Analysis of the Gemini data By Oleg Likhatchev Aerospace and Mechanical Engineering Department University of Arizona
Contents in Brief Introduction: What can we learn from the Gemini data? • Pressure and velocity data analysis for the primary mirror: * Autocorrelation functions * Power Spectral Densities • Buffeting forces on the secondary mirror: * Semi-empirical theory * Spectral analysis of unsteady forces on the secondary mirror
The Gemini Telescope
Pressure Sensors Layout -X +X -Y
Velocity Real Time Records c00030oo
Pressure Real Time Records c00030oo
c00030oo Velocity Autocorrelations at +X
c00030oo Velocity Autocorrelations at -X
c00030oo Pressure Autocorrelations <U>=5.81 m/s t=4.4 sec St=0.2 L=5.1 m <U>=1.78 m/s t=14 sec St=0.2 L=4.98 m
Wind Buffeting Quasi-Steady Assumption
Comparison of PSD’s for Static and Dynamic Pressures
Pressure Sensor #7 Velocity at –X c00030oo <U>=5.81 m/s; f=0.8 Hz; St=0.2; L=1.45 m <U>=5.81 m/s; f=1.0 Hz; St=0.2; L=1.14 m
Pressure Sensor #12 Velocity at +X c00030oo <U>=1.78 m/s; f=0.26 Hz; St=0.2; L=1.4 m
Pressure Sensor #23 Velocity at -Y c00030oo <U>=0.74 m/s; f=0.67 Hz; St=0.2; L=0.22 m
Pressure PSD’s for Sensor #12(+X) Upwind Side of the Mirror 1 Cases c04530oo and c04530co <U>=7.94 m/s L=1.2 m St=0.2 <U>=7.3 m/s L=1.2 m St=0.2
Pressure PSD’s for Sensor #12(+X) Upwind Side of the Mirror 1 Cases c04530oo and t04530oo <U>=7.94 m/s L=1.2 m St=0.2 <U>=7.3 m/s L=1.2 m St=0.2
Buffeting Forces on the Secondary Mirror
Buffeting Forces on a Rigid Circular Cylinder in Cross Flows (Water Tunnel Experiment, So & Savkar 1981 ) Lift Drag Strouhal Lift & Drag Re=1E+5 Buffeting Lift & Drag Re=2E+5 Re=3E+5
Experimental Drag and Lift Coefficients
Semi-empirical Theory of Buffeting Forces
Buffeting Drag and Lift
Buffeting Drag on the Second Mirror
Unsteady Lift Due to Fluctuating Drag
Buffeting Forces Case c00030oo
Buffeting Forces Case c09030oo