Effect of the alidade thermal behavior on the pointing accuracy of a large radio telescope

The alidade’s non-uniform temperature field of a large radio telescope is very obvious under solar radiation.Estimating a radio telescope’s pointing errors,caused by the alidade deformation under solar radiation,is significant to improve the telescope’s pointing accuracy.To study the effect of the alidade thermal behavior on the pointing accuracy of a large radio telescope,a temperature experiment is first carried out in a 70-m radio telescope on a sunny day.According to the measured results,the temperature distribution rule of the alidade is summarized initially.In addition,the alidade’s temperature field is calculated by finite element thermal analysis.The simulated results are proved to be in good agreement with the experimental results.Finally,the alidade deformation under solar radiation is computed by finite element thermalstructure coupling analysis.The telescope’s pointing errors caused by alidade deformation are estimated via the alidade’s node displacements.The final results show that the effect of alidade thermal behavior on the telescope’s elevation pointing errorsΔε2+Δεr is much more than the effect on the telescope’s crosselevation pointing errorsΔε1.The maximum ofΔε2+Δεr is more than 45″,while the maximum ofΔε1 is less than 6″.This study can provide valuable references for improving the pointing accuracy of large radio telescopes.

A Reverse-Design Strategy for the Track Error of the Qi Tai Telescope Based on Pointing Accuracy

The Qi Tai Telescope(QTT),which has a 110 m aperture,is planned to be the largest scale steerable tele-scope in the world.Ideally,the telescope’s repeated pointing accuracy error should be less than 2.5 arc seconds(arcsec);thus,the telescope structure must satisfy ultra-high precision requirements.In this pur-suit,the present research envisages a reverse-design method for the track surface to reduce the difficulty of the telescope’s design and manufacture.First,the distribution characteristics of the test data for the track error were verified using the skewness coefficient and kurtosis coefficient methods.According to the distribution characteristics,the azimuth track error was simulated by a two-scale model.The error of the long period and short amplitude was characterized as large-scale and described by a trigonometric function,while the short period and high amplitude error was characterized as small-scale and simulated by a fractal function.Based on the two-scale model,effect of the error on the pointing accuracy was deduced.Subsequently,the relationship between the root mean square(RMS)of the track error and the RMS of the pointing accuracy error of the telescope was deduced.Finally,the allowable RMS value of the track error was derived from the allowable pointing accuracy errors.To validate the effectiveness of the new design method,two typical radio telescopes(the Green Bank Telescope(GBT)and the Large Millimeter Telescope(LMT))were selected as experimental examples.Through comparison,the theoretical calculated values of the pointing accuracy of the telescope were consistent with the measured values,with a maximum error of less than 10%.

Influence of chamber misalignment on cased telescoped(CT) ammunition accuracy

As part of a research program, it was desired to better understand the impact of the rotating chamber alignment with the barrel throat on the precision and accuracy of a novel cased telescoped(CT) ammunition firing rifle. In order to perform the study, a baseline CT ammunition chamber which was concentric with a Mann barrel bore was manufactured. Additionally, six chambers were manufactured with an offset relative to the barrel bore. These chambers were used to simulate a misaligned chamber relative to the bore axis. Precision and accuracy tests were then performed at 200 m in an indoor range under controlled conditions. For this project, 5.56 mm CT ammunition was used. As the chamber axis offset relative to the gun bore was increased, the mean point of impact was displaced away from the target center. The shift in the impact location is explained by the presence of in-bore yaw which results in lateral throw-off and aerodynamic jump components. The linear theory of ballistics is used to establish a relationship between the chamber misalignment and the resulting projectile mean point of impact for a rifle developed to fire CT ammunition. This relationship allows for the prediction of the mean point of impact given a chamber misalignment.

