View source for OpenFOAM/C3/Unstructured-mesh-generation-using-Gmsh/English

Tutorial: Unstructured Mesh generation using GMSH


Script and Narration: Pavan Mehta


Keywords: Video tutorial, CFD, GMSH, unstructured mesh, curved lines, circular arc, ruled surface



{| style="border-spacing:0;"
| style="border-top:0.05pt solid #000000;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| <center>'''Visual Cue'''</center>
| style="border:0.05pt solid #000000;padding:0.0382in;"| <center>'''Narration'''</center>

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| Slide 1
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| Hello and welcome to the spoken tutorial on '''Unstructured Mesh generation using GMSH.'''

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| Slide 2: Learning Objective
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| In this tutorial we will learn to

* Create an '''unstructured mesh '''in '''GMSH'''
* Create plane''' surfaces'''
* Basic manipulations using the file with extension '''.geo'''



|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| Slide 3: System requirement 
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| To record this tutorial I am using 

* '''Ubuntu Linux Operating system 14.04''' 
* '''GMSH version 2.8.5'''
* '''OpenFOAM version 2.4.0''' 



|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| Slide 4: Pre-requisite
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| This tutorial is a continuation of:

Creation of sphere using GMSH


We have already learnt to create a sphere using GMSH earlier.


If you don't know how to do so, refer to the '''GMSH '''spoken tutorials in the '''OpenFOAM '''series on this website.

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| Slide 5: Sphere Geometry and Domain
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| Here is our problem statement.


This picture shows the flow direction and boundary faces.


We will now learn how to create an '''unstructured mesh '''using '''GMSH'''.

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| Slide 6: Points for Domain (slide)
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| Note that the size of the domain is 45 X 30 X 30, and the radius of the sphere is 1.


However, these dimensions can vary from problem to problem.


The points for the domain are as shown here.

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| Narration
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| Let us switch to '''GMSH '''now.


Here is the sphere we created earlier.

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| Pause recording and create the points and lines of the domain.
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| I have also created all the points and lines of the domain.


To create the points of the domain, kindly refer to the tutorial mentioned earlier.

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| Selecting the option plane surface


Using this option, selecting the edges
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| Now, select the option '''plane surface. '''


Then select the respective edges for the surface. The selection will be displayed in red.

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| Press '''E'''
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| Press '''E''' on the keyboard to execute the selection.


On doing so, we can see the dotted lines.

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| Pause recording and create all the surfaces.
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| Repeat the process until all surfaces are created.

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| Select''' Physical Groups '''>> Add >> '''surface'''
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| Now, select the option '''Physical Groups''', then '''Add''' and then '''surface.'''

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| Select the four faces for wall >> Press '''E'''
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| Now, select these four faces for the '''wall''' and press '''E '''on the keyboard.

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| Select the face for inlet >> Press '''E'''
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| Select the front face for '''inlet '''and press '''E. '''

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| Select the face for outlet >> Press '''E'''
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| Select the back face for''' outlet''' and press '''E. '''

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| Close '''GMSH'''
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| Now close '''GMSH.'''

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| Open sphere1.geo file >> go to the bottom 
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| Now, open the '''sphere1.geo '''file in '''gEdit Text Editor.'''


Note that there are additions to this file.


Also note that the identification numbers for the entities is in continuation of the earlier series.

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| Replace the numerical values to a variable d
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| As done earlier, replace the numerical values.


Use the letter''' d''' for the domain''' mesh''' variable.

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| Typing d = 0.5; at the beginning of the document
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| Then, at the beginning of the file type 

'''d = 0.5;'''

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| Narration
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| To name the boundaries, change the numerical value with your desired name, as demonstrated.

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| Replacing the integer with “wall”
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| The first physical surface, we made in the interface was '''wall'''.


So, here, we will replace it with '''wall.'''

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| Replacing the integer with “inlet”
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| The second physical surface, we made in the interface was '''inlet'''.


Hence, here, we will replace it with '''inlet.'''

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| Replacing the integer with “outlet”
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| The third physical surface, we made in the interface was '''outlet.'''


So, here, we will replace it with '''outlet.'''

