快速评价微杜瓦真空寿命及应用北大核心CSCD

微杜瓦内置吸气剂是一项关键技术,使红外微杜瓦内部长期维持高真空状态,保证红外探测器组件全寿命周期内可靠工作。采用传统方法预测微杜瓦真空寿命不仅耗时,而且难以及时指导微杜瓦设计和技术改进。通过分离影响杜瓦真空寿命的核心因素:贮存温度和吸气剂用量,采用单因素实验的方法评价微杜瓦真空寿命,实现真空寿命的快速评价。结合内置吸气剂的杜瓦高温贮存实验,预估室温下真空寿命。另外,采用杜瓦内置真空规技术,极大地缩短了内置吸气剂杜瓦的高温贮存试验时间,为微杜瓦的吸气剂用量配置和技术改进提供及时的信息资源。     

快速评价微杜瓦真空寿命及应用

微杜瓦内置吸气剂是一项关键技术,使红外微杜瓦内部长期维持高真空状态,保证红外探测器组件全寿命周期内可靠工作。采用传统方法预测微杜瓦真空寿命不仅耗时,而且难以及时指导微杜瓦设计和技术改进。通过分离影响杜瓦真空寿命的核心因素:贮存温度和吸气剂用量,采用单因素实验的方法评价微杜瓦真空寿命,实现真空寿命的快速评价。结合内置吸气剂的杜瓦高温贮存实验,预估室温下真空寿命。另外,采用杜瓦内置真空规技术,极大地缩短了内置吸气剂杜瓦的高温贮存试验时间,为微杜瓦的吸气剂用量配置和技术改进提供及时的信息资源。     

基于材料放气特性的杜瓦真空失效时间研究

杜瓦真空失效的两类模式是漏气和材料放气。漏气是导致杜瓦真空早期失效的主要原因,可通过工艺控制手段解决真空短命问题,材料放气是制约长寿命杜瓦真空寿命的根本原因。杜瓦放气特性是进行杜瓦真空失效时间计算的基础,建立杜瓦材料放气特性的合理测试方法成为评估杜瓦真空失效时间的关键。本文分析了小孔流导法和压强上升法测试杜瓦放气特性存在的固有问题,提出了进行杜瓦放气量测试的合理方案。杜瓦放气量测试是杜瓦真空可靠性研究的有效手段。杜瓦的放气特性不仅可用于杜瓦真空失效时间的评估,而且可用于计算杜瓦真空加速寿命试验的加速因子。     

40T混合磁体外超导磁体杜瓦真空系统设计

根据40 T稳态混合磁体外超导磁体杜瓦对真空的要求,对杜瓦真空系统进行了设计计算,计算结果如下:杜瓦真空系统包括粗抽泵机组和主泵机组,其中粗抽泵机组由两套ZJ-70罗茨泵和2XZ-15直联式旋片真空泵组成,可将杜瓦真空抽至1 Pa;主泵机组由两套F250/1500涡轮分子泵和2X-30旋片式机械泵串联组成,可将杜瓦真空...     

大型空间环境模拟器设备液氮制冷系统杜瓦管的研制

液氮系统是大型空间环境模拟设备中的主要分系统之一，在大型空间模拟器的液氮流程中，采用杜瓦管供液的结构形式，也是近年来国外大型空间模拟器中所采用的主要供液方式，介绍了大型空间环境模拟器液氮制冷系统中杜瓦管的作用、结构、使用情况及特点，并根据现场调试，维护等自身因素限制，设计了一种比较简便实用的测试真空试件，经过现场对杜瓦管的调试验收，使杜瓦管的真空性能得到保证，经历了多项试验，杜瓦管始终处于良好使用状态，方便而可靠地保证了对系统，热沉等分系统的供液。     

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。     

斯特林制冷机静态真空系统设计与试验

静态真空是星载斯特林制冷机在地面进行各项性能试验的必备条件,它主要由杜瓦和真空保持系统组成。主要介绍斯特林制冷机杜瓦和真空抽气系统的设计。通过试验证明,该系统能够满足斯特林制冷机进行性能试验所需的真空条件。     

提升红外焦平面探测器杜瓦组件的贮存寿命

杜瓦内真空度退化和芯片盲元增加是影响红外焦平面探测器杜瓦组件贮存寿命的两大方面。杜瓦组件的排气策略直接关系到红外红外探测器杜瓦的真空寿命和红外芯片的贮存寿命,是影响红外探测器杜瓦组件可靠性的关键。本文以杜瓦放气率测试技术为依托,结合杜瓦组件在贮存环境下的退化规律和模型预测杜瓦贮存寿命。最后,综合平衡排气温度/时间对杜瓦真空寿命及芯片盲元损耗的影响,提供一种实现红外芯片和杜瓦真空同时失效的技术途径。     

