A user-friendly yield criterion for metals exhibiting tension-compression asymmetry

The aim of this paper is to model the yielding asymmetry of pressure-insensitive metals, including but not limited to Ni₃Al alloys. The main focuses are put on the flexibility and manipulative convenience. The parameters of theory are kept to a minimum and can be determined by as few tests as possible. These requirements are fulfilled by constructing a yield function using the second and third-invariants of a linearly transformed stress tensor. The proposed yield criterion has a simple mathematical form and has only seven parameters when used in three-dimensional stresses. Compared with existing theories, the new yield criterion has much fewer parameters, which makes it very convenient for practical applications. The coefficients of the criterion are identified by an error minimization procedure. Applications to a Ni₃Al based intermetallic alloy as well as a Cu-Al-Be shape memory alloy and comparison to other criteria show that the proposed criterion has nearly the same predictive ability and flexibility with other criteria. The proposed yield criterion can estimate the coefficients by using less data, which is a big advantage compared with other similar theories, especially when there is a limited number of experimental data.     

高速滚动轴承弹性流体动力润滑分析

直接采用弹性流体动力润滑（ＥＨＬ）分析方法计算了高速滚动轴承中滚子与内、外套圈接触区的油膜厚度、油膜动压力和润滑油牵引力;分析了载荷、转速及滚子数等参数对轴承打滑损伤的影响。理论分析结果与所作实验结果在较宽的工况范围内吻合较好。     

深远空连续推进动力与施图林格解的解析

针对太阳系远深距离的探测将是人类下一阶段深空探测活动的主要目标。这一目标的实现依赖于探测器连续推进动力技术的突破。从描述连续常值推力下太空飞行的施图林格解出发,对其中反映的深远空飞行任务有效载荷比、任务时间、飞行距离等关键参数与发动机性能之间的关系进行了深入分析。给出了在特定任务时长、特定飞行距离要求下发动机比冲、功率需要满足的条件及其对有效载荷比、最终飞行速度等指标的影响。此外,基于二体轨道动力学对太阳系行星探测的大椭圆转移轨道和转移能量进行了推导,并对连续推力的太阳帆任务方案涉及的关键技术指标做了理论性的计算。这些结论是对深空探测连续推力方案基础理论的归纳,可以为我国未来开展深远空探测活动提供重要的启发和指导。     

浅析"三大规范"编写

本文较为详细地介绍了中国燃气涡轮研究院“三大规范”编制与实施过程中的目标的确定、总体规划、采取的措施、应用效果、存在的问题及解决方法,可为同行编制“三大规范”提供借鉴和参考。     

Three dimensional temperature field in a conducting sphere due to an arbitrarily located split ring heating source

Thermal control of spacecrafts plays an important role in space missions. In the design stage the preliminary thermal analysis of the spacecraft requires an estimate of the conductive thermal resistance between the various spacecraft components. With this in mind, the fully three dimensional problem of determining the thermal field in a conducting sphere with an asymmetric split ring current carrying heating source is resolved in an analytical or almost analytical form, implying either a closed form solution or utmost expressions involving a simple numerical integration. This has immediate application for evaluation of thermal resistance in spacecrafts. Green's function integral techniques are used. Comparisons are made with series solutions and also with purely numerical solutions to contrast the simplicity and highlight the elegance of the present method. Parametric studies reveal expected behavior.     

飞机着陆进近穿越风切变的轨迹响应

大气紊流和风切变对飞行活动影响较大,尤以低空风切变危害最大,严重威胁着民航飞行的安全。鉴于飞行器对抗大气扰动的实际能力有限,正确的飞行对策是回避或改出危险的大气扰动区。本文对某训练飞机着陆进近遭遇风切变时飞机轨迹的变化进行了模拟仿真计算。结果表明,采用恒定迎角策略,即采用最大允许迎角（抖动迎角）和最大油门时,改出效果最佳。同时计算出了某训练飞机在水平风为0时,所能抵抗的最大垂直阵风强度;以及在垂直阵风为0时,所能抵抗的最大水平风强度。     

空间真空环境下密封电磁继电器的触点失效研究

密封电磁继电器有其固有的漏率,在应用于空间真空环境下由于气体泄漏使得其内部气体压力逐渐降低,导致继电器的触点在低气压环境下工作失效（负载切换时）。文章选择国产继电器样品对上述机理进行了试验验证,并对继电器内部气体压力与触点电弧失效的规律进行了研究。     

关于轰燃定义、机理和判据的讨论与分析

通过对常见的几种轰燃定义的对比分析,对轰燃进行了新的定义,认为轰燃是室内火灾发展到一定阶段引起非连续介质着火燃烧的现象;在此基础上,根据燃烧学原理提出了轰燃发生的机理,即可燃挥发份和高温烟气层接触发生的剧烈氧化还原反应;并提出了预测轰燃的通用判据,即火灾时室内其它可燃物热解产生的可燃挥发份迅速和空气混合,达到其着火浓度下限且接触到超过可燃物自燃点的高温烟气层。     

Ion-acoustic waves in unmagnetized collisionless weakly relativistic plasma of warm-ion and isothermal-electron using time-fractional KdV equation

Collisionless unmagnetized plasma consisting of a mixture of warm ion-fluid and isothermal-electron is considered, assuming that the ion flow velocity has a weak relativistic effect. The reductive perturbation method has been employed to derive the Korteweg–de Vries (KdV) equation for small – but finite-amplitude electrostatic ion-acoustic waves in this plasma. The semi-inverse method and Agrawal’s method lead to the Euler–Lagrange equation that leads to the time fractional KdV equation. The variational-iteration method given by He is used to solve the derived time fractional KdV equation. The calculations show that the fractional order may play the same rule of higher order dissipation in KdV equation to modulate the soliton wave amplitude in the plasma system. The results of the present investigation may be applicable to some plasma environments, such as space-plasmas, laser-plasma interaction, plasma sheet boundary layer of the earth’s magnetosphere, solar atmosphere and interplanetary space.     

驾驶员模型对驾驶员诱发振荡评估结果的影响

在飞机设计中,应用不同的驾驶员模型来预测驾驶员诱发振荡(PIO)是避免人机系统出现不良耦合的重要途径之一。以人-机闭环系统为研究对象,以某一电传飞机为例,采用Ⅱ型PIO的开环发生点OLOP评估准则,分别使用增益驾驶员模型和修正Neal-Smith驾驶员模型对人机闭环系统中的PIO易感性进行了分析、评估,对比研究了不同驾驶员模型对OLOP评估准则评估结果的影响。仿真结果表明:不同的驾驶员模型对Ⅱ型PIO评估准则(OLOP)的评估结果有较大的影响,相同驾驶员模型下不同的驾驶员增益对评估结果也有影响。在使用OLOP评估准则时应充分考虑驾驶员模型对评估结论的影响。