Salome and cfMesh parametrization

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Edited by author.
Last edit: 00:59, 27 April 2016

I did a little research on combining cfMesh, Salome and OpenFoam to create completely free and Open-source CFD simulation. So I want to share my experiences and maybe somebody can give me some advice to correct me or use part of what I did. I tried to create parametric Ahmed body simulations and I had some success, so I created a little tutorial. I will explain how to create parametric geometries with Salome and meshes with cfMesh. All files explained in these thread can be downloaded from tutorials page: Parametric Ahmed body.

1 Salome geometry[edit]

First goal is to create completely automatic and parametric geometries. For that I used Salome and it's python scripting. For rest I used Bash scripting.

  • Create working directory (eg. ahmed) and inside it create directory named FoamSetup. In that directory place all OpenFoam case needed files and directories ("0", "constant" and "system" directories; all files in them controlDict, fvSolution, meshDict, RASProperties, p, U, ...).
  • Create python script template in Salome using GUI.
  • Run Salome and create geometries you need for simulation. Key is to GET SURFACES. VOLUMES ARE NOT NEEDED BUT YOU CAN USE THEM.
  • With volumes is easier to work with so use them to create flow domain
  • DO NOT DELETE AND REDO PARTS OF GEOMETRIES because numbering of faces will be wrong when python script is runned over and over. You will get bad geometries after.
  • Create groups of faces in a way you want to have patches in OpenFoam (Inlet, Outlet, ...).
  • Dump study to create python script.
  • Edit created python script
  • Here is presented python script for creating Ahmed bodies with different slant angles. All edited parts (from originally dumped script) are commented:
 ### This file is generated automatically by SALOME v7.4.0 with dump python functionality
 
 import sys 
 import salome 
 salome.salome_init() 
 theStudy = salome.myStudy 
 import salome_notebook 
 ### 
 ### GEOM component 
 ### 
 import GEOM 
 from salome.geom import geomBuilder
 
 # for solving math problems
 import math
 import SALOMEDS
 
 # library for checking and creating folders 
 import os.path
 
 # library for getting script path 
 import inspect 
 
 # get python script location/path 
 path = os.path.dirname(os.path.abspath(inspect.getfile(inspect.currentframe())))
 
 geompy = geomBuilder.New(theStudy) 
 O = geompy.MakeVertex(0, 0, 0) 
 OX = geompy.MakeVectorDXDYDZ(1, 0, 0) 
 OY = geompy.MakeVectorDXDYDZ(0, 1, 0) 
 OZ = geompy.MakeVectorDXDYDZ(0, 0, 1) 
 O_1 = geompy.MakeVertex(0, 0, 0) 
 OX_1 = geompy.MakeVectorDXDYDZ(1, 0, 0) 
 OY_1 = geompy.MakeVectorDXDYDZ(0, 1, 0) 
 OZ_1 = geompy.MakeVectorDXDYDZ(0, 0, 1) 
 Box_1 = geompy.MakeBoxDXDYDZ(9000, 4000, 2000) 
 geompy.TranslateDXDYDZ(Box_1, -2000, -2000, 0) 
 listSubShapeIDs = geompy.SubShapeAllIDs(Box_1, geompy.ShapeType["FACE"]) 
 listSubShapeIDs = geompy.SubShapeAllIDs(Box_1, geompy.ShapeType["FACE"]) 
 listSubShapeIDs = geompy.SubShapeAllIDs(Box_1, geompy.ShapeType["FACE"]) 
 listSubShapeIDs = geompy.SubShapeAllIDs(Box_1, geompy.ShapeType["FACE"]) 
 Inlet = geompy.CreateGroup(Box_1, geompy.ShapeType["FACE"]) 
 geompy.UnionIDs(Inlet, [3]) 
 Outlet = geompy.CreateGroup(Box_1, geompy.ShapeType["FACE"]) 
 geompy.UnionIDs(Outlet, [13]) 
 Bottom = geompy.CreateGroup(Box_1, geompy.ShapeType["FACE"]) 
 geompy.UnionIDs(Bottom, [31]) 
 Slip = geompy.CreateGroup(Box_1, geompy.ShapeType["FACE"]) 
 geompy.UnionIDs(Slip, [23, 27, 33]) 
 Box_2 = geompy.MakeBoxDXDYDZ(1044, 389, 288) 
 geompy.TranslateDXDYDZ(Box_2, 0, -194.5, 50) 
 Fillet_1 = geompy.MakeFillet(Box_2, 100, geompy.ShapeType["EDGE"], [5, 8, 10, 12]) 
 