大型射电望远镜日照热误差及其补偿的仿真研究

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。

基于历史建筑修缮与保护需求的地面三维激光扫描仪点距精度实验分析

为研究地面激光扫描技术对历史建筑修缮与保护的实用意义,满足对历史建筑修缮与保护的需要,本文采用Focus3D X330地面激光扫描仪(Terrestrial Laser Scanning,TLS)对扫描距离、水平入射角2个影响因素进行点距精度实验分析,以扫描仪内外符合精度作为站点布设依据,寻求扫描仪的最佳数据区间,得到符合精度要求的高质量测量数据。实验结果表明,扫描距离在5—15 m内,内外符合精度中误差均不超过4 mm,超过15 m后内外符合精度中误差急剧上升且波动较大;水平入射角为75°—90°时,内外符合精度中误差均不超过2 mm,在15°时中误差出现最大值且波动大。上述结果可为历史建筑的修缮与保护所需的数据采集提供参考依据。

公路隧道施工水平位移及收敛量测精度确定方法与衡量方法探讨

隧道施工监控量测是隧道工程专业与测绘工程专业的交叉领域,在精度要求方面,隧道专业和测绘专业的规范标准中都有相关的条文说明,但不同规范标准之间存在侧重和差异,这给使用者在参考时造成一定的困扰。为了明确公路隧道施工监控量测水平位移监测精度要求,通过分析现行的国家标准、行业标准中的相关规定,结合多本现行规范中关于精度要求的说明,给出一种以确定允许变形量→确定衡量标准(中误差)→确定最大允许误差(中误差限差)为思路的精度确定方法,和计算实测数据中误差→对比计算中误差与中误差限差→判断数据可信度的精度衡量方法,并通过实测数据论证其合理性。结果表明,文中提出的精度确定方法、精度衡量方法及仪器选用能满足公路隧道水平位移监测或收敛监测的工作需求。

船行波对H-ADCP影响分析研究

作为当今世界上最先进的测流仪器,水平式声学多普勒流速剖面仪(Horizontal Acoustic Doppler Current Profiler,H-ADCP)因其精度高、速度快等突出优势在河流中的应用越来越广泛,但在航运业发达地区,由于受船行波的影响,很难得到稳定可靠的流速数据,阻碍了HADCP在平原河网地区的应用和推广。目前技术上很难做到完全消除船行波的影响,本文将HADCP应用在平原河网地区对流速进行测量,并分析了船行波对测量精度的影响。从H-ADCP设备选型、测量和安装方式、测量预处理、数据后处理等多方面入手,可以有效消减船行波对H-ADCP的影响,从而提高测流精度。同时,通过实验测量断面一天内平均流速变化情况,得到受船行波影响后的流速波形,然后采用数据处理手段,验证了所提方法的可行性。

Accuracy Analysis of Stewart Platform Based on Interval Analysis Method

A Stewart platform is introduced in thc 500 m aperture spherical radio telescope（FAST） as an accuracy adjustable mechanism for teed receivers. Accuracy analysis is the basis of accuracy design. However, a rapid and effective accuracy analysis method for parallel manipulator is still needed. In order to enhance solution efficiency, an interval analysis method（lA method） is introduced to solve the terminal error bound of the Stewart platform with detailed solution path. Taking a terminal pose of the Stewart platform in FAST as an example, the terminal error is solved by the Monte Carlo method（MC method） by 4 980 s, the stochastic mathematical method（SM method） by 0.078 s, and the IA method by 2.203 s. Compared with MC method, the terminal error by SM method leads a 20% underestimate while the IA method can envelop the real error bound of the Stewart platform. This indicates that the IA method outperforms the other two methods by providing quick calculations and enveloping the real error bound of the Stewart platform. According to the given structural error of the dimension parameters of the Stewart platform, the IA method gives a maximum position error of 19.91 mm and maximum orientation error of 0.534°, which suggests that the IA method can be used for accuracy design of the Stewart platfbnn in FAST. The 1A method presented is a rapid and effective accuracy analysis method for Stewart platform.

