Steady-state hydraulic models, such as WaterGEMS, simulate systems in which a dynamic equilibrium has been achieved and where changes in head or flow take minutes to hours. WaterGEMS can also solve such systems using a steady state run. In contrast, WaterGEMS also simulates hydraulic systems whose balance has been upset by rapid control-valve operation or other emergencies—all occurring in seconds or fractions of a second.

With HAMMER's added simulation power comes a higher computation cost, since many time steps must be calculated for a transient solution, using more complex equations to track dynamic changes systemwide. Fortunately, HAMMER automatically adjusts its solution method to minimize execution time, while delivering detailed and accurate solutions. HAMMER uses one or both of these algorithms:

Method of Characteristics (MOC) solution of the full continuity and momentum equations for a Newtonian fluid (i.e., elastic theory), which account for the fact that liquids are compressible and that pipe walls can expand under high pressures.

Differential equation solution of simpler momentum and continuity equations based on rigid-column theory, which assumes liquids are incompressible and pipes are rigid. This simpler method is not used by default.

HAMMER uses MOC system-wide for every simulation by default. The simpler, faster rigid-column algorithm can also applied in specific reaches for a few special applications if you enable this option. Although the MOC is preferred, due to its greater accuracy, both methods are described separately below.