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# GENERAL

Defines options for the General subsurface flow mode.

## Options

- GAS_COMPONENT_FORMULA_WEIGHT <float>
- Specifies the molecular weight of the gas component in grams per mole.
- TWO_PHASE_ENERGY_DOF <string>
- Specifies the unknown solved for the energy degree of freedom. Options are: AIR_PRESSURE, TEMPERATURE.
- ISOTHERMAL
- Disables the energy calculation.
- NO_AIR
- Disables the gas component calculation.
- MAX_PRESSURE_CHANGE <float>
- Attempts to control subsequent time steps so that maximum pressure change is <float>.
- MAX_TEMPERATURE_CHANGE <float>
- Attempts to control subsequent time steps so that maximum temperature change is <float>.
- MAX_CONCENTRATION_CHANGE
- Attempts to control subsequent time steps so that maximum change in dissolved air mole fraction is <float>.
- MAX_SATURATION_CHANGE
- Attempts to control subsequent time steps so that maximum saturation change is <float>.
- SATURATION_CHANGE_LIMIT
- Not yet supported.
- PRESSURE_CHANGE_LIMIT
- Not yet supported.
- TEMPERATURE_CHANGE_LIMIT
- Not yet supported.
- MAX_CFL
- Maximum CFL permitted (local pore water velocity * dt / local grid spacing). Recommend setting to 1.0 for better convergence of Darcy fluxes. This limits flow distance to a single grid cell per time step.
- IMMISCIBLE
- Toggles on multiphase flow in a two-phase state without miscibility of phase components.

## Options that may improve convergence

### Notes

- ITOL refers to a tolerance based on an infinity norm: max|x
_{i}|

- MAX_ITERATION_BEFORE_DAMPING <integer>
- Specifies the threshold number of Newton iterations before damping is imposed.
- DAMPING_FACTOR <float>
- The scalar value by which the solution is damped once damping is imposed.
- MAXIMUM_PRESSURE_CHANGE <float>
- Truncates maximum pressure change in a Newton iteration. (Not to be confused with MAX_PRESSURE_CHANGE in OPTIONS of process model block.)
- WINDOW_EPSILON <float>
- Specifies the tolerance or window that must be exceeded before phase change will occur.
- ITOL_SCALED_RESIDUAL <float>
- Convergence based scaling the residual by the accumulation term: max|R
_{i}/A_{i}| < tolerance where A is approximately vol * por * sat * den * xmol / dt for phase mass conservation and vol * (por * sat * den * U + (1-por) * denrock * C_{p}* T) / dt for energy conservation**calculated at the previous time level (t)**. - ITOL_RELATIVE_UPDATE <float>
- Convergence based on relative update of primary dependent variables: max|dx
_{i}/X_{i}| - TOUGH2_ITOL_SCALED_RESIDUAL <float> <optional float>
- Similar to ITOL_SCALED_RESIDUAL except A
_{i}is**calculated at the previous Newton iteration**. The first float (e_{1}) is the tolerance.**Second optional float**(e_{2})**needs further explanation.** - NO_TEMP_DEPENDENT_DIFFUSION
- Turns off temperature-dependent diffusion coefficients.
- DIFFUSE_XMASS
- Diffusion is based on gradients in mass fraction, not mole fraction.
- HARMONIC_GAS_DIFFUSIVE_DENSITY
- Use harmonic distance weighted average for gas density in gas diffusion calculation.
- ARITHMETIC_GAS_DIFFUSIVE_DENSITY
- Use arithmetic average for gas density in gas diffusion calculation.
- ANALYTICAL_DERIVATIVES
- Turns on analytical derivatives.

## Examples

... PROCESS_MODELS SUBSURFACE_FLOW flow MODE GENERAL OPTIONS !WINDOW_EPSILON 1.d-4 ISOTHERMAL TWO_PHASE_ENERGY_DOF TEMPERATURE GAS_COMPONENT_FORMULA_WEIGHT 2.01588D0 ! kg/kmol MAXIMUM_PRESSURE_CHANGE 1.0D6 ! truncates pressure change / / / ...

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