FAST主动反射面健康监测系统数据处理方法研究及应用

基于FAST主动反射面健康监测系统的多传感器测点与海量监测数据,提出一种数据处理方法,对系统采集的温度、应力、风速及索力等数据进行处理;采用多项式回归分析数据相关性,辨识温度梯度对应力的影响。利用提出的数据处理方法对不同工况下圈梁结构应力、索力和温度之间的相关性进行分析。分析结果表明,圈梁结构应力与温度显著相关,且在索网未变位期间圈梁结构应力主要受温度影响,索网变位期间主要受索力影响。通过对数据的处理可识别影响结构内力的主要因素,并有效分离温度变化对应力的作用,为后期运行维护提供数据支持。     

基于振动测量的视宁度测量方法研究

根据像运动法测视宁度的原理,研究了一种新的视宁度测量方法,可以用口径为10 cm左右的望远镜测视宁度,并能排除人为因素和仪器光学质量的影响。原理是用加速度传感器测量望远镜的振动,并从单个星像的抖动中扣除镜筒振动的影响。为此设计了一套测量振动装置,进行了观测,并与差分像运动视宁度监测仪(Differential Image Motion Monitor,DIMM)作了比较,发现该方法在一定程度上消除了望远镜抖动对像运动法测视宁度的影响,但不能完全消除。     

FAST单元面板面型检测算法研究

500 m口径球面射电望远镜(Five-hundred-meter Aperture Spherical Radio Telescope,FAST)是一个超大口径的可动望远镜,有三项技术创新,一是选址,二是轻型馈源索支撑,三是主动反射面。在主动反射面上,单元面板的面型和面板的出厂加工精度对电磁波在反射面的汇聚有很大影响。FAST主反射面由4 600块三角形反射面板拼接而成,每块面板为边长11 m三角形,这对FAST反射面面板的测量技术提出了更高的要求。摄影测量直接在影像上进行量测,无需接触物体本身;所摄影像信息丰富,可以从中获得所研究物体的大量几何信息和物理信息;适用于大范围、多目标测量,效率高。目前世界上最大的射电望远镜,如GBT和ARECIBO都是采用摄影测量技术进行反射面面形检测。在对现有的面型检测技术调研并试验后,提出基于数字近景摄影测量的方法,对FAST反射面11 m单元面板的面型进行检测,数分钟完成反射面板面型的一次检测,测量精度达到2.5 mm,经过调整后的单元面板的面型精度达到了3.0 mm,结果表明摄影测量应用于FAST反射面单元面板面型检测是可行的。     

FAST馈源支撑系统中质量阻尼器的初步设计

500m球面射电望远镜(FAST)的馈源支撑系统存在大跨度柔性索支撑结构,馈源仓容易受到外界干扰源的激励引起振动,影响馈源舱内接收机定位和指向的性能和精度.质量阻尼器作为一种有效并且可靠的振动控制设备,得到了深入的研究和应用.本文从质量阻尼器的基本原理出发,初步设计出一种应用于FAsT馈源支撑系统的被动和主动质量阻尼器模型.数值分析和仿真实验结果表明质量阻尼器对FAST馈源仓的振动有明显的抑制效果.     

大射电望远镜索牵引并联机构索力优化分析

为对大射电望远镜馈源支撑系统索牵引并联机构实施控制、获得准确的索长信息,采用精确的悬链线方程建立舱体非线性静平衡方程组来求解索力,进而获得大跨度下刚索索长。提出了线性简化模型——赝曲线模型,该模型保证了解算精度,大大提高了解算效率,为实时控制及进一步大规模计算提供了便利。在给定位置下,利用赝曲线模型对姿态角进行搜索,得到满足索力约束条件的姿态角集合。在此基础上,以索力均匀分布为优化目标对索力进行优化,从而保证系统良好的力特性,避免钢索之间的干扰。数值计算说明了赝曲线模型的精确性和快速性,最后利用赝曲线模型得到了优化后精确的索力、姿态角与索长。     

