航空发动机轴承外环装配工艺引起的转子系统非线性振动

针对某型航空发动机涡轮后支点轴承外环装配工艺参数的特点,实验研究了轴承外环与衬套配合为过盈配合、间隙配合和过渡配合时的转子振动特性;同时研究了温度场和外环拧紧力矩参数对配合关系的影响而导致的转子振动特性变化.结果表明:轴承外环与衬套为间隙配合时,引起发动机振动出现次谐波、高倍频和1阶非线性共振;外环锁紧螺母力矩增大只对外环是间隙配合时的振动有抑制作用;轴承座的温度场可导致轴承外环与轴承座的过渡配合变为间隙配合,并影响振动特性.     

外旋流器旋流数对三级旋流流场特性的影响

采用二维粒子图像测速(2D-PIV)流场测试技术,试验研究了相同进口条件下多种旋流数组合旋流器出口冷态流场,分析比较了外级旋流器旋流数对流场结构的影响.研究结果表明:外级旋流器旋流强弱并不是回流区形成的主要决定因素；随着外级旋流器旋流数的增加,涡心有向前及向外移动的趋势,其回流区轴向长度逐渐变长,最大回流速度逐渐减小；回流区形状同时受外级旋流器旋流数及内级旋流器旋流数的影响,当外级旋流器旋流数相对内级旋流器旋流数足够大时,较易出现尾迹区；在旋流器出口附近,外级旋流器旋流数较小时旋流器组合流场的湍流强度峰值较大.      

一种外环水平结构双轴光纤惯导系统旋转方案设计方法

目前国内外长航时高精度自主惯导系统多采用双轴旋转调制自动补偿技术,而旋转方案设计对系统导航精度影响至关重要.双轴惯导系统按结构可分为外环水平结构和外环航向结构两类.分析了外环水平结构双轴惯导系统在旋转方案设计中的局限性,考虑到光纤陀螺输出特性,指出外环水平结构双轴光纤惯导系统不宜采用传统旋转方案,并提出了一种该类双轴光纤惯导系统的旋转方案设计方法,最后对所设计旋转方案与十六位置旋转方案进行试验对比,试验表明此设计方案导航精度提升了71％.     

Modified Barker and Huffman Sequences in Combination Codes

lt is possible that usable combination codes can be obtained if Barker and Huffman sequences are chosen as the inner and outer codes. lt is shown that an improvement in either energy efficiency or time sidelobe structure will result either from a modification of a Huffman sequence or from a modification of a Barker sequence. Results are given for a combination code of length 91, with inner and outer codes of length 7 and 13.     

Three-dimensional atmospheric entry problem using method of matchedasymptotic expansions

A composite solution consisting of an outer solution, an inner solution, and a common solution is obtained. The outer solution arises from the gravitationally dominant region, whereas the aerodynamically dominant region contributes to the inner solution. The common solution accounts for the overlap between the outer and inner regions. In contrast to previous work, this simplified methodology yields explicit analytical expressions for various compounds of the composite solution without resorting to any type of transcendental equation that can be solved only by numerical methods. The present method is application for obtained autonomous guides and control strategies for a variety of aerospace vehicles     

脉冲爆震发动机爆震管壁换热及冷却的实验

利用Pt100热电阻对脉冲爆震发动机(PDE)在有、无水冷状态下爆震管壁沿轴向的温度分布进行了实验研究.实验结果发现爆震管同一轴向位置处,爆震外管壁温度随爆震频率的增加而增加.同一爆震频率时,距推力壁位置越远,爆震外管壁温度相对越高.向爆震管换热系统中通入冷却水之后,爆震外管壁温度有明显的降低,并且爆震外管壁温度梯度也有一定的下降,20Hz时加水冷之后,PDE工作16s时,爆震外管壁温度最高可降低106.5℃.      

融合式内外层结构受力特性分析

重复使用飞行器(RLV)在机身内部安装贮箱,形成融合式内外层结构,其受力特性的分析对减轻结构重量、提高结构可靠性有重要意义。针对RLV融合式内外层结构提出静定结构和静不定结构共三种连接方案,采用有限元分析方法对其进行静力分析;并通过改变内外层结构的厚度,来探究厚度对其传力比例的影响。结果表明:静不定结构连接方式比静定结构更加合理;通过改变厚度的方法来调整轴向载荷在内外层中的分配比例,可以使内外层结构均得到充分利用。     

