Encastre and coupling at the same time. Problem with nodes used twice
Encastre and coupling at the same time. Problem with nodes used twice
(OP)
Good afternoon to all of you!
I am facing a problem that may be really easy but I can't find the clue.
I have a model of vertebrae C5 and C4 with the intervertebral disc between both.
I want to submit the whole model to a rotation. But I also want to encastre the base of the inferior vertebrae. My aim is to see the resultant moments.
I am using a coupling constraint between a reference point (situated outside the model) and the model itself. I use this reference point to rotate the whole model.
I am using encastre in the base of the vertebrae.
However abaqus exits with an error because nodes used in the coupling are also used in the encastre.
Does anyone know how to solve this problem?
Thank you very much. I really need help.
Please find attached a pdf with images.
I am facing a problem that may be really easy but I can't find the clue.
I have a model of vertebrae C5 and C4 with the intervertebral disc between both.
I want to submit the whole model to a rotation. But I also want to encastre the base of the inferior vertebrae. My aim is to see the resultant moments.
I am using a coupling constraint between a reference point (situated outside the model) and the model itself. I use this reference point to rotate the whole model.
I am using encastre in the base of the vertebrae.
However abaqus exits with an error because nodes used in the coupling are also used in the encastre.
Does anyone know how to solve this problem?
Thank you very much. I really need help.
Please find attached a pdf with images.





RE: Encastre and coupling at the same time. Problem with nodes used twice
"Does anyone know how to solve this problem?"
Yes, you don't use nodes in the coupling if they are in the boundary condition.
RE: Encastre and coupling at the same time. Problem with nodes used twice
The problem is that I need to submit the whole model to the rotation.
As I need to fix the base, there will be nodes of the base that will be in the boundary condition while they are in the coupling because I have to rotate the whole model.
RE: Encastre and coupling at the same time. Problem with nodes used twice
What shall the nodes do that are in both definitions?
RE: Encastre and coupling at the same time. Problem with nodes used twice
My aim is to obtain the momentum necessary to rotate the vertebrae a certain angle.
I want to simulate a whiplash. For this, first I need to validate the model.
So imagine the base of the inferior vertebra can't move. Now I want to rotate the rest of the vertebrae and obtain the momentum needed to rotate it.
RE: Encastre and coupling at the same time. Problem with nodes used twice
But I think, that the elements close to the BC will fail pretty soon.
RE: Encastre and coupling at the same time. Problem with nodes used twice
Do you know another way to do the same but using a different technique?
I have thought about create a new part to act like a table, put the BC to the table, put the model on top of the table, and rotate the model.
RE: Encastre and coupling at the same time. Problem with nodes used twice
When some edges are part of these two regions, then you can easily fix that. Decide in which definition the edge(s) shall not be. Then edit that definition and select again the faces. Before you confirm your selection, press down CTRL key and click on the edges that should not be in there. Confirm that.
RE: Encastre and coupling at the same time. Problem with nodes used twice
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RE: Encastre and coupling at the same time. Problem with nodes used twice
RE: Encastre and coupling at the same time. Problem with nodes used twice
Exactly IcebreakerSours! I am trying to replicate Panjabi and White models!
Finally I have opted for the eassiest solution (I didnt think about it before :S ) I am going to put the intervertebral disc below C5 and set the BC there.
However now I have a problem with the contact properties. By now I have tried two options:
• Surface to surface just in the surfaces in touch of different parts; this is interverebral discs with base and tops of vertebrae.
In this case Abaqus exits after 6 attempts with warning messages “Displacement increment for contact is too big”
• General contact. This time applied to the whole model.
In this case Abaqus aborts saying that some of the elements have volume 0.
As you can see the parts are form of multiple instances.
Please can you give me advice in this topic?
Thank you very much!
RE: Encastre and coupling at the same time. Problem with nodes used twice
b) Discs do not articulate at the interfaces. You have to tie those nodes.
Be careful! Your basics (FE, functional anatomy of the spine, and ex vivo testing) need some polishing.
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RE: Encastre and coupling at the same time. Problem with nodes used twice
So acording to you which would be the boundary conditions I would need to apply?
How can I fix the whole vertebral body (as you say in a) and at the same time rotate it?
What do you mean at point b? Should I use as unique interaction a tie between intervertebral discs and vertabrae?
Thank you for your support, I am starting to desperate :(
RE: Encastre and coupling at the same time. Problem with nodes used twice
A part of the top and the bottom vertebra is fixed in an epoxy/resin mixture so the gripping of either end becomes easy. Bottom end is fixed and the top end is loaded with pure moments, and the motion of each vertebra is computed by post-processing of marker data (with markers rigidly adhered to many locations on the specimen).
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Are you new to this forum? If so, please read these FAQs:
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RE: Encastre and coupling at the same time. Problem with nodes used twice
*********************************************************
Are you new to this forum? If so, please read these FAQs:
http://www.eng-tips.com/faqs.cfm?fid=376
http://www.eng-tips.com/faqs.cfm?fid=1083