超重力下相变材料熔化过程的数值模拟

通过数值模拟的方法,研究了地球重力和超重力条件下相变材料(PCM)的熔化过程,分析了超重力对PCM熔化过程的影响。采用的超重力大小为5倍和10倍地球重力,方向与热流进入方向相反。模拟结果表明,由于PCM导热系数偏小,熔化初期加热面发生过热,须通过耦合其他强化换热措施予以减弱甚至消除。超重力对于PCM熔化过程的影响十分显著。随着超重力的增加,熔化界面的波动幅度增大,熔化速度加快,加热面温度下降,这是因为熔化过程中液相的自然对流作用显著增强。此外,超重力对PCM熔化过程的增强幅度会随超重力的增加而减小,表明超重力的强化换热作用有一定限度,当超过一定值时,该强化作用的效果相对减弱。     

Machining fixture for adaptive CNC machining process of near-net-shaped jet engine blade

Low stiffness and positioning problems are difficulties and challenges in the precise machining of near-net-shaped blades. This paper aims to achieve high accuracy in manufacturing by fixture- and deformation-control in the adaptive CNC machining process. Adaptive CNC machining technology is first analyzed, and new fixture-evaluation criteria and methods to evaluate the adaptive CNC machining process fixture design are built. Second, a machining fixture is designed and manufactured after analyzing its positioning scheme, clamping scheme, materials (PEEK-GF30), and structure characteristics. Finally, the designed fixture is analyzed by FEA and experimentally verified by a cutting experiment. The results show that the deformation of the blade is an overall rigid-body displacement, the main deformation of the blade-fixture system occurs on the four clamping heads, and this fixture can effectively protect the blade from local deformation. The proposed clamping-sequence method reliably and effectively controls the local maximum deformation of the blade. The system stiffness is increased by 20 Hz, with each clamping force increased by 200 N. Both high- and low-frequency displacement in roughing milling or finishing milling are acceptable relative to the accuracy demand of blade machining. This fixture and an adaptive CNC machining process can achieve high accuracy in blade manufacturing.     

净升力对临近空间浮空器上升航迹的影响分析

基于临近空间浮空器动力学与热力学耦合关系,研究分析上升过程飞行航迹与内部气体热性能。建立临近空间浮空器初始充气量模型、热模型和上升过程动力学模型,通过飞行试验验证了数学模型的准确性。仿真计算了某高空科学气球的上升航迹,得到了气球净升力对爆破高度、速度等飞行航迹性能参数的影响,分析了参数变化规律与变化原因。研究结果表明,随着净升力的增加,爆破高度迅速降低,而气球上升速度逐渐上升,且上升速度的增大比爆破高度的减小相对于净升力的变化更加敏感,表明气球的净升力对航迹性能参数存在重要影响。研究结果可为临近空间浮空器设计、试验和应用提供理论参考。     

容错控制系统的可靠性建模及模型化简

在容错控制系统的设计过程中,进行系统的可靠性建模和分析求得容错控制系统可靠性是一项非常重要的工作。它是许多设计工作,如设计方案的选择优化和一些设计参数的确定等的重要理论依据。在容错控制系统的可靠性分析中,利用马尔柯夫过程理论对容错控制系统进行可靠性建模能够较为真实地描述系统的实际工作情况,但是由于容错系统为了达到高可靠性而有采用了大量的冗余配置及重构技术,使得该可靠性模型往往变得相当复杂。因此,对     

Flow response hysteresis of throat regulation process of a two-dimensional mixed-compression supersonic inlet

The variable geometry supersonic inlet tends to decrease the throat area to reduce the Mach number upstream of the terminal shock, so as to reduce the flow loss. However, excessive Internal Contraction Ratio(ICR) exposes the inlet to a greater risk of unstart, which inevitably results in a process of increasing the throat area to aid the inlet restart. In the above throat regulation process, the inlet undergoes the start, unstart, and restart states in turn. In order to reveal the flow structure...     

