OpenFOAM/C3/Introduction-to-SnappyHexMesh/English-timed
From Script | Spoken-Tutorial
| Time | Narration |
| 00:00 | Hello and welcome to the spoken tutorial on Introduction to snappyHexMesh in OpenFOAM. |
| 00:07 | In this tutorial, we will learn about
the parameters in snappyHexMesh to generate Mesh in OpenFOAM. |
| 00:14 | As a pre-requisite, the user requires:
Surface data files in STL format, located in constant/trisurface sub-directory of the case directory A domain with hex mesh snappyHexMeshDict dictionary located in the system sub-directory of case. |
| 00:35 | To record this tutorial, I am using:
Ubuntu Linux operating system 12.04 OpenFOAM version 2.2.2 ParaView version 3.12.0 |
| 00:50 | Let us learn to create a Mesh with the snappyHexMesh utility. |
| 00:55 | The steps are as follows-
Step 1 : Create a base mesh by using blockMesh utility Step 2 : Refine base mesh Step 3 : Remove unused cells Step 4 : Snap mesh to surface Step 5 : Add layers. |
| 01:18 | We will open the terminal and enter the path for flange as shown. Type: cd space OpenFOAM-2.2.2/tutorials/mesh/snappyHexMesh/flange and press Enter. |
| 01:40 | Now type "ls" and press Enter. There are two folders constant and system. |
| 01:50 | Type cd space system and press Enter. |
| 01:55 | Now type ls and press Enter. You can see snappyHexMeshDict file. |
| 02:04 | To view the contents of the file, type: -gedit space snappyHexMeshDict and press Enter.(Note that H, M and D here are in capital letters.) |
| 02:19 | This will open up the snappyHexMeshDict file. |
| 02:23 | snappyHexMeshDict file contains all the instructions and the entire process revolves around this file. |
| 02:32 | With the first rows of snappyHexMeshDict, you can activate or skip sections of the process. |
| 02:40 | In the geometry section, all active regions that take part in snappy process can be defined. |
| 02:50 | The parameters that govern the process of cell splitting are described in castellatedMeshControls section. |
| 02:58 | The parameters that are listed below are well explained in snappyHexMeshDict file. nCellsBetweenLevels defines the number of cells for each refinement level. |
| 03:12 | The higher it is, the more gradual the mesh will be. |
| 03:17 | In the Explicit feature edge refinement section, you can set specific refinement level for geometry’s feature edges. The ".eMesh" file can be obtained with the surfaceFeatureExtract utility. |
| 03:34 | In the surface-based refinement section, you can set the refinement levels of all surfaces defined in geometry file. |
| 03:45 | Mesh selection is a very important parameter. If the chosen point is inside the surface described in geometry file, then snappyHexMesh will create the internal mesh. |
| 03:59 | Otherwise, the external part (i.e. inside the blockMesh) is meshed. |
| 04:04 | The next step involves moving cell vertex points onto the surface geometry. |
| 04:12 | The snapping process is carried out by four parameters:
nSmoothPatch tolerance nSolveIter nRelaxIter. |
| 04:23 | These parameters control the number of iterations and tolerance between mesh and STL surface. |
| 04:32 | nSmoothPatch option specifies the number of times the exterior (that is the boundary wall) should be iterated. The mesh will become smoother if the number of iterations are more. |
| 04:46 | Tolerance option specifies the distance the program should look for a point to snap. The distance will be the number that is in tolerance. |
| 04:58 | nSolveIter option specifies the number of times the snapping part of snappyHexMesh should be run. |
| 05:07 | nRelaxIter option specifies the number of times the mesh should run a relaxing script, that removes bad mesh points. |
| 05:19 | The process of mesh layer addition involves shrinking the existing mesh from the boundary and inserting layers of cells. |
| 05:27 | The first group of parameters define the dimensions for layers and surface, on which they will be attached. |
| 05:36 | RelativeSizes option (that is true or false) changes the way to read the parameters given next.
true: next parameters define the layers' dimensions as parameters. false: next parameters define directly the layers' dimensions. |
| 05:55 | In layers option, you can define the number of layers and the patch on which to attach the layers. It must be an STL (Bold text) patch in geomery sub-menu, and not a user defined region. |
| 06:10 | ExpansionRatio parameters set the growth factor of the layers (that is ratio between two subsequent layers). |
| 06:19 | finalLayerThickness parameter sets the thickness of the last layer. minThickness parameter sets the minimum allowable thickness of layer. |
| 06:34 | Advanced settings is the second group of parameters. It contains more specific controls that can help in layer creation. |
| 06:45 | FeatureAngle is the angle above which the surface will not be extruded. |
| 06:52 | nRelaxIter option specifies the number of times the mesh will run a relaxing script. |
| 07:00 | maxFaceThicknessRatio option specifies the maximum allowable value of aspect ratio. |
| 07:10 | meshQualityControls parameter sets the minimum thresholds to generate mesh in snap and add-layers parts. |
| 07:18 | In 99% of the cases, it is better to leave the default values. But sometimes, you can deactivate one or more controls to force mesh generation. |
| 07:30 | These are the different parameters in snappyHexMeshDict. These parameters are important to generate mesh using snappyHexMesh utility. |
| 07:40 | Let us summarize. |
| 07:42 | In this tutorial, we learnt different parameters in snappyHexMesh to generate mesh in OpenFoam. |
| 07:50 | Watch the video available at this URL:
http://spoken-tutorial.org/What_is_a_Spoken_Tutorial It summarizes the Spoken Tutorial project. If you do not have good bandwidth, you can download and watch it. |
| 08:03 | The Spoken Tutorial Project team:
Conducts workshops using spoken tutorials. Gives certificates to those who pass an online test. For more details, please write to:contact@spoken-tutorial.org |
| 08:21 | Spoken Tutorials are part of Talk to a Teacher project. It is supported by the National Mission on Education through ICT, MHRD, Government of India.
More information on the same is available at following URL: http://spoken-tutorial.org/NMEICT-Intro |
| 08:37 | This is Chaitrali Ghodke from IIT Bombay, signing off. Thanks for joining. |
