<title>Wind buffeting effects on the Gemini 8-m primary mirrors</title>

Abstract

One of the critical design factors for large telescopes is control of primary mirror distortion caused by wind pressure variations. To quantify telescope wind loading effects, the Gemini Observatory has conducted a series of wind tests under actual mountaintop conditions. During commissioning of the southern Gemini Telescope, simultaneous measurements were made of pressures at multiple points on the mirror surface, as well as wind velocity and direction at several locations inside and outside the dome. During the test we varied the dome position relative to the wind, the telescope elevation angle, the position of windscreens in the observing slit, and the size of the openings in the ventilation gates. Five-minute data records were made for 116 different test conditions, with a data-sampling rate of ten per second. These data sets have been processed to provide pressure maps over the surface of the mirror at each time instant. From these pressure maps, the optical surface distortions of the primary mirror have been calculated using finite-element analysis. Data reduction programs have been developed to enhance visualization of the test data and mirror surface distortions. The test results have implications for the design of future large telescopes.

Wind loads on ground-based telescopes

“…Full-scale data are available from measurements taken at Gemini South Observatory. [3][4][5] More extensive data under more controlled conditions have been collected in an ϳ1% scale wind-tunnel experiment. 6 Finally, computational fluid dynamic (CFD) analyses 7 have been validated against these data sources and used primarily to understand differences between different sources of data.…”

Control of the California Extremely Large Telescope primary mirror

“…There are three sources we consider: a comprehensive data set collected at Gemini south, 8 analysis (e.g. Padin 9 ), and the data analyzed herein from Keck.…”

Integrated modeling tools for large ground-based optical telescopes

“…The time-dependent vector wind velocity applied is a sample of real wind velocity data obtained in measurements around the secondary mirror of the Southern Gemini telescope. 17 The mean wind speed was about 5 m/s. The drag forces were calculated by assuming a cylinder of 2 meters diameter and height.…”