设计的二次电源在实现高效率大功率输出的同时,有效地实现器件的一级降额散热,满足高可靠性的批产需求。     

尺度效应下均压槽结构对空气静压轴承自激振动的影响

空气静压轴承表面的均压槽结构能有效提高轴承的承载特性,但气膜内由于湍动能变化引发流场振动,形成非线性的自激涡振,影响系统的动态稳定性.为了提高空气轴承的稳定性,基于静压气体润滑理论和稀薄气体动力学基本原理,建立空气静压轴承的气膜流场数学模型;通过数值模拟和实验测试相结合,分析了直槽、环槽、复合均压槽在不同均压槽截面形状...     

PLS概念模型及其应用

工作流技术重点关注如何将已经抽象的企业业务模型描述成计算机可理解和自动处理的流程及其自动处理所需要的各种资源或条件,而并不关心如何对业务进行抽象才能最恰当地反映企业的实际需要.针对此问题,提出了一套通用的点线面一体化业务分析概念模型,即PLS模型(Point-Line-Surface Conceptual Model),定义了用PLS模型分析系统所涉及的各种元素,并分析了PLS模型元素和EPC(Event-driven Process Chains)元素间的映射关系,从而通过PLS构建的系统可以用EPC描述.为验证模型的实用性,以南水北调中线干线工程建设管理信息系统为例,详细阐述了如何利用PLS模型分析企业业务并用EPC描述.      

概率密度函数分析监测发动机气动不稳定征兆

对某型单轴涡喷发动机节流过程中的喘振故障进行了试验研究。在手工关闭放气带的情况下,该型发动机的共同工作线确定地穿越喘振区域,从最大状态收油门减速将会导致该型发动机进入不稳定工作。数据分析中发现压气机第一级静子机匣壁面静压对节流最为敏感,且静压脉动分量的概率密度函数分布随节流有规律地发生变化。定义了概率密度函数特征值θ来量化这种变化。进一步的数据分析表明,θ可以反映压气机第一级端部的流动分离情况,可以作为试验发动机节流过程中的气动稳定性指标。与直接检测模态扰动和短周期扰动相比,监测θ的变化可以为该型发动机提供较长的失速预警时间。      

某发动机后机匣的低循环疲劳寿命试验研究

本文从标准循环载荷的确定、试验件及其安装设计、全尺寸机匣多点协调加载应力试验和循环试验、批准循环寿命和使用寿命的确定等几方面具体介绍某发动机后机匣低循环疲劳寿命试验研究的方法和概况。      

星载大功率固放组件中常用基板材料的出气及其微波特性研究

随着星载大功率固放组件复杂度和输出功率的不断提高,因其内部材料出气而导致产品性能异常的情况时有发生。以大功率固放组件常用介质基板材料出气产生的水汽、氢气和氧气作为研究对象,研究了高功率微波信号作用下基板材料出气气体对大功率固放组件微波特性的影响;对出气的气体成分进行了定量测试试验验证,随后通过真空烘烤对基板进行除气处理;首次结合产品应用和环境试验进行了补充试验,通过增加长期和高温储存试验来模拟实际工况;试验结果表明除气措施可有效降低基板材料出气气体的含量,降幅超过79.1%;最后选取一组试验后的测试试验数据对基板除气的有效性进行了仿真验证,为星载大功率固放组件的进一步优化奠定了基础。     

High-velocity impact responses of 2618 aluminum plates for engine containment systems under combined actions of projectile form and oblique angle

Ballistic impact tests were carried out with examined projectiles of the Ti-6Al-4V titanium alloy to investigate the impact response of the 2618 aluminum plates at a nominal velocity of 210 m/s. The influence of projectile forms and oblique angles on damage formation was particularly discussed by applying different loading conditions such as multiple projectile forms and oblique angles. Additionally, the numerical simulation method was employed to provide further insight into the characteristics of damage and target responses. The Johnson-Cook(J-C)constitutive model with revised failure parameters was used to support the simulations to assess target responses and characteristics of the damage created from different impact conditions. Results show that there is a significant transition in the deformation mode as changes of the projectile form are applied. Moreover, the cracks on the back of the 2618 aluminum alloy plates impacted by the solid plate projectile and the hollow blade projectile tend to locate at different positions, which are supposed to be influenced by local bending and stretching. The work in this paper may provide guidance for the design of fan blade containment systems.     

Old tail lobes effect on the solar-wind – Magnetosphere energy transport for the 27 August 2001 substorm

The magnetic flux of tail lobes Ψ is divided in two parts of comparable values Ψ₁ and Ψ₀₂, with the first that appears during substorm and the second, observed before substorm start. The first was named “new magnetic flux”, the second – “old magnetic flux”. The first, Ψ₁, is known to play a definitive role in the energy transport from the solar wind into the magnetosphere-ionosphere-atmosphere system, but the role of Ψ₀₂ in this transport is not well known. From the 27 August 2001 substorm data we study the involvement in the above transport process of the old flux Ψ₀₂. This involvement is observed in the polar cap (PC) area, which existed prior to the substorm and is called respectively “the old PC”. In this study, as distinct from earlier works, we use the balance equation of the energy stored in magnetosphere and energy consumed. Activation of the old PC magnetic flux Ψ₀₂ was found to increase the energy input by ∼85% in the event under consideration.