openfoam workshop 1 st november 2010 postprocessing the black art of scripting
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OpenFOAM workshop 1 st November 2010 Postprocessing & the black art of scripting. Sandy Wright. Postprocessing. Paraview Open source, multi-platform Based on VTK toolkit http://www.paraview.org/ Can compile or download exe ParaFOAM Reads native FOAM formats

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postprocessing
Postprocessing
  • Paraview
    • Open source, multi-platform
    • Based on VTK toolkit
    • http://www.paraview.org/
    • Can compile or download exe
  • ParaFOAM
    • Reads native FOAM formats
    • Can be very difficult to install correctly
    • NOT installed on Iridis
the basics
The basics
  • Cell centred data v node centred
  • Filters
    • Colour by ..
    • Slice
    • Clip
    • Vectors (Glyphs)
    • Calculator
  • Save Data
customisation
Customisation
  • Custom filters (Tools->create custom filter)
  • State files (same can be achieved via python script)
  • Background images (Edit->View settings)
  • Customised colour maps
adaptability
Adaptability
  • Parallelisation (pvbatch can be run via mpi)
  • State files & filters platform independent (up to a point)
  • Server-client (ie store files on one machine, use graphics processing of the one in front of you)
  • Python scripting...
visualisation of cases on iridis
Visualisation of cases on iridis
  • Run paraview on iridis via X tunnelling/ exceed – slow for large models
  • Tar & Gzip ./VTK & processor*/VTK– large files (typically 1-2 GB when zipped)
  • Lower mesh resolution via mapFields– lose resolution, but v useful for quick viewing etc (and smooths out hot spots etc !!)
  • Extract and port surfaces only (100’s of MB only)
map fields
Map fields
  • Make new run dir (lets call it low_res)
  • Copy constant & system dirs to low_res dir
  • Make timestep folder (equiv to last time step of full solution) in low_res
  • Create / copy template field data files (eg U, p) in low_res/timestep
  • Create blockMeshDict of required density in low_res/constant/polyMesh
  • Create mapFieldsDict in low_res/system
  • blockMesh >> LOG-map_fields.txt
  • mapFields ../full_solution_dir -parallelSource -sourceTime 1803 >> LOG-map_fields.txt
scripting
Scripting

“A scripting language is a programming language that allows control of applications and the environment etc without requiring compilation.”

  • Unix/Linux
    • Bourne shell (aka Bash)
    • C shell
    • Others(Korn, mudsh, fish, scsh, pysh ...)
  • Python

“Python is an interpreted, object-oriented, high-level programming language with dynamic semantics”

shell scripts
Shell scripts
  • Basically a copy of what you would type on the command line, but...
    • Allows decision making (if/else)
    • Simple (e.g. arithmetic) operators
  • Why
    • Avoid mistakes in repetitive commands
    • Incorporation of command line exe’s leads to very powerful tools
    • Daisy chain different scripts together
  • Redirection (< > >>), standard streams (0,1,2...)
  • Example of openfoam running script
  • Example of ‘house keeping’ script
different shells
Different shells
  • Shebang ( #!/bin/bash )
  • Iridis is run on Bourne/Bash
  • Good practise
  • Why Bash
    • http://www.faqs.org/faqs/unix-faq/shell/csh-whynot/
    • Redirecting streams (eg stderr to stdout => 2>&1 )
  • Mix ‘n’ match
command line editors
Command line editors
  • Why ? Surely this went out with the punch card ....
    • Template script file
    • Repetitive searches in LARGE files
  • SED
    • sed \'s/yourword/myword/g\' infile >outfile
  • head
    • head –n 5 infile > outfile
python
Python
  • Easy to learn and readable
  • Object orientated
    • Libraries & routines out there to be used!
  • Lists
    • a = [\'spam\', \'eggs\', 100, 1234]
    • >>> a
      • [\'spam\', \'eggs\', 100, 1234]
    • >>> a[3]
      • 1234
  • For loops (note indenting)
      • for i in range(24):

Example of Paraview python script

resources
Resources
  • http://www.paraview.org/Wiki/ParaView
  • http://www.cfd-online.com/Forums/
  • > paraview -?
  • Google !!!
scripting resources
Scripting resources
  • http://www.python.org/
  • http://docs.python.org/tutorial/
  • http://docs.python.org/release/2.5.2/tut/tut.html
  • http://www.soton.ac.uk/~sesg3020/index.html
  • http://www.hypexr.org/bash_tutorial.php
  • http://tldp.org/LDP/abs/html/
  • http://www.eng.cam.ac.uk/help/tpl/unix/sed.html
  • http://www.grymoire.com/Unix/Sed.html
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