FAST馈源舱倾覆的理论分析及试验研究

FAST望远镜馈源舱通过6根钢索悬浮于空中,在运行过程中其倾角连续变化,存在发生倾覆的风险。通过舱索系统的静力学理论分析和模型试验对FAST馈源舱的最大倾覆角进行了研究。基于舱倾角最大的优化原则和舱-索系统静力平衡,对索力和姿态角的限定等约束条件,建立了求解舱最大倾角(倾覆角)的目标优化函数,利用牛顿迭代法解得了舱在其运行轨迹面(焦面)的倾覆角,同时研究了重心改变对倾覆角的影响。通过舱索系统3 m缩尺模型对理论分析结果进行了验证,得到了模型舱在给定位置的倾覆角,试验结果与理论计算结果比较吻合。最后分析了馈源舱原型在整个焦面上的倾覆角,结果表明馈源舱在实际工作过程中是安全的,不会发生倾覆。     

无线传感器网络中基于时钟漂移补偿的时间同步技术

在分析和总结现有时间同步算法的特点及其存在问题的基础上,提出了一种在无线传感器网络的时间同步协议（TPSN）中同时考虑节点时钟偏移和频率漂移率的改进算法。该算法利用连续两次同步过程中所记录的时间信息来估算节点时钟的偏移和频率漂移率,并进行补偿。同传统算法相比,此算法通讯成本较低、精度较高。最后通过数学分析和仿真的方法对所提出的改进算法进行了验证。     

基于生物学同步模型的WSN群同步算法研究

在研究现有无线传感器网络时间同步算法的基础上,为进一步满足大规模网络对同步算法精度和扩展性的需求,将生物学同步模型引入无线传感器网络中,提出一种分布式的群时间同步算法,并进行仿真验证。结果表明,该算法能够使具有不同初始相位的网络节点最终达到相位同步,满足网络同步要求。     

宽范围数字化精密频率测量系统的研制

由于奈奎斯特采样定律的限制,传统的数字化精密频率测量设备难以对频率较高的信号进行高精度的精密频率测量.作者研制了一种宽范围数字化精密频率测量系统,能够通过基于频谱分析的粗测过程和基于欠采样的精测过程,克服奈奎斯特定律的限制.实验表明,该宽范围数字化精密频率测量系统对于10 MHz信号的测量(相对)频率偏差为1.13×10-11,测量稳定度达到1×10-12量级.     

关于使用VFC技术测频的浅析

目前,我们有可能利用 VF 转换技术进行高精度的频率测量,如果把经典比相方法和该技术结合起来,则相位显示的精度将能得到较大的提高,因而频率计数器的±赫误差可被忽略。正因为如此,该方法可进一步扩展经典比相技术的测频精度,所以,这种方法有可能适用于现代原子频标的高精度频率测量。本文讨论了一些有关把检相电压转换为频率以用于测频的有关问题,诸如该方法的基本关系式。主要误差项韵分析和讨论,这又包括了 V—F 转换器件的非线性误差及相位比较系统的噪声电压 Vn,以及系统可能达到的测频灵敏度和该方法的有关一些技术问题。     

A preliminary study on photogrammetry for the FAST main reflector measurement

The Five-hundred-meter Aperture Spherical radio Telescope(FAST) is the largest single-dish radio telescope in the world. In this paper, we apply photogrammetry to measure local area surface accuracy of the FAST main reflector. Contrast with the existing photogrammetric methods that need to stick the cooperation target on the panel. In this paper, we directly detect nodes according to their natural feature. Analyzing the FAST reflector composition, we propose a two-step Hough transform method for node detection. Due to the high similarity of the neighboring area around nodes, it is hard to match two images by the feature matching method. Therefore, we apply the nodes combination approach to obtain the homography matrix between two photos for nodes matching. After nodes detection and matching,triangulation and bundle adjustment algorithms are adopted for 3 D reconstruction. During the experiment,the adjusted node position deform a local area of the FAST main reflector into a spherical cap with a radius of 300 m. The experimental result shows that the measurement accuracy of the sphere with a radius of 300 m is 12.299 mm, indicating that it is feasible to apply photogrammetry for the FAST main reflector measurement.     

