POST PROCESSOR

APURVA PRAKASH
MUKUL GUPTA

Indian Institute of Technology - Kanpur


 


Contents

Motivation

There is a freeware software called Visual3, developed by MIT Fluid Dynamics Research Laboratory, for post processing purposes. This was used by Dr. Sanjay Mittal of Aerospace Dept. of IIT Kanpur. But the software had problems. Like it was not user friendly and required a lot of memory. Moreover it required workstations of high configurations like OpenGL, 128MB Ram, 24 bit Color monitor etc, which were not available in IITK. So he asked us to make a post processor which can help him in his research and will solve the above mentioned problems. Hence work for a 2D as well as 3D post processor started. Later on this post processor was also used by Dr. Gautam Biswas and Dr. K. Murlidhar of the Computational Fluid Dynamics Lab of Mechanical Dept. IIT Kanpur.
 
 

Introduction

Post Processor, as the name suggests, is a software for post processing purposes developed by Mukul and Me. This can perform functions like contour, isosurface, vector plotting, sectioning, volume rendering, etc. This takes in data of the domain in the form of a grid, which can be structured or unstructured, with triangular or quadrilateral elements in 2D and their equivalents in the 3D.
 
 

Example

Take an example of a square plate made of metal which is heated from below. Problem is to study the temperature distribution in the plate. The whole problem can be broken into three steps -
  • Pre Processing - In this step, problem is defined by working out the known and unknown variables. By deciding on the type of equations to be used etc. The important part of this step is to decide the domain and then distritize it, by generating a grid for it, either structured or unstructured.
  • Processing - The results are evaluated for the problem by solving the known equations like the heat equation or the Navier Stroke equation, using some well defined numerical method like the FEM or FDM etc. on the node points of the grid.
  • Post Processing - This step involves inspection and interpretation of the results, using some visual method for the purpose.

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    Methodology

    As already told, this post processor works on a domain which is discritized and a mesh has been generated for it. Then through any computational method like, finite element or finite volume, the domain has been solved.

    Hence the following three sets of data are already known

  • The grid node points - x,y and z.
  • The connectivity of grid elements.
  • The degree of freedom data like pressure, temperature etc. on node points.

    • The number of points, elements and number of degree of freedoms are also known.

    The grid can be following type

  • Structured grid

    •     - Body fitted geometry
        - Square geometry
  • Unstructured grid


    • The grid element can be of following two type

  • Parallelopiped (Quadilateral in 2D)
  • Tetrahedron (Triangle in 2D)


    • Seperate modules for contour plotting (on sectioned planes if in 3D),  isosurface (only in 3D), vector plotting, sectioning (in 3D), volume rendering (in 3D) and shading (on sectioned planes in 3D) etc. have been developed and can be called from the main module. Some very good algorithms have been developed for sectioning and volume rendering purposes.

    The final output is colored for which a color map can also be defined. But by default a color scheme with red for the maximum value and blue for the minimum value is used.
     
     

    Results

    Isosurfaces for two different values with lighting effects


     




    This code has been extensively used by us and others here in IIT Kanpur, for a period of two years now. Computational Fluid Dynamics Laboratories of both Aerospace as well as Mechanical Engineering have used this program. The results shown below have only been graphically simulated using this software by different people, but mostly by us. The results belong to different people who are either Professors or Ph.D. students in the above mentioned departments. The work has been split into seperate pages for the convinence.

    Have a look at these pages

  • Arun Kumar Saha, Dr. Gautam Biswas

    •    - 2D work
       - 3D work
  • Debashish Misra, Dr. K. Murlidhar

    •    - 3D work
  • P. K. Maji, Dr. Gautam Biswas

    •    - 3D work
  • Dr. Sanjay Mittal

    •    - 2D work
       - 3D work
     
     

    The Code

    We started to work on this project in second year at IIT Kanpur, and still we think we are only half way through. So you imagine how ambitious this project is.

    The code has been developed mostly in C language, but few parts are in C++ also. OpenGL has been used for graphics. We are able to compile and run the program on almost any platform, even on a PC with Linux using Mesa graphics, which is a clone of OpenGL and is a freeware.

    First we started with one version for both 2D and 3D. Later 2D and 3D version were seperated. 2D Version is now called 2Dpro and 3D Version is called postpro ( large RAM requirement, but fast ) and  smallpro ( small RAM requirement, but slow ).

    Soon we do plan to put the executables here on the Web, once the documentation for the code is ready.

    If you want a copy of the program email me at [email protected]
     
     

    Scope for Improvement

  • User Interface is not ready at the moment. Though pull down menus on mouse buttons are available. Very soon user interface will also be developed using either tcl/tk or glut libraries.
  • No documentation available for the software on how to use it or how to define the input etc. As the code will develop we do hope to write something for it.

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    References

  • MIT Fluid Dynamics Research Lab : http://raphael.mit.edu
  • OpenGL Official Website : http://www.sgi.com/software/opengl
  • Mesa Website : http://www.ssec.wisc.edu/~brianp/Mesa.html


    • This project was made by Mukul Gupta and Apurva Prakash  in the May, 1997. (Guide : Dr. Sanjay Mittal)
    This page was last updated on 16th November, 1998