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# Constrain a surface in the direction of the normal at each node

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Posts: 55
Topic starter
(@james.lockley)
Trusted Member
Joined: 8 years ago

Hello everyone, I wish to apply BCs to a surface that I have defined in ABAQUS. I would like to constrain each node in this node set in the direction of the normal to the surface at that point. Does any one know if there is a way to do this? Obviously it wouldnt make sense to define a new local coordinate system for each and every node because there are so many of them.

Thanks ðŸ™‚

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Posts: 124
(@bw_composite)
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Joined: 17 years ago

Hi there Rm447,

I am not familiar at all with ABAQUS but in ANSYS you could, after having defined all the geometric area of your interest as only one area in the pre-processor, apply a constraint equation to it, so that the deflection, for example, in the x - direction (global system) is a certain ratio of the deflection in the y - direction, the ratio being a function of the orientation of the area with respect to the global system.

If the area is not perpendicular to any global then you would need of course two equation, but still would be simple.

Hope this helps, let us know

Muzialis

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(@jorgen)
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Joined: 5 years ago

Does your surface have cylindrical or spherical symmetry? If so, then you could simply switch to the appropriately coordinate system.

If that does not work, then I would have to think about it ,)

-Jorgen

Posts: 55
Topic starter
(@james.lockley)
Trusted Member
Joined: 8 years ago

Dear Jorgen and Muzialis,

The problem is that this is not an analytical surface and I dont know the equation for it, neither does it have any sort of symmetry. Its a geometry obtained from 3D reconstruction of MRI scans.

I thought since the normal to the surface at each node must be known by ABAQUS, then may be there is an easy way to constrain each of the nodes in that direction. Any thoughts?

Thanks again!

Posts: 124
(@bw_composite)
Estimable Member
Joined: 17 years ago

Rm447,

thanks for your clarification, I wrongly assumed the surface was geometrically defined (actually my advice refreed to the trivial case of a planar surface..).

I can not see an easy way around your problem, if not constraining each node (or maybe a set of suitbaly defined lines) individually as suggested by you (the normal orientation is something you could easily get from ANSYS, and with ABAQUS I am sure would be the same).

Let us know how it goes

Muzialis

Posts: 3998
(@jorgen)
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Joined: 5 years ago

Perhaps you can create another part that has the same outside surface geometry as the part that you are interested in. You can then make the new part rigid and assign contact surfaces. That way you have constrained the motion...

-Jorgen

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