Optimization of welding parameters on welding distortion and stress in S690 high-strength steel thin-plate structures

The 60-meters submillimeter telescope is a large astronomical facility under proposed with the advantages of high sensitivity and large field of view, which mainly planned to observe the low temperature gas and dust in the universe. The aperture of primary reflector is 60 meters, and the requirement of surface error is 30μm rms which enables it to observe in the wavelength of 0.65mm to 3mm. In order to achieve the high accuracy requirements of telescope, the primary reflector is design to be composed of CFRP segments in one of the conceptual design schemes, similar to Large Millimeter Telescope (LMT). The natural limit of surface accuracy and pointing accuracy of telescope will be improved after the application of CFRP with the advantages of high specific stiffness and low thermal expansion, etc. This paper describes the initial development of a 3 meters prototype CFRP reflector segment, mainly including the design process of support truss and manufacture status of panel and truss.

Initial development of high accuracy carbon fiber reinforced plastics (CFRP) reflector segment for the 60-meters submillimeter telescope

The azimuth wheel-rail of large aperture radio telescope is the key component, it not only sup-ports the whole weight of the antenna, but also directly affects the pointing performance of the antenna with its surface accuracy. The whole weight of the radio telescope is hundreds or even thousands of tons, its azimuth frame rollers have great contact stress with the wheel-rail surface, repeated rolling can cause rolling contact fatigue on the wheel-rail surface, resulting in wear, cracks and other damage to the wheel-rail, and even lead to failure or fracture of the wheel-rail in serious cases, so it is very important to monitor the damage of the antenna wheel-rail. In order to visually detect the use of antenna wheel-rail surface, this paper proposed the method using electromagnetic ultrasonic detection to detect the damage of antenna wheel-rail surface for the first time. Based on the electromagnetic ultrasonic nondestructive testing principle, the simplified wheel-rail model containing wear, corrosion and crack damage is simulated. The results show that this method can effectively detect the surface damage of the antenna wheel-rail surface, and it can provide an important reference for the research of wheel-rail damage detection of large radio telescope. 

A Method for Detecting Surface Damage of Large Reflector Antenna Wheel-Rail Based on Electromagnetic Ultrasonic Technology


 The wind load influence on the large aperture radio telescope performance has become one of the key factors to further improve its performance in complex environment. Obtaining the wind load distribution on the telescope aperture is very important to estimate its influence and reduce the wind disturbance on the telescope system. The aperture of the radio telescope structure can be as large as 100 m and whilst, the wind load value in the vertical direction normally varied with the height, therefore, the uniform wind load on the aperture assumption is not suitable for the radio telescope with large aperture. In this paper, a gradient segments superposition method for calculating the wind load on the reflecting surface of the large aperture radio telescope has been proposed to improve the calculation accuracy of wind load. The proposed method has been constructed by combining two regional divisions. For the first division, since the wind speed increases with the altitudinal height, reflecting surface has been evenly divided in the altitudinal direction. For the second division, it is assumed that the wind load coefficient of the reflecting surface in different rings are different and then, the reflecting surface has been divided into several uniform rings. This method improves the estimation accuracy significantly for the telescope with larger aperture. For the 110m aperture radio telescope, the wind load estimation results differ by 28%. After that, a structural dynamics model of telescope has been established and a fuzzy PID controller has been designed to reduce wind disturbance. The Root Mean Square Error (RMSE) of telescope pointing under wind disturbance has been reduced by 67.8%. It is suggested that the proposed wind load estimation method has lay a solid foundation for the design of the large telescope system under wind disturbance.

Large telescope wind load estimation with gradient segments superposition and its servo control

Reflector antennas are extensively used in radio astronomy, satellite communication, and other industries; however, a complex interaction exists between their electrical performance and structure manufacturing process, installation errors, environmental loads, and other factors; thus, with the increase of antenna aperture and frequency band, the difficulty of antenna design and manufacturing increases. To address this technical issue, this paper focuses on the current state of reflector antenna electromechanical coupling theory modeling and compensation technology development and outlines the impact of errors on antenna electrical performance, such as main and subreflector deformation of the structure and feed source position offset from the angle of error classification. The paper also sorts out the full-path electrical performance compensation method of reflector antenna in service from active main and sub-surface technique, array feed technology, and other methods. A review of the current state of affairs aids in the development of theoretical methods and the creation of more complete antenna designs. It also allows for more accurate prediction of antenna service performance and more effective achievement of comprehensive compensation under full working conditions, ultimately assisting in achieving the performance index of the antenna.

pdf/a-review-of-full-path-electromechanical-coupling-modeling-ipupgifc6c.pdf

A review of full-path electromechanical coupling modeling and compensation for reflector antennas