Studying solutions for the fatigue of the FAST cable-net structure caused by the process of changing shape

The Five-hundred-meter Aperture Spherical Radio Telescope(FAST) is supported by a cable-net structure,whose change in shape leads to a stress range of approximately 500 MPa.This stress range is more than twice the standard recommended value.The cable-net structure is thus the most critical and fragile part of the FAST reflector system.In this study,we first search for a more appropriate deformation strategy that reduces the stress amplitude generated by the process of changing shape.Second,we roughly estimate the tracking trajectory of the telescope during its service life,and conduct an extensive numerical investigation to assess the requirements for fatigue resistance.Finally,we develop a new type of steel cable system that satisfies the cable requirements for construction of FAST.     

Recognition of FAST reflector nodes based on Canny operator

The reflector system of Five-hundred-meter Aperture Spherical radio Telescope(FAST) is designed as 4450 rigid panels supported by a flexible cable-net structure. We use 10 total stations to measure2225 nodes of the cable-net and then control the shape of the reflectors. Every time, it takes at least 35 minutes to finish the calibration of the whole cable-net once. It is indeed far too inefficient. Thus, we developed a set of highly efficient instrument CRRS(CCD Rotation Ranging System). It is based on photogrammetry and can finish the measurement in 1 minute. However, the target we used in CRRS is active target, and it has serious electromagnetic interference problems to affect the use of FAST. Take the above reasons into consideration, we plan to identify the nodes by taking the gap between the reflector panels as the feature condition. The new method can take the place of active targets to finish the measuring task. The present work focuses on the following aspects. First, combined with the characteristics of FAST reflector images,the representative algorithms of image edge detection are discussed. Second, the process of node extraction is introduced in detail so that we know that it works. In addition, experimental results are given to draw a conclusion so that Canny algorithm was used for continuous research of reflector edge detection.     

FASTL波段多波束馈源设计的初步分析

把抛物面天线的偏焦理论应用于FASTL波段多波束馈源系统的设计,分析了馈源喇叭横向偏焦距离与相应波束偏离角之间的关系,结合多波束射电望远镜扫描方式的要求,给出了FASTL波段多波束馈源的工作带宽、多波束馈源中相邻喇叭的间距以及喇叭口径大小的限制,并对正六边形阵列中处于不同位置的喇叭对应的波束的主瓣情况作了详细计算和分析。由此说明了FASTL波段多波束馈源采用19波束的可行性。另一方面,根据得到的工作频率带宽和喇叭口径大小的情况,对OMT和喇叭类型的选择进行了探讨。本文给出了FASTL波段多波束系统的大概轮廓,为进一步精确设计指明了方向。     

Experimental Research of First Feed-Support System of FAST

First feed support system, which is one of the key technologies of Five hundred meter Aperture Spherical Telescope (FAST) was discussed in this paper. A 1:30 scaled model (20 m × 20 m × 6 m) has been built to make systemic research on the feasibility of the system. The root mean square of pointing error of moving cable car was measured and the displacements of cable car within the wind speed of 8 m/s, which is the maximal wind speed of the place where the FAST will be located, were evaluated. Then the total maximal pointing error of cable car was computed. Experimental results demonstrate that the total pointing error of the cable car is less than 50 cm, the required pointing accuracy error of the system. This revised version was published online in July 2006 with corrections to the Cover Date.     

An open-loop control algorithm of the active reflector system of FAST

An open-loop control algorithm is put forward for continuous paraboloid deformation of the active reflector system of the Five-hundred-meter Aperture Spherical radio Telescope(FAST).The method is based on a calibration database and interpolation in 2D spatial domain and temperature domain,respectively.It is completely independent of real-time measurement of cable nodes so that it has advantage of working all-weather and no additional electro-magnetic interference(EMI).Furthermore,its control accuracy can be effectively improved via reasonable layout of the calibrated paraboloids and increasing calibration accuracy.Meanwhile deformation safety is considered via calibration as well.Finally its control accuracy is also confirmed via site measurements of paraboloid deformations.     

