Autodesk Simulation Mechanical and Multiphysics

[#1]

Here's another problem I hope you guys can help me out with.

So I'm running a coupled steady state fluid/thermal simulation.

It stops during the first load case with the following statement:

 ****
 **** Iteration starts for velocity and temperature updates 
 ****
 

 For Buoyancy Force ::   LC No. =    2          Total No. of Intvs =    1 
 ------------------------------------------------------------------------ 
 Current      No.        Load  Turbulent  Max. No.  Convergence Tolerance
 Intv No.  Steps   Multiplier      Model    Iters      (Temp.)     (Vel.) 
       1       8    1.00e+000        off      500    1.00e-003  1.00e-003
 ------------------------------------------------------------------------ 

 Intv No.  Step No.  Iter. No.  Euc. Norm (Vel.)   Euc. Norm (Temp.) 
       1         1          1     Rlx =  0.200        Rlx =  0.200  


 **** Error: Failed in invoking the process: C:\PROGRA~1\Autodesk\SIMULA~1\FRUN03.EXE 

There are no errors or warnings in ANY of the other log files.

There is the following, though, but I don't know what it means:

    1     1  1.250E-01   0.00  1.250E-01  1           2   |R/F|u =   5.8E-07c
    1     1  1.250E-01   0.00  1.250E-01  1           2   |R/F|v =   3.8E-07c
    1     1  1.250E-01   0.00  1.250E-01  1           2   |R/F|w =   7.6E-08c
 **** Non-positive diagonal entry detected in ILU method
      switch to SSOR Preconditioner
    1     1  1.250E-01   0.00  1.250E-01  1          50   |R/F|p =   2.1E+00 
    1     1  1.250E-01   0.00  1.250E-01  1         100   |R/F|p =   2.0E+00 
    1     1  1.250E-01   0.00  1.250E-01  1         150   |R/F|p =   2.1E+00 
    1     1  1.250E-01   0.00  1.250E-01  1         200   |R/F|p =   2.3E+00 
    1     1  1.250E-01   0.00  1.250E-01  1         250   |R/F|p =   2.4E+00 
    1     1  1.250E-01   0.00  1.250E-01  1         300   |R/F|p =   2.8E+00 
    1     1  1.250E-01   0.00  1.250E-01  1         350   |R/F|p =   2.9E+00 
    1     1  1.250E-01   0.00  1.250E-01  1         400   |R/F|p =   2.9E+00 
    1     1  1.250E-01   0.00  1.250E-01  1         450   |R/F|p =   3.4E+00 
    1     1  1.250E-01   0.00  1.250E-01  1         500   |R/F|p =   3.6E+00 
    1     1  1.250E-01   0.00  1.250E-01  1         550   |R/F|p =   3.8E+00 
    1     1  1.250E-01   0.00  1.250E-01  1         600   |R/F|p =   4.1E+00 
    1     1  1.250E-01   0.00  1.250E-01  1         650   |R/F|p =   4.2E+00 
    1     1  1.250E-01   0.00  1.250E-01  1         700   |R/F|p =   4.5E+00 
    1     1  1.250E-01   0.00  1.250E-01  1         750   |R/F|p =   4.7E+00 
    1     1  1.250E-01   0.00  1.250E-01  1         800   |R/F|p =   4.9E+00 
    1     1  1.250E-01   0.00  1.250E-01  1         850   |R/F|p =   5.2E+00 
    1     1  1.250E-01   0.00  1.250E-01  1         900   |R/F|p =   5.2E+00 
    1     1  1.250E-01   0.00  1.250E-01  1         950   |R/F|p =   5.4E+00 
    1     1  1.250E-01   0.00  1.250E-01  1        1000   |R/F|p =   5.8E+00 
    1     1  1.250E-01   0.00  1.250E-01  1        1001   |R/F|p =   5.8E+00m

Somebody?  Anybody?

I've tried changing load cases, I've tried changing the meshing...  But without some clue as to what the problem is, I'm stuck.

[#2]

Anyone??  Anyone??

More information:  If I run the simulations uncoupled, they work fine.  (Albeit I don't know if I can trust the uncoupled results given the wonky results I posted in another thread.)

I still get the "Non-positive diagonal entry detected in ILU method switch to SSOR Preconditioner" notice, but who knows what that means.

[#3]

Hi,

I would just like to share with you what I know as I had experienced something like this a few months back. 

FRUN would be the fluid solver. The failure would mean that the solver crashed. This might be due to the setup  of the analysis. Try changing the fluid boundary conditions or maybe increase the iterations for the ramp up of the fluid boundary conditions. If it doesn't work, try performing a transient analysis.

Regards

Ilyas

[#4]

Hi Ilyas,

Thanks for the suggestions; I'll give them a try.  Right now I'm running uncoupled and it appears to be working.  I'll give the coupled a shot later.  Since the solver runs uncoupled, I thought it might be an interface problem where the output from the command line routines was being misinterpreted.  I tried running FRUN03 from the command line so I could see the output myself, but I didn't know the input parameters and haven't figured out what file to point it to, yet.

Thanks,

Todd