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Calculate moment of inertia for hollow section


bean125

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This may have been discussed before. Try checking the list of Similar Threads shown at the bottom of the page or do a search on the word 'inertia'.

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First, create regions, both for border lines and for inner loop (or loops). Then use subtract command to get your hollow section. Run massprop once, read Centroid and set UCS to that coordinates. Then run massprop once again and read Moments of inertia.

Massprop.jpg

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I've seen this method before and was always curious as to why the need to run MASSPROP, reset the UCS and then run MASSPROP again. I can see that the Moments of Inertia are different but if you look at the Principal Moments in the first run you will get the same data without having to rerun the MASSPROP and without resetting the UCS....unless someone can show me different.

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You are right Bill... But Moments of Inertia are given around X and Y axis in this order. Principal moments of inertia are given minimum and maximum, in this order, as you can see in my example above. Further, if the shape is not symmetrical, those values are not the same.

Here is another example

2Moments.png

And what about radii of gyration? In your other posts about Mom of Inertia, you collect this data too. The correct ones are those given about CG and not about WCS.

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I've seen this method before and was always curious as to why the need to run MASSPROP, reset the UCS and then run MASSPROP again. I can see that the Moments of Inertia are different but if you look at the Principal Moments in the first run you will get the same data without having to rerun the MASSPROP and without resetting the UCS....unless someone can show me different.

 

Well ruffle my hair, and call me Elvis! Bill, looks like a point has been made, you might just as well write us a new lisp reflecting that fact. Have you had a chance yet to pitch that nice new one you were working on to the client? Good luck there.

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Well in honor of the King's (Elvis') Birthday tomorrow....

 

I think I will write a LISP which does this very thing. As I have confessed several times, my engineering skills are pretty good, but only good enough to get me in trouble. That's why I usually leave the calc book preparation to the PE's.

 

Peanut budder and nana sandwiches for everyone!

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Hi,

 

A few hints about Moments of Inertia:

 

 

  • Change color prior to converting the closed objects into regions so as to ascertain that they have actually been converted into regions.
  • Use centroid.vlx to automatically create a point at the centroid of the subtracted region Note: Centroid will duplicate the object. I don't know if there is a solution to that. With Selection Cycling on, you can easily delete the duplicate object.
  • Use tab so that you can write only massp [tab] to get massprop

 

If you want to delete all the centroid points, use epts.lsp (erase points)

 

Regards, Nicolas.

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Well in honor of the King's (Elvis') Birthday tomorrow....

 

I think I will write a LISP which does this very thing. As I have confessed several times, my engineering skills are pretty good, but only good enough to get me in trouble. That's why I usually leave the calc book preparation to the PE's.

 

Peanut budder and nana sandwiches for everyone!

 

What shall we call it ........ LISP me tender?

No doubt it will soar to the top of the charts, as it should be.

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No I was thinking more of Lisp House Rock.....or Burnin' Lisp!

 

Either one of these is better than "You Ain't Nothin' But a Lisp Coder"

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No I was thinking more of Lisp House Rock.....or Burnin' Lisp!

 

Either one of these is better than "You Ain't Nothin' But a Lisp Coder"

 

Burnin' Lisp ........ where there's smoke, there's fire.

If the shoe fits......

Hats off to the lisp-meister!

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