椭圆轨道非合作目标交会接近策略与控制

文章研究了追踪航天器与失控旋转非合作目标航天器在椭圆轨道中的交会接近策略与控制。在接近策略方面,首先,根据目标航天器大致结构设定一个安全的停泊点,使追踪航天器交会至停泊点;其次,通过在停泊点对旋转目标航天器姿态的观测,分析和预测其运动并确定合适的抓捕点位置,设计安全的接近轨迹,使追踪航天器沿着该轨迹接近至理想的抓捕实施点位置。在控制方面,考虑实际系统中的不确定性,只利用两航天器之间相对位置的测量信息,设计基于特征模型的自适应控制方法实现交会接近。最后通过数学仿真模拟整个交会接近过程,验证了文中所提出的接近策略和控制方法。     

On the origin of cosmic rays in the spiral galaxy NGC 3310

The problem of cosmic ray production in the spiral galaxy NGC 3310 is addressed by analysing and comparing optical and radio continuum data. Tentative results indicate that on global scales relativistic electrons may be produced in the shock front associated with teh density wave while on local scales extreme population I objects may be producing them. It is inferred that the same conclusions apply to all cosmic rays produced in the disk.     

Optimal location and shape definition of elliptical ventilation openings on aero engine turbine rotors with stress concentration effect

The aero engine turbine rotors are under strong centrifugal load and the highest thermal load. The ventilation openings on the rotors are inevitable, because air flow need to pass through them to cool the temperatures down and keep the air pressure balanced in internal aero engine. The ventilation openings will lead to stress concentration effect. In this paper, the stress concentration factor of elliptical opening on rotating disc is deduced by superposition method. How to define the optimal lo...     

椭圆形超燃燃烧室内燃料喷射和掺混性能研究

为了优化超燃燃烧室的工作效率和性能,针对椭圆形超燃燃烧室内的燃料壁面垂直喷射方案,通过求解雷诺平均Navier-Stokes方程的数值模拟方法对不同燃料喷射方案进行研究,着重分析了不同喷注位置的壁面曲率值、喷嘴直径以及反射激波干扰对流场特征及燃料掺混特性的影响。研究表明,喷注位置的壁面曲率对燃料掺混的影响程度与喷嘴直径相关。当喷嘴直径较大时,壁面曲率值越小,燃料的掺混效率越高,但总压恢复系数越低;当喷嘴直径较小时,壁面曲率的改变对燃料横向喷流方案的掺混效率和总压恢复影响很小。在相同喷射动压比下,不同喷嘴直径方案的流场特征以及燃料喷射掺混特性均存在相似性,缩小喷嘴直径能够提高燃料的掺混效率。就本文的研究状态,喷嘴直径为4mm的方案在燃烧室出口处的掺混效率比直径为10mm方案的高出约46.7%。此外,通道中的激波/掺混层相互干扰会大幅降低燃料穿透深度,但产生的剧烈剪切运动能够提高燃料掺混效率。     

Thermodynamical Properties of the ICM from Hydrodynamical Simulations

Modern hydrodynamical simulations offer nowadays a powerful means to trace the evolution of the X-ray properties of the intra-cluster medium (ICM) during the cosmological history of the hierarchical build up of galaxy clusters. In this paper we review the current status of these simulations and how their predictions fare in reproducing the most recent X-ray observations of clusters. After briefly discussing the shortcomings of the self-similar model, based on assuming that gravity only drives the evolution of the ICM, we discuss how the processes of gas cooling and non-gravitational heating are expected to bring model predictions into better agreement with observational data. We then present results from the hydrodynamical simulations, performed by different groups, and how they compare with observational data. As terms of comparison, we use X-ray scaling relations between mass, luminosity, temperature and pressure, as well as the profiles of temperature and entropy. The results of this comparison can be summarised as follows: (a) simulations, which include gas cooling, star formation and supernova feedback, are generally successful in reproducing the X-ray properties of the ICM outside the core regions; (b) simulations generally fail in reproducing the observed “cool core” structure, in that they have serious difficulties in regulating overcooling, thereby producing steep negative central temperature profiles. This discrepancy calls for the need of introducing other physical processes, such as energy feedback from active galactic nuclei, which should compensate the radiative losses of the gas with high density, low entropy and short cooling time, which is observed to reside in the innermost regions of galaxy clusters.     