 # Instead of pure dimensions put variable that is going to be changed/parametrized. In this case it is "Slant_angle".
 # Dimensions needed for chamfer are 2 lengths or angle in radians and length.
   # Here I have angle and length and I replaced them with equations with one unknown – "Slant_angle".
 Chamfer_1 = geompy.MakeChamferEdgeAD(Fillet_1, math.cos(Slant_angle*(math.pi/180))*222, Slant_angle*(math.pi/180), 46, 54) 
 
 # Get Id's of all faces that make ahmed body; in this case ahmed body is called "Chamfer_1" (Salomes automated naming could change faces numbers)	 
 Ids = geompy.SubShapeAllIDs(Chamfer_1,geompy.ShapeType["FACE"]) 
 
 Ahmed = geompy.CreateGroup(Chamfer_1, geompy.ShapeType["FACE"]) 
 
 # Create group Ahmed from collected faces above
 geompy.UnionIDs(Ahmed, Ids) 
 
 geompy.addToStudy( O, 'O' ) 
 geompy.addToStudy( OX, 'OX' ) 
 geompy.addToStudy( OY, 'OY' ) 
 geompy.addToStudy( OZ, 'OZ' ) 
 geompy.addToStudy( O_1, 'O' ) 
 geompy.addToStudy( OX_1, 'OX' ) 
 geompy.addToStudy( OY_1, 'OY' ) 
 geompy.addToStudy( OZ_1, 'OZ' ) 
 geompy.addToStudy( Box_1, 'Box_1' ) 
 geompy.addToStudyInFather( Box_1, Inlet, 'Inlet' ) 
 geompy.addToStudyInFather( Box_1, Outlet, 'Outlet' ) 
 geompy.addToStudyInFather( Box_1, Bottom, 'Bottom' ) 
 geompy.addToStudyInFather( Box_1, Slip, 'Slip' ) 
 geompy.addToStudy( Box_2, 'Box_2' ) 
 geompy.addToStudy( Fillet_1, 'Fillet_1' ) 
 geompy.addToStudy( Chamfer_1, 'Chamfer_1' ) 
 geompy.addToStudyInFather( Chamfer_1, Ahmed, 'Ahmed' ) 
 if salome.sg.hasDesktop(): 
   salome.sg.updateObjBrowser(1) 
 
 # Export the geometries as .stl files to folder defined in variable "path" at beginning 
 geompy.Export(Ahmed, "%s/Ahmed.stl" % path, "STL_ASCII") 
 geompy.Export(Bottom, "%s/Bottom.stl" % path, "STL_ASCII") 
 geompy.Export(Inlet, "%s/Inlet.stl" % path, "STL_ASCII") 
 geompy.Export(Outlet, "%s/Outlet.stl" % path, "STL_ASCII") 
 geompy.Export(Slip, "%s/Slip.stl" % path, "STL_ASCII")

2 BASH script for installing temporary Salome session[edit]

  • In created working directory, create Bash script named "salomePythonScriptReader" (or whatever you wish to call it)
  • Add first part of script which installs temporary Salome session to working folder:
 #!/bin/bash 
 # how to run it: ./[PATH]/salomePythonScriptReader ./[PATH]/PYTHON_SCRIPT_NAME.py
 # in ahmed example to start script you need to execute it: ./ahmed/salomePythonScriptReader ./ahmed/ahmed.py
 
 # get path to base case folder and python script (/home/...../ahmed) 
 scriptPath=$(cd `dirname "$1"` && pwd) # path to salomePythonScriptReader script
 casePath=$(cd `dirname "${BASH_SOURCE[0]}"` && pwd) # path to ahmed.py python script
 pythonScriptNameExt=$(basename $1) # get name of python script. It will be ahmed.py
 pythonScriptName=`echo "$pythonScriptNameExt" | cut -f1 -d'.'` # remove file extension from name of python script. It will be just ahmed
 
 # remove directory SalomeSession if it exist in working directory 
 if [ -d "$casePath/SalomeSession" ]; then 
     rm  -r $casePath/SalomeSession 
 fi 
 
