基于T5离子推力器无拖曳飞行技术

GOCE是世界上首次应用无拖曳飞行技术的科学测量卫星,用于测量地球重力场和稳态海洋环流.大气阻尼补偿系统是实现无拖曳飞行的重要技术支撑,其核心单元是T5 离子推力器.基于T5 离子推力器无拖曳飞行,论述了从入轨测试到执行任务的技术特点、运行及性能.并对T5 离子推力器在大气阻尼补偿系统中的应用做了总结,提出了离子推力器发展应用的建议.     

10 cm发散磁场离子推力器地面试验验证研究

10cm口径离子推力器是我国针对超低轨道监测卫星研制的发散磁场型离子推力器。为了验证该推力器的工作参数是否满足在轨工作的指标要求,进行了性能测试、环境试验测试等一系列试验,试验结果表明：兰州空间技术物理研究所研制的10 cm口径离子推力器三个正交方向的基频分别为601 Hz、583 Hz和736 Hz,满足星载产品基频大于150 Hz的要求。经过1 600g量级的冲击试验后,推力器无异常;经过力学试验以及25.5个循环的热真空试验后,推力器工作性能基本无变化;推力器各工况点的束流发散全角均在30°以内,推力偏斜角度不超过1°,20 mN工况点的二价离子占比为14.1%,基于推力电参数测量方法得到的推力值整体误差为0.95%。地面测试结果证明,国产10 cm口径发散磁场离子推力器的各项性能均满足超低轨道监测卫星的任务要求。     

高推力密度离子推力器研究

离子推力器是一种先进的空间推进技术,由于其高比冲,长寿命等特性而获得了广泛的应用,但是受其束流密度的限制,其推力密度也受到限制。然而在轨道转移、深空探测主推进等应用需求中,不但要求其比冲高,还要求其推力大,以缩短航天器轨道转移和巡航时间。受航天器的体积和功率限制,大推力要求离子推力器在一定比冲下具有较高的推力密度。为了提高离子推力器的推力密度,以25cm离子推力器为研究对象,通过改善离子推力器束流平直度和栅极可引出最大束流密度,有效提高了平均束流密度。试验结果显示在3500s比冲下,平均束流密度达到75A/m2,推力密度达到4.1N/m2。     

励磁电流对离子推力器推力变化影响研究

离子推力器磁场是影响放电室等离子体密度的关键因素之一,在其他参数配合下通过调节磁场对推力进行宽范围精确调节。为了揭示磁场与推力之间的变化关系,从理论分析角度建立励磁电流和推力器推力之间的关系模型,根据理论模型得到的影响趋势,设计并进行了推力调节试验,得到了磁场与推力之间的关系曲线,验证了理论分析的正确性。试验证明,励磁电流对推力变化影响,之间存在非线性关系。     

真空弧推力器技术研究

微纳卫星因其简单、经济、可靠越来越广泛应用于空间任务,传统的推进系统通常不能应用于微纳卫星平台。真空弧推力器(VAT)是一种利用真空中正负极之间放电产生等离子体射流的电推进装置,适用于微纳卫星的理想电推进类型,具有比冲高、效率高、质量小和使用固态推进剂等优点。介绍了同轴型和环型真空弧推力器系统方案及实验测试结果,针对环型真空弧推力器开展了数值计算研究,利用PIC方法重点考察了磁场对推力器性能的影响,主要包括磁场对等离子体密度分布和离子速度分布的影响;实验测试包括电参数测试、离子速度测量和微小推力器测量等,结果表明真空弧推力器具有良好的性能。     

基于超导差分加速度测量原理的微推力测量方案

随着微推进技术的快速发展,微推力器推力的测试与标定也日益困难。为实现微推力的精密测量和动态特性测试,通过分析超导重力梯度仪的差分加速度测量原理、仪器的构成和原理电路等,提出了一种基于高温超导差分加速度测量原理和SQUID检测技术微推力测量方案,其推力测量范围为10^-7-10^-2N、测量频带从直流至4Hz。根据检验质量的动力学方程和超导回路磁通量守恒方程,导出了推力与输出差分电流的传递函数,分析了影响测量的主要噪声。方案可应用于微推力的测量,并有进一步提高推力测量精度的潜力。     

