Q. I have encountered the following error message in a FLOTRAN analysis. What should I do about it?
*** ERROR ***
Coefficient matrix has a negative diagonal.
Probably indicates divergent solution.
VX Node= 1341.
A. The negative diagonal error occurs due to spatial oscillations in the solution associated with the advection method. Most often, this happens near an the Outlet, and in turn means that the outlet region is too close to regions where the flow is undergoing changes.
If it is not possible to change the problem domain, the best thing to do is to use Modified Inertial Relaxation (as per the section on Advection Discretization in the Fluids Analysis Guide). It can be applied to temperature, momentum (as in this case, since the error was reported for VX) and turbulence.
See the FLDA,MIR command. Appropriate values are between 0 and 1. It is best to use as low as possible a number, but using 1.0 should be okay. Try 0.5 and raise it if necessary. Note that you may have to apply this to turbulence as well.
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Q. I have encountered the following error message in a FLOTRAN analysis. What should I do about it? *** ERROR *** Coefficient matrix has a negative diagonal. Probably indicates divergent solution. VX Node= 1341. A. The negative diagonal error occurs due to spatial oscillations in the solution associated with the advection method. Most often, this happens near an the Outlet, and in turn means that the outlet region is too close to regions where the flow is undergoing changes. If it is not possible to change the problem domain, the best thing to do is to use Modified Inertial Relaxation (as per the section on Advection Discretization in the Fluids Analysis Guide). It can be applied to temperature, momentum (as in this case, since the error was reported for VX) and turbulence. See the FLDA,MIR command. Appropriate values are between 0 and 1. It is best to use as low as possible a number, but using 1.0 should be okay. Try 0.5 and raise it if necessary. Note that you may have to apply this to turbulence as well. |
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