一种面向服务的业务过程建模语言

通过对现有业务过程建模语言的分析指出了其对面向服务支持的不足,以可视化过程建模语言VPML(Visual Process Modeling Language)为基础,提出了一种面向服务的可视化过程建模语言VPML-S,并提出了该语言的概念设计框架,简述了其通用的建模元素;使用UML类图设计了该语言的元模型,在此基础上建立了语言的形式化模型;分析和评估了VPML-S中的服务元素所提供的将活动映射为Web服务的面向服务功能,嵌入子过程元素所提供的多个业务过程之间的复用机制,管道元素所提供的多个业务过程的协作机制以及VPML-S和其它语言所建立的业务过程模型的互操作支持机制;评述了VPML-S的可视化图符替换、元模型扩展机制;最后通过一个网上购物流程实例说明VPML-S为面向服务的环境下的业务过程复用、协作和互操作提供了有效的支撑.      

基于改进层次分析法的民用飞机修理级别非经济性分析

修理级别分析（level of repair analysis,简称LORA）是飞机保障性分析的一个重要内容,是在设计阶段评估维修对飞机成本影响的一种系统分析方法。在缺乏相关修理级别经济性分析数据的前提下,经过对多种国际主流机型维修大纲和维修手册的研究,分析了飞机修理级别分析的影响因素,建立了层次化的综合评价指标体系,同时又通过专家打分法将定性评价指标进行量化。在此基础上,运用灰色关联分析对修理级别方案进行综合排序,从而选出最优的修理基地。最后通过实例分析说明了本文所提模型的合理性。     

基于工作过程导向的课程体系开发探索

阐述基于工作过程导向的课程方案的开发思路和步骤,提出这种方法开发课程方案时的难点问题。     

基于工作流的飞机质量问题归零过程控制

 为解决使用维护阶段飞机质量问题的闭环处理过程不易建模和控制的难题,给出一种基于工作流的层次化建模和过程控制方法。首先以中国航天行业标准中质量归零管理要求为基础,对维修保障中质量问题处理的业务特点进行了分析;通过扩展工作流给出业务流程的层次化建模方法,并利用工作流引擎为用户提供及时、可靠的归零处理任务调度能力。利用此方法可有效地将复杂的质量问题处理过程分解为独立的流程模型。对典型的技术质量处理过程进行了详细讨论。最后,以某航空制造企业的协同服务管理系统为例说明本文方法的具体系统实现及可行性。     

Designing a power plant with highest efficiency:results from SFB 561

The goal of Collaborative Research Centre(SFB) 561 "thermally highly loaded,porous and cooled multi-layer systems for combined cycle power plants" is to expand the current technological and scientific knowledge on power plants in order to achieve total efficiencies of 65% in a combined cycle power plant in the year 2025.Therefore,the aero-thermomechanical,structural-mechanical,materials' scientific and production fundamentals for the development of steam and gas turbine components that are able to withstand highest thermal loads are being worked out within this SFB.This means for the gas turbine that combustion chamber outlet temperatures of 1520℃ at 1.7MPa are to be attained.In order to control these high temperatures,it is not only required to develop new materials' solutions,including thermal barrier coatings,but also to apply improved cooling techniques,as for example effusion cooling.This novel cooling concept is to be realised through open-porous structures.These structures can consist of drilled open-porous multi-layer systems or open-porous metallic foams.The development of graded multi-layer systems is also extremely important,as the grading will enable the use of coolant in dependence of the requirements.The live steam parameters in the high pressure turbine are expected to be increased up to approximately 700℃ with pressure of 30MPa.These elevated steam parameters can be encountered with Ni-base alloys,but this is a costly alternative,associated with many manufacturing difficulties.Therefore,the SFB proposes cooling the highly loaded turbines instead,as this would necessitate the application of far less Ni-base alloys.To protect the thermally highly loaded casing,a sandwich material consisting of two thin face sheets with a core of a woven wire mesh is used to cover the walls of the steam turbine casing.The current state of the research shows that by utilising innovative cooling technologies a total efficiency of 65% can be reached without exceeding the maximum allowable material temperature,thereby prolonging the life-span.