Draft

# Intro:

The tension in members of the telescope changes as we move the dome, ch, azimuth, and tiedown tensions. The lifetime of a beam is counted in the number of times the change in tension goes through a cycle. If the change in tension during the cycle remains less then 16Kips/sqIn then  the cycle does not affect the lifetime of the member.

Amman and Whitney (21may10) provided a table of stress ranges for members over 100% capacity (.pdf). Using their simulator, they moved the telescope through a range of motions and looked to see how the stress changed in a particular truss (I'm not sure what they used for tiedown tensions in the calculation).

The following sections contain:

# The dataset: (top)

The telescope position is recorded once a second to disk. Some properties of this dataset are:
• Data includes 2004.5 through 2010
• There are a few days of missing datafiles (disc problems etc.). this is less than 1 % for any given year.
• There are times when the data samples are invalid (time, position..). This can occur during an encoder failure or when  part of the system is powered down to be worked on. This data is not "missing" since the telescope can not move when this maintenance occurs (so no cycles can occur).
• 2007 was the platform painting project. The telescope motion was stationary for a large part of this year.

# Examples of telescope motions (top)

The plots show the az, za, and unbalanced moments for various observing modes used at the telescope:
• Aeronomy azimuth swings (.ps) (.pdf):
• Page 1: 14jun05: dome=15,ch=15, unbalanced moment +/- 9500KipFeet.
• Page 2:  08sep05: dome=15, ch=0, unbalanced moment:+/- 13500 KipFeet
• both of these used .4 degrees/second in azimuth.
• About 95 (360 degree) cycles per day.
• Number 2 is the typical run mode.
• Driving dome up and down in za at az = 0 degrees (galfacts) (.ps) (.pdf): 07dec08
•  az=180 degrees, ch=8.8, dome=2 to 19.6 degrees.
• Unbalanced moment -19500 to 11000 KipFeet.
• this takes 20 minutes to go up,down.. 3 cycles per hour and runs for 4 to 6 hours a day.
• 3 days of typical tracking (.ps) (.pdf) 23-25apr05
• top: azimuth position
• middle: dome position
• bottom: unbalanced moment at td 12.
• The large swings in moment come from swinging the azimuth arm through 360 degrees with dome at 19.6 degrees.
• the typical use of the telescope looks like these days rather than the repetitive motions of the first two plot.

# Number of cycles using change in moment: (top)

The number of cycles on the telescope was computed using the change in the unbalanced moment (at a corner). The Amplitude of the change for a cycles was computed for changes greater than:  [5000,10000,15000,20000] kip feet.
The computation constisted of:
• Compute the unbalanced moment on the azimuth arm as a function of time (from the dome motion).
• Project this unbalanced moment on the 3 corners of the triangle (0,120,240) degrees:
• UnbalMomentCorner=UnbalMomentArm * cos(azimuthCorner- azimuthOfArm)
• For each corner process all the data (once a second sampled) counting the number of cycles performed.
• A cycle consists of:
• The (Max - Min moment seen surpasses the specified amplitudeDifference (ampDif).
• It must then go in the opposite direction (once the first ampDif is found)
• It should then return by +/- ampDif/2
• The order of the difference (increasing the decreasing or decreasing then increasing) is handled by the program.

The plots show the change in unbalanced moment on the telescope 2004.5 through 2010 (.ps) (.pdf) using the above definition:
• Page 1. the number of cycles by year for each corner and the 4 Amplitudes
• The cycle amplitudes used were:
•  Frame Amplitude  (kipFeet) 1 > 5000 2 > 10000 3 > 15000 4 > 20000

• For each frame Black is corner 12, red is corner 4 and green is corner 8.
• The dashed blue line shows the yearly median counts (excluding 2004,2007, and 2010)
• Year notes:
• 2004 is a half year
• 2007 is the platform painting year which had limited motion.
• 2010 had the za limited because of the broken beam repair.
• Page 2: Integrated cycles 2004.5 thru 2010 for the 4 cycle amplitudes.
• The total cycles for  2004.5 thru 2010 is plotted versus cycle amplitude.
• the 3 colors are corner 12,4,8.
• Page 3-6: Histogram of cycle depth for each year
• Each line in a frame is a histogram of the cycle depth for a given year.
• For each cycle counted, the program ,kept track of the actual cycle amplitude.
• The histogram binwidth is 800 kipfeet.
• Each frame has 7 histograms (one for each year).
• The 3 frames on each page are corners 12,4, and 8.
• Each page is shows a different Cycle amplitude : 5000,1000,15000,20000 KipFeet change.
• Some bins with spikes probably correspond to repetitive motions of the telescope.

# Summary:

## Number of telescope cycles using Amplitude of unbalanced moment change:

 Amplitude KipFeet corner12 totCyles corner 4 totCycles corner 8 TotCycles > 5000 48665 53061 52568 > 10000 29838 28155 27620 > 15000 15469 15536 14985 > 2000 8320 8773 8384

• The above table shows the accumulated cycles for the 6.5 years.

 Amplitude KipFeet Median Yearly cycles > 5,000 9378 > 10,000 5418 > 15,000 2980 >20,000 1704

• The median cycles/year has excluded the 2004,2007, and 2010 data

## Unbalanced moments for typical motions:

• Some of the motions used on the telescope:
• World day az swings:
• dome=15,ch=15 = 9500 Kipfeet.
• dome=15, ch=0 = 13500 kipFeet.
• Galfacts za nodding
• az=0, dome 2 to 19.6 deg
• max unbalanced moment: 18500 KipFeet
• min unbalance moment: - 9000 KipFeet
• Usually 3 cycles/hour
• swinging from source set to source rising
• will have a moment of +/- 19500 kipfeet *cos(azRise,set - corneraz)
• it can take 1.5 to 2.5 hours to track a source rise to set.
• The tiedown tensions were not used at all in this computation.

processing:x101/110204/agccyclesdif.pro, agccycleslev.pro

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