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Old   July 22, 2008, 02:27
Default Questions about GROUND
  #1
mahe
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Hello everyone

When I read polis of 'the sructure of ground',I'm so puzzled about GROUND,GREX,GRND and the relationships between the GRND and GROUND. Could anyone tell me?

Thank you

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Old   July 22, 2008, 04:59
Default Re: Questions about GROUND
  #2
mike
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The PHOENICS CFD solver calls the FORTRAN subroutines GREX and GROUND at various points in the solution cycle. Subroutine GREX conatins the built-in physical models and boundary conditions, and Subroutine GROUND is where the user inserts FORTRAN coding for any non-standard physical models and/or boundary conditions.

GRND is a flag in the input file that instructs the PHOENICS CFD solver to access Subroutine GROUND so as to compute the quantity of interest specified by the user via FORTRAN coding in the appropriate Group & Section of GROUND. For example, setting RHO1=GRND in the Q1 input file means that the CFD solver will visist Group 9 Section 1 of GROUND so as to compute the the density of the first phase.
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Old   July 22, 2008, 06:02
Default Re: Questions about GROUND
  #3
mahe
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Dear mike Thank you for your response.However,There is still something which I don't understand clearly. setting RHO1=GRND in the Q1 input file means that the CFD solver will visist Group 9 Section 1 of GROUND so as to compute the the density of the first phase. However,in the polis ,it says that GROUND is a blank module in which users can insert their own coding.

If GROUND is a blank module,where does solver find it? in the GREX?

Waiting for you response.

Thank you
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Old   July 22, 2008, 06:37
Default Re: Questions about GROUND
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mike
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I don't really understand your question, but as I said in my earlier posting, GROUND is a user-accessible subroutine where the user inserts FORTRAN Coding for non-standard modelling and boundary conditions. Since there are no non-standard models in GROUND, it follows that GROUND is a blank subroutine in the sense that the user MUST insert the appropriate coding in the appropriate group and section of GROUND.

If you look inside the copy of GROUND provided on the installation (in the folder /PHOENICS/D_EARTH, as I recall) you will see that GROUND is a FORTRAN subroutine containing various groups and sections, and various computed GO TO statements that are used to direct the solver to the appropriate group and section, depending on the prevailing values of the INTEGER variables IGR and ISC.

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Old   August 7, 2008, 10:06
Default Re: Questions about GROUND
  #5
hervé
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If I understand well your comment.....

GROUND is not completely a BLANK module, for it is not an "empty" file. As a text file, I invite you to edit it and you will notice the presence of an existing full Fortran structure (i.e. full of "if" and loops coding). As you may notice, this fortran structure includes appropriate comments for the user, whose desire might be to ADD personnal Fortran commands to be integrated in the existing structure.

If nothing is ADDED by the user in the GROUND file, whilst the Q1 refers to it (for example, as Mike suggested, RHO1=GRND), the solver EARTH is likely to result in a failure as early as the very first iteration (the Fortran command being not found).

GREX has a structure pretty similar to the GROUND file, which it controls. "GREX" is also a short for "GRound EXample", which means that you can find great inspirations and/or simple tipps in the GREX commands to help your programming in GROUND.

Hope it helps a bit. Alternatively, you may like to consult the PLANT entry in POLIS to avoid the need of self FORTRAN coding in GROUND.

Also don't forget that, in either case, you need a recompilabe version of PHOENICS to perform these tasks.

Yours,
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