Scalable framework of intelligent RFI flagging for large-scale HI survey data from FAST

Radio frequency interference (RFI) identification is a key step in radio data processing. In order to efficiently process huge volumes of data produced by modern large radio telescopes, such as the Five-hundred-meter Aperture Spherical radio Telescope (FAST), exceptional balance between accuracy and performance (throughput) is required for RFI flagging algorithms. RFI-Net is a single-process RFI identification package based on deep learning technique, and has achieved a higher flagging accuracy than the classical SumThreshold method. In this paper, we present a scalable RFI flagging toolkit, which can drive parallel workflows on multi-CPU and multi-GPU clusters, with RFI-Net as its core detector. It can automatically schedule the workload and aggregate itself after errors according to the running environment. Moreover, its main components are all pluggable, and can be easily customized according to requirements. The experiments with real data of FAST showed that using eight parallel workflows, the toolkit can process sky survey data at a speed of 66.79 GB/h, which means quasi-real-time RFI flagging can be achieved considering the data rate of FAST extragalactic spectral line observations.     

The design of China Reconfigurable ANalog-digital backEnd for FAST

The Five-hundred-meter Aperture Spherical radio Telescope(FAST)was launched on 2016 September 25.From early 2017,we began to use the FAST wideband receiver,which was designed,constructed and installed on the FAST in Guizhou,China.The front end of the receiver is composed an uncooled Quad Ridge Flared Horn feed(QRFH)with the frequency range of 270 to 1620 MHz,and a cryostat operating at 10 K.We have cooperated with the Institute of Automation of the Chinese Academy of Sciences to develop the China Reconfigurable ANalog-digital backEnd(CRANE).The system covers the 3 GHz operating band of FAST.The hardware part of the backend includes an Analog Front-end Board,a wideband high precision Analog Digital Converter,and a FAST Digital Back-end.Analog circuit boards,field programmable gate arrays,and control computers form a set of hardware,software,and firmware platforms to achieve flexible bandwidth requirements through parameter changes.It is also suitable for the versatility of different astronomical observations,and can meet specific requirements.This paper briefly introduces the hardware and software of CRANE,as well as some observations of the system.     

Design and optimization of cross bow-tie dipole feed with cavity for FAST

A cross bow-tie dipole feed with cavity and symmetrical E and H plane pattern is presented for the Five hundred-meter Aperture Spherical radio Telescope(FAST).In this paper we describe the design,optimization and simulation results of a wide-band cross dipole feed with cavity covering the frequency range from 300 MHz to 600 MHz for FAST.The main goals of our design are to ensure that,(1)we cover the octave bandwidth,(2)the feed has symmetrical E and H plane pattern,and(3)the physical dimension is suitable for mounting it in the reserved position of the FAST feed cabin.The initial results indicate that we have met most of our design goals.This kind of feed had been equipped with the multi-beam receiver to carry out observation on the platform of FAST cabin.     

Detecting radio afterglows of gamma-ray bursts with FAST

Using the generic hydrodynamic model of gamma-ray burst(GRB) afterglows, we calculate the radio afterglow light curves of low luminosity, high luminosity,failed and standard GRBs in different observational bands of FAST’s energy window.The GRBs are assumed to be located at different distances from us. Our results rank the detectability of GRBs in descending order as high luminosity, standard, failed and low luminosity GRBs. We predict that almost all types of radio afterglows except those of low luminosity GRBs could be observed by a large radio telescope as long as the domains of time and frequency are appropriate. It is important to note that FAST can detect relatively weak radio afterglows at a higher frequency of 2.5 GHz for very high redshift up to z = 15 or even more. Radio afterglows of low luminosity GRBs can only be detected after the completion of the second phase of FAST. FAST is expected to significantly expand the sample of GRB radio afterglows in the near future.