It is one of the key technologies to manufacture the Xinjiang 110 m radio telescope (QTT) antenna with high-precision and has the single panel accuracy of 0.07 mm (RMS). QTT is a homology structure based on active surface meaning that the number of panels should be kept to minimum, while ensuring the panel accuracy, in order to meet the requirements for antenna structure and performance optimization. The difficulty for improving the surface precision increases as the panel size increases, creating numerous challenges in fabrication of large panel with high precision. Based on the honeycomb sandwich structure and the aluminum skin structure, the improved negative pressure forming technology is used to carry out high precision panel forming test. The test results show that a panel with area less than 1.5 m² meets the requirement. However, the current craft for panel fabrication in local China is unable to develop a single panel with area larger than 5 m². In order to meet the demands of QTT, the structure of combination panel is studied. Based on both rigid and equal flexible supports structure, the traditional and transitional sub-frame combination panel forms and traditional joint combination panel are simulated. The results show that the transitional sub-frame method could meet the required precision and quantity, but the complicated sub-frame structure attracts high development cost and increases the overall weight of the panel, which will also lead to increased complexity in antenna design and influence electrical performance. In contrast, although the traditional joint-combination-panel structure meets the precision requirement, the number of panels is not controlled within the ideal ranges. Future plan for improvement of the panel accuracy needs to be developed.

/pdf/development-challenges-for-the-xinjiang-110-m-radio-3gc7nxogit.pdf

Development challenges for the Xinjiang 110 m radio telescope (QTT) high accuracy panel structures

The smooth operation of radio telescopes is essential in radio astronomy. This paper establishes the importance of radio telescopes via examples of the discovery of gravitational waves, the merger of neutron stars, and the first black hole photograph. As radio astronomy advances, radio telescopes require larger apertures and higher pointing accuracy, resulting in a closer structural-electromagnetic coupling. To solve the coupled structural-electromagnetic problem of radio telescopes, the development of a coupled structural-electromagnetic theory is key to the smooth and efficient operation of large-aperture radio telescopes. To this end, this paper describes the development of radio telescopes built and put into operation in the last decade, as well as those under construction and to be built, and emphasizes the importance of coupled structural-electromagnetic theory in the design, manufacture, and operation of radio telescopes. Then, the paper systematically summarizes the application of coupled structural-electromagnetic theory in radio telescopes. Finally, future research hotspots of electromechanical coupling are proposed based on the development of radio astronomy and the performance requirements of large-aperture radio telescope antennas.

大型射电望远镜天线发展动态及机电耦合应用

Considering the stringent requirement of the pointing accuracy up to 2.5″ of the world’s largest full steerable radio telescope, this paper studies the welding experiment of the azimuth track of the antenna. First, the opposite deformation jig and welding process were designed for the QTT’s azimuth track. Then, the welding process was numerically simulated using a finite element model. The simulation results show that a better welding effect will be obtained by appropriately reducing the opposite force on the basis of the original. The three deformation processes of the track are regulated by the opposite deformation jig. The results show that the opposite deformation jig designed for QTT’s azimuth track can make the amount of deformation and flatness meet the design requirements. Finally, nondestructive testing was carried out to check the welding quality of the track surface and interior. The results show that there are no obvious defects in the welds of the azimuth track. The constraint jig and welding processes designed for QTT are effective and feasible.

Numerical Simulation and Test Study on Track Welding of QTT

The influence of thermal deformation on the performance of reflector antennas has become increasingly significant with the increasing aperture and working frequency. The use of a thermal compensation database is an efficient method to compensate for the deformation caused by the non-uniform temperature distribution. However, how to efficiently and accurately match and call the database remains as one of the tough challenges for the antenna thermal compensation system to achieve real time compensation. Therefore, this study proposes a data match and call method for the thermal compensation database of the reflector antenna, matching the database from three aspects: the overall rms match of temperature data, the similarity area match of each data sample, and the key area match of key structural positions. The validation of this method is demonstrated in an example. The difference between the pointing adjustment amount calculated by the matched data and the collected data was found to be less than 1″, which satisfied the requirements of practical engineering, thus achieving real-time thermal compensation of the antenna.

Accurate Data Match and Call Method for the Thermal Compensation Database of the Reflector Antenna

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Development challenges for the Xinjiang 110 m radio telescope (QTT) high accuracy panel structures

大型射电望远镜天线发展动态及机电耦合应用

Numerical Simulation and Test Study on Track Welding of QTT

Accurate Data Match and Call Method for the Thermal Compensation Database of the Reflector Antenna