Large Telescope Wind Load Estimation with Gradient Segments Superposition and its Servo Control

Abstract

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.