微阴极电弧推力器放电特性研究北大核心CSCD

相对于大型卫星,微纳卫星具有模块化、发射灵活、可编队飞行等特点。微阴极电弧推力器(μ-CAT)是一种适用于微纳卫星的推进装置,具有体积小、质量轻、功耗小等特点。本文分析了μ-CAT的工作原理,对推力器结构进行了设计,并利用高真空电推进实验平台,完成了对推力器放电特性实验装置的搭建。在高真空条件下对μ-CAT进行了点火试验,测试了推力器放电时的伏安特性曲线,分析了单脉冲周期的电压电流变化规律。随后分别在有无外加磁场的条件下,采用法拉第探针测量了μ-CAT等离子体离子电流空间分布情况,实验结果表明磁场具有减小等离子体羽流发散角的作用。研究工作可为后续推力器放电参数优化设计和羽流测量工作提供理论指导。     

微阴极电弧推力器放电特性研究

相对于大型卫星,微纳卫星具有模块化、发射灵活、可编队飞行等特点。微阴极电弧推力器(μ-CAT)是一种适用于微纳卫星的推进装置,具有体积小、质量轻、功耗小等特点。本文分析了μ-CAT的工作原理,对推力器结构进行了设计,并利用高真空电推进实验平台,完成了对推力器放电特性实验装置的搭建。在高真空条件下对μ-CAT进行了点火试验,测试了推力器放电时的伏安特性曲线,分析了单脉冲周期的电压电流变化规律。随后分别在有无外加磁场的条件下,采用法拉第探针测量了μ-CAT等离子体离子电流空间分布情况,实验结果表明磁场具有减小等离子体羽流发散角的作用。研究工作可为后续推力器放电参数优化设计和羽流测量工作提供理论指导。     

真空电弧推力器技术发展现状及趋势

随着微纳卫星平台技术的迅猛发展,应用真空电弧推力器作为其姿态控制和轨道转移的动力来源得到了研究人员的重视。相比于传统的冷气推进和离子电推进,真空电弧推力器具有小型化、低功耗、低电压、高效率、高比冲、宽范围可调、低成本、长寿命和高可靠性等技术优势。在调研国外真空电弧推力器技术发展的基础上,介绍了真空电弧推力器的系统组成、基础理论、工作原理和关键技术,简要分析了真空电弧推力器的技术特点、研究进展和发展趋势,为未来真空电弧推力器的技术研究和研制提供了参考。     

双单摆式微推力测量系统的研究

为了实现空间微推力器的高精度推力测量,提出了一种电容桥式差分读出的双单摆推力测量方案,其测量频带从10-3Hz～0.016 Hz,可实现分辨率为0.1μN,量程1 mN的微推力测量。与意大利帕多瓦大学设计的双单摆微推力差分测量系统相比,方案具有更强的共模抑制能力,操作简单易行。     

Insertion of triangulated surfaces into a meccano tetrahedral discretization by means of mesh refinement and optimization procedures

In this paper, we present a new method for inserting several triangulated surfaces into an existing tetrahedral mesh generated by the meccano method. The result is a conformal mesh where each inserted surface is approximated by a set of faces of the final tetrahedral mesh. First, the tetrahedral mesh is refined around the inserted surfaces to capture their geometric features. Second, each immersed surface is approximated by a set of faces from the tetrahedral mesh. Third, following a novel approach, the nodes of the approximated surfaces are mapped to the corresponding immersed surface. Fourth, we untangle and smooth the mesh by optimizing a regularized shape distortion measure for tetrahedral elements in which we move all the nodes of the mesh, restricting the movement of the edge and surface nodes along the corresponding entity they belong to. The refining process allows approximating the immersed surface for any initial meccano tetrahedral mesh. Moreover, the proposed projection method avoids computational expensive geometric projections. Finally, the applied simultaneous untangling and smoothing process delivers a high‐quality mesh and ensures that the immersed surfaces are interpolated. Several examples are presented to assess the properties of the proposed method.     

