# non-linear BC and source

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 October 22, 2005, 00:34 non-linear BC and source #1 Murali Guest   Posts: n/a Hi, Does anybody know how to program a non-linear boundary condition for a user-defined scalar ? Consider this example: d^c dc --- + (--)^2 = 0 dx^2 dx With boundary condition: @x=0 C=0 dC @x=1 -- = C^2 -----> Non- linear boundary condition dx The analytical solution of this is : e(1-exp(-x)) ------------ (e-1)^2 SORSCA with POSDAT works fine for modeling source terms. But how to model a non-linear BC ? It seems to be not working through BCDEFW and POSDAT. I tried to put it as source in the last cell, but it fails too. Please let me know.

 October 22, 2005, 06:37 Re: non-linear BC and source #2 DenizeN Guest   Posts: n/a But what is you problem ? Howe are you set the BC ? And what is not working ?

 October 22, 2005, 13:18 Re: non-linear BC and source #3 Murali Guest   Posts: n/a My problem is as follows: BCDEFW is the subroutine where we set user defined scalar value. since my boundary condition is non-linear I have to use POSDAT to calculate the non-linear value and pass this value to BCDEFW. i.e in BCDEFW I would have some code like: Code in POSDAT: =============== COMMON /MYSCALAR/SCALVAL IF (IBND .EQ. -42) THEN SCALVAL = T(ICELL,1+1)^2 END IF (IBND is the boundary number) Code in BCDEFW: ============== COMMON /MYSCALAR/SCALVAL IF (IBSTAR .EQ. 42) THEN SCALAR(01) = SCALVAL END IF The SCALVAL is originally calcualted using POSDAT at level 1 and passed by COMMON block to BCDEFW. SOmehow, this does not seem to yield proper results (convergence is attained though). Is there anything more to do when I write non-linear boundary conditions ?

 October 24, 2005, 13:49 Re: non-linear BC and source #4 DenizeN Guest   Posts: n/a Whay You are not write: Code in BCDEFW: ============== COMMON /MYSCALAR/SCALVAL IF (IBSTAR .EQ. 42) THEN SCALAR(01) = TC^2 END IF or something else like this ? why you use POSDAT ? what function you want to calculate ? may be you write what are you want to do. You must set function on boundary type f(Temperature) ?

 October 25, 2005, 18:01 Re: non-linear BC and source #5 Murali Guest   Posts: n/a Dear Denizen, When I tried that it is always diverging. Can you do a favor ? Can you just send me a small (working) example of STAR-CD subroutine code where you have succesfully implemented a non-linear Bouncary condition. say for example dc/dx = c^2 please ? It will be must appreciated.

 October 27, 2005, 07:29 Re: non-linear BC and source #6 DenizeN Guest   Posts: n/a I have'not prepeared code to you situation. But i do not see any problem to calculfnt you BC. Code in BCDEFW: ============== COMMON /MYSCALAR/SCALVAL IF (IBSTAR .EQ. 42) THEN SCALAR(01) = e(1-exp(-x))/(e-1)^2 END IF but you are must set offset to you BC this analitical solution means x=from 0 to .... but you BC is located somwhere x=from 45.54 to 99.34 ensure that it is all fine

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