1. Analysis of the Gemini dataBy
Oleg Likhatchev
Aerospace and Mechanical
Engineering Department
University of Arizona

2. 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

3. The Gemini Telescope

4. Pressure Sensors Layout-X +X -Y

5. Velocity Real Time Records c00030oo

6. Pressure Real Time Records c00030oo

7. c00030oo Velocity Autocorrelations at +X

8. c00030oo Velocity Autocorrelations at -X

9. 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

10. Wind Buffeting Quasi-Steady Assumption

11. Comparison of PSD’s for Static and Dynamic Pressures

12. 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

13. Pressure Sensor #12 Velocity at +X c00030oo
<U>=1.78 m/s; f=0.26 Hz; St=0.2; L=1.4 m

14. Pressure Sensor #23 Velocity at -Y c00030oo
<U>=0.74 m/s; f=0.67 Hz; St=0.2; L=0.22 m

15. 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

16. 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

17. Buffeting Forces on the Secondary Mirror

18. 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

19. Experimental Drag and Lift Coefficients

20. Semi-empirical Theory of Buffeting Forces

21. Buffeting Drag and Lift

22. Buffeting Drag on the Second Mirror

23. Unsteady Lift Due to Fluctuating Drag

24. Buffeting Forces Case c00030oo

25. Buffeting Forces Case c09030oo