Hydraulic transient flow is also known as unsteady fluid flow. During a transient analysis, the fluid and system boundaries can be either elastic or inelastic:

Both branches of transient theory stem from the same governing equations. Bentley HAMMER CONNECT uses the more advanced elastic theory systemwide for virtually every simulation, but it can also switch to the faster rigid-column theory (in specific reaches and for special applications) to reduce execution time, as discussed in Rigid-Column Simulation.

The continuity equation and the momentum equation are needed to determine V and p in a one-dimensional flow system. Solving these two equations produces a theoretical result that usually corresponds quite closely to actual system measurements if the data and assumptions used to build the numerical model are valid. Transient analysis results that are not comparable with actual system measurements are generally caused by inappropriate system data (especially boundary conditions) and inappropriate assumptions.