The Inner Heliosphere - Outer Heliosphere Comparison for Cosmic Ray Modulation

This paper summarizes cosmic ray data on both galactic and anomalous particles in the inner and outer heliosphere near the sunspot minimum in 1995 and 1996 at the end of solar cycle 22. These data come from the IMP spacecraft in the inner heliosphere and the Voyager and Pioneer spacecraft in the outer heliosphere. In the inner heliosphere, the cosmic ray intensities at all energies in 1996 have recovered to almost the same maximum values they had at the last sunspot minimum in 1987 and the intensities are an even closer match to those observed two 11-year cycles earlier in 1976. In the outer heliosphere beyond 40 AU the intensity recovery is very slow and the intensities at all energies and for all species are almost constant in 1995-96 indicating that little further recovery can be expected in this cycle. The intensity of galactic cosmic rays in 1996 is only 0.3-0.5 of that observed at the same radius of 42 AU in 1987 and for anomalous cosmic rays this ratio is only 0.1-0.2. This suggests a dramatically different entry of particles into the heliosphere in the two cycles for both types of particles as well as significantly different particle flow characteristics in the outer heliosphere. The net result of these different characteristics is that near the Earth only a relatively small intensity difference is observed between successive 11-year solar cycles whereas in the outer heliosphere the differences between cycles become very large and may even dominate the overall modulation.     

A vision-based navigation approach with multiple radial shape marks for indoor aircraft locating

Since GPS signals are unavailable for indoor navigation, current research mainly focuses on vision-based locating with a single mark. An obvious disadvantage with this approach is that locating will fail when the mark cannot be seen. The use of multiple marks can solve this problem. However, the extra process to design and identify different marks will significantly increase system complexity. In this paper, a novel vision-based locating method is proposed by using marks with feature points arranged in a radial shape. The feature points of the marks consist of inner points and outer points. The positions of the inner points are the same in all marks, while the positions of the outer points are different in different marks. Unlike traditional camera locating methods （the PnP methods）, the proposed method can calculate the camera location and the positions of the outer points simultaneously. Then the calculation results of the positions of the outer points are used to identify the mark. This method can make navigation with multiple marks more efficient. Simulations and real world experiments are carried out, and their results show that the proposed method is fast, accurate and robust to noise.     

绕流问题的区域收缩法及其数值解

本文提出了一种适于绕流问题的数值方法,它考虑了流场中不同区域内不同的物理现象,给出了外部边界条件的良好逼近。使用这种方法可以节省大量的计算机存贮单元和计算时间,也可以推广到三维绕流问题的数值计算。     

湍流等离子体尾迹雷达散射截面的计算及其影响因素分析

针对一阶畸变波Born近似模型,深入分析了湍流内外尺度和电子数密度脉动值对雷达散射截面的影响,并且给出了关于湍流外尺度的一个经验的,能被工程上较好使用的公式.在以上分析的基础上,计算了几种高程条件下再入小钝头锥体等离子尾迹的雷达散射截面,与已有实验结果进行了对比分析.分析和计算结果表明,湍流的外尺度和局部电子数密度值对雷达散射截面值影响较大;湍流内尺度变化的影响不大.     

Chemical and Physical Processing of Presolar Materials in the Solar Nebula and the Implications for Preservation of Presolar Materials in Comets

Chemical and physical processes in the outer solar nebula are reviewed. It is argued that the outer nebula was a chemically active environment with UV photochemistry and ion-molecule chemistry in its low density regions and grain-catalyzed chemistry in Jovian protoplanetary subnebulae. Presolar material was altered to greater or lesser extent by these spatially and temporally variable processes, which mimic many features of interstellar chemistry. Experiments, models, and observations are recommended to address the questions of presolar versus nebular dominance in the outer solar nebula and of how to distinguish interstellar and nebular sources of cometary volatiles. This revised version was published online in June 2006 with corrections to the Cover Date.     

双旋流模型燃烧室的燃烧特性

同轴双旋流进气能建立起有利于燃烧的流场,文献[1]的结果表明,同轴的内外两股旋流反向旋转时,边界层内的紊流强度和雷诺应力很高,对强化混合和燃烧有利。据文献[2]报导,用这种双旋流改装了JT-8D火焰筒,取消了火焰筒上的主燃孔与掺混孔,试验实测的慢车状态燃烧效率高达99%。表明这种燃烧室方案在燃气轮机和工业燃烧装置中有着广阔的应用前景。本文重点研究两个径向式叶片旋流器在同轴反向旋转条件下的燃烧特性,包括燃烧效率、熄火边界和出口温度场等。      

