大型射电望远镜日照热误差及其补偿的仿真研究

Numerical Study on Solar Thermal Error and its Compensation of Large Radio Telescope

射电望远镜广泛应用于射电天文、测控导航等领域,随着其工作频率的升高、口径的增大,日照引起的结构热变形对其性能的影响愈发严重;本文针对待建的新疆110 m口径射电望远镜,建立了其日照热力耦合模型,分析了天线在不同时刻、风速及姿态下的温度、变形情况,总结了结构日照温度场、变形场的时空分布特征,最后采用最佳吻合抛物面方法对反射面精度进行了评价,并通过副反射面位置补偿量的变化趋势揭示了天线热变形的共性规律及机理。结果表明:对于日照引起的天线热变形误差,风速越大,结构温度分布越均匀,其越接近等温膨胀变形,反射面形状精度越高;温差引起的结构不均匀变形是反射面精度下降的主要原因,温差越大结构的不均匀变形越大,反射面的形状精度越低;同一姿态不同风速下反射面热误差空间分布具有相似性,该分布与太阳直射点位置直接相关,且会跟随直射点位置发生变化,但由于日照强度、风速等因素的不同,其变形幅度不同。各种姿态下反射面精度变化规律相似,与风速的相关性均为反射面精度随风速上升而提高;采用副反射面位置补偿技术可明显缓解日照热误差影响。本文的分析方法与结论对大口径全可动射电望远镜的设计建造及其热误差控制具有一定参考价值。

Radio telescope is widely used in the fields of radio astronomy and navigation.The electromagnetic performance of radio telescope is heavily affected by the structural thermal deformation due to solar heating as the working frequency and aperture increases.To understand the solar thermal behaviors of the 110 m telescope to be built in Xinjiang,we established a thermal-mechanical coupling model to simulate the temperature/displacement fields at different solar times and wind speeds,and concluded the spatial and temporal characteristics.Then we evaluated the reflector precision using the best fit parabolic method and revealed the law and mechanism of antenna thermal deformation by the trend in sub-reflector’s position compensation.Results show that large wind speed leads to uniform expansion and thus high reflector accuracy when the solar heating causes thermal deformation error.The decrease in reflector accuracy is largely attributed to the non-uniformly deformation of antenna structure caused by non-uniform temperature filed.Larger temperature difference results in more non-uniformly deformation and thus lower reflector accuracy.For the antennas with the same attitude but different wind speeds,they have similar reflector error distributions that can change with the position of sunlight direct incident point.However,the magnitude of deformation varies with the sunlight intensity and speed.The reflector precision increases with the increasing wind speed and has a similar law of variation for various attitudes.The thermal error can be greatly compensated by the sub-reflector repositioning.The approach and results of this paper will provide valuable guidelines for the design and construction of large radio telescope as well as its thermal error control.