define a boundary condition to follow a sphere surface

[mountluoupc]

Hi there, I am new to Abaqus,and I'm modelling the interaction between a cylinder indenter and organ tissue of semi-sphere shape. I want the indenter follow and pressure the sphere surface. Is it possible to define a boundary condition to follow around the sphere surface at a constant velocity in one step? instead of creating several steps in which the indenter only moves by linear distance? Thanks.

 

[IRstuff]

Shouldn't you have posted this in the ABAQUS forum?

TTFN
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Need help writing a question or understanding a reply? forum1529

Of course I can. I can do anything. I can do absolutely anything. I'm an expert!

 

[mountluoupc]

Hi IRstuff, it is my first time to post in the forum... Any suggestions? Thanks.

 

[acspain]

mountluoupc,

1. Please provide a picture or sketch, this will enable better responses.
2. You will want to use contact pairs to deal with the interaction between your parts (assuming you don't already know this).
3. You can specify a cylindrical or spherical coordinate system, then use that coordinate system to specify your boundary condition which can be set to be velocities.

In case you are not aware, this sounds like it could be a difficult analysis to run once it is setup. Please make liberal use of the manuals as they will direct you on which switches to throw.

I hope this is helpful.

 

[mountluoupc]

Hi acspain,

Thanks for your reply and it is helpful.

1.I have attached the sketch (section view) of the organ tissue of semi-sphere shape to this post, hope it can help a bit. My task is to use a cylinder indenter to follow its surface(in global coordinates, its path is x^2+y^2=r^2,z=0).
2.you mean interactions like those with "frictionless" etc. properties? Yes, I have defined the frictionless interactions between the indenter and organ tissue.
3.I think your suggested method is what I want, but how can I specify a spherical coordinate system and define the boundary condition so that the indenter can do a sphere following? Can you reveal more details? Thanks.

 

[acspain]

mountluoupc,

1. Still somewhat confused, please add an isometric view of both parts in contact. My impression so far is that your indenter is coming down from the top (reference your recently added picture)and that the indenter is moving in a circular path with no height change.
2. Yes, but choosing frictionless will make your analysis harder to solve. Nothing in this world is frictionless, so adding a bit of friction will make a nod towards reality and make your analysis easier to solve. .05 would be a good starting point but feel free to experiment.
3. This is where I am going to send you to the documentation. First start with the Keywords manual and look up *Transform, this will provide a quick idea of how this card works. Then under the Reference in the *Transform entry, follow it to the User's Manual which will go in greater depth. From there you can follow additional references that will illustrate how to set it up in the GUI. It has been a while since I have used this card and I directly edited the input file to do so. The software and documentation has changed over the years and I don't want to send you down the wrong path.

Good luck.

 

[mountluoupc]

Hi acspain,

Thanks for your reply and patience.

1. I have uploaded one stretch of the intender-organ interaction to this post, and from the stretch you can also see the path of the indenter.
2. Thanks for your suggestion.
3. I'm still reading the manual you suggested and it is very useful. But I still have no idea how to use a local spherical coordinate system to define such a boundary condition...

http://mat1.uibk.ac.at/download/sti...rtat=pt01ch02s01aus09.html#usb-int-ptransform

Besides, I have another question which may sound naive. For now I am only working in the GUI of Abaqus, but you mentioned you can edit such values in input file. Can you tell me how to edit input file and what is its advantage? Many thanks.

 

[acspain]

mountluoupc

Ok, now I understand what you want to do.

Try the following; create a reference point at the center of your spherical part and couple (constraints) it to your indenter. Now create a boundary condition for the reference point with all degrees of freedom set to 0 except for the ur degree of freedom that will describe the rotation about the axis you want.

In your working folder is the input file (*.inp) this is the file that the solver uses to set up and solve the analysis. In previous releases of Abaqus, probably still today, there is functionality in the solver that has not made it into the GUI pre-processor yet. So the only way to use that functionality is to add it into the input file directly using a text editor such as VIM. Additionally if you are running the analysis on a server, you may need to physically move the input file to the server and the run the job from the command prompt. If there is a small error in the input file on the server, it is faster to edit the input file directly instead of through the GUI, then move the file again.

Have a good day!

 

[mountluoupc]

Hi acspain,

Many thanks for your advice! It works by using your method! Though I still don't know how it works in details... And the indenter stops at the top of the sphere due to some reason. I define many steps in which the indenter follow the sphere surface by 1 radian at each step, I don't know why it gets stuck at the top...

Thanks for your introduction to inp file and it really helps! I think I still have a lot of basic knowledge to learn...