|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:email@example.com
|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.|