Establishment of the GPS Monitoring Network in North China, the Relation of Horizontal Crustal Movement to Stress Field and Seismicity

In the paper, the establishment, measurement, data-processing program and monitoring accuracy of the GPS seismic monitoring network in North China, especially in the Capital-Circle area, have been presented briefly. The relation of horizontal crustal deformation to tectonic movement, stress-field variation and seismicity has been analyzed in detail. The results indicate that the accuracy of GPS measurement has reached the order of 10-9 and the annual rate of horizontal crustal deformation in North China is about 4 ~5 mm. Horizontal crustal movement is a direct indication of the regional stress field. Therefore, by monitoring the time-sequence variation of horizontal crustal motion, it would be possible to investigate the change in the stress field, to analyze the tendency of seismicity and to determine the seismogenic zones.

基于柔性铰链的大口径望远镜并联调整机构

为减小地基大口径望远镜在光学追踪过程中重力变形对成像质量的影响,设计了一种基于柔性铰链的高侧向刚度、亚微米精度并联调整机构。首先,介绍了系统组成并针对技术指标的要求,开展了两自由度柔性铰链设计。建立了柔性铰链并联机构的等效运动学模型和刚度模型,搭建了并联机构刚柔耦合运动学仿真系统,分析了柔性铰链对机构精度的影响。最后,搭建实验测试系统,来验证柔性铰链的设计合理性和并联调整平台刚柔耦合运动学分析的准确性。仿真和测试结果表明,柔性铰链转动刚度误差控制在3.54%之内,小位移(微米/角秒量级)运动精度达亚微米量级,大位移(毫米/度)运动精度与仿真结果对比误差控制在微米量级,机构侧向刚度优于60 N/μm,能够满足地基望远镜光学成像的要求。

大口径地基太阳望远镜温度传感器标定方法

热控系统是大口径地基太阳望远镜的重要组成部分,它能最大限度地减小主镜面的视宁度效应和内部视宁度效应。在热控系统中,温度传感器是监控主镜表面、热光阑表面和环境真实温度的“眼睛”,因此,其精度对热控系统乃至整个望远镜的性能均有影响。针对现有商用传感器精确度不高、零点和响应曲线随时间变化而变化等缺陷,在将其组装入太阳望远镜之前,必须先对其进行标定。本工作采用一元线性回归的标定方法,通过修正传感器的响应曲线,从而提高传感器的测量精度。建立相应的实验装置,验证了该标定方法的可行性和有效性。验证结果表明,温度传感器的测量误差由1.5 ℃以上降低到0.05 ℃以下,可以满足大型地基太阳望远镜热控制系统的要求。

超高层建筑水平变形智能监测精度提升方法研究

通过理论分析与工程实践相结合,针对某超高层建筑水平变形监测项目的监测精度提升方法展开研究。通过GNSS技术、倾角传感器及高精度测量机器人的联合应用,将顶层质量较好的GNSS监测数据与中低层质量较好的倾角传感器监测数据结合,并辅以高精度测量机器人进行验证,最终得到较理想的监测结果,将误差控制在工程要求范围内,实现超高层建筑水平变形智能监测的精度提升。

大型集装箱船抗扭箱及舷侧总段搭载建造精度控制

为提升超大型集装箱船货舱抗扭箱和舷侧结构搭载的精度和效率,在应用总段卧式建造方法时,必须考虑总组和搭载2个阶段总段直线度状态发生变化带来的影响。以某24 000 TEU集装箱船为例,通过研究其舷侧总段的划分情况、结构特点、搭载吊装工艺和相关总组搭载实际建造精度数据等,得出该舷侧总段在总组和搭载2个阶段的直线度的变化量及发生该变化的原因。在此基础上,提出应用工艺可行的预变形总组工艺,优化搭载吊码布置方案,对总段预变形量进行模拟计算,提升抗扭箱和舷侧总段结构搭载建造精度。

