Design of the solar telescope GREGOR under dynamic wind loads

Abstract

The operational wind speed for the 1.5 m solar telescope GREGOR which will be erected in 2004 on the Spanish island of Tenerife is specified at 20 m/s. At this wind speed the seeing conditions at the telescope site are good for observations of the solar physics and the effects of internal seeing will be minimized by the wind blowing through the largely open telescope structure. The requirements for an absolute pointing accuracy of 1 arcsec rms and for a relative pointing error of 0.25 arcsec rms have to include the wind load influences. In this paper the numerical analyses of the structural response under static and dynamic wind loads and their impact on the telescope design are presented. For the analyses a response spectrum method using a finite element program system and a time history simulation including the servo system were utilized. For the analyses and simulations detailed finite element models of the telescope were used. The dynamic wind loads on the structure were calculated using a wind turbulence spectral density function and simulated wind speed time histories including site-specific wind characteristics. A pointing model taking into account the displacements of the telescope's mirrors with respect to the adjusted configuration was included in the investigations.