A Warning message in AFT Arrow

The final network solution was not within tolerance for a local iteration. This was determined by AFT Arrow’s Auto-Detect feature. The Solver ignored this and continued on. If a network solution is obtained but this out of tolerance situation exists, AFT Arrow attempts the network solution again up to five times in a row. If the out of tolerance situation remains, AFT Arrow ceases further attempts and displays the convergence notification, then gives this warning in the output. The property can be any of several solver parameters and depends on the actual subroutine where the problem occurred.

Along with the warning, the Error value and Tolerance are displayed, along with a Code #. For AFT Arrow to consider this local iteration to be converged, the Error value needs to be less than the displayed Tolerance. This Tolerance is not the tolerance the user can specify in the Tolerance panel, but rather an internal “hard-wired” tolerance that has been set by the software developers and arrived at through experience. The Code # identifies the subroutine where the problem occurred. This information is not of  much assistance to the user, but can be of help to AFT technical support staff when troubleshooting models.

If the Error value is relatively close to the displayed Tolerance, it is generally safe to ignore this warning. If it is much larger, the remainder of the output is probably invalid.

In either case, changing the solution method in the Analysis Setup window frequently solves the problem.

Another potential cause of this warning is if an orifice junction is causing choked flow, but no CdA for Sonic Choking value is specified.