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Frame Analysis of curved frame members

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Message 1 of 8
craigtsa
1894 Views, 7 Replies

Frame Analysis of curved frame members

I am trying to run a frame analysis of a chasis which consists of 4 curved and numerous straight members. I used the frame generator to create the chasis using 3/4 and 1/2 inch piping. In frame analysis mode these curved members are neglected by the simulation and therefore leave me with inconclusive results. Is it possible to somehow get the simulation to recognise these members?
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Message 2 of 8
pcrawley
in reply to: craigtsa

And there is one of FG's most frustrating limitations... You'll have noticed the warning message that says something like "unsupported members"?

FG' one of those really good tools that has the potential to be "awesome" if it ever gets finished.
Peter
Message 3 of 8
sgauthier
in reply to: pcrawley

Sorry to dig up an old ghost here.  But my team is running into this as well on Inventor 2017.  Did this issue ever get resolved?  Has the Frame generator analysis tool been improved to support analysis of curved frame members?

 

Thanks,

Stephan

Message 4 of 8
Binga
in reply to: sgauthier

Hello. It is not an issue with Inventor. Is an "issue", or "conceptual limitation", of the method used.
When you want to simulate curved elements, you need to break them into several straight elements. You also need to be careful with the node type between the elements.
Look for "Curved beam in the finite element method" and you will see many formulations to this element. But I have never seen this implemented in commercial softwares.


Gilberto Binga
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Message 5 of 8
michael_r_gerrard
in reply to: Binga

Forgive me asking this again. But from what I've read Frame Analysis doesn't mesh and use FEA. It simply uses bending beam equations. (or have I got that wrong) As such it doesn't need to know how the break up the arc, it just needs to know the radius of the frame line, the cross section of the member, the loads and constraints, and correct equation for a curved member.

Message 6 of 8

Correct.  The Frame member itself only provides the section properties to the analysis tool — no meshing.

Peter
Message 7 of 8


@michael_r_gerrard wrote:

...It simply uses bending beam equations. (or have I got that wrong) As such it doesn't need to know how the break up the arc, it just needs to know the radius of the frame line, the cross section of the member, the loads and constraints, and correct equation for a curved member.


I have highlighted several words in your description above.

What is the "radius of a line"?

What is the "correct equation for a curved member" (any member - you can make one up)?

If possible, refer to beam analysis equations in the Machinery's Handbook or on-line resource so that I can reference the appropriate equation.

 

AFAIK - there are three different mathematical analysis techniques in Inventor stress analysis:

1. Mesh

2. Thin Feature

3. Beam (straight line members)

 

Each of these is appropriate analysis technique dependent on the geometry.


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Message 8 of 8

I'm at home so it's not that straightforward for me to put a screenshot of what i'm talking about up. But if you could picture a 2D sketch of a straight line, with an arc on the end. This forms part of a wider structure, but for now, it's all we need to consider. You can use this sketch to create a frame with Frame Generator. FG will break the arc into segments of straight lengths, but the underlying sketch still has a true arc, which is a section of a circle with a known radius.
A very quick google of "Curved Beam Calculation" led me to this http://courses.washington.edu/me354a/Curved%20Beams.pdf
Which is, I ASSUME, the type of calculation going on in the background on Frame Analysis. Just for straight beams.
It's quite possible that answer to the above assumption is simply "No that's not what it's doing in the background"
Or, it might be the case that it is the same kind of equation, but adding this it would break the way it currently Frame Analysis works and need a ground-up redesign of some matrices that are in the "Hard Math Problem" section of engineering.

Either way, I'm out of my depth.
Time to consider workarounds.

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