Browsing by Author "De Lange, Billy"

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    High accuracy numerical model of the SALT mirror support truss
    (Stellenbosch : Stellenbosch University, 2011-12) De Lange, Billy; Venter, Gerhard; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
    ENGLISH ABSTRACT: Although a numerical model of the mirror support truss of the Southern African Large Telescope (SALT) has already been developed during the design thereof, this thesis focuses on the development of the methods and techniques that would result in a more accurate numerical model of the actual structure that could be used as a basis for a numerical control system. This control system will compensate for de ections in the structure by adjusting the positioning of the individual mirror segments of the primary mirror. The two main components from which the support truss is constructed are the steel nodes, and the struts that connect to them. For this project a smaller, simpler laboratory model was designed and built to have geometrical properties similar to that of the support truss. The methods and techniques that were investigated were carried out on this model. By using numerical design optimisation techniques, improved numerical models of the different strut types were obtained. This was done by performing tests on the struts so that the actual responses of the struts could be obtained. Numerical models of the struts were then created and set up so that they could be optimised using structural optimisation software. Once accurate strut models had been obtained, these strut models were used to construct a numerical model of the assembled structure. No additional optimisation was performed on the assembled structure and tests were done on the physical structure to obtain its responses. These served as validation criteria for the numerical models of the struts. Because of unforeseen deformations of the structure, not all of the measured structural responses could be used. The remaining results showed, however, that the predictive accuracy of the top node displacement of the assembled structure improved to below 1.5%, from over 60%. From these results it was concluded that the accuracy of the entire structure's numerical model could be signi ficantly improved by optimising the individual strut types.