高温工作型红外探测器杜瓦漏热分析与测试

基于高温工作型红外探测器杜瓦组件的发展趋势,对影响杜瓦漏热指标至关重要的传导漏热和辐射漏热作了分析,提出杜瓦设计改进的方法。概括了杜瓦漏热测试的常规方法,并分析其在高工作温度杜瓦漏热测试方面的缺陷。采用真空保护量热法,实现高工作温度型杜瓦组件漏热的可靠测试,推动第三代红外焦平面探测器组件的发展。     

提升红外焦平面探测器杜瓦组件的贮存寿命北大核心CSCD

杜瓦内真空度退化和芯片盲元增加是影响红外焦平面探测器杜瓦组件贮存寿命的两大方面。杜瓦组件的排气策略直接关系到红外红外探测器杜瓦的真空寿命和红外芯片的贮存寿命,是影响红外探测器杜瓦组件可靠性的关键。本文以杜瓦放气率测试技术为依托,结合杜瓦组件在贮存环境下的退化规律和模型预测杜瓦贮存寿命。最后,综合平衡排气温度/时间对杜瓦真空寿命及芯片盲元损耗的影响,提供一种实现红外芯片和杜瓦真空同时失效的技术途径。     

Materials selection for a cooling plate using control area diagrams

Merit indices are used to rank materials and are of fundamental importance in materials selection. Traditionally, merit indices have only been available for elementary design cases. In the present paper merit indices are generalised to cooling systems where heat flow and strength are design criteria in a materials optimisation framework. A cooling tube and a cooling plate are considered. A new concept, merit exponent is used that is related to the merit indices. A definition of the merit exponent is given also for cases with many design variables. In each design case a number of merit exponents are involved. It is a nontrivial task to identify which they are and when each of them is applicable. For this purpose control area diagrams (CAD) are used. A CAD is a diagram with the controlling properties on the axes, and areas where one or more constraints are active. For the cooling systems the controlling properties are heat conductivity and strength. The active constraints define the relevant merit exponent. The constraints involve the controlling properties and geometrical variables. Principles are established for how to set up the CAD and to derive the merit exponents.     

一类离心调速器的Hopf分岔及其混沌控制

研究了受外部扰动的离心调速器系统的复杂动力学行为。通过系统运动的拉格朗日方程和牛顿第二定律,建立了离心调速器系统的动力学方程,应用Lyapunov直接方法分析了该系统平衡点的稳定性。利用相图分析了系统超混沌吸引子的特性,通过Poincaré截面和Lyapunov指数研究了系统的超混沌行为,通过仿真系统的分岔图和相图分析了系统通向混沌的道路,并且验证了该系统的分岔图与Lyapunov指数谱是完全吻合的。通过对系统施加非线性反馈控制器,并选取合适的反馈系数,可以获得各种不同的所需的稳定周期轨道。对受外部扰动的离心调速器系统施于此控制,计算机数值模拟结果表明,这种控制方法简便有效,控制范围广。     

卫星遥感图像中类圆形油库的自动识别方法

油库是典型军事目标之一,对其识别是卫星图像判读的一项重要内容,传统的方法是通过判读员进行人工判读,工作量非常大是其缺点之一。为了克服这一缺点,本文提出了一种类圆形油库的自动识别方法。首先利用Kapur熵法对图像进行阈值分割,得到二值图像：然后对二值图像中的白像素进行最近邻聚类形成团块,并计算其面积以及体态比和矩形度等形状参数;最后利用油库近似圆形和成群分布的特点对油库群进行识别和定位。实验结果表明该方法对于高分辨率卫星遥感图像中的类圆形油库的识别是很有效的。     

Application of Particle Methods to Static Fracture of Reinforced Concrete Structures

Particle methods for modeling reinforced concrete are described. The reinforcements are modeled by finite elements and are coupled to the particle method by Lagrange multipliers. The method is applicable to nonlinear problems, problems with moderate to severe cracking and deformable interfaces. Applications to the static response of reinforced concrete structures where the concrete is discretized with particles and the reinforcement with elements are described. The method is also tested for several static problems where no relative displacements between the concrete and the reinforcement are allowed.     

