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02.06.2005 14:37:40
BIGRED210
BIGRED210
Posts 2

Question: What is the unit of measure for Moment of Inertia under Mass Properties in the English system?


I am also puzzled by this: the same model gives different Radius of Gyration in K4 and CKD19. I am running both, position my CG at the origin, getting the same mass, CG etc. but different RoG. Which one is correct?


Thanks

08.06.2005 08:57:26
Jay Burkett
Jay Burkett
Posts 8

I just did a quick check and compared CK19.01 to KC4.0.2.


I created a 1"Ø rod 100" long centered at the origin.


For KC4.0.2


Rx=28.8685959728, Ry=28.8685959703, Rz=.353553493763


For CK19.01


Rx=28.868596, Ry=28.868596, Rz=.35355339


The only difference I got was in the 6th digit of the Rz values.  The others were different becasue CK 19.01 truncates to 6 decimal places.  If I had to guess, I would think that this is a rounding error of some sort.


Outside of school, I've never met anyone that actually that actually had a use for the Radius of Gyration since it relates to the rotaional inertia of an object about an axis.   Do you use this value in your work?  Just curious ...


Jay 


Jay Burkett
UPS Airlines
Louisville, KY



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Jay Burkett
UPS Airlines
Louisville, KY

08.06.2005 11:23:00
BIGRED210
BIGRED210
Posts 2

Hi Jay,


Thanks for your note. I put in more work into it and it seems to me that in the case of an assembly having multiple solids the RoG is wrong in KC4 when you interogate for the TOTAL. (The individual parts could be OK, I did not check). A real bummer! I am using it to size a motor and transmission components for rotating a massive steel assembly.


Regards,


Peter

08.06.2005 12:21:22
Jay Burkett
Jay Burkett
Posts 8

Peter,


I guess you do need that value to be correct!  As it currently exists, KC does not do assemblies well.  It assumes the assembly is homogenous w.r.t. material.  We have asked them to fix this.  Note, I'm am not holding my breath!


Jay Burkett
UPS Airlines
Louisville, KY



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Jay Burkett
UPS Airlines
Louisville, KY

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