跨音叶栅三维激波损失的改进模型

在低展弦比、低轮毂比的轴流压气机中激波结构常常是三维的。叶尖区域的三维激波损失在整个流场的激波损失中占有十分重要的比例。Ｗｅｎｎｅｒｓｔｒｏｍ和Ｐｕｔｅｒｂａｕｇｈ于１９８４年推出的三维激波损失模型忽略了激波在叶尖区域的流动结构。通过分析叶尖区域的激波结构及其与机匣附面层流动的相互作用,提出了考虑叶尖区域激波与附面层相互作用所引起的激波结构及强度变化的跨音叶栅三维激波损失的改进模型,应用改进模型计算得出的结果和实验结果符合的很好。     

直升机多模态控制律的全飞行包线设计

根据直升机飞行模态的特点,提出了一种的内／外回路控制结构,将不同飞行模态通过内／外回路结构有机地联系起来,不仅简化了直升机多模态控制律的设计,还简化了模态转换的控制器结构。最后,用这种结构将直升机多模态控制律的全飞行包线设计分解为内回路的控制器切换和外回路的模态转换,设计思路避免了传统的增益调参。     

四旋翼无人机非奇异终端滑模位置控制器设计

针对四旋翼无人机存在模型不确定性、在野外飞行时易受外界环境干扰问题,首先采用牛顿-欧拉法进行系统建模;然后按照内外环控制结构,外环位置控制器输出姿态指令作为内环姿态控制器的输入,内环采用串级PID控制器,重点针对外环设计了一种非奇异终端滑模控制器,并基于Lyapunov理论证明了位置子系统的稳定性,得出系统误差能够在有限时间收敛到0的结论;最后,通过定点控制和轨迹跟踪仿真,表明控制器具有较快的响应速度和良好的抗干扰性能,能够快速精确地进行轨迹跟踪。     

基于整机的中介轴承外圈剥落故障振动分析

针对某典型双转子航空发动机中介轴承外圈疲劳剥落故障诊断问题,基于整机振动耦合动力学模型,导入中介轴承外圈早期剥落故障模型,通过数值积分方法获取故障激励下的整机振动响应。提取并分析了中介轴承外圈剥落故障特征,从信号分析中发现:①出现了4倍外圈故障特征频率及其两侧以外圈旋转频率为间隔的调制边频带;②随着不平衡量增加,特征频率分量基本不变,边频带变得更加突出;③随着轴承游隙的增加,外圈故障引起的冲击更为强烈,特征频率及其调制边频均显著增加。通过比较从轴承座到机匣各测点信号的故障特征,结果表明中介轴承早期疲劳剥落产生的冲击通过轴承座传递到机匣将产生很大程度的衰减,在机匣测点信号中轴承故障特征基本消失。     

Plasmasphere Response: Tutorial and Review of Recent Imaging Results

The plasmasphere is the cold, dense innermost region of the magnetosphere that is populated by upflow of ionospheric plasma along geomagnetic field lines. Driven directly by dayside magnetopause reconnection, enhanced sunward convection erodes the outer layers of the plasmasphere. Erosion causes the plasmasphere outer boundary, the plasmapause, to move inward on the nightside and outward on the dayside to form plumes of dense plasma extending sunward into the outer magnetosphere. Coupling between the inner magnetosphere and ionosphere can significantly modify the convection field, either enhancing sunward flows near dusk or shielding them on the night side. The plasmaspheric configuration plays a crucial role in the inner magnetosphere; wave-particle interactions inside the plasmasphere can cause scattering and loss of warmer space plasmas such as the ring current and radiation belts.     

PDE在模拟冲压进气条件下的台架推力修正

研究射流模拟冲压进气条件下,气源喷口尺寸和气源压头对脉冲爆震发动机(PDE)地面台架测量推力的影响及消除外阻对测量推力的影响的措施.研究结果表明,由于PDE外阻存在使PDE地面台架测量推力偏小,采用PDE进气道前装承力锥的方法,可以消除PDE外阻对PDE地面台架试验推力测量的影响,获得PDE实际内流推力.在试验结果基础上,提出一个PDE地面台架试验内流推力修正公式并在试验中得到验证.      

某型燃气轮机内、外机匣振动传递的动力学分析

为确定某型燃气轮机整机试车中内、外机匣径向振动力的传递关系,建立了机匣的有限元模型,利用ANSYS软件进行了0-2000Hz内的谐响应分析。在共振状态下,外机匣振动峰值相对于内机匣的增大值,计算结果为13．38％,台架振动测量结果为12．7％,二者具有很好的一致性,表明计算模型和方法正确。上述方法可为燃机振动检测限制值的确定,以及进一步研究内、外机匣的轴向和周向振动传递提供参考。