High accuracy numerical model of the SALT mirror support truss

[摘要] ENGLISH ABSTRACT: Although a numerical model of the mirror support truss of the SouthernAfrican Large Telescope (SALT) has already been developed during the designthereof, this thesis focuses on the development of the methods and techniquesthat would result in a more accurate numerical model of the actual structurethat could be used as a basis for a numerical control system. This controlsystem will compensate for de ections in the structure by adjusting the positioningof the individual mirror segments of the primary mirror.The two main components from which the support truss is constructedare the steel nodes, and the struts that connect to them. For this project asmaller, simpler laboratory model was designed and built to have geometricalproperties similar to that of the support truss. The methods and techniquesthat were investigated were carried out on this model.By using numerical design optimisation techniques, improved numericalmodels of the different strut types were obtained. This was done by performingtests on the struts so that the actual responses of the struts could beobtained. Numerical models of the struts were then created and set up so thatthey could be optimised using structural optimisation software. Once accuratestrut models had been obtained, these strut models were used to construct anumerical model of the assembled structure. No additional optimisation wasperformed on the assembled structure and tests were done on the physicalstructure to obtain its responses. These served as validation criteria for thenumerical models of the struts.Because of unforeseen deformations of the structure, not all of the measuredstructural responses could be used. The remaining results showed, however, that the predictive accuracy of the top node displacement of the assembledstructure improved to below 1.5%, from over 60%. From these results it wasconcluded that the accuracy of the entire structure's numerical model couldbe signi ficantly improved by optimising the individual strut types.

[发布机构] Stellenbosch University