Edge-Cracks in Single Crystals Under Monotonic and Cyclic Loads

Basic solutions are obtained for edge-cracks lying along the primary slip plane in a single crystal. The study is motivated by Stage I fatigue crack growth wherein crack orientation is controlled by the slip direction and continued growth is dependent on the crack overcoming barriers to slip. Plasticity is assumed to occur as slip along planes inclined at 45^ to the surface. Problems where slip is limited to persistent slip bands are considered side-by-side with the problem where slip is not confined. Results for both monotonic and cyclic loadings are presented, with emphasis on the crack tip opening and sliding displacements. Both small and large scale yielding are considered. Preliminary results are given for interaction with barriers to slip, such as a grain boundary. This revised version was published online in July 2006 with corrections to the Cover Date.     

双中心矩阵反问题及其在电网络理论中的应用

本文研究双中心矩阵反问题。建立了双中心矩阵反问题的最小二乘解,得到了解的具体表达式。讨论了用双中心矩阵反问题的解构造给定矩阵的最佳逼近问题,给出该问题有解的充分必要条件和解的表达式。设计了相应的算法并给出了其在电网络理论中的应用。     

Applicability of the method of fundamental solutions to interaction of fully nonlinear water waves with a semi-infinite floating ice plate

In this research effort, a meshless numerical model was developed to study the hydroelastic interaction of an incident wave with a semi-infinite horizontal floating plate. It is assumed that the fluid is homogenous, inviscid and incompressible. Fundamental solution of the governing Laplace equation is considered to be radial basis functions. In this method, only a few boundary points are located on the boundary. Moreover, there are a few source points that are located outside the computational domain. Two additional source points are introduced to deal with the plate's edge conditions. The problem is solved using collocations at only a few boundary points. When density and thickness of the plate are reduced to zero, good agreements with other numerical works are observed.     

Static and dynamic analysis of an FGM doubly curved panel resting on the Pasternak-type elastic foundation

The static, dynamic, and free vibration analysis of a functionally graded material (FGM) doubly curved panel are investigated analytically in the present paper. The FGM Panel is originated from a rectangular planform and its principle curvatures are considered to be constant. All mechanical properties of the FGM panel are assumed to vary continuously through the thickness according to a power law formulation except Poisson’s ratio, which is kept constant. A Pasternak-type elastic foundation containing damping effects is considered to be in contact with the panel during deformation. The elastic foundation reacts in both compression and tension. Equations of motion are established based on the first order shear deformation and the modified Sanders shell theories. Following the Navier type solution, the established equations are reduced to time-dependent ordinary differential equations. Using the Laplace transform, the time-dependency of the problem is eliminated. The solutions are obtained analytically in the Laplace domain and then are inverted to the time domain following an analytical procedure. Finally, the analytical results are verified with those reported in the literature.     

HYPERSINGULAR BEM FOR TRANSIENT ELASTODYNAMICS

The topic of hypersingular boundary integral equations is a rapidly developing one due to the advantages which this kind of formulation offers compared to the standard boundary integral one. In this paper the hypersingular formulation is developed for time-domain antiplane elastodynamic problems. Firstly, the gradient representation is found from the displacement one, removing the strong singularities (Dirac's delta functions) which arise due to the differentiation process. The gradient representation is carried to the boundary through a limiting process and the resulting equation is shown to be consistent with the static formulation. Next, the numerical treatment of the traction boundary integral equation and its application to crack problems are presented. For the boundary discretization, conforming quadratic elements are tested, which are introduced in this paper for the first time, and it is shown that the results are very good in spite of the lesser number of unknowns of this approach in comparison to the non-conforming element alternative. A procedure is devised to numerically perform the hypersingular integrals that is both accurate and versatile. Several crack problems are solved to show the possibilities of the method. To this end both straight and curved elements are employed as well as regular and distorted quarter point elements.     

等离子喷涂ZrO2涂层孔隙定量分析

利用等离子喷涂技术制备了两种不同结构的梯度热障涂层.利用定量金相技术对两种涂层富陶瓷区域不同位置的孔隙率、孔隙大小和形态进行了定量分析.结果表明:两涂层富陶瓷区域孔隙率相近,其中界面处孔隙率较高,但在6%以下;孔隙大小服从相似的概率分布,其中直径在1～10um范围内的孔隙含量最多,在72%～80%之间,其次是1um以下的孔隙,在20%～25%之间,而10um以上的孔隙含量在0.2%～4%之间;孔隙形状同样服从相近的概率分布,而且等轴孔隙比重最大,在82%～87%之间,其次为不等轴孔隙,在13%～17%之间,缝隙状孔隙最少,在0.1%～0.4%之间.说明涂层结构对富陶瓷区域的孔隙没有影响.