1. WOLFSON UNIT OpenFOAM workshop 1 st November 2010 Postprocessing & the black art of scripting Sandy Wright

2. WOLFSON UNIT Postprocessing Paraview –Open source, multi-platform –Based on VTK toolkit –http://www.paraview.org/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

3. WOLFSON UNIT The basics Cell centred data v node centred Filters –Colour by.. –Slice –Clip –Vectors (Glyphs) –Calculator Save Data

4. WOLFSON UNIT Customisation Custom filters (Tools->create custom filter) State files (same can be achieved via python script) Background images (Edit->View settings) Customised colour maps

5. WOLFSON UNIT 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...

6. WOLFSON UNIT Visualisation of cases on iridis 1.Run paraview on iridis via X tunnelling/ exceed – slow for large models 2.Tar & Gzip./VTK & processor*/VTK– large files (typically 1-2 GB when zipped) 3.Lower mesh resolution via mapFields– lose resolution, but v useful for quick viewing etc (and smooths out hot spots etc !!) 4.Extract and port surfaces only (100’s of MB only)

7. WOLFSON UNIT 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

8. WOLFSON UNIT 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”

9. WOLFSON UNIT 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

10. WOLFSON UNIT 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/http://www.faqs.org/faqs/unix-faq/shell/csh-whynot/ –Redirecting streams (eg stderr to stdout => 2>&1 ) Mix ‘n’ match

11. WOLFSON UNIT 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

12. WOLFSON UNIT 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

13. WOLFSON UNIT Resources http://www.paraview.org/Wiki/ParaView http://www.cfd-online.com/Forums/ > paraview -? Google !!!

14. WOLFSON UNIT 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