大型空间环境模拟器的一种液氮制冷系统

介绍了我国新研制一台大型空间环境模拟器ＫＭ６所采用的以液氮以制冷介质的带文丘利管的单项密闭泵增压循环制冷系统,并给出了该制冷系统的调试结果。     

玻璃钢复合材料无磁杜瓦真空性能研究

讨论了玻璃钢复合材料无磁杜瓦的真空性能。提出了采用三层模式壳体结构、加热、充CO2置换气体、放置活性炭等提高和保持杜瓦夹层真空度、减少抽空时间的方法。同时简述了影响夹层真空度测量的相关因素。研究结果表明:玻璃钢复合材料放气率是影响夹层真空度的主要因素;在液氮温度下杜瓦夹层动态真空度可达5×10-4Pa,并可长期使用而真空度不变。     

基于减压降温原理的过冷液氮冷却系统研制

随着超导技术的迅速发展,为超导材料提供低温环境的制冷系统得到了越来越多的关注。本文详细介绍了一种基于减压降温原理的高温超导电机过冷氮冷却系统,包括技术指标及相关要求、总体结构、关键技术、热负荷分析与计算等。系统采用减压降温获得过冷液氮,冷却电机中超导线圈。液氮进口温度68K,出口温度72K。主要由供液杜瓦、过冷箱、抽空泵、超导线圈杜瓦、返液杜瓦、低温管路及温度仪表组成。试验证明,该冷却系统设计合理、操作方便,成功实现了超导电机的加载运行。     

HT-7U超导托卡马克装置低温杜瓦的真空问题

分析了HT－7U大型全超导托卡马克装置低温杜瓦内的真空状况，对影响真空指标至关重要的磁体主机氦泄漏漏率作了计算，介绍了在试验杜瓦成功实现超导磁体正常运行的真空调试与检漏实践。     

垂直上升管内气液两相流动特性的数值模拟

某空间模拟器的液氮制冷系统采用了结构简单、可靠性高、最节能的重力自循环系统.基于气液两相流理论,建立了垂直上升管内液氮气液两相流动的一维均相流模型;数值模拟不同入口压力下的管内压力、质量流量、管壁温度和质量含气率等参量,研究其变化规律.计算结果表明,建立的数学模型能够详细描述重力自循环系统垂直上升管内液氮流动的流体动力特性,为空间模拟器液氮制冷系统的研制提供了重要的基础数据和理论参考依据.     

基于参数化设计方法的空间环境模拟器集成设计北大核心CSCD

目前常采用的空间环境模拟器设计模式是不同的分系统利用各自的三维造型软件构建产品的三维几何模型,然后导出到Auto CAD中进行二维的图纸表达。此种设计模式不利于开展协同设计,同时在不同设计软件转换时容易造成设计表达错误。此外,日益激烈的市场竞争,也对空间环境模拟器的快速响应设计提出了更高的要求。因此,根据空间环境模拟器设计流程分析以及设计过程的实际需求,针对容器、热沉、真空、氮流程等分系统设计特点,提出了空间环境模拟器集成设计平台方案;基于统一的数字化设计平台,开展各分系统的协同设计,从而提高产品设计的规范性和重用性,实现空间环境模拟器的数字化高效集成设计。     

基于参数化设计方法的空间环境模拟器集成设计

目前常采用的空间环境模拟器设计模式是不同的分系统利用各自的三维造型软件构建产品的三维几何模型,然后导出到Auto CAD中进行二维的图纸表达。此种设计模式不利于开展协同设计,同时在不同设计软件转换时容易造成设计表达错误。此外,日益激烈的市场竞争,也对空间环境模拟器的快速响应设计提出了更高的要求。因此,根据空间环境模拟器设计流程分析以及设计过程的实际需求,针对容器、热沉、真空、氮流程等分系统设计特点,提出了空间环境模拟器集成设计平台方案;基于统一的数字化设计平台,开展各分系统的协同设计,从而提高产品设计的规范性和重用性,实现空间环境模拟器的数字化高效集成设计。     

中子慢化器低温及真空性能测试系统设计北大核心CSCD

中子慢化器低温及真空性能测试系统,用于验证中国散裂中子源氢慢化器的低温性能和真空密封性。此套系统由供液系统、气体加热系统、流量控制系统、温度与压力监测系统组成,采用液氮替代液氢作为测试介质,通过加热器对液氮直接加热的方式获得低温氮气。每根输液管道都是独立的真空单元,配有真空抽口,采用双层不锈钢管道,管道之间做绝热处理。通过控制加热器与内管的装配精度来保证气体换热效率。使用Lakeshore Model 336温控仪和TELEDYNE HASTINGS流量控制器进行气体温度和流量调节。该系统气体输出温度精度达到±5 K,气体输出流量约500 L/min±10%。此套系统不仅为大型低温系统提供安全可靠的低温测试工作介质,同时节约了实验成本,将来在航空航天领域能得以应用推广。     

