Specialist and rarely-used keywords¶
This grid section keyword allows to the user to change the gravity vector from its default value. However if the user attempts to initialize the problem using hydrostatic equilibration, and a non-default gravity value, the code will return an error.
GRAVITY <gx gy gz>: Specifies gravity vector components (default: 0. 0. -9.8068)
See example below, where the gravity effects are neglected
GRID TYPE structured ORIGIN 0.d0 0.d0 0.d0 GRAVITY 0.d0 0.d0 0.d0 NXYZ 500 1 100 BOUNDS 0.d0 0.0 0.0 250.d0 1.d0 50.d0 / END
This is only valid if mode is TOIL_IMS. If present, the following heuristic is executed in the nonlinear solver: if an update from the nonlinear solver would change a saturation value in a cell by more than 20% of its original value, then the update of that saturation value is set to change the value by 20%. Like most heuristics, it is not useful in every situation or model.
PFLOTRAN will aim to have no more than this value as the change in pressure each timestep, adapting the timestep length accordingly. In effect after a timestep where the pressure change exceeded this value, the timestep length will decrease, after a timestep where the pressure change was less than this value, the timestep length may increase if permitted by other factors. The default value is 5.0d5 Pa.