A Critical Warning message in AFT xStream

Full Message text is:

The characteristic speed exceeded the maximum determined from estimated maximum pipe temperature and Mach number at X seconds, Pipe Y, Section Z.

 

This critical warning indicates that at some time during the simulation the characteristic speed exceeded the maximum characteristic speed, which is equivalent to the MOC grid section length divided by the time step. If this happens the solver in xStream will attempt to interpolate properties outside the MOC characteristic grid, which may introduce instability and inaccuracies to the solution.

The Estimated Maximum Pipe Temperature During Transient and/or the Estimated Maximum Pipe Mach Number During Transient in the Sectioning panel should be increased to increase the maximum characteristic speed.

For more information about the MOC solution, please refer to the Pipe Sectioning and Method of Characteristics pages. This warning message is generated when points R or L are outside of points 1 or 3 in Figure 1 on the Pipe Sectioning page.