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# Abaqus CAE - Which case can tell the difference from continuum coupling and structural coupling?

## Abaqus CAE - Which case can tell the difference from continuum coupling and structural coupling?

(OP)
Hello everyone,

I read this article "https://www.eng-tips.com/viewthread.cfm?qid=474874".It said continuum coupling distributes the forces and moments at the reference node as the coupling nodes forces only,and structural coupling distributes the forces and moments at the reference node as the coupling nodes forces and moments.

It said that "Continuum coupling couples translation of the reference node to the average translation of the coupling nodes, and rotation of the reference node to the translation and rotation of the coupling nodes. Structural coupling couples the motion of the reference node to the the translation and rotation of the coupling nodes". It means continuum couipling distributes the forces and moments at the reference node as the coupling nodes forces and moment.
After that, I check the abaqus input file manual "https://help.3ds.com/2023/english/dssimulia_establ...". If I want to distributes the forces and moments at the reference node as the coupling nodes forces only, I need to add rotational coupling = continuum in input file.

In my memory, continuum coupling distributes the forces and moments at the reference node as the coupling nodes forces, so I am so confused about that,

I did an analysis to find what's going on. I created a rectangular beam 0.1mm along the x-axis*0.2mm along the y-axis. The reference node is offset the center of rectangualr beam by 20mm. Case 1,I fixed rectangular beam and a force (10,0,0) at reference node.Case 2, I fixed rectangular beam and a moment (10,0,0) at reference node.
I want to know the reaction force and moment generated from rectangular beam to understand the difference about continuum and structural coupling. The results show that continuum and structural coupling produce the same reaction force and moment in those cases. The cases may not show the differences about continnum and structural coupling. I also add "rotational coupling = continuum" in input file to check the result. It showed no reaction moment.

If any cases can show the difference about continnum and structural coupling, please tell me!
Also, I am so curious about why abaqus don't use this way "continuum coupling distributes the forces and moments at the reference node as the coupling nodes forces only". Can someone explain this, please?

Thank you so much!

Replies continue below

### RE: Abaqus CAE - Which case can tell the difference from continuum coupling and structural coupling?

You won't find a better explanation than in Abaqus documentation chapter Constraints --> Surface-based Constraints --> Coupling constraints (paragraph "Distributing coupling constraints"). Basically, structural coupling has some benefits (compared with the default continuum coupling) when it's used with shells.

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