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Design and Study of the 1m Primary Mirror and Its Supporting System

Author: ZhangDongGe
Tutor: LiYaoBin
School: Graduate Schoo,Chinese Academy of Sciences
Course: Mechanical Manufacturing and Automation
Keywords: Primary mirror supporting system optimization design topology optimization surrogate model
CLC: TH743
Type: Master's thesis
Year: 2010
Downloads: 129
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Abstract


The larger aperture mirror is adopted in telescope system for the higher resolution. The optimization design of the mirror and its supporting system can be beneficial to the lightweight design and the better surface accuracy of the reflector, which is the key indicator of the image quality. In order to achieve the optimization of the 1m primary mirror and its supporting system, the flowing words has been done in this paper.(1) To determine the maximum aperture can be acquired by center fixed support alone, the conical SiC mirror with sector lightweight whole was selected as the specimen, which has the balanced geometry and mechanical properties. The structural parameters in SiC mirror were analyzed by single-factor test for the sensitivity. The maximum aperture is determined by trend of the sensitivity analysis. The maximum aperture is less than 800mm by the center fixed support alone.(2) The compound supporting system was optimized by ANSYS for 1m mirror. The (Finite Element Method) FEM model of the axial and radial supporting system were built in parametric loads and constraints respectively, then the optimal design model was set up in Design Opt in ANSYS. Four options of radial supporting were compared by the optimal value, which were produced by Design Opt. The best one was picked out by the performance curve from horizontal to vertical. The drawing of the supporting system is given at last.(3) Topology optimization was implemented for the lightweight design of the primary mirror, the Homogenization method and Evolutionary Structural Optimization (ESO) was carried out in Workbench and APDL respectively, and the principle of Homo and ESO were illustrated in this section. The Solid Isotropic Microstructure with Penalization (SIMP) was introduced as the amendment for avoiding the solitude elements in ESO, which will corrupt the stiffness and mass matrix in FEM. Optimal material distribution was got form the common feature based on the topology results. Some modifications were appended to existing lateral lightweight method which has a better effect (>20%) in axial multipoint supporting system, and the blind hole can be used in central section instead of through hole.(4) The Back Propagation Artificial Neural Network (BPANN) was adopted to express the implicit relationship of surface displacement and the parameters of the mirror by the comparison of Response Surface Method, Kriging model. Sample data was got from parametric finite element model under the guide of statistics. So the explicit relationship among the mirror parameters and the displacement in reflector surface were expressed in the BPANN model. Random test was carried out to verify the model, the mean absolute error between BPANN models and (Finite Element Method) FEM model. Two axial support optimization examples were carried out with the participation of the optimization algorithm. The result shows that the surrogate model has a better effect for the optimization of the axial support than existing approximate formula and FEM method. This design method is polished by the development of special tool box in Matlab, which makes the above proceeding exact and convenient to extensive use.

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CLC: > Industrial Technology > Machinery and Instrument Industry > Instruments, meters > Optical instruments > Telescope
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