 # to install Salome TUI session in working directory you need path to files "appli_gen.py" and "config_appli.xml".
 # next 2 lines of code searches user directory ~/ for Salome installation. 
 # ON FIRST RUN IT WILL TAKE SOME TIME (MINUTE OR TWO) afterwards only a second or two!
 # path to "appli_gen.py" python script and "config_appli.xml" can be manually setup by commenting "find" command and entering path on your own.
 appliPath=$(find ~/ \( ! -wholename *Trash* \) -wholename *bin/salome/appli_gen.py -print -quit) 
 configPath=$(dirname $appliPath) 
 
 # start Salomes python script to install temporary Salome session to working folder
 python $appliPath --verbose --prefix=$casePath/SalomeSession --config=$configPath/config_appli.xml
 
 #start Salome session in TUI 
 source ${casePath}/SalomeSession/runAppli -t 

3 BASH script for running created temporary Salome session in loop[edit]

After the part for installing temporary Salome session to working directory we need to change and run python script over and over (in a loop). Append this part to created bash script to run session and python scripts in parametric way:

 # uncomment this block for PARAMETRIC salome session (: <<'PARAMETRIC' is just bash block commenting)
 #: <<'PARAMETRIC' 
 
 # "Slant_angle" is variable in python script "ahmed.py" (created above as example) that is changing.
   #"pythonValues" is array of values which will be substituted in python script.
 pythonVariable="Slant_angle" 
 pythonValues=(25 35) # for this example it will be array of slant angles for ahmed body.
 
 # for loop:
   # reads python script and finds string "Slant_angle"
   # changes string "Slant_angle" to values defined in "pythonValues" (25, 35)
   # runs Salome session executing changed python script 
 for i in "${pythonValues[@]}" 
 do 
     # remove case directories if they exist 
     if [ -d "${pythonScriptName}_$i" ]; then 
         rm  -r ${pythonScriptName}_$i 
     fi 
 
     # create case directories with names as combination of python script name and "pythonValue". In this example directories will be "ahmed_25", "ahmed_35"
     mkdir -p $casePath/${pythonScriptName}_$i/constant/triSruface 
 
     # copy OpenFoam case files and directories, from "FoamSetup" directory, to each generated case directory
     cp -r $casePath/FoamSetup/* $casePath/${pythonScriptName}_$i 
 
     # copy new Salome python script to case directory. In this example ahmed.py will be copied and named ahmed_25.py
     cp $scriptPath/$pythonScriptNameExt $casePath/${pythonScriptName}_$i/${pythonScriptName}_$i.py	 
 
     # change string "Slant_angle" with array values (25, 35) 
     sed -i "s/$pythonVariable/$i/g" $casePath/${pythonScriptName}_$i/${pythonScriptName}_$i.py 
 
     # run Salome session and python script 
     cd $casePath/SalomeSession 
     ./runSession python $casePath/${pythonScriptName}_$i/${pythonScriptName}_$i.py 
 
     # move generated .stl files to directory "triSurface" 
     mv $casePath/${pythonScriptName}_$i/*.stl $casePath/${pythonScriptName}_$i/constant/triSruface 
 done 
 
 # terminate salome sessions (with "killSalome.py" python script located in the same directory as "appli_gen.py") and delete directory "SalomeSession" 
 killPath=$configPath 
 python $killPath/killSalome.py 
 rm  -r $casePath/SalomeSession 
 
 # end part of bash block commenting
 #PARAMETRIC

4 BASH script for running created temporary Salome session only ones[edit]

This part is for nonparametric running of python script. It does same thing like parametric one except it only goes trough script ones. Append it to bash script instead of parametric one if want to use it (or insert both of them and comment out one you don't want to use). Since code is similar to parametric one it is not as thoroughly explained.

 # uncomment this block for NONPARAMETRIC salome session
 #: <<'NON_PARAMETRIC' 
 
 # run Salome session and read python script 
 if [ -d "case_${pythonScriptName}" ]; then 
     rm  -r case_${pythonScriptName} 
 fi 
 mkdir -p $casePath/case_${pythonScriptName}/constant/triSurface 
 cp -r $casePath/FoamSetup/* $casePath/case_${pythonScriptName} 
 
 # run python script 
 cd $casePath/SalomeSession 
 ./runSession python ${scriptPath}/${pythonScriptNameExt} 
 
 # move .stl files to "triSurface" directory 
 mv ${scriptPath}/*.stl ${casePath}/case_${pythonScriptName}/constant/triSurface 
 
 # terminate salome sessions and delete directory "SalomeSession" 
 killPath=$configPath 
 python $killPath/killSalome.py 
 rm  -r $casePath/SalomeSession 
 
 #NON_PARAMETRIC 

5 Preparation of created boundary .stl files for cfMesh[edit]

After creating geometry boundary .stl files it is time to mesh the domain. Although it is not implemented in bash script it can be added very easily, because even meshing can be done automatically now thanks to Creative Fields, Ltd. and their free cfMesh.

