dynamic loading of td's from telescope motion.

    On 03feb10 a failed beam was found on the platform where tiedown 12 backstay cables attach to the the platform. To get an idea for how the tension in the tiedowns varies with telescope motion, 3 different projects that use repetitive telescope motion were selected  (a fourth day was also  included to show  typical tracking of sources).

    The projects were:

• tracking sources. This is a 24 hour stretch where sources were tracked.
• Galfacts:
  
• The azimuth sits at 360 or 180 degrees. The ch is at 8.834.
•  The dome moves from 2 to 19 degrees za in about 8 minutes.
• This typically runs for 6 hours a day.  A session  could last for 30 days.
• Igalfa:
• azimuth at 360 or 180 degrees, ch at 8.834
• dome moves over a shorter distance (say 2 to 10 degrees) in about 12 minutes.
• This typically runs for 2 hours a day.  A session  would last for 21 days.
• aeronomy az swings.
• dome at 15 degrees, ch at  0 degrees.
• azimuth  rotates 360 degrees in 15 minutes.
• the rotation continues for 3 to 7 days.

• The tiedown tensions are color coded:
• black: td12 (az=360)
• red: td4 (az=120)
• green:td8 (az=240)
• the tensions plotted are the sum of the tensions in the two cables at each tiedown.
  

• Page 1: tracking sources:
• This does not contain any repetitive motions.
  
• Top: tiedown tension vs hour of  day
• Hi tension: 85 kips, low tension close to 0.
• Middle: azimuth position
• Bottom: Gregorian za position (the ch was set at 8.834 deg).
• Page 2: galfacts
• Top: tiedown tension vs hour of day.
• Td12 tension varies the most (55 kips) because the azimuth is pointing at td12. The dome moving up/down in za causes the change in the tension. Temperature was stable (midnight).
• Bottom: Dome motion in za. This is moving at close to slew speed (.04 deg/sec)
• Page 3:  igalfa
• Top: tiedown tension vs hour of day.
• td12 change in tension is 31 kips.
• Bottom: za position of dome during motion.
• Page 4: aeronomy azimuth swings:
• Top: tiedown tension.
• The temperature was 72F during this dataset.
  
• all 3  tiedowns have a change in tension of about 50 kips.
• Td12  pattern is regular while td 4,8 are not as symmetric. This is because the azimuth turnaround occurs at +/- 180 degrees azimuth (which points at td 12).
• Bottom: azimuth position during the  run.

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