Structural form selection of supporting structures for WFOS of TMT

ZHENG Ling-yu1, ZHANG Da-xu1, AMAN·Shrestha1, SONG Zhen-sen1, GAO Sheng-bin1, XU Teng2, XU Ming-ming2
(1.School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiao Tong University,
Shanghai 200240, China; 2.National Astronomical Observatories/Nanjing Institute of
Astronomical Optics & Technology, CAS, Nanjing 210042, China)

Abstract: Aiming at the problem of the low bearing capacity and lightweight rate of WFOS of TMT, a shell supporting structure scheme was proposed for the existing truss supporting structure scheme. The finite element models for two type of structures were developed. The performance of truss structure and shell structure, both composed of invar, were evaluated from the aspects of mass, displacement, stress and fundamental frequency. By the principal of equivalent stiffness, the thickness of carbon fiber composite shell components were determined. The results indicate that under the action of gravity in the most unfavorable direction of rotation, the mass of the composite structure is 1.93 t with a fundamental frequency of 7.98 Hz. The maximum relative displacement between each optical element is 0.286 mm, and the maximum stress is 30.94 MPa. Hence, the composite shell structure meets the design requirements which makes it an ideal supporting structural form. The results of this study can guide the selection and design of the supporting structure for optical instruments of extremely large telescopes.
Key words: thirtymeter telescope（TMT）; wide-field spectrograph (WFOS); structure selection; finite element analysis (FEA)