Artificial Transient - Initial pressure/flow conditions at Pipe X Station Y are not steady (Error = Z%)

A Critical Warning message in AFT Impulse.

Full Message Text

There are several variations of this message:

• Artificial Transient - Initial pressure conditions at Pipe X Station Y are not steady (Error = Z%)

• Artificial Transient - Initial flow conditions at Pipe X Station Y are not steady (Error = Z%)

Explanation

AFT Impulse detected an Artificial Transient in the model. A full explanation of Artificial Transients is found on the topic linked in the previous sentence, but in summary, it is a mismatch between the steady-state results and the "zero time step" of the transient simulation. The steady-state results are used to initialize the Method of Characteristics transient solution methodology. There will always be a mismatch due to the nature of the different solution methodologies; however, it should be within a small tolerance. In the case of this Critical Warning, the tolerance was exceeded. In general, Artificial Transients will affect your results, and you should be careful to understand what is happening.

Required Action

Read the Troubleshooting Artificial Transients topic and follow the steps in an effort to eliminate the Artificial Transient. Use engineering judgment to determine if the magnitude of error is acceptable.