Speeding up a steady-state solution

A number of techniques may be used to speed up solution convergence for steady-state runs.

If you find that your model has not converged, or is converging too slowly, you must first determine the cause of the problem:

• Specify Card 9 PRINT TRACE, PRINT ILUTRACE, and PRINT HYDTRACE Cards. These will at each iteration print a summary both to the screen and to the report log file, from which you will be able to determine whether your model is converging too slowly, or whether the solution is oscillating.
• Specify a Card 9 PRINT HFGROUP Card. This will print the values of each conductance and the elements it connects to the report log file. This is generally an extremely useful tool for model debugging.

If you find your solution is oscillating, try the following:

• If you have a very nonlinear model that is oscillating, try lowering the DT parameter to 0.3 or lower.
• If you have a hydraulic model that is oscillating, specify a low hydraulic damping parameter with Card 9 PARAM HYDDAMP.

Ill-conditioning may occur when the sum of the conductances of some elements is much larger than the conductances for the rest of the model. You can get the conductance sums from the PRINT HFGROUP printout to the report log file.

If your steady-state model is converging slowly, try increasing the DT parameter to 1.