What do you mean by flow input?

To answer your second, rather concerning, question...

A hydraulics program evaluates flow rates, friction losses, heat input/output, pumps, etc. They're used to size pumps, control valves, etc.

A stress analysis/flexibility analysis is performed after the system is laid out (all valve, equipment, etc known). It looks at the supports, piping materials, relevant pipe code, loads (equipment nozzle loads, PSV forces, seismic/wind, etc), and ensures the piping is routed/supported correctly so it should not fail.