Controls

*CONTROLS, FIELD=COUPLE, SOLVER=Solver_type, VOLUME COUPLING=Coupling_type,   UNDRAINED STIFFNESS=Calculation_of_undrained_stiffness

Optional Parameters

SOLVER

Defines the type of solver used for the coupled analysis. Valid values are:

- INCREMENTAL (Default)

- ITERATIVE

VOLUME COUPLING

Defines the algorithm used for the coupling of the Geomechanical and Porous Flow fields (how the volume strain is treated). Valid values are:

- UNDRAINED (Recommended for low permeability dominated problems)

- FIXED STRESS (Recommended for high permeability dominated problems)

For more information about the coupling algorithms see the Overview of Coupling Solution Strategies manual page.

UNDRAINED STIFFNESS

Defines the name of the volume strain update algorithm (how the undrained stiffness is treated) to be used in the coupling. Valid model names are:

- CONSTANT:  Constant stiffness (default if VOLUME COUPLING=UNDRAINED) In this case a constant undrained stiffness is used when computing the pore pressure change in the mechanical field. This assumption is very stable and is suitable for low permeability systems. For more freely draining systems however it may result in a significant difference between the intra-step pore pressure evaluation in the mechanical field and the actual pore pressure computed in the porous flow field. Consequently the "VARIABLE GROUP" method is generally recommended.

- VARIABLE GROUP:  Variable stiffness on Group Basis (Recommended) This method automatically computes an approximate undrained stiffness based on the average pore pressure change in the previous step in the porous flow field. This approximate undrained stiffness therefore accounts for the influence of drainage and results in intra-step pore pressure prediction in the mechanical field that is much closer to the true pore pressure change computed in the porous flow field. To improve stability a factor-of-safety is always applied to the approximate undrained stiffness.

- FIXED STRESS:  Fixed stress (default if VOLUME COUPLING=FIXED STRESS)

*CONTROLS, FIELD=COUPLE, SOLVER=INCREMENTAL, VOLUME COUPLING=UNDRAINED, UNDRAINED STIFFNESS=VARIABLE GROUP

1Coupling control data is defined for the current simulation stage

2Solver is set to incremental and coupling will be computed using the undrained coupling algorithm with the coupling stiffness being variable on group basis.

*CONTROLS, FIELD=DISPLACEMENT,  CRITICAL FACTOR=Value, POROUS FLOW=Porous_flow_type, SOLVER=Solver_type

Compulsory Parameters

POROUS FLOW

Defines the type of porous flow. Valid values are:

Optional Parameters

CRITICAL FACTOR

Defines the value for the critical time step scaling factor (Default value 0.9 for 2D problems, 0.7 for 3D problems). The explicit algorithm is conditionally stable and the time step used for the simulation should be smaller than the critical time step.  Practically, the critical time step can only be computed approximately and to ensure stability the time step is set to a factor times the critical value; i.e.

         Δt=Δtcrit·fcrit

where Δt is the time step used in the simulation, Δtcrit is the calculated critical time step and fcrit is the critical factor.

SOLVER

Selects the solver for the geomechanical field. Valid values are:

- EXPLICIT (Default)

- IMPLICIT (currently not available)

*CONTROLS, FIELD=DISPLACEMENT, CRITICAL FACTOR=0.7, POROUS FLOW=DRAINED, SOLVER=EXPLICIT

1Control data is provided for the geomechanical field.

2The critical time step factor is set to 0.7 (the critical time step computed from *TIME SCALING will be multiplied by 0.7).

3Porous flow type is set to drained.

4An explicit solver will be used to solve the geomechanical field.

*CONTROLS, FIELD=GLOBAL, DURATION=Value,  PLOT TIME=Value,  PLOT STEP=Value,  NUMBER PLOTS=Value,  SCREEN STEP=Value,  NUMBER SCREEN=Value,  RESTART TIME=Value, NUMBER RESTART=Value

Compulsory Parameters

DURATION

Defines the duration (time) of the current simulation Stage/Step.

Optional Parameters

PLOT TIME

Defines the duration (time) between two consecutive plot results outputs (Default: not used).

PLOT STEP

Defines the frequency (number of time steps) between two consecutive plot results outputs. If PLOT STEP=END a plot will be output at the end of the current simulation stage (Default: END).

NUMBER PLOTS

Defines the number of plot outputs to be performed during the current control stage (Default: not used).

SCREEN STEP

Defines the frequency (number of time steps) between two consecutive screen log outputs (analysis information written in the command prompt screen).

NUMBER SCREEN

Defines the number of screen outputs to be performed during the current control stage (Default: not used).

RESTART STEP

Defines the number of time steps between each restart output  If RESTART STEP=END a plot will be output at the end of the current simulation stage (Default: END).

RESTART TIME

Defines the duration (time) between two consecutive updates of the current simulation status to a restart file (Restart file output within a simulation stage/step). The generated restart file will be named as "Datafilename.rst". (Default: Output at end of step).

RESTART NUMBER

Defines the number of restart outputs to be performed during the current control stage. (Default: not used).

*CONTROLS, FIELD=GLOBAL, DURATION=2.0, PLOT TIME=0.3, PLOT STEP=-1, SCREEN STEP=1000, RESTART STEP=END

1Global control data is provided for the current simulation stage which has a duration of 2 Ma (problem units).

2A plot file will be output every 0.3 Ma.

3A plot file will be output at the end of the current simulation stage.

4Simulation information will be printed into the command prompt screen every 1000 steps.

5A restart file will be output at the end of the current simulation stage.

*CONTROLS, FIELD=PORE FLUID PRESSURE, TIME STEP=Time_step_value, NUMBER STEPS=Value,   GEOMECHANICAL FACTOR=Value

Optional Parameters

TIME STEP

Defines the value (size) for the porous flow time step. If not defined NUMBER STEPS must be defined instead.

NUMBER STEPS

Defines the number of time steps for the porous flow field to be used in the current control stage. If not defined TIME STEP must be defined instead.

GEOMECHANICAL FACTOR

If defined it automatically sets the mechanical time step (*TIME SCALING is not required) by specification of the ratio between the number of geomechanical time steps to the number of flow time steps (defined by either NUMBER STEPS or TIME STEP). The recommended value is problem dependent with larger values reducing dynamic effects at increased computational cost. It is recommended to use a minimum value of 100 mech steps per flow step.

*CONTROLS, FIELD=PORE FLUID PRESSURE, TIME STEP=0.02

1Global control data for Fluid Flow field is provided.

2The flow time step is set to 0.02 Ma (problem units).

*TIME SCALING, TYPE=OPTIMAL, TARGET TIME=1E-4

*CONTROLS, FIELD=DISPLACEMENT, CRITICAL FACTOR=0.7, POROUS FLOW=COUPLED, SOLVER=EXPLICIT

*CONTROLS, FIELD=PORE FLUID PRESSURE, GEOMECHANICAL FACTOR=100

1The mechanical time step is set to 0.0001 Ma (problem units) using *TIME SCALING keyword.

2The porous flow field is set to coupled in the geomechanical control data so that porous flow control data is required.

3A factor of 100 mechanical steps per flow step is defined in the porous flow control data. Consequently the porous flow step is set to 0.01 Ma (problem units).

*CONTROLS, FIELD=TEMPERATURE, TIME STEP=Time_step_value, NUMBER STEPS=Value

Optional Parameters

TIME STEP

Defines the value for the thermal flow time step. If not defined NUMBER STEPS must be defined instead.

NUMBER STEPS

Defines the number of steps to be used during the current stage for the thermal field. If not defined TIME STEP must be defined instead.