Abstract
FAST focus cabin is suspended and driven by 6 parallel large span cables. Low stiffness of cables makes the cabin sensitive to disturbance and difficult to control. Structural damping then becomes a key factor that can improve control ability. Therefore, a reasonable damping estimation is important for system design. In this paper, a practical damping identification method is developed based on Ibrahim-time-domain algorithm. The method shows satisfied performance on accuracy and reliability in simulation test and is utilized in vibration experiments to identify damping ratios of both single cable model and FAST 3 m scale cable suspension model. Finally, a preliminary analysis of the damping properties is given out based on the results of identification.
Highlights
FAST will be the largest single dish radio telescope in the world [1]
A preliminary analysis of the damping properties of FAST cable suspension is given out based on the results of damping identification
Similar to sampling frequency analysis, two models of 3 degrees of freedom (DOF) oscillatory system were created to study the accuracy of identification using different signal lengths which are expressed as duration of vibration
Summary
FAST (five-hundred-meter aperture spherical radio telescope) will be the largest single dish radio telescope in the world [1]. The Stewart manipulator is used to isolate feeds from cabin vibration by adjusting the length of 6 linear actuators in real time. A number of model experiments and simulations of FAST feed support system were carried out to study the structural dynamics and control ability. In the 1970s, the well-known Ibrahim-time-domain (ITD) method was proposed [6, 7], which is featured in solving eigenvalues and eigenvectors of the system matrix. A modified damping identification method based on ITD is firstly. Comparing with standard ITD method, the modified method needs only measuring one node and has satisfied accuracy of damping identification, which is more practical and reliable in vibration experiments. The proposed method is utilized in vibration experiments of both single cable model and downscaled FAST cable suspension model. A preliminary analysis of the damping properties of FAST cable suspension is given out based on the results of damping identification
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