First we need to prepare created .stl files for meshing with cfMesh. Each .stl file represent one patch, so to create closed domain all patches have to be combined in to one “big” .stl file. One thing you have to be careful about is to set patches names in new combined .stl file.

Example is shown for Bottom.stl file in Ahmed geometry. Bottom.stl file looks like this:

 solid 
  facet normal  0.000000e+00  0.000000e+00 -1.000000e+00 
    outer loop 
      vertex -2.000000e+03 -2.000000e+03  0.000000e+00 
      vertex -2.000000e+03  2.000000e+03  0.000000e+00 
      vertex  7.000000e+03  2.000000e+03  0.000000e+00 
    endloop 
  endfacet 
  facet normal  0.000000e+00  0.000000e+00 -1.000000e+00 
    outer loop 
      vertex  7.000000e+03 -2.000000e+03  0.000000e+00 
      vertex -2.000000e+03 -2.000000e+03  0.000000e+00 
      vertex  7.000000e+03  2.000000e+03  0.000000e+00 
    endloop 
  endfacet 
 endsolid

When all .stl files are combined together, part for patch Bottom should look like this:

 ….
  endfacet 
 endsolid Inlet
 solid Bottom
  facet normal  0.000000e+00  0.000000e+00 -1.000000e+00 
    outer loop 
      vertex -2.000000e+03 -2.000000e+03  0.000000e+00 
      vertex -2.000000e+03  2.000000e+03  0.000000e+00 
      vertex  7.000000e+03  2.000000e+03  0.000000e+00 
    endloop 
  endfacet 
  facet normal  0.000000e+00  0.000000e+00 -1.000000e+00 
    outer loop 
      vertex  7.000000e+03 -2.000000e+03  0.000000e+00 
      vertex -2.000000e+03 -2.000000e+03  0.000000e+00 
      vertex  7.000000e+03  2.000000e+03  0.000000e+00 
    endloop 
  endfacet 
 endsolid Bottom
 solid Outlet
 ….

For that purpose I have written little bash script I called "stlCombine" which combines .stl files and outputs "mergedStl.stl" file.


EDIT: On OSX head command with -1 option doesn't work so change that line from tail -n +2 $file | head -n -1 >> $outputPath/mergedStl.stl to tail -n +2 $file | tail -r | tail -n +1 | tail -r >> $outputPath/mergedStl.stl

 #!/bin/bash 
 # how to run it: ./stlCombine [PATH TO DIRECTORY WITH .stl FILES] [PATH TO OUTPUT DIRECTORY] 
 # example with ahmed is ./stlCombine ./ahmed/ahmed_25/constant/triSurface ./ahmed/ahmed_25
 
 # get .stl files location/path specified with running script (from example ./ahmed/ahmed_25/constant/triSurface) 
 filePath=$(cd $1 && pwd) 
 # get merged file output location/path specified with running script (from example ./ahmed/ahmed_25)
 outputPath=$(cd $2 && pwd) 
 
 # check if file mergedStl.stl exists. If it does delete it. 
 if [ -f $filesPath/mergedStl.stl ] 
 then 
     rm $filesPath/mergedStl.stl 
 fi 
 
 # remove all temporary files from input directory (where .stl files are located) 
 if [ -d "$filePath/*~" ]; then 
     rm $filePath/*~ 
 fi 
 
 # add patch name: 
   # change first and last line of every file in input location from solid to solid [.stl FILE NAME] and from endsolid to endsolid [.stl FILE NAME]
   # merge them together
 # example is from "solid" to "solid Bottom" and from "endsolid" to "endsolid Bottom" 
 for file in $filePath/*.stl 
 do 
     # get .stl file name
     fileName=`basename $file` 
     # remove .stl file extension
     patchName=`echo "$fileName" | cut -f1 -d'.'` 
     
     # append line solid [.stl FILE NAME] (eg. solid Bottom ) to file mergedStl.stl
     echo "solid $patchName" >> $outputPath/mergedStl.stl
     
     # copy all lines except first and last one from loaded .stl file and append them to mergedStl.stl
     tail -n +2 $file | head -n -1 >> $outputPath/mergedStl.stl 
     
     # append line endsolid [.stl FILE NAME] (eg. endsolid Bottom ) to file mergedStl.stl
     echo "endsolid $patchName" >> $outputPath/mergedStl.stl 
 done

6 Running cfMesh[edit]

Setting up mesh dictionary (meshDict) for cfMesh is easy and very good explained in its documentation (cfMesh documentation) and tutorials. Running stlCombine and cfMesh (after generating geometries and case directories with explained bash script "salomePythonScriptReader") is simple and those few commands can be appended to script "salomePythonScriptReader". Now we have completely automatized geometries and mesh generation. If you decide to go step further, It is possible to append OpenFoam commends to bash script "salomePythonScriptReader" and run simulations on created cases.

