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## Simulation Mechanical and Multiphysics

Active Contributor
Posts: 46
Registered: ‎09-21-2010

# adding bc to prescribed displacement

473 Views, 10 Replies
10-15-2010 12:25 AM

Hi

I would just like to know how is it possible to add a bc to a node where there is still a prescribed displacement (of course in another dof).

Each time i try, i have the error message saying : prescribed displacement non active

Thanks!

Employee
Posts: 398
Registered: ‎05-06-2010

# Re: adding bc to prescribed displacement

10-15-2010 05:06 AM in reply to: benalain

BC and PD are allowed to be applied on different DOFs of a node.

I bet your model needs double-check.

If your model is complicated, you can create a simple one ( maybe just one element) to see if there is still the same problem.

Of course, you are also welcome to share your model here.

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Distinguished Contributor
Posts: 316
Registered: ‎03-24-2010

# Re: adding bc to prescribed displacement

10-15-2010 05:40 AM in reply to: benalain

I remember also having this problem. As far as I know, though, you can simply att the other BC as a prescribed displacement by use of a "custom" vector though. For example, if you set a prescribed displacement along the X-vector, I think the node is still free to move in the Y-and Z-directions. However, if you make a prescribed displacement with a vector of (X,Y,Z) = (1,0,0), the node will be constrained also in Y and Z.

I'm unsure how this works with rotations at the same node. Does anyone know if you can apply both a rotational and translational prescribed displacement at the same node simultaneously? I don't see why it shouldn't work...

Employee
Posts: 398
Registered: ‎05-06-2010

# Re: adding bc to prescribed displacement

10-15-2010 05:49 AM in reply to: bjorn_fallqvist

I attached a MES model here.

Both BC and PD have been applied on nodes along the top surface.

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Employee
Posts: 37
Registered: ‎05-14-2008

# Re: adding bc to prescribed displacement

10-15-2010 05:51 AM in reply to: benalain

yes, as Bjorn explained, try using Custom vector!

Active Contributor
Posts: 46
Registered: ‎09-21-2010

# Re: adding bc to prescribed displacement

10-15-2010 06:04 AM in reply to: benalain

OK, i will try and let you know.

And i also remember that sometimes, it is better to input a custom vector than the X Y or Z one. But it shouln't be the case.

ALAIN

Active Contributor
Posts: 46
Registered: ‎09-21-2010

# Re: adding bc to prescribed displacement

10-15-2010 06:18 AM in reply to: benalain

Here is a model where i add a displacement in the Z direction (defined by a customer vector) and constraints also the X and Y direction.
And there is the error message

Employee
Posts: 398
Registered: ‎05-06-2010

# Re: adding bc to prescribed displacement

10-15-2010 06:28 AM in reply to: benalain

The BC is to constrain Tx and Ty, and the PD is (0,0,1), so there are incompatible on X and Y direction.

the PD should be applied on only Z direction, instead of "Vector".

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Active Contributor
Posts: 46
Registered: ‎09-21-2010

# Re: adding bc to prescribed displacement

10-15-2010 06:45 AM in reply to: S.LI

OK i see i can not define the vector but only clic on scalar X, Y or Z

If i input the vector as custom, it is not accepted.

So what is the solution if the displacement direction is not in those global directions.

Thanks

Employee
Posts: 398
Registered: ‎05-06-2010

# Re: adding bc to prescribed displacement

10-15-2010 06:51 AM in reply to: benalain

Since you constrain, for example, X direction, your loads/PD on the same direction will make no sense.

For example, if X is constrain, and you want to apply PDs along both Y and Z. Then you have to apply them separately.

In another word, there should be two PDs in the model, one for Y and another for Z.

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