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adding bc to prescribed displacement

10 REPLIES 10
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Message 1 of 11
benalain
1169 Views, 10 Replies

adding bc to prescribed displacement

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!

10 REPLIES 10
Message 2 of 11
S.LI
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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Message 3 of 11
bjorn_fallqvist
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...

Message 4 of 11
S.LI
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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Message 5 of 11
shakeel.mirza
in reply to: benalain

yes, as Bjorn explained, try using Custom vector!

Message 6 of 11
benalain
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

Message 7 of 11
benalain
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

 

The file is here : http://www.yousendit.com/download/ZGJlU2Vxa0REbUpFQlE9PQ

Message 8 of 11
S.LI
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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Message 9 of 11
benalain
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

Message 10 of 11
S.LI
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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Message 11 of 11
xli
Alumni
in reply to: S.LI

Reform my language a little bit, hope it is better:

 

A PD is defined on one DOF of a node. Specifying an axis direction in UI will produce a PD for that DOF; but using vector in UI will make three PDs applied on three DOFs respectively on the node. If you also have defined BC on same node that eliminates corresponding DOF as unknown, then one of three PDs is supposed applying on not defined DOF, you got the error/warning message. 

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