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convective flux exceeded stability limit!

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Old   January 10, 2019, 02:43
Default convective flux exceeded stability limit!
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Ebrahim Hamid
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Dear Flow3D users;

I run simulation with General Moving Objects option, after few seconds I get this message " convective flux exceeded stability limit" then the software start to re-estimate very long time to solve the problem. Suddenly the simulation ends and it dos not reach to the end of the time that I need.

Your help is highly appreciated.
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Old   February 19, 2019, 12:03
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Try setting up an initial time step (in numerics tab) much smaller than the time step you see in the simulation manager at t=0.
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Old   June 27, 2020, 17:12
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Use Solver Text Output to Diagnose Errors
1. Locate the Warnings & Errors button above the runtime plots. It means warnings are
2. After the meshblock mismatch errors discussed in There is one warning, which is displayed
Solver Messages:
convective flux exceeded stability limit
at t= 3.0009E-02 cycle= 1 iter= 51 delt= 3.0009E-02 mesh block 4
restarting cycle with smaller time step
maximum failure ratio = 2.26944E+00 is in x-coordinate direction
at cell ( 82, 34, 17) mesh block 4
3. The meaning is as follows:
a. At t = 0.03 seconds, a packet of fluid tried to move more than one cell at a time. The packet
probably accelerated unexpectedly, which is why the solver didn’t predict the velocity of the
packet. The stability limit is the requirement that fluid packets only move one cell per time
step. The solver takes care of the problem by restarting the time step with a smaller dt.
b. The error occurred in Mesh Block 4, the conforming block.
c. The offending cell number is i, j, k = 82, 34, 17. Remember that i,j,k values are block-specific,
while x,y,z values are global.
d. The problematic fluid packet was moving in the x-direction. In the next step you will find the
problem cell and identify why the problem occured.
4. Use the small X in the upper right corner of the dialog to close the Warnings & Errors.
5. Scroll up through the text output displayed below the plots and find the same warning. Notice
that the cell location and mesh block are not given in this summary.
6. Select Diagnostics > Solver Errors from the menu at the top of the screen: the same information
is displayed. Some errors report additional information to the Solver Errors file, so it should
always be checked.
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