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Active Contributor
klnkai
Posts: 36
Registered: ‎12-13-2011

Model not tied down because of rigid elements

169 Views, 7 Replies
04-26-2012 07:26 AM

Hi,

 

in my model the loads engage through rigid elements. The model itself is more or less a round pipe. The rigid elements run to the center, where the loads are applied.

Now my problem is that from one day to the other the solver does not produce a solution.

As soon as I introduce the rigid elements an error occurs "The model may be not tied down" after each analysis.

If I suppress the rigid elements, everything is fine. However, the issue should not be the connection to the parts, because I used right-click -> remote load

 

Does anyone have an idea what could be the matter with this issue?

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Employee
S.LI
Posts: 398
Registered: ‎05-06-2010

Re: Model not tied down because of rigid elements

04-26-2012 07:37 AM in reply to: klnkai

Linear Static Stress or Nonlinear Static Stress?

 

1.) Make sure the connection between the Rigid part and regular parts are good enough to constrain all DOFs, three translational and three rotational ones.

2.) if possible, you may try MES. It should not complain "tie down" issue.

3.)please consider to share either model or log file, which are helpful.

 

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Active Contributor
klnkai
Posts: 36
Registered: ‎12-13-2011

Re: Model not tied down because of rigid elements

04-26-2012 07:59 AM in reply to: S.LI

My type of analysis is linear static stress.

 

I apply this to solid elements, but it worked for weeks and now it does not. What do you mean by "good enough"?

 

Btw: Beam elements with a high stiffness show the same problem.

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Employee
S.LI
Posts: 398
Registered: ‎05-06-2010

Re: Model not tied down because of rigid elements

04-26-2012 08:07 AM in reply to: klnkai

What has happened during these weeks :smileyhappy:? Updated software?

 

BTW:

I never know high stiffness beams could lead to similar issues.

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Active Contributor
klnkai
Posts: 36
Registered: ‎12-13-2011

Re: Model not tied down because of rigid elements

04-26-2012 08:32 AM in reply to: S.LI

Yes, a software update is one of the things that changed.

 

After thinking about your comment about the DOF, now I tried to use only translational DOF.

 

This does not produce the error, but now my question becomes how to apply moments to the center of these elements?

 

For example if my moment is 10kNm,

would another rigid line element with a length of 1m and a force of 10kN be correct (of course with the respective directions)?

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Employee
S.LI
Posts: 398
Registered: ‎05-06-2010

Re: Model not tied down because of rigid elements

04-26-2012 08:48 AM in reply to: klnkai

I'm not sure if I got you right.

You want to apply a moment load to a rigid body, and you got the error.

 

1.) ASIM provides a way to apply remote moments. Select a surface and apply this moment. Code will automatically convert this moment to nodal force.

2.)directly apply this moment to a rigid body? I'm not sure.

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Active Contributor
klnkai
Posts: 36
Registered: ‎12-13-2011

Re: Model not tied down because of rigid elements

04-26-2012 09:32 AM in reply to: S.LI

After you mentioned that it could be an issue regarding degree of freedom, I tried to use rigid elements with only 3 translational and no rotational degree of freedom (like the solid elements) and it seems to work.

However, I would like to apply moments to these elements, but I guess this is not possible when there is no rotational DOF.

So I guess I will have to apply these moments by forces and auxiliary elements that provide the distance. Is that correct?

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Employee
S.LI
Posts: 398
Registered: ‎05-06-2010

Re: Model not tied down because of rigid elements

04-26-2012 09:49 AM in reply to: klnkai

Did you try this?

Capture.PNG

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