OpenFOAM/C3/Introduction-to-SnappyHexMesh/English-timed

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.

Contributors and Content Editors

PoojaMoolya, Pratik kamble, Sandhya.np14