Factors influencing the CPU time

The CPU time required by a hydrodynamic simulation depends on the size of your model, on the number of time steps in your simulation, on which features you have specified for the simulation and on the general computational speed of your computer.

If you wish to estimate how a change in your specifications for a hydrody­namic simulation changes the CPU time required without specifying the model set-up and doing a verification, the following guidelines can be used:

·         The CPU time varies linearly with the number of water points (or compu­tational points) in the model.

·         The CPU time also varies linearly with the number of time steps, if flood­ing and drying is not selected. If this feature is selected the variation as a function of the number of time steps is only approximately linear.

·         The CPU time is increased by the factors listed below if the correspond­ing features are selected. The factor is relative to a simulation where no results are saved on disk and where none of the features are selected.

Factor   .

1.10:      Manning numbers applied instead of Chezy numbers.

1.15:   Flooding and drying.

1.25:   Saving the results in all grids for each time step.

If you wish to calculate the CPU time required by a simulation (in real CPU seconds, not elapsed seconds) the following formula can be used:

Number of time steps x Number of water points x Factors / BCS

where BCS (basic computational speed) is the number of water points which your computer processes in one CPU second. “Factors” refers to the factors listed above.