The VST telescope primary mirror safety system: simulation model and mechanical implementation

Abstract

The VST telescope is a wide field survey telescope being installed at Cerro Paranal (Chile). Due to the geological nature of the area, telescopes in Chile are always submitted to unpredictable and sometimes severe earthquake conditions. In order to clarify some aspects of VST telescope seismic behavior not well represented by linear procedures like Response Spectrum Analysis, a transient nonlinear analysis of the whole telescope has been foreseen. A mixed approach Finite Element -Matlab-Simulink has been introduced and a linear FE model of the telescope has been developed, with all nonlinear devices sources modelled as linear elements. The FE model has been exported to Simulink, using a space state representation. In Simulink all nonlinearities are appropriately modeled and a base excitement corresponding to accelerograms compliant with Paranal MLE response spectrum is applied. Resulting force-time histories are then applied to a detailed finite element model of mirror, to compute stress field. The paper describes both Simulink and mirror FE analysis, giving also an overview of the actual safety system mechanical implementation, based on analysis results.