How to model a liquid (water) / gas (foam or air) Fire Protection piping system in AutoPIPE?
AutoPIPE is concerned only with the integrity (Stress) design of the system against specific design codes for various loading conditions and is typical of most Pipe Stress programs. The additional built in fluid transient capability of AutoPIPE provides the fluid transient loads at direction/size changes for valve opening/closing events. It has a simplified pessimistic approach and calculates the Joukowski pressure surge for rapidly opening/closing valves and the dynamic effect as the pressure wave travels round through the piping system. It does not account for any complex flow conditions and has no reflected wave or multiphase capability.
Use the link to view the seminar to help explain the capability: http://pages.info.bentley.com/videos/?Filter=AutoPIPE. At this time AutoPIPE unable to handle this very complicated mixed condition of compressible (air) and incompressible (water) fluids by itself.
However, for AutoPIPE fluid transient to work the contents have to be either all fluid or all gas (i.e. single phase). This flow condition is something for a CFD problem for a complex fluid flow program like ANSYS, FlowMaster, PipeNet.
Fire protection systems are generally cold and have only weight and pressure considerations for analysis. Where systems are simple and hand calculations would suffice, users could also consider using AutoPIPE. Furthermore, If the CFD programs are used and can produce the time history inputs, then one could use AutoPIPE to perform a stress analysis on flow events.
Note, as of Feb 2020, AutoPIPE does not have any NFPA compliance piping codes. User's must select an piping code from the list of available codes. Some companies in the past have used AutoPIPE for designing fire protection ring mains and distribution lines for strength and structural integrity above and below ground.
Modeling approches
Bentley AutoPIPE