OpenFOAM workshop 1 st November 2010 Postprocessing & the black art of scripting

OpenFOAM workshop1st November 2010Postprocessing & 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 • Can be very difficult to install correctly • NOT installed on Iridis

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

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 • 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 • 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 • 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 “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 • 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 • 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 • 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 • 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 • http://www.paraview.org/Wiki/ParaView • http://www.cfd-online.com/Forums/ • > paraview -? • Google !!!

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

OpenFOAM workshop 1 st November 2010 Postprocessing & the black art of scripting