Error comment ... 1

[chooga4eva]

the following error comment displays:

Analysis Input File Processor completed successfully.
Error in job 1650: The rigid bodies with the reference nodes contained in node set ErrNodeRefNodeNoRot1Axis have atleast one axis about which the rotary inertia magnitude is zero, and the rigid bodies have atleast one rotational degree of freedom which is unconstrained. Either rotary inertia must be defined at the reference nodes or all of the rotational degrees of freedom at the reference nodes must be constrained.

Where in abaqus can i go to constrain all rotational dofs? I have gone to constraints---rigid body--- not sure what to use (though i have played around with all of them and got the same error)

 

[gwolf2]

I think you are trying to "run before you can walk". Have you any formal structural engineering or FE qualifications?

I'm not trying to be rude, it's just that you seem to be trying to do very complicated things (which I would find challenging after 20 years detailed FE experience) and yet asking very basic questions.

I advise you to simplify your models right down, understand the basics and then build up the complexity very slowly until you get back to youre real world model.

gwolf.

 

[chooga4eva]

Well you are not making it any easier now.

I am simply applying my case scenario, checking if its do-able, if it isn't then I'll make further assumptions and simplifications.

I'm sorry but what exactly is complicated that I am doing? lol

 

[corus]

The reference point needs to be restrained rotationally in the load module.

ex-corus (semi-detached)

 

[gwolf2]

> I'm sorry but what exactly is complicated that I am doing? lol

If it's not complicated then why are you posting here all the time?

 

[chooga4eva]

well in my opinion it isn't "complicated", and I am just having problems because I'm a newbie with Abaqus.

 

[amubashar]

Just to reiterate gwolf2's point, modelling of bone is a complicated process. To start with, what assumptions are you making about bone material? From your other posts, it looks like you are using a homogeneous linear elastic material. From our own material characterisation, we know that bone is a highly non-homogeneous material. Properties change from one specimen to other based on age, health etc. Even specimens of similar aged and health show variations of up to 50% in properties. All this means that fe models can't provide reliable results, especially when they are based on very simple material models. In your other post you mentioned that you want to "define a point at which elasticity of bone no longer holds". What failure criteria should be used? Is failure brittle or ductile? Is mesh sensitivity going to be an issue?
My point is that development of bond modelling methodologies is still a topic of research and not knowing doesn't mean it’s simple.

 

[chooga4eva]

To amubashar,
I appreciate your comment and having studied biomedical sciences I already know this very well. It is well documented that bone is inhomogeneous and hence its true modelling is very difficult. But i believe I have never mentioned in this forum that I was modelling true bone as it were. If you look at the video i have posted I have got a very simple geometry and material properties have also been extensively simplified.
Funny though, in this thread I didn't mention nor was referring to bone, the rigid body stated in this thread couldn't have obviously been bone as bone is deformable so this thread is referring to another part which is merely a rigid block. So I'm not sure why your are referring to bone.

I suppose then, the rigid block that I am trying to constrain all rotational dofs is very complicated!!! Thank you both for letting me know this.

 

[corus]

FFS, restrain it in the load module.

ex-corus (semi-detached)

 

[chooga4eva]

Thank you all for being so helpful.

 

[jithus]

chooga4eva,

Do not get discouraged by the commments. The community is extremely helpful but just that might have got ticked off because of your query (basic) on rigid body motion. I wouldn't go into that but lets talk about the solution of your current problem.

I'm assuming that your impactor or rigid body is moving along a particular axis or a combination of them if it is going to impact the bone at an angle. Then what that error means is that in your BC definitions you need to restrict the appropriate rotations and translations.
For ex: Lets say your rigid body is moving only along z-dir.
i) Go to Load module->BC->Velocity and select all the 3 rotations and V1 and V2 and the region as the reference point of the rigid body. This needs to be defined for the step Initial. For the subsequent steps this would be propagated.
ii) Next, go to Predefined field and make sure that only V3 has the required velocity input and V1 and V2 have 0. None of the rotation fields need to be defined. This also is defined for the Reference point and step Initial.

This was just an example. Depending on your Rigid body movement required make the changes. Try this and let me know if it works fine for you. All the best.

 

[Nileo2005]

Rigid bodies need to be told how to move with a constraint on the reference point, Load Module>Constraint, or told some info like mass and rotational inertias connected to the reference point so Abaqus can calculate its acceleration and what not on its own, assigned from property Module>Special>Inertias>Create.