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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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

OpenFOAM workshop1st November 2010Postprocessing & the black art of scripting

Sandy Wright


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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