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

WOLFSON UNIT

OpenFOAM workshop1st November 2010

Postprocessing & the black art of scripting

Sandy Wright

WOLFSON UNIT

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

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The basics

• Cell centred data v node centred• Filters

– Colour by ..– Slice– Clip– Vectors (Glyphs)– Calculator

• Save Data

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Customisation

• Custom filters (Tools->create custom filter)

• State files (same can be achieved via python script)

• Background images (Edit->View settings)

• Customised colour maps

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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...

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Visualisation of cases on iridis1. Run paraview on iridis via X tunnelling/ exceed –

slow for large models2. 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)

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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

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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”

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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

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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

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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

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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

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Resources• http://www.paraview.org/Wiki/ParaView

• http://www.cfd-online.com/Forums/

• > paraview -?

• Google !!!

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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