中子慢化器低温及真空性能测试系统设计

中子慢化器低温及真空性能测试系统,用于验证中国散裂中子源氢慢化器的低温性能和真空密封性。此套系统由供液系统、气体加热系统、流量控制系统、温度与压力监测系统组成,采用液氮替代液氢作为测试介质,通过加热器对液氮直接加热的方式获得低温氮气。每根输液管道都是独立的真空单元,配有真空抽口,采用双层不锈钢管道,管道之间做绝热处理。通过控制加热器与内管的装配精度来保证气体换热效率。使用Lakeshore Model 336温控仪和TELEDYNE HASTINGS流量控制器进行气体温度和流量调节。该系统气体输出温度精度达到±5 K,气体输出流量约500 L/min±10%。此套系统不仅为大型低温系统提供安全可靠的低温测试工作介质,同时节约了实验成本,将来在航空航天领域能得以应用推广。     

用铜丝作传感器的简单液氮液面监浏器

本文介绍的是一种简单、紧凑和可靠的液氮液面监测器。此种监测器用细铜丝连续监测杜瓦容器内的液氮液面。监测器有一只相似计和作为指示器的高发射二极管，液面分辨率好于±10mm。介绍了传感器结构和传感电路。。监测器装有一套液氮自动重新充填系统和供给探测器高偏压的远距离断路，还装有一台警报器。当液氮液面过低或供液用完时，就会发出声响。     

Eikonal equation‐based front propagation for arbitrary complex configurations

This paper presents a front propagation method using the Eikonal equation, ?? ? ?? = 1, in which, ? represents the smallest Euclidean distance field to the front to be propagated. The offset capturing approach consists in first calculating the ? field over a uniform Cartesian grid fully covering the front to be propagated, and then constructing the iso‐? curves or surfaces as the propagated result. The calculation of ? uses a 3D numerical scheme, the Fast Sweeping Scheme. Validation for accuracy of the method is presented using academic test cases. A real 3D industry application, draft tube with two piers, is successfully propagated and demonstrated using special boundary conditions to cope with inlet and outlet planes during front propagtion. This application involves the propagation of a front that exhibits both concave and convex shape regions, sharp corners, and local tangent plane surface discontinuities as well as a multi‐connected domain. Copyright © 2007 John Wiley & Sons, Ltd.     

1.16 Extremely uniform thin films by vacuum deposition from a ‘tube source’

A vacuum deposition device without moving parts called ‘tube source’ has been developed which is capable of producing from a small area source on plane extended fixed substrates thin films with 10 times less thickness variation than a film would show deposited from the same small area source as the one used with the ‘tube source’ at the same distance but without the tube source arrangement. For example, using the tube source, a film deposited on a flat circular substrate of 10.4 cm diameter shows a thickness variation less than ± 0.4% at a substrate to source distance of 23.2 cm. The tube source consists of a wide cylinder. At one end on the axis of the cylinder there is a small area source, for example, a $\text{1}\text{2}$ in. commercial dimple boat electrically heated and filled with the material to be deposited; from the other end flat substrates were positioned in a plane perpendicular to the cylinder axis at varying distances. A disc with its plane also perpendicular to the axis and its center on it was suspended with three very thin stretched wires inside the tube in such a way that no vapor atoms could hit the substrate directly, in other words the disc forms a shadow for the source on the substrate. Hereby, the arrival of vapor atoms can be made much more random depending on the geometry (distance of substrate from top end plane of cylinder, distance of source from bottom end plane, a.o.). The tube could be heated by nichrome wire wrapped around it to change the reflectivity of the vapor atoms. Optimum thickness distributions on the substrate were determined by Monte Carlo methods using a computer as well as analytically.     

