Defining a circle 2

[JayZ900807]

Hello everyone.

Does anyone know how to define a circle (a face) in the input file. I have been able to define the basic shape of a semi-circle, but i am having difficulty with generating the nodes and elements.

Any help would be greatly appreciated

Thank You!

 

[vumat721]

Are you trying to create line elements? It's unclear what you are trying to accomplish...

 

[JayZ900807]

Hello

ultimately i would like to create a circular face with a mesh that converges in on the circle's centre.

Is this possible?

 

[vumat721]

You should be able to. Though you might find it easier to use CAE, rather than try to do it directly in the input file.

I would recommend working on 1/4 of the circle at a time by partitioning your circle with lines (i.e. from 9:00 to 3:00 and 12:00 to 6:00 in terms of a clock). Then you can apply a bias to the nodes along these lines so that there are more nodes near the center. Then mesh it...

 

[JayZ900807]

Hello
I need to be able to define the circle in the input file as i want to perform a parametric study.

I cannot do this in CAE, as otherwise this comes up as co-ordinate data in the input file, which is far more difficult for me to parameterize.

Do you know how to define a circle in the input file?

 

[vumat721]

If you want to mesh the face of a circle, you have to do it with coordinates. The automatic node creation in input files is only good along straight lines (i.e. shortest distance from Point A to Point B), it doesn't work along an arc between two points.

You could probably do what you need to do with some Abaqus python scripting

 

[JayZ900807]

Hi Vumat and thanx for your reply.

Your right. I will be doin my parametric study using python scripting. However i am not completely sure of how i would apply the mesh using co-ordinates. If it's not too much trouble, would you be able to explain this, by applying this to my input file? (which i have attached).

Many thanks in advance
Jay

 

[vumat721]

You will not use the built-in parameterizing functionality of Abaqus. You need to use a more manual parameterization method using Python. This is described in an example in the documentation: section "8.3 Investigating the skew sensitivity of shell elements" in the v6.8 Scripting User's Manual.

This example goes through all the steps of creating the model in CAE and parameterizing it. Once you run through that example, you'll have an idea about how to apply it to your model.

 

[vumat721]

Let me clarify.... In this situation, you don't have an input file, Abaqus/Python will automatically create it as you proceed through parameter iterations.

 

[JayZ900807]

Hello Vumat and thanks again for your reply.

So yes, i am first creating a 'user-defined input file', and i am using various examples (such as section "8.3 Investigating the skew sensitivity of shell elements") to help me acheive this.

I then want to parameterize this input file using the built-in parameterizing function of Abaqus. I already know how to parameterize the input file. The problem however is that i don't no how to define a circular face (and its mesh) in the 'user-defined input file'.

I hope this makes it clear of what i am tryin to acheive
Regards

 

[mrgoldthorpe]

*NGEN, LINE=C, NSET=NCIRC
<node_start>, <node_finish>, <node_step>, <node_centre>

 

[mrgoldthorpe]

..or perhaps

*NGEN, LINE=C, NSET=<node_centre>
<node_start>, <node_finish>, <node_step>, <node_centre>

 

[JayZ900807]

Hello Mr goldthorpe and thanks for your replies.

However, my real problem is that i don't no how to generate the elements incrementally for the circle.

Do you know how i could go about this? I know how to do this for squares, but i just cant do it for the circle!!

Thanks again an advance!

 

[vumat721]

(Apologies for not catching the node ngen for circles before!!! I'm so hooked on CAE now that I forget how things used to be done!)

Meshing a circle using Elgen and Ngen in the input file is very challenging (which you've already determined). I believe the only way to do it, is to tie a box inside the circle. The reason is that it's difficult to get the node numbering to work out for Elgen. Though somebody who is super tricky might get it to work (I was wrong before, so I might be wrong here!). There shouldn't be any issue with using a tie constraint. Attached is a quarter circle input file (and the new input file created with "abaqus j=temp parametercheck") which has the mesh density and radius parameterized. You could extrapolate this to a full circle with a bit more effort.


(An aside... If you don't want to do a tie, then you will likely have to use CAE and run your parameter study as in section 8.3 of the script users documentation. Note that this is very very very different (and much much more powerful) than the type of parameterization that you are trying to use which is outlined in "16.1.1 Scripting parametric studies" in the analysis documentation.... i.e. there are two ways to do parametric studies: 1) pure python with CAE, 2) input files with python (via psf file and *parameter in input file))

 

[JayZ900807]

Hello Vumat and thanks for your help.

Do you by any chance have the original input file? (not parameterized).

The thing is that i actually want to perform a parametric study on a cylinder rather then on a circle? If i am able to make a circle from your quarter circle example, then is it possible to extrapolate this to create a user defined cylinder?

If so, then do you know how I would need to define this in the input file?

Thank you again for all your advice and help

 

[vumat721]

The pes file is the "not parameterized" version of the input file.... If you want a cylinder, it's actually much easier! You don't need the box or the tie condition. You just need to define two arcs with ngen, use nfill to create the nodes between them, then use elgen to generate the elements. From there, yes, you can use more ngen,nfill, and elgen commands to extrude your face into a cylinder.

Study how the pes file creates the mesh (you can import it in into CAE using the Import Model command, and then turn on node and element labels).

 

[JayZ900807]

Thanks for your invaluabale advice again. You've been really helpful!!

I want to try extruding the quarter circle to give a quarter cylinder. However, i'm having difficulty in doing this as i'm unsure on how i would do the node numbering. Do you have any tips on how i could do this?

 

[vumat721]

This is how you could do it... There might be other ways. Create one face of the quarter circle. Let's say the nodes on that face are numbered 1 to 783 (I'm making this up). Now, let's say you want 20 layers of nodes from that face to the other end. Copy the face to end face with ncopy:

*Ncopy, old set=face1_name, change number=20000, new set=face2_name, shift
<offset in x-dir>,<offset in y-dir>,<offset in z-dir>

This has created the end face offset from the first face, and the node numbers are 20001 to 20783. Now, use nfill to create the layers of nodes in between

*Nfill
face1_nset, face2_nset, 19, 1000

This will create 19 layers of nodes. The first is numbered 1001-1783, the second 2001-2783, etc.


(I guess you want a solid cylinder? for some reason i thought you wanted a tube when you wrote cylinder )

 

[JayZ900807]

Hello Vumat and thanks again for the very helpful advice.

Yes that is correct, i am tryin to generate a cylinder. However, i want to generate a cylinder with a changing cross-sectional area. Do you have any advice on how i could do this?

 

[vumat721]

so you just want to change the diameter?