《工程测量标准》平面控制网基本精度探析

本文就现行《工程测量标准》(GB 50026-2020)中平面控制网的构建方式、等级划分以及基本精度指标的来源给予解读,同时列举国家大地测量控制网的布设方法、技术要求和精度指标的发展和演变过程,分析工程测量平面控制网与国家大地测量控制网的关联和差异,以及工程测量产品形式的变化,提出解决问题的思路和建议。

近水平煤层井上下微震联合监测技术及应用

准确探测顶板岩层微震活动位置,尤其是震源垂直定位位置是了解覆岩空间结构特征的重要依据,对实现冲击地压精准防控具有重要意义。受限于软件算法和近水平煤层工作面测站布置方式,井下传统微震监测系统测得微震事件垂直方向定位精度低,无法满足覆岩结构运移精准监控的需求。鉴于此,在井下微震监测系统的基础上,增加地面监测台站,构成井上下微震联合监测系统,并在石拉乌素煤矿3111盘区开展工程示范。数据分析可知,井上下微震联合监测系统对能量大于1.0×10^(3)J的微震事件监测效果更佳,监测到的微震事件高程平均比井下传统微震监测系统高35.2 m,震源定位结果普遍跟矿井实际条件更加贴合,表明增加地表监测台站可有效提高震源垂直定位精度。研究成果对实现近水平煤层覆岩空间结构精准探测提供经验借鉴和指导。

海上×油田水平井优质筛管防砂精度优选实验研究

文章采用室内动态驱替实验的方法探索出砂规律,优选筛管防砂精度,为水平井防砂设计提供实验支撑。利用岩芯驱替装置,基于储层真实岩芯和油砂制作填砂管岩芯,模拟该油田水平井全生命周期产液量范围内防砂筛网不同孔径、不同筛网层数、不同筛网组合方式下的出砂规律。通过系列防砂实验优选得到防砂筛网的精度以177μm较优,筛网的层数为2层,筛网的组合方式为1层595μm支撑网+1层177μm过滤网+1层595μm支撑网+1层177μm过滤网,现场4口井的应用情况表明防砂效果优良,可为后续井的防砂设计提供借鉴。

一种测量导轨平行度的改进方法

通过制作专用的测量板,对卧式挤压机外导向式导轨结构的平行度进行测量,克服了两导轨之间平行度无法直接测量的困难,从而达到导轨结构改变但测量准确,操作方便的目的,不仅满足装配精度和使用要求,而且保证了产品质量。

基于模态分析的卧式平压平模切机模切精度分析

模切机是重要的印后加工设备,其两个重要的性能指标是模切速度和模切精度。首先,介绍卧式平压平模切机和模切单元的组成与工作原理,并详细介绍模切单元双肘杆机构;其次,概述影响模切精度的因素;最后,应用ANSYS对模切单元进行模态分析,发现蜗轮蜗杆啮合产生的激振频率会造成设备振动而影响模切精度,因此开机与运行过程中的频率需避免与激振频率重合。

1m望远镜主反射镜的支撑和装配

考虑大口径光学望远镜中主反射镜的支撑精度直接影响光电探测设备的整机性能,本文根据光学系统对口径为1 000mm的主镜的支撑精度要求和光电设备中主镜的使用情况,采用轴向和径向组合支撑的结构形式来完成对主镜的支撑,并通过有限元法对支撑位置进行理论分析和计算。实验显示,在轴向18点浮动支撑、径向3点柔性支撑的情况下,主镜能够达到较高的面形精度。针对传统装调工艺不能获得理想的面形精度,探索了新的主镜装调方法。用干涉仪对带有支撑的主镜进行实时测量并进一步进行修磨,使主镜在装配完成后达到λ/18的面形精度。该方法满足了本项目的指标要求,也为更大口径主镜的装调提供了一种新的思路。