高超声速双模块内转式进气道的流动特性研究-Part II 攻角影响

为了研究飞行攻角对高超声速双模块内转式进气道流动的影响,本文通过试验和仿真方法,获得了0°,4°和6°攻角条件下进气道模块内的流动结构。结果表明：在本文研究的攻角范围内,进气道均可起动,进气道压缩面侧的压力变化体现了基准流场的流动特性。在耦合作用下进气道模块间压缩面诱导的激波形态沿流向由弓形逐渐发展为钟形,并且在外压缩激波的扫掠影响下进气道的三个角区出现了强度不同的旋涡结构。进气道压缩面侧的角区旋涡随着攻角的增加而逐渐增强,而进气道出口截面上低能流区域随着攻角的增加而逐渐减小。低能流区域内的二次旋涡呈现不同的变化趋势,位于上半截面的旋涡随着攻角的增加其逐渐向上移动,而位于下半截面的旋涡位置基本保持不变。     

一种基于FMEA的故障诊断贝叶斯网络快速构建方法

贝叶斯网络(BN)建模问题一直是其在故障诊断应用领域的瓶颈,实际的工程系统中,贝叶斯网模型构建存在许多困难,提出一种基于故障模式影响分析(FMEA)的BN建模技术.首先,在分析现有FMEA所包含的故障信息基础上,提出基于单条FMEA记录的贝叶斯网络片段构建方法;然后,利用故障模式与故障原因因果传递关系将贝叶斯网络片段集成为系统贝叶斯网络模型;最后,以某型飞机前轮转弯系统为例进行BN模型构建和分析.结果表明:本文基于FMEA建立的BN模型不仅避免了传统建模过程中对大量工程经验的需求,并且突破了FMEA定性分析能力,能够有效融合多源信息对工程系统进行定量分析和故障诊断.     

四轮起落架飞机地面滑跑转弯分析

现代飞机对其地面滑跑性能的要求日益提高,同时要求能够在条件更加苛刻的环境下运行.以四点式起落架布局飞机为研究对象,基于阿克曼转向几何原理,推导该飞机地面滑跑时两个前轮之间的转角关系.在Adams/Aircraft中建立四点式起落架飞机虚拟样机,并进行其地面滑跑仿真分析.探讨四点式起落架飞机不同前轮作为主动操纵轮时,对转弯半径的影响.结果表明:在相同滑跑条件下,当前轮操纵转弯时,四点式起落架飞机比常规的前三点式起落架飞机拥有更小的转弯半径;当主轮差动刹车转弯时,四点式起落架飞机的转弯半径略大于三点式起落架飞机;四点式起落架飞机的两前轮同时为主动操纵轮时,飞机的转弯半径最小.     

中轨卫星移动通信系统小区驻留时间分布的研究

在中轨卫星移动通信系统中 ,确定小区驻留时间分布对于合理地规划切换策略具有十分重要的意义。文中指出了地球固定覆盖与卫星固定覆盖两种方式下小区驻留时间分布不同的原因。提出一种仿真计算卫星固定覆盖方式下小区驻留时间分布的方法 ,得出了数值结果 ,并与地球固定覆盖方式下的小区驻留时间分布作了比较     

On the association of quiet-time Pi2 pulsations with IMF variations

The association of quiet-time Pi2 pulsations with the variations of the interplanetary magnetic field (IMF) has been examined by using three reported events, occurring during extremely quiet intervals, of which the first was on 10 March 1997, the second 27 December 1997, and the third 11 May 1999. For the first event, the onset time of ground Pi2s maps to the IMF structure bearing a variation cycle of north-to-south and north again as seen by Wind in the upstream region and Geotail in the magnetosheath. Likewise, the second and the third events have respectively, four and three recurrent turnings propagating to the Earth sensed by multiple satellites. The comparison of geomagnetic perturbations, auroral brightenings, and energetic particle data in the magnetotail with the IMF observations shows successive substorm-like activations accompanied by ground Pi2 onsets. For a clear variation cycle, the first Pi2 burst appears 36 ± 8 min after southward turning of the IMF and the second one follows14 ± 4 min after a northward turning. Moreover, ground Pi2 onsets recur under low IMF clock angle conditions. These observational results can be interpreted with the prevailing models of externally triggered substorm. But the solar wind coupling to the magnetosphere under quiet conditions proceeds in a less efficient way than under substorm time conditions. Consequently, we suggest that recurrent quiet-time Pi2s can be associated with IMF variations and their cause can be the same as those for substorm times.     