Nonlinear dynamics of tubes carrying a pulsatile flow

The nonlinear dynamics of a cantilever tube conveying a pulsatile flow and undergoing planar motions is investigated. The mean flow is near its critical value at which the downward vertical position of the tube gets unstable by flutter and executes limit-cycle oscillations. The pulsations in the flow are assumed to be small and harmonic with frequency nearly twice that of the limit cycle. To study the nonlinear dynamics, the method of averaging is utilized and the governing partial differential equation is reduced to a dynamic system on the plane. These two first-order differential equations depend on three parameters and govern the dynamics of the amplitude of motion of the tube. The planar system is studied for its qualitative behaviour using ideas from the local bifurcation theory and a local bifurcation set in the parameter plane is constructed. Using ideas from codimension-two unfolding of singularities, this bifurcation set is further refined. The resulting partial bifurcation set and the associated phase portraits in the various regions of the flowrate-detuning parameter plane show that the averaged equations have constant as well as periodic solutions. The stabifity type and the number of these solutions changes from one region to another. This explains how periodic or 'phase-locked' oscillations of the cantilever tube bifurcate into amplitude-modulated or almost-periodic motions.     

On finite plane strain of an isotropic incompressible hyperelastic material

Abstract

The purpose of this paper is to derive a new formulation of the governing equations for the complex variable in the deformed configuration of an isotropic incompressible hyperelastic material, assuming that the material undergoes a constant finite axial stretch and then a finite plane strain.

As an application we consider the circular shear of a tube of such a material and, if we do not take into account torsion, it is proved that the plane deformation is given by an ordinary differential equation of second order, the integration of which requires the determination of the first derivative of the unknown function at the outer wall of the tube and the knowledge of the strain‐energy function. The axial stretch of the tube can be determined through two equations only when the strain‐energy function is specified.     

The metallography of fracture in cast nickel aluminium bronze

In tube burst tests, and in slow bend tests, crack propagation in nickel aluminium bronze produces crack faces normal to the tension stress even though plastic deformation preceding fracture occurs under conditions of generalized plane stress. Shear lips are observed to be about 1.0 mm deep and, therefore, much less than the critical plane stress plastic zone radius which is around 40 to 50 mm in tube tests. Fractographic and metallurgical examinations reveal that the crack path is dictated by metallurgical structure and that the small shear lips and flatness of the crack faces arise from a cumulative mode of fracture dictated by structural features rather than as a result of constraint stresses.     

Interaction between a stationary vortex tube and an infinite plane

A law of pressure variation in a near-wall radially converging flow formed in a viscous contact between a free vortex tube and a plane is found analytically.     

Heat transfer in the thermally stabilized sections of channels with a laminar non-newtonian fluid flow

An approximate method is described for solving the problem of heat transfer for laminar non-newtonian fluid flow in the thermally stabilized sections of a plane channel and a circular tube under conditions of constant wall temperature.     

Measurement of propagation time dispersion in a scintillator

One contribution to the time resolution of a scintillation detector is the signal time spread due to path length variations of the detected photons from a point source. In an experimental study, a rectangular scintillator was excited by means of a fast pulsed ultraviolet laser at different positions along its longitudinal axis. Timing measurements with a photomultiplier tube in a detection plane displaced from the scintillator end face showed a correlation between signal time and tube position indicating only a small distortion of photon angles during transmission. The data is in good agreement with a Monte Carlo simulation used to compute the average photon angle with respect to the detection plane and the average propagation time. Limitations on timing performance that arise from propagation time dispersion are expected for long and thin scintillators used in future particle identification systems.     

Flux Pinning-Induced Stress in a Long Hollow Cylindrical Superconductor Restricted by a Metal Tube

The tensile stress in a hollow cylindrical superconductor completely restricted by a metal tube in a parallel magnetic field is investigated. Using the plane strain approach, analytical expressions for the stress distribution of the superconductor and the contact stress between the metal tube and the superconductor are obtained and show that both the ratio of Young’s modulus and thickness ratio of the high-temperature superconductors and the metal tube significantly affect the stress distribution in the superconductor explicitly. In addition, the flux pinning-induced stress in the above-mentioned superconductor is systematically studied by the exponential critical state model during the field cooling process. The results indicate that the metal tube can reduce effectively the tensile stress in the hollow cylindrical superconductor during the magnetization process. The findings suggest that the appropriate selection of material parameters and size of the metal tube can improve superconductor performance efficiently.     

The effect of temperature on the fracture of polycarbonate

The fracture toughness of polycarbonate was obtained over the temperature range 20 to ? 120° C. There is a strong thickness dependence which is described in terms of plane stress and plane strain values which are insensitive to temperatures above ?40° C but the plane stress value increases below this temperature. This change is associated with theβ transition and stable crack growth was observed in this region with accompanying instabilities arising from adiabatic heating at the crack tip.