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how to define boundary condition along surface normal direction

how to define boundary condition along surface normal direction

how to define boundary condition along surface normal direction

(OP)
Hi,

I have a curve-shaped object that I am modeling to have the boundary nodes fixed in the surface normal direction, while allowing tangential movement. How can I specify such a boundary condition then? I looked up "*TRANSFORM" keyword, but it seems that the local coordinate system is very simple, only Cartesian, cylindrical, or spherical. I don't want to specify a local Cartesian coordinate for each of my boundary node. Maybe this is not the way it should be handled.

Someone knows how to do this? It's probably very simple, but I just haven't got the answer. Thanks very much!

 

RE: how to define boundary condition along surface normal direction

There is an option "allow separation after contact" on the contact property > mechanical > normal behaviour. Maybe this can be used by deselect it.

RE: how to define boundary condition along surface normal direction

(OP)
Thanks for the tip, but that's not the case for me. I don't really have contact definition involved -- all I need is to specify that the nodes on the outer boundary can only move tangentially, but not in the normal direction.

RE: how to define boundary condition along surface normal direction

Typically you will get better answers if you describe what you are trying to model with pictures or CAE files then pose your question.  With more information there may be a simpler or more accurate solution.  

For instance what shape is the surface?  If this is a hip joint then a simple radial constraint may be appropriate...

I hope this helps.

Rob Stupplebeen
https://sites.google.com/site/robertkstupplebeen/

RE: how to define boundary condition along surface normal direction

(OP)
Hi Rob,

Thanks for your reply -- unfortunately, I do not have a CAE file to show what it looks like as I generate Abaqus input files directly without using CAE.

The question is more of a generic in nature -- I know when implementing the finite element code for analysis, it's actually quite easy to specify normal/tangential boundary conditions for boundary nodes (i.e., multiplying a rotational matrix when assembling into the stiffness matrix). However, just don't know how to do this in Abaqus.

The specific problem I am trying to solve is to model the human brain -- I wanted the brain boundary nodes to be able to move in tangential direction, but fixed in the normal direction. The shape is more complex than a simple sphere, as the nodal normal direction differs at different location.

Can you please elaborate a little bit more on "radial constraint"?

Thanks!

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