共查询到20条相似文献，搜索用时 62 毫秒
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为满足大口径地面射电望远镜的高精度要求,开展射电望远镜热影响研究,保持结构的热稳定性,对提高望远镜指向精度有重要意义。以改造后南山26 m天线为研究对象,利用FEMAP软件建立座架结构模型,设定边界条件,得到某年6月4日全天各时刻天线座架上的温度场分布,将温度场结果与结构耦合,得到热变形,建立了温度测量系统,与仿真结果相比,当天局部最高温度可达31.33℃,最大温差可达10℃,最大位移量可达1.8 mm,与实测结果变化规律基本一致。分析座架温度分布规律及其变形影响,为后期天线的温度补偿和结构优化提供参考依据。 相似文献
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大型射电望远镜的天线背架具有结构复杂和节点多等特点,若能够较为精确地重构天线背架的温度场,将对背架热变形等分析有很大帮助。通过在天线结构上安装一定数目的传感器,测量指定位置的温度值,利用距离反比加权插值方法与这些离散的温度值来重构天线背架的温度场,并对不同姿态下的温度场进行分析。而距离反比加权插值效果与距离计算方式、距离方次以及搜索半径相关,以交叉验证的方式对距离反比加权插值方法进行了优化,使精度优于0.5℃。另外,通过插值方法可得出任意时刻的背架温度场,并对不同状态下的背架温度场进行分析,得出影响温度场分布的因素,以及不同方向温差对天线造成的焦距误差与指向误差。 相似文献
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针对大口径射电望远镜主反射面在日照作用下产生温度梯度及形变问题,建立了完整的温度测量及精度评估的系统。在特定的测量条件下,利用红外热像仪测量了望远镜主反射面的温度,获得了不同时刻的温度分布情况,并得到最大温差为7.8℃。采用全息法分析主反射面的精度变化情况,得到由于温度变化导致的最大误差为0.33 mm。结果表明:温度对望远镜主反射面的精度影响较大,需采取合适的测试系统实时监测温度,并调整主反射面板以提高精度。 相似文献
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本文对云南天文台十米射电望远镜的指向跟踪精度的影响因素做了比较详细的分析和讨论,提出了一些改进的措施,论证了天线系统指向精度达到33″、工作在1.3cm波段的可能性。 相似文献
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φ25米射电望远镜是我国目前最大的射电望远镜。本文简地介绍了该射电望远镜的天线结构和它的特性，天线的安装过程以及调整精度。 相似文献
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中国科学院新疆天文台25 m南山射电望远镜(25 m NSRT)受日照导致天线结构温度不均匀,其指向精度和效率均有一定程度的损失.为研究25 m NSRT日照下的热力学特性,构建了晴空下射电望远镜热环境参数和热力学有限元模型,考虑了射电望远镜背架、面板等结构件对光线的反射和遮挡作用,通过比较25 m NSRT典型观测工况下各构件的平均温度、均方根温差、单位温差特征距离等特性参数,发现各部件热容量的差异是天线部件间存在大尺度温差现象的主要原因;分析了各类俯仰角和太阳照射角下天线背架结构的温度分布特征,表明日照区域的背架结构温度呈近似线性分布,平均梯度可达0.25℃·m-1. 相似文献
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Solar System Research - Finding and studying possible collisions of asteroids approaching the Earth requires a significant amount of computation. This paper describes the R0 program created to... 相似文献
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Many asteroids with a semimajor axis close to that of Mars have been discovered in the last several years. Potentially some of these could be in 1:1 resonance with Mars, much as are the classic Trojan asteroids with Jupiter, and its lesser-known horseshoe companions with Earth. In the 1990s, two Trojan companions of Mars, 5261 Eureka and 1998 VF31, were discovered, librating about the L5 Lagrange point, 60° behind Mars in its orbit. Although several other potential Mars Trojans have been identified, our orbital calculations show only one other known asteroid, 1999 UJ7, to be a Trojan, associated with the L4 Lagrange point, 60° ahead of Mars in its orbit. We further find that asteroid 36017 (1999 ND43) is a horseshoe librator, alternating with periods of Trojan motion. This asteroid makes repeated close approaches to Earth and has a chaotic orbit whose behavior can be confidently predicted for less than 3000 years. We identify two objects, 2001 HW15 and 2000 TG2, within the resonant region capable of undergoing what we designate “circulation transition”, in which objects can pass between circulation outside the orbit of Mars and circulation inside it, or vice versa. The eccentricity of the orbit of Mars appears to play an important role in circulation transition and in horseshoe motion. Based on the orbits and on spectroscopic data, the Trojan asteroids of Mars may be primordial bodies, while some co-orbital bodies may be in a temporary state of motion. 相似文献
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In the text-books of astronomy, sections generally related to the Moon deal with the orbital elements of the Earth-Moon system such asa, e, i, ,
and the time of perigee passage. While the MEAN of the first of the three elements do not vary, mean longitude of the ascending node-mean longitude of the lunar perigee and the time of perigee passage undergoes secular as well as periodic changes due predominantly to the action of the Sun's gravitational attraction. While to a certain degree, explanations related to the calculation of the lunar orbit parameters are given, not a single graphical representation of these short- or long-periodic changes are presented. We allow the number of data related to these periodic changes must cover a large span of time; and if regression of the line of nodes or advances of the line of apses are to be graphically seen, data covering 18.61 and 8.85 yr, respectively, are needed. In this work we particularly aim at the graphical representation of the periodic changes of the line of nodes. 相似文献
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P. Maltby 《Solar physics》1972,26(1):76-82
Observations of the penumbral intensity of sunspots in 13 wavelength regions are presented. In 4 wavelength regions 54 sunspots are measured. In the other wavelength regions the number of sunspots considered ranges from 3–19.The penumbral intensity alters with position within the spot. This intensity variation is found to be comparable with the change in intensity from one spot to another. The penumbral intensity is found to be independent of spot size in the sample considered.The penumbra model of Kjeldseth Moe and Maltby (1969) with = 0.055 is supported by the measurements. 相似文献
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Magnetars are the neutron stars with the highest magnetic fields up to 1015–1016 G. It has been proposed that they are also responsible for a variety of extra-galactic phenomena, ranging from giant flares in nearby galaxies to fast radio bursts. Utilizing a relativistic mean field model and a variable magnetic field configuration, we investigate the effects of strong magnetic fields on the equation of state and anisotropy of pressure of magnetars. It is found that the mass and radius of low-mass magnetars are weakly enhanced under the action of the strong magnetic field, and the anisotropy of pressure can be ignored. Unlike other previous investigations, the magnetic field is unable to violate the mass limit of the neutron stars. 相似文献