Certification Institutions Expected to Update and Transfer Information on Present Standards

Standards are the basis for production enterprises to organize production, ex-factory inspection, trade (delivery) and technical exchanges, product certification, quality arbitration and supervision.……     

Flow calorimeter for enthalpy increment measurements on condensed gases

A flow calorimeter for enthalpy increment measurements on condensed gases is presented. A better knowledge of the properties of the liquefied natural gas is needed, and therefore a liquid loop has been designed for our flow calorimeter. The fluid loop in the calorimeter is designed in order to avoid the two-phase region, since two phases would give compositional disturbances in the measurements. The avoidance of the two-phase region is made possible by increasing the pressure of the test fluid after the measurement section, then heating the fluid at super-critical pressure past the critical point. Finally, the fluid is throttled to the low-pressure gas state at the inlet condition of the compressor that circulates the fluid. To perform the pressure increase, a new cryogenic pump has been designed. To evaluate the new equipment, measurements were taken on liquid ethane over the temperature range 146–256 K at pressure between 0.9 and 5.1 MPa.     

Refrigerators Enter a New Era of Health Preservation Frestech initiates the establishment of China's first standard for household sterilization refrigerators

On November 30, 2007, the China Association for Standardization (CAS) held a press conference at Beijing Diaoyutai State Guest House. Leaders from the China Household Electric Appliance Research Institute, the China Household Electric Appliance Association, and the China Consumers' Association attended and made speeches.……     

Optimum-Simulation von Ernteprozessen

Zusammenfassung Bei der Gestaltung von Ernteprozessen — beispielsweise des Prozesses Mähdrusch, Körnertransport und -abnahme — als transportverbundene Fließarbeitsverfahren mit mindestens zwei verschiedenen Arbeitsmitteln gibt es einen großen Optimierungsspielraum. Solche Prozesse sind mehrstufige Bedienungsprozesse mit gemischter Anordnung der Bedienungseinrichtungen. Außerdem besitzen sie stark ausgeprägte räumliche Aspekte. Es wird vor allem gezeigt, welche Merkmale solcher Prozesse in Simulationsmodellen abgebildet sein müssen, welche Zielgrößen in Abhängigkeit von welchen Einflußgrößen unter Berücksichtigung welcher Prozeßbedingungen ermittelt werden sollten und wie der Bewertungsprozeß zur Ermittlung der gewünschten Informationen gestaltet werden muß.     

A study of centrifugal cast high boron high speed steel

In the present study a high‐boron high speed steel (HSS) roll material was designed. Many expensive alloy elements have been substituted by cheap boron alloy, and high‐boron high speed steel roll has been manufactured by centrifugal casting method. The microstructures, mechanical properties and wear resistance of centrifugal casting high‐boron high speed steel roll have been investigated by optical microscopy (OM), scanning electron microscopy (SEM), and X‐ray diffraction (XRD) analysis, hardness test, impact test and wear test. The results indicated that the solidification microstructures of high‐boron high speed steel roll consisted of M₂(B,C), (W,Mo)₂(B,C), M₃(B,C), M₂₃(B,C)₆ type borocarbides and martensite, a small amount of retained austenite. Borocarbides were continuously distributed over the grain boundary. After quenching from 1050 °C, local broken network appeared in partial borocarbides, and fine secondary borocarbide precipitated from the matrix. After tempering from 525 °C, the amount of precipitated borocarbide increased significantly. After heat treatment, the hardness of high‐boron high speed steel roll excelled 60 HRC, and its impact toughness excelled 8.0 J/cm². The single groove steel rolling amount of high‐boron high speed steel rolls increases by 500% than that of bainite cast iron roll, when the rolls are used in K₁ mill housing of bar mill.     

Thixotropy of Systems with Shear Thinning and Plastic Flow Behavior

The definition of the thixotropy is a decrease in viscosity with time in shear and a subsequent recovery of viscosity after the shear deformation is removed.We ...     

Brainstorming for ISO Strategy 2016-2020

正Responding to ISO’s appeal for survey for the to-be-developed ISO Strategy Plan for 2016-2020,SAC hosted a special workshop over the needs and comments of various fi elds on June 8 in Beijing.The workshop was attended by ISO President-elect and Ansteel General Manager Zhang Xiaogang,SAC Vice-Administrator Yu Xinli,and 30 experts from     

CNAS Passes APLAC's PTP Review

正The review group of Asia Pacific Laboratory Accreditation Cooperation(APLAC)carried out a 4-day peer review of the proficiency testing provider(PTP)for China National Accreditation Service for Conformity Assessment(CNAS)from July 28 to 31,2014.CNAS passed the PTP review with excellent performance.Two senior peer reviewers of APLAC made a comprehensive,rigorous and detailed review of CNAS’s PTP accreditation activities,and made the on-spot inspection of the review groups in Shanghai and Shenzhen respectively.