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| Typing Surface Loop()={};


and highlighting
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| Now type''', Surface Loop''',''' ID''' which is the next integer in round brackets


equals the IDs of all surfaces of the domain in braces

which is 43, 45, 47, 49, 51 and 53

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| Typing Volume()={};


and highlighting
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| For definition of volume, use '''Volume, ID''' which is the next integer in round brackets


equals the IDs of the two surfaces in braces


Which is 29 and 56

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| Typing Physical Volume();


and highlighting
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| For physical volume, use '''Physical Volume''', '''ID''' which is the next integer in round brackets


equals the IDs of the volume in braces


which is 58

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| Save and close sphere1.geo
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| Save this file and close it.

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| In the terminal >> type '''gmsh sphere1.geo'''



| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| Now, using the terminal reopen '''GMSH '''by''' '''typing: 


'''gmsh sphere1.geo '''and press '''Enter'''

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| Narration
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| In '''GMSH''', a bottom to top approachis followed


* That is, first '''1D mesh''' is created
* Using '''1D mesh, 2D mesh '''is created
* Using '''2D mesh, 3D mesh''' is created



|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| 1D mesh creation, by pressing F1 key
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| For 1D mesh creation, press '''F1''' key.

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| 2D mesh creation, by pressing F2 key
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| For 2D mesh creation, press '''F2''' key.

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| 3D mesh creation, by pressing F3 key
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| For 3D mesh creation, press '''F3''' key.

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| Point to the status bar.
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| This may take a while. Watch the progress in the status bar.


It shows '''Done '''now.

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| 
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| Once the '''mesh '''is created, we need to optimize it 

to remove faulty cells.

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| Optimizing mesh using Optimize 3d Netgen option
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| For optimization click on Modules , then Mesh and then on '''Optimize 3d Netgen '''option

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| Point to the status bar.
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| This may also take a while.


Once again, watch the progress in the status bar.

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| Saving mesh and closing terminal
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| To save the '''mesh''' go to file, '''save mesh''' and close the '''terminal.'''

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| Slide 7: Importing mesh in OpenFOAM
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| Create '''OpenFOAM''' '''case''' directory without the '''constant '''folder


In the '''case''' directory, copy the newly created file '''sphere1.msh'''


Using the '''terminal''' window, go to the '''case''' directory of this problem.

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| Open a new terminal >> type '''gmshToFoam sphere.msh'''
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| Once you are in the '''case''' directory,


Type: '''gmshToFoam sphere1.msh '''and press '''Enter'''


To convert the '''mesh'''


Ensure that the same '''boundary names''' are there in the files of folder 0, before proceeding to the next step.

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| Slide 8: Summary 
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| Let us summarise. 

In this tutorial we have learnt to:


* Create an '''unstructured mesh '''in '''GMSH'''
* Create plane''' surfaces'''
* Basic manipulations using the file with''' '''extension''' .geo'''



|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| Slide 9: Assignment
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| As an assignment,


Make refinement in the''' mesh''' by changing the values of:


'''s, d '''and


'''Mesh.CharacteristicLengthFromCurvature'''

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| Slide 10: About FOSSEE 
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| '''OpenFOAM''' series is created by the '''FOSSEE Project, IIT Bombay'''. 


'''FOSSEE''' stands for Free and Open Source Software for Education. 


This project promotes the use of free and open source software tools. 


For more details, please visit: [http://fossee.in/ http://fossee.in/] 

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| Slide 11: About Spoken tutorials 



| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| The video at this link summarises the Spoken Tutorial project. 

Please download and watch it. 

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| Slide 12: 

About Spoken tutorials 



| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| The Spoken Tutorial Project Team conducts workshops and gives certificates on passing online tests. 

For more details, please write to us. 

|-
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:none;padding:0.0382in;"| Slide 13: Acknowledgement 
| style="border-top:none;border-bottom:0.05pt solid #000000;border-left:0.05pt solid #000000;border-right:0.05pt solid #000000;padding:0.0382in;"| Spoken Tutorial Project is funded by NMEICT, MHRD, Government of India. 

More information on this Mission is available at this link.


This is Pavan Mehta from FOSSEE Project, IIT BOMBAY signing off. 

Thanks for joining.

|}