Couple_control_data
Contents
Data Structure: Couple_control_data |
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"Coupled field Control Data" data structure |
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Couple_control_data NUM=ival where ival is the data structure number |
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Overview The Couple_control_data structure defines solution algorithm, output and termination data for the current stage for the multi-field coupled simulations. Both two and three field coupling can be performed and the primary data to be specified is the list of active field names ( Field_names ). Apart from the field names the majority of the data to control the time step, termination and output is defined in the control data for the primary field. The primary field is defined as: •Geomechanical field - if it is active, otherwise •Porous flow field - if it is active and Geomechanical field is not active, otherwise •Thermal field
By default a staggered incremental coupling scheme is used where each field is solved sequentially in the order
Thermal Field - > Porous Flow Field - > Geomechanical Field
Optionally an iterative algorithm can be used for the geomechanical/porous flow field ( Solution_algorithm =2). Iterative coupling can be either a fixed number of iterations, or based on a pore pressure convergence norm ( Pore_converge_tolerance)
Notes •Many of the parameters are set by default. The minimum data comprises the list of field names •By default all relevant data is passed between each field. Alternatively the specific data to be transferred may be specified using Transfer_data_mech, Transfer_data_flow and Transfer_data_therm •One data structure is required for the whole analysis
Examples demonstrating the usage of Couple_control_data include: •All multi-field coupling examples |
 | Solution_algorithm Solution algorithm for coupled field |
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Defines the solution algorithm for coupled field. Valid values are: • "Incremental" - Incremental coupling (Default) • "Iterative" - Iterative coupling
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| Volume_strain_coupling Flag denoting volume strain coupling algorithm |
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Three options for coupling the volumetric strain for coupled geomechanical/porous flow analysis are available: • "None" - No loading due to volume strain in the porous flow field • "Fixed_stress" - The fixed stress algorithm includes the effect of rock compressibility into the storativity term of the porous flow field which is updated prior to the geomechanical field. The volume loading term in the porous flow field is then defined by the total stress rate divided by the drained bulk modulus as opposed to the volume strain rate. The total stress rate is evaluated based on the values at time t. The fixed stress algorithm can be used with both the incremental and iterative solution strategies. For the iterative algorithm the total stress rate is evaluated at time t for the first iteration and subsequently the value for the previous iteration is used. • "Undrained" - The undrained algorithm solves the porous flow field first using the standard equations with the volume strain loading evaluated from the volume change. The geomechanical field is then solved assuming a locally undrained response leading to an increase in pore pressure. This local increase in pore pressure is then removed in the next step and replaced by the local increase in the next step. Consequently there is always a difference between the pore pressure in the mechanical field and the porous flow field. If the coupling steps become too large this difference can become large so care must be taken to ensure that the time steps are sufficiently small.
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| Pore_converge_tolerance Tolerance for pore pressure convergence |
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Defines the tolerance for pore pressure convergence. This is only used if iterative coupling for the geomechanical/porous flow fields is selected. If iterative coupling is active and the Pore_converge_tolerance is not defined then a fixed number of iterations will be performed corresponding to Maximum_number_iterations.
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| Undrained_pore_converge_tolerance Tolerance for pore pressure convergence for undrained analysis |
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Defines the tolerance for pore pressure convergence for undrained analysis. Defaults to Pore_converge_tolerance if not defined. Used with Pore_converge_tolerance if iterative coupling for the geomechanical/porous flow fields is selected.
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| Maximum_number_iterations Maximum number of iterations |
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Defines the maximum number of iterations for iterative coupling of the geomechanical and porous flow fields. If the pore pressure convergence tolerance is not specified then the number of iterations in each step is set to Maximum_number_iterations.
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| Field_names Active field names |
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Specifies the names of the active fields. Valid names are: • "Geomechanical" - Geomechanical field • "Porous_flow" - Porous flow field • "Thermal" - Thermal field
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| Volume_update_model Volume strain update algorithm |
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Defines the name of volume strain update algorithm to be used in the coupling. Valid model names are: • "Constant" - Constant stiffness (default if undrained algorithm). 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 "VariableGroup" method is generally recommended. • "VariableGroup" - 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 fixed stress algorithm).
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| Volume_update_data Data controlling volume strain update algorithm |
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Data controlling volume strain update algorithm for Volume_update_model type "VariableGroup". Three values are required: •Location 1 - Minimum scale factor for the bulk stiffness modulus (default 0.25, previously 0.01) •Location 2 - Maximum allowable change between coupling time steps (default 0.05, previously 0.2) •Location 3 - Safety factor to improve stability which must be >1 (default 1.5, previously 2.0)
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| Target_number_iterations Target optimal number of iterations |
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Target optimal number of iterations ( Ntarg) for an incremental analysis with variable time stepping. The target number of iterations is used to control the increment step size in simulations with variable increment size ( Solution_algorithm = 5) such that;
Δtnext(inc) =Δtcurr(inc)(Ncurr/Ntarg) where: Δtcurr(inc) is the current incremental time step, Δtnext(inc) is the next incremental time step and Ncurr is the number of iterations for the current step
Notes If Target_number_iterations = 0 (default) then a constant number of iterations will be used.
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