Sleep and cognitive function of crewmembers and mission controllers working 24-h shifts during a simulated 105-day spaceflight mission

The success of long-duration space missions depends on the ability of crewmembers and mission support specialists to be alert and maintain high levels of cognitive function while operating complex, technical equipment. We examined sleep, nocturnal melatonin levels and cognitive function of crewmembers and the sleep and cognitive function of mission controllers who participated in a high-fidelity 105-day simulated spaceflight mission at the Institute of Biomedical Problems (Moscow). Crewmembers were required to perform daily mission duties and work one 24-h extended duration work shift every sixth day. Mission controllers nominally worked 24-h extended duration shifts. Supplemental lighting was provided to crewmembers and mission controllers. Participants' sleep was estimated by wrist-actigraphy recordings. Overall, results show that crewmembers and mission controllers obtained inadequate sleep and exhibited impaired cognitive function, despite countermeasure use, while working extended duration shifts. Crewmembers averaged 7.04±0.92 h (mean±SD) and 6.94±1.08 h (mean±SD) in the two workdays prior to the extended duration shifts, 1.88±0.40 h (mean±SD) during the 24-h work shift, and then slept 10.18±0.96 h (mean±SD) the day after the night shift. Although supplemental light was provided, crewmembers’ average nocturnal melatonin levels remained elevated during extended 24-h work shifts. Naps and caffeine use were reported by crewmembers during ∼86% and 45% of extended night work shifts, respectively. Even with reported use of wake-promoting countermeasures, significant impairments in cognitive function were observed. Mission controllers slept 5.63±0.95 h (mean±SD) the night prior to their extended duration work shift. On an average, 89% of night shifts included naps with mission controllers sleeping an average of 3.4±1.0 h (mean±SD) during the 24-h extended duration work shift. Mission controllers also showed impaired cognitive function during extended duration work shifts.These findings indicate that extended duration work shifts present a significant challenge to crewmembers and mission support specialists during long-duration space mission operations. Future research is needed to evaluate the efficacy of alternative work schedules and the development and implementation of more effective countermeasures will be required to maintain high levels of performance.     

A parameterized geometry design method for inward turning inlet compatible waverider

Intensive studies have been carried out on generations of waverider geometry and hypersonic inlet geometry. However, integration efforts of waverider and related air-intake system are restricted majorly around the X43A-like or conical flow field induced configuration, which adopts mainly the two-dimensional air-breathing technology and limits the judicious visions of developing new aerodynamic profiles for hypersonic designers. A novel design approach for integrating the inward turning inlet with the traditional parameterized waverider is proposed. The proposed method is an alternative means to produce a compatible configuration by linking the off-the-shelf results on both traditional waverider techniques and inward turning inlet techniques. A series of geometry generations and optimization solutions is proposed to enhance the lift-to-drag ratio. A quantitative but efficient aerodynamic performance evaluation approach （the hypersonic flow panel method） with lower computational cost is employed to play the role of objective function for opti- mization purpose. The produced geometry compatibility with a computational fluid dynamics （CFD） solver is also verified for detailed flow field investigation. Optimization results and other numerical validations are obtained for the feasibility demonstration of the proposed method.     

时变因素作用下薄壁筒工件车削振动特性与实验

针对薄壁筒类工件的切削颤振问题,采用理论建模、数值仿真和实验测试相结合的方法,研究切削过程中时变工件厚度和切削位置对薄壁筒振动特性的影响规律.利用有限元法建立主轴-卡盘-工件工艺系统模型,分析不同壁厚、切削力位置对薄壁筒切削系统的固有模态、频率响应函数的影响.结合模态实验与切削振动实验表明:薄壁筒周向壳体模态对于壁厚的...     

IET短周期涡轮实验台

本文介绍了中国科学院工程热物理研究所（IED最新建成的暂冲式短周期涡轮实验台的装置结构和关键设备的研制原理及性能，描述了短周期涡轮实验过程、实验台的控制系统和测试系统，展示了本实验台的部分标志性实验结果。实验结果表明：实验台的建造是成功的，充分体现了短周期实验的长处，对验证和发展涡轮的设计与计算具有实际应用价值。     

芳纶纤维材料低温冷却车削加工性能

芳纶纤维复合材料在传统车削加工中易出现严重起毛和高温烧蚀等缺陷。为了提高其切削性能,采用液氮作为低温冷却媒介进行车削加工试验,并对材料的干车削及低温车削试验结果进行了分析,对液氮低温车削机理进行了探讨。结果表明,随着主轴转速的增加,材料表面质量得到一定改善,特别是在1 340r/min时得到了最佳表面;在低温车削中,在各种转速条件下,材料表面质量都较好;在相同的主轴转速下,低温车削表面质量都好于干车削,且纤维起毛、高温烧蚀被有效抑制。说明降低切削温度对芳纶纤维材料车削缺陷的改善有积极作用。