There are few guidlines that are needed to be followed when using cfMesh. Read about them in thread: cfMesh tips & tricks

7 Tips[edit]

When I created first few meshes, cfMesh created hole where Ahmed body is. Something like in the picture on the right.

cfMesh error

My first guess was, that happened because patch Ahmed in .stl file had face vectors pointing in wrong direction (because they were created from another volume in Salome). Vectors are defined in .stl file as "facet normal [VECTOR VALUES]". It can be seen in Bottom.stl in 2. line ("facet normal 0.000000e+00 0.000000e+00 -1.000000e+00"). At that point I have written another bash script that rotates face vectors in .stl file. After I finished script I realized it is not necessary. Face vectors weren't problem to cfMesh. The problem was mesh was set to coarse. Afterwards I realized IF cfMesh DOES SOMETHING THAT YOU DIDN'T WANT (LIKE THAT HOLE I SHOWED OR DOESN'T REFINE MESH IN SOME SPECIFIED AREA) PROBLEM IS IN meshDict AND REFINEMENT SETTINGS. If somebody has some other experiences please do share. :)

Still I will put here that vector rotating script. Maybe someone will find it handy for something else.

 #!/bin/bash 
 # how to run it: ./vectorRotation [PATH TO .stl FILE] (eg. ./vectorRotation ./mergedStl.stl)
 
 # get file name and location 
 filePath=$(cd `dirname "$1"` && pwd) 
 # get file name with extension
 fileNameExt=$(basename $1) 
 # get the file name without extension
 fileName=`echo "$fileNameExt" | cut -f1 -d'.'` 
 
 # remove inverted file if it already exist 
 if [ -f $filePath/inverted$fileNameExt ]; then 
     rm $filePath/inverted$fileNameExt 
 fi 
 
 # read file line by line 
 while read line 
 do 
     # check if line has string facet normal	 
     if  "$line" == *"facet normal"*  
     then 
         # if it has, extract vector coordinates 
         x[1]=$(echo "$line" | awk -F' ' '{print $3}') 
         x[2]=$(echo "$line" | awk -F' ' '{print $4}') 
         x[3]=$(echo "$line" | awk -F' ' '{print $5}') 
         # rotate vector coordinates 
         i=0 
         # go trough x array created one step above 
         for num in "${x[@]}" 
         do 
             i=$[$i +1] 
             # check if number is negative
             if  $num == -*  
             then 
                 # if truth remove first number character (that is minus sign)
                 x[i]=${x[$i]#?} 
             else 
                 # if false prepend minus sign to number
                 x[i]="-${num}" 
             fi 
         done 
         # reconstruct line with new numbers 
         ortLine=" facet normal " 
         # append numbers to first string facet normal
         for string in "${x[@]}"		 
         do 
             ortLine="$ortLine $string" 
         done; 
         # push reconstructed line to inverted .stl file
         echo "$ortLine" >> $filePath/inverted$fileNameExt 
     else 
         # if the line doesn't have string facet normal push the line to inverted .stl file
         echo "$line" >> $filePath/inverted$fileNameExt 
     fi 
 done < $1 
 
 # remove .stl extension from original file (so it is invisible to other scripts) 
 mv $filePath/$fileNameExt $filePath/$fileName
Kruno (talk)11:54, 18 July 2014

Hi Kruno, great work, thanks for the effort.

Could you provide a minimal working case that does what you want ? I think I can help with Salome and cfmesh, but I'd like to see the whole thing as one block instead of several parts.

Cheers.

Ben

Bennn (talk)18:19, 11 August 2014

Hi Ben, Thank you. Sorry for not responding but I wasn't aware of your message. I didn't log on to wikki and I didn't get a notification on email about your message. I just created tutorial file and I will put it online. Sorry for delay ones again.

Best regards, Kruno

Kruno (talk)00:59, 23 September 2014