OpenFOAM/C3/Introduction-to-SnappyHexMesh/English

Tutorial: Introduction to snappyHexMesh in OpenFOAM.

Script and Narration: Chaitrali Ghodke.

Keywords: Import STL file, background hex mesh, snappyHexMeshDict.

Visual Cue	Narration
Slide 1	Hello and welcome to the spoken tutorial on Introduction to snappyHexMesh in OpenFOAM.
Slide 2 : Learning Objectives	In this tutorial, we will learn about The parameters in snappyHexMesh to generate Mesh in OpenFOAM.
Slide 3: Pre-requisite	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
Slide 4: System Requirement	To record this tutorial, I am using Ubuntu Linux operating system 12.04 OpenFOAM version 2.2.2 ParaView version 3.12.0
Slide 5: Methodology for snappyHexMesh	Let us learn to create a Mesh with the snappyHexMesh utility. 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
Ctrl+Alt+t simultaneously Type cd OpenFOAM-2.2.2/tutorials/mesh/snappyHexMesh/flange	We will open the terminal and enter the path for flange as shown. Type cd OpenFOAM-2.2.2/tutorials/mesh/snappyHexMesh/flange and press Enter.
Type ls	Now type ls and press Enter. There are two folders constant and system.
Type cd system	Type cd space system and press Enter.
Type ls	Now type ls and press Enter. You can see snappyHexMeshDict file.
Type gedit snappyHexMeshDict	To view the contents of the file type - gedit snappyHexMeshDict and press Enter. (Note that H, M and D here are in capital letters.)
	This will open up the snappyHexMeshDict file.
Slide 5 :	snappyHexMeshDict file contains all the instructions and the entire process revolves around this file.
Activation rows	With the first rows of snappyHexMeshDict, you can activate or skip sections of the process.
Geometry	In the geometry section, all active regions that take part in snappy process can be defined.
castellatedMeshControls section.	The parameters that govern the process of cell splitting are described in castellatedMeshControls section.
CastellatedMeshControls	The parameters that are listed below are well explained in snappyHexMeshDict file.
nCellsBetweenLevels	nCellsBetweenLevels defines number of cells for each refinement level. The higher it is, the more gradual the mesh will be.
Explicit feature edge refinement	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.
Surface based refinement	In the surface-based refinement section, you can set the refinement levels of all surfaces defined in geometry file.
Mesh selection	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. Otherwise the external part (inside the blockMesh) is meshed.
	The next step involves moving cell vertex points onto the surface geometry.
SnapControls Settings for the snapping	The snapping process is carried out by four parameters: nSmoothPatch tolerance nSolveIter nRelaxIter These parameters control the number of iterations and tolerance between mesh and STL surface.
nSmoothPatch	nSmoothPatch option specifies the number of times the exterior (the boundary wall) should be iterated. The mesh will become smoother if the number of iterations are more.
tolerance	Tolerance option specifies the distance the program should look, for a point to snap. The distance will be the number that is in tolerance.
nSolveIter	nSolveIter option specifies the number of times the snapping part of snappyHexMesh should be run.
nRelaxIter	nRelaxIter option specifies the number of times the mesh should run a relaxing script, that removes bad mesh points.
addLayerControls	The process of mesh layer addition involves shrinking the existing mesh from the boundary and inserting layers of cells. The first group of parameters define the dimensions for layers and surface, on which they will be attached.
relativeSizes	RelativeSizes option (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.
layers	In layers option, you can define the number of layers and the patch on which to attach the layers. It must be anBold text STL patch in geomery sub-menu, and not a user defined region.
expansionRatio	ExpansionRatio parameters sets the growth factor of the layers (ratio between two subsequent layers).
finalLayerThickness	finalLayerThickness parameter sets the thickness of the last layer.
minThickness	minThickness parameter sets the minimum allowable thickness of layer.
Advanced settings	Advanced settings is the second group of parameters. It contains more specific controls that can help in layer creation.
featureAngle	FeatureAngle is the angle above which the surface will not be extruded.
nRelaxIter	nRelaxIter option specifies the number of times the mesh will run a relaxing script.
maxFaceThicknessRatio	maxFaceThicknessRatio option specifiess the maximum allowable value of aspect ratio.
meshQualityControls	meshQualityControls parameter sets the minimum thresholds to generate mesh in snap and add-layers parts. 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.
	These are the different parameters in snappyHexMeshDict. These parameters are important to generate mesh using snappyHexMesh utility.
	<PAUSE> Let us summarize.
Slide 6: Summary	In this tutorial we learnt : Different parameteres in snappyHexMesh to generate mesh in OpenFoam.
Slide 7: About Spoken tutorials	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.
Slide 8: About Spoken tutorials	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
Slide 9: Acknowledgement	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 link http://spoken-tutorial.org/NMEICT-Intro
About the contributor	This is Chaitrali Ghodke from IIT BOMBAY signing off. Thanks for joining.

Contributors and Content Editors

Chaitralighodke, Nancyvarkey