Verification Methodology

The AFT xStream software is a gas transient and steamhammer analysis product intended for use by trained engineers. As a technical software package, issues of quality and reliability of the technical data generated by the software are important. The following description summarizes the steps taken by Applied Flow Technology to ensure the high quality of the technical data.

1. Comparison with open literature examples

There are not many published examples for gas transient systems available for comparison with AFT xStream. However, AFT xStream has been compared to several published systems with known analytical solutions, including Sod's shock tube example and a pipe rupture case from Moody.

2. Transient solver checks for artificial transient to ensure true steady initial conditions

Before running the transient solution, AFT xStream always runs the MOC Steady solution with no transient boundary conditions in effect. It then compares the initial conditions to the MOC Steady calculation to see if significant differences exist. If so, a warning is generated.

3. Steady-state and transient solution at time zero are self checking

AFT xStream has two Solvers – one for the steady-state and one for the transient. They use two entirely different solution algorithms. First the AFT Arrow Steady Solver is run, and then the results are used to initialize the MOC Transient Solver. Before the transient solver is actually run, the MOC Steady solution is run. If the Arrow Steady and MOC Steady solutions disagree, a warning is generated. Thus if there were fundamental calculation errors in either method then an artificial transient would be generated and the user warned. This does not ensure all transient calculations afterward are correct, but does ensure that the fundamental transient equations are being properly represented.