help needed regarding fixing and moving objects in different steps

[Mary rs]

Hi,

I need to fix two objects in a step and let those move in next step along U1. These two objects are connected by an axial connector. Most part of them are enclosed with a box and are coupled. The objects and the box should be fixed in a way that entire objects and the box do not move in step 1 and then move in step 2. When I am applying boundary condition to the box and the part of the objects enclosed by the box then the part of the objects outside the box are moving but I want entire object to be fixed. If I deactivate and reactivate the connectors, the outside part of the objects are still moving and I am having convergence issues too. For clear understanding, I have attached a sketch. Please let me know if it is still not clear. Any help would be highly appreciated. Thanks.

 

[Mustaine3]

Your question is not clear and precise. Are you talking about a relative movement or an absolute? What can move in step 3 - everything or just specific objects?

You should write questions in a way, that people who are not familiar with your model can understand it.

 

[Mary rs]

Hi Mustaine3,

I am talking about relative movement.

In step 1, I want both the objects and the box to be fixed.
In step 2, I want both the objects to move along U1 (with connector displacement) and the box to be fixed.

I could solve the question that I asked previously. In step 1, I applied boundary condition on entire objects and box to fix them.

But I am facing a different issue. I inactivated the boundary conditions (which were in step 1 for the two objects and the box) in step 2, applied boundary condition just on the middle of the box (the entire box should be in its place and not move) and let both the objects move along U1. But as I see the result, the objects are not displacing straight along U1. Instead they are bending. I don't want them to be bent but vertically displace.

 

[Mustaine3]

I still don't get it. Make a small example and attach the .inp file.

 

[Mary rs]

Hi Mustaine3,

I am sorry that it was not clear. I could not attach the input file so I have attached a sketch here. I hope this will make you easier to understand. I think the issue is with the local coordinate system. I am not very sure on what coordinate system should I use when I assign boundary condition and fix the box to all degrees of freedom. In what cases, should transform coordinate system be used? I have looked the documentation but I am little confused regarding this part. I will try to upload my .inp file. Thank you.

 

[IceBreakerSours]

How are the rods being displaced? If they are driven by BCs, then you could simply constrain other DOFs.

As I have urged before, please seek in-person guidance. Online forums aren't ideally suited for learning the basics.

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[Mary rs]

Rods are being displaced with an axial connector. Since I had to fix this little soon so I asked for help. Thanks for your help and suggestion. I will learn and fix the issue.

 

[IceBreakerSours]

Step 1 (OP): Understand the technical issue.
Step 2 (OP): Formulate and communicate question.
Step 3 (Helper): Understand question.
Step 4 (Helper): Propose solutions.
Step 5 (OP): Try proposed solutions.
Iterate
Step 6 (OP): Have a drink and be happy.

We are stuck somewhere in steps 1/2/3.

Can you upload the model?

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