椭圆轨道编队的构形变化控制方法

推导了椭圆轨道编队的一些典型构形模态,指出椭圆轨道卫星编队的模态不同于圆轨道的构形模态,是极为丰富的。基于T-H方程的解析解,推导了副星在沿航向常值推力作用下的椭圆轨道编队的构形变化控制方法。推导的构形变化控制方法,通过合理的选择控制量的作用时刻,可达到大量节约燃料的目的。最后,给出仿真算例。     

Radio-faint BL Lac objects and their impact on the radio/gamma-ray connection

Radio and gamma-ray emissions in Active Galactic Nuclei (AGNs) are both related to the presence of relativistic particles in jets. With the advent of the Fermi Large Area Telescope (LAT), and thanks to its large sensitivity up to several GeV, many observational results are changing our understanding of these phenomena. BL Lac objects, which made up only a fraction of the known extragalactic gamma-ray source population before Fermi, have now become the most abundant class. However, since they are relatively weak radio sources, most of them are poorly known as far as their parsec scale structure and multi-wavelength properties are concerned. For this reason, we have selected a complete sample of 42 low redshift BL Lacs (independently of their gamma-ray properties) to study with a multi-wavelength (radio, optical, X-ray, gamma-ray) approach. Here, we present results and images of sources in the sample (most of which have never been observed before), using new VLBA observations at 8 and 15 GHz. Beyond this sample of BL Lacs, the population of gamma-ray AGNs has also dramatically enlarged in the Fermi era, permitting us to discuss the presence of a correlation between radio and gamma-ray properties with improved statistical significance. We explore the radio-gamma relation with several hundreds sources and using both simultaneous and archival radio data, thus tackling the impact of time variability.     

摄动条件下椭圆轨道卫星相对运动研究

基于严格定义的相对轨道要素,考虑非球形引力、大气阻力和三体引力等摄动力的影响,用拟平均根数法添加相关摄动项,推导了椭圆轨道摄动条件下无奇点的卫星近距离相对运动模型。分析了考虑摄动力的影响时相对轨道要素的特性,并据此分析了各摄动力对卫星相对运动轨道预报精度的影响,比较了有无摄动的相对运动模型与精确解间的误差。算例验证了方法与结果的正确性和有效性。研究结果完善了相对轨道要素的基本理论,并将其适用范围拓展至摄动条件下的椭圆基准轨道卫星相对运动研究领域。     

基于回转基准面的椭圆振动辅助切削微织构过程仿真研究

仿生研究表明,具有凹坑、沟槽等微结构的表面具有减阻、自清洁等优异性能,微结构表面在航空航天、船舶、光学等领域有广泛的应用,对于节省能源、减阻降噪、降低污染和提升产品性能等具有重要的意义。为了有效预测椭圆振动辅助切削加工微织构的效果,依据椭圆振动装置的共振频率和回转类基准面的转动速率,给出了一种椭圆振动辅助切削微织构的轨迹规划方法,通过对周期振动载荷进行傅里叶级数的转化,在刀具有限元模型上加载了椭圆振动载荷,建立了基于回转面的椭圆振动辅助切削微织构的有限元仿真模型。基于建立的有限元仿真模型,对不同振动参数下的椭圆振动辅助切削微织构加工过程中的瞬时Mises应力分布和切削力进行分析,验证了微织构加工轨迹的正确性,为进一步的微织构加工提供了参考。     

Primordial Helium and ΔY/ΔZ from H II Regions and from Fine Structure in the Main Sequence Based on Hipparcos Parallaxes

The primordial helium abundance YP is important for cosmology and the ratio Y/Z of the changes relative to primordial abundances constrains models of stellar evolution. While the most accurate estimates of YP come from emission lines in extragalactic H II regions, they involve an extrapolation to zero metallicity which itself is closely tied up with the slope Y/Z. Recently certain systematic effects have come to light in this exercise which make it useful to have an independent estimate of Y/Z from fine structure in the main sequence of nearby stars. We derive such an estimate from Hipparcos data for stars with Z Z and find values between 2 and 3, which are consistent with stellar models, but still have a large uncertainty.