Abaqus Interaction, dont understand why this wont work 1

[garethsimons]

Hey,

I am currently doing research that involves using Abaqus to run simulations. The simulation I am running is for a skull model to impact a floor, unfortunately when I run the simulation the skull passes through the floor as if it wasn't there. I have got the model to work successfully using predefined fields set in the initial step with an encastre on the floor also set in the initial step. I now want to involve angular velocity so I need to use boundary conditions so I have supressed the predefined fields and created boundary conditions on the skull in a step called step1 I have also deleted the encastre on the floor in the initial step and created an encastre in step1. When the simulation is complete the skull passes through the floor and doesn't impact it, this is really frustrating as I can not understand why this happening, any help would be greatly appreciated.

 

[xerf]

You have to define a contact interaction between the surfaces which could potentially come in contact.

 

[garethsimons]

I have contact interactions defined and they work fine when the velocity on the model is defined as a pre-defined field but seems to ignore them when its switched to boundary conditions, is there something I need to change to the interaction? there defined in step1.

Thanks

 

[rstupplebeen]

What boundary conditions? If it is gravity and you are running Abaqus Standard then the model will travel infinitely far and miss the contact because of a rigid body motion because there is no inertia. Hope this helps.

Rob Stupplebeen

 

[garethsimons]

sorry about this, I'm not the best at describing things but I'll give it another go, the simulation is being run through Abaqus explicit, the set up when it works is:

-There are two parts, the floor and the skull model
-There are two steps defined: Initial and step1(created and dynamic explicit)
-There is 2 interactions created 1 is a general contact interaction set for step1 and the other is for the brain inside the skull and its interactions with the fluid around it also set for step1
-Floor encastre under boundary conditions
-There is also a rigid body constraint on the floor
-There is a predefined field for the skull set in the initial step, this is where its velocity is set currently at -3 in the z direction

This model works fine and gives good results i want to run this simulation the exact same except with angular velocity involved and from what I've been told I need to use boundary conditions on the skull, so I supressed the predefined field on the skull and created a velocity boundary condition on it, when I run the simulation like this the skull ignores the floor and passes through it.

Thanks for all your help so far, I really appreciate it.

 

[Nileo2005]

I'e had this problem before, alas I tried a few things before rerunning it when i fixed it, so I'm not quite sure which did the trick. I'd check:
1. You say you have created the interactions, but did you assign them correctly? With two different interactions I'd try createing a surface on each contact face, assign a trivial 'Global property assignment' under the 'Edit Interaction' menu and define 'Individual property assignments' to each interactions to be sure Abacus is defining and assigning correctly.
2. Assign an inertia property to the floor. Sometimes my models get finikey about this, so just apply some minute inertia like 1e-9 and ones in the rotational inertias.

Hope this helps. I know its not a brilliant fix or anything, but most of the time, for me anyway, its the little, overlooked stuff that cause the most problems...

 

[achilles03]

Can you attach or post the step-definition part of your input file? (i.e. all the interactions, surface definitions, interaction definitions, etc). That might help us identify the problem.

Dave

 

[samv1900]

I have had this problem, and I am still struggling to find a solution.

I cannot get two objects to collide in Abaqus. I am posting the file with two objects. A very helpful abaqus professional said that it is impacting, but I can't see it even if the time step is very very small. Since the first step itself i see the object moving in the opposite direction to where it is specified to move.

Else it just passes thru the other object. but, no contact whatsoever if the two objects are not initially brought in contact.

I have also posted this in the other thread:

http://www.eng-tips.com/viewthread.cfm?qid=235407&page=1

Any help greatly appreciated. File is uploaded.

Thanks
Sam

 

[samv1900]

Also:

garethsimons (Mechanical):

It's good that you see a contact. Gives me some hope that baqus can do my problem as well. Do you see the impact if you have a really realy mall step. Can you post the file, I just need to see what your set up is, although, I have almost the same set up, I dont see any impact between the 2 objects in my model. I have posted my file in the link above. Thanks for any help you can extend!

Sam

 

[samv1900]

Problem solved !

1. Abaqus has a hard time to simulate contact invlocing rigid bodies. If you can make really hard deformables then perform the analysis.

2. missing element property: create a set for the elements, then designate property.

Thank to all you guys and John!

Regards
Sam