How to make periodic boundary condition

Hamidreza Dehghani How to make periodic boundary condition
Email: dehghanihamid2@gmail.com
1- Mesh the model
2- Create a “mesh part”: in Mesh module from menu  Mesh  Create Mesh Part  OK
3- Convert Solid (Mesh) to Shell: in Mesh module from menu  Mesh  Edit…
4- Change the Element type to Surface : Fist Select all the Mesh Part Then in Mesh module from
menu  Mesh  Element type
Choose like below photo

5- Delete all the elements and nodes except one surface that you want to make periodic boundary
condition: in Mesh module from menu  Mesh  Edit…
Then choose all the elements that you want to delete
Take into account that still there are nodes that you should delete

Then delete nodes
You can select all and deselect the nodes that you need by holding Ctrl

6- Copy the surface that you have in other sides that you want to create boundary condition: in
Assembly module  Create instance  choose Fluid-Mesh-1 (the surface that you made)
In model tree in assembly hide the other model to see just the surface

Then, Instance  Radial pattern  select the surface  done  select axis: choose Z-axis
Then you can have them in X-Y plane by radial patter of the two surfaces in X-Z plane around X-axis

7- Put all the surfaces in one instance: Instance  Merge/Cut 

8- Create section and assign it to our Meshpart surfaces.
In property module  Material  Manager  Create…

Then, Section  Manager  Create…
Then, OK.

Note that it should be really weak compared to our original model because we do not want it to affect
our results.
Section  assignment manager  Create…
Ok.

9- Delete unnecessary sets: until now as you can see in the above photo we have 49 sets that just 7
of them are valid. The reason is that using several times of copy. So first it is better to delete
invalid sets: In part module you can delete them like in the following photo
10- Create necessary sets for Tie and Equation: we need to put each surface that we are made in
one Node set and also we need to create some Geometry sets from each surface in original
geometry corresponded with its mesh surface…
In assembly module  Tools  Set  Manager

You can choose any name that you want but in this file this name refers to a node set from our
Meshpart in the surface normal to X-axis and in positive part of X-axis
Continue this step and make one set for each surface of our meshpart.
Then we should make Geometry Sets from each surface of our original geometry corresponded
to our Meshpart surfaces to make Tie between them. To select surfaces in our original assembly
we can hide the Mesh-Part-1 and show the Fluid-1

Then again in assembly module  Tools  Set  Manager

Hold Ctrl key and deselect all the outer borders of the selected geometry to become like this:
Then make a Geometry set of one node (it is not important which one) and name it as “Node”.
We will use this set in future for a trick
In the end, we should have the sets like the highlighted ones in the following photo.

11- Tie the Meshpart surfaces to their corresponding surfaces in the original geometry:
Interaction module  constraint  manager  create..
Choose the Node Region:

In right hand side click on “sets…”
By checking the box of “Highlight selection in the viewport”, you will see the Set in the viewport
like the above photo.
Click on Continue.

Choose Node Region
Continue…
Normally, the stronger region should be the Master surface (like what we have done until here)
but the point is that as then in the Equation part the Meshpart surface will be the master
surface we should put it here as the Master as well because one region cannot be Master and
Slave in the same file…
By clicking on continue you will see the below window.

Click on Switch surfaces and then OK…
Do this for all sides and make all Ties like the ones that are highlighted in the following photo.
12- Create Equation constraints: Here we will make periodic boundary condition
Interaction module  constraint  manager  create…

This is what we want to create:
However, by clicking OK we will have and error:

Nevertheless, we know that it is possible to make Equation Constraints between two surfaces
that are equal (Equality here is the reason of making new meshpart surfaces). Therefore, we
should use a trick to do that…
In the second line, we choose a Set that we have made from a single Node. And make Equation
Constraints for all sides.

Do the same for other sides to have the following highlighted constraints:

13- Replace the Set “Node” in the second line with sets “meshpart-node-X- (or Y- or Z- in their
cases)”
To do that we need to make an input file (.INP) from this model and change it from there.
In Job module  Job  Manger  Create
Create one job with all the default setting:
Click on Write input
Go to the direction of work directory in windows and open the file ‘your job name’.inp (here it is
Fluidpart-periodicZ).
In that file find *Equation

Change the word “Node” with the couple of the first set in each one.

14- Run it: Open “Abaqus Commands”
write CD “the direction of edited input file” and click Enter
Then write: abaqus job=”the input file name”.inp inte and click Enter

How to make periodic boundary condition

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