WARNING in usermpc: no MPC is generated for the mean rotation in node

swaraj

While performing a Non-Linear Static 3D analysis, I got this error.
In my analysis, I am simulating the deformation of a Cap like structure when placed on a fixed object.
So the object which is fixed is also the master surface for the contact with Cap. The error is showing in the nodes of the object which is fixed support and also the master surface of the contact.
Can the overlap of this two condition may cause this error.

Victor

I think you uploaded the wrong file since it has no constraints or contacts.

*WARNINGs in CCX are common and usually harmless. My guess is that this wouldn't be a problem since a fully fixed surface can't rotate so maybe it doesn't need any MPCs to connect that rotation to the slave.

Does the displacement in the solution look reasonable? Nothing bent the wrong way or penetrating contacts?

swaraj

The simulation ended in Jacobian Error.
I have a doubt. I want the inner surface of shell to be in contact with the fixed object.So what should I do. Should I activate show thickness and then select the inner elements or just select the mesh elements without activating the show thickness button?

and also does the thickness direction of Shell matters, calculation point of view?

Victor

The *ERROR will be where it failed. CCX stops when there's an *ERROR, but keeps going with *WARNING.

The view options don't affect how the contact is applied, as long as you don't select the edges of the elements. It should also work just as well with the shell offset direction either way. Just select the faces on the correct side for contact, which you already have.

I think the reason it failed was a lack of constraints on the cap part. Contact doesn't usually constrain anything initially, so it has rigid body motion before the contacts close and a static solution can be found. A simple way to correct that is to apply fixed supports through very soft elements so they support it gently but don't carry any significant reaction force. Probably a good idea to start with a few patches of fixed support to make sure that this solves the problem, then replace them with more realistic soft supports later. I'm trying that now but it's quite slow to solve.

swaraj

Hi @Victor.
Whats the process of constraining a body with weak springs to restrict rigid body movement. As you said body which is only constrained by contact may undergo rigid body motion until the contact close which may lead to convergence failure. Can you explain how to do it?

Victor

What I find easiest is to extrude a small element (select a face then Mesh tools -> Extrude) and assign it a new material with low Young's modulus and apply fixed support to the new face. It ends up looking like this picture.

The next version of Mecway (12) will have elastic support for CCX so you won't need to make the new element or material.

swaraj

Should i have to give bonded contact between extruded elements and the contact object?

Victor

No need because it'll still be sharing the same nodes.

swaraj

Hey @Victor
In an .inp file where can i find the material properties. Which key should I search for?

Victor

The lines following

*MATERIAL,NAME=YourMaterialName