# User:Mburton/HydroGeoSphere Simulation Control

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Many of the inputs required for a HydroGeoSphere simulation are configured in the *Simulation Control* dialog, which is accessed by right-clicking on the simulation in the Project Explorer. By default, HydroGeoSphere assumes saturated, steady-state flow that is solved using the control volume finite element method solved forward in time. This data can be left as is, or it can be changed in the *Simulation Control* dialog. Data input options include, but are not limited to: time stepping, output, zones, and initial conditions. The following is a full list of parameters available in the *Simulation Control* dialog.

## General Tab

The *General* tab in the *Simulation Control* dialog for the HydroGeoSphere model is where general settings for the input data on the other tabs of the *Simulation Control* dialog are defined. This tab gives GMS a general framework for the HydroGeoSphere simulation, the details of which can be refined on other tabs.

*Description*– This purpose of this textbox is to enter a description that will appear at the top of the grok file.*Transient flow*– This checkbox adds a time-stepping, transient flow solution.*Unsaturated*– This checkbox adds a variably-saturated flow solution.**Finite difference***Finite difference mode*– Uses the finite difference approach rather than default finite element method.*Control volume*– Uses the control-volume finite difference approach instead of the default standard finite difference approach. This option results in a conservative scheme with better numerical stability than the default approach.

**Domains***Porous media*– Include the porous media domain. This option is always on.*Surface flow*– Include the surface flow domain.*Dual nodes for surface flow*– Use the dual-node approach to define the discrete surface flow domain. This option is always on.

*ET*– Include the ET (evapotranspiration) domain.

## Units Tab

The default units in a HydroGeoSphere model are kilogram-metre-second. The *Units* tab in the *Simulation Control* dialog is where the units for mass, length, time, and the value for gravitational acceleration are defined.

**Units**– A dropdown menu that converts the default values into the specified system. It does not convert properties specified in any grok, porous media properties (.mprops), etc. files.*Kilogram-metre-second**Kilogram-metre-minute**Kilogram-metre-hour**Kilogram-metre-day**Kilogram-metre-year**Kilogram-centimetre-second**Kilogram-centimetre-minute**Kilogram-centimetre-hour**Kilogram-centimetre-day**Kilogram-centimetre-year*

**Gravitational acceleration**– Set a default gravitational acceleration value.

## Saturated Flow Tab

HydroGeoSphere defaults to saturated flow for the flow simulation. The *Saturated flow* tab of the *Simulation Control* dialog is where the default values for saturated flow can be modified.

*No fluid mass balance*– This checkbox suppresses the calculation of fluid mass balance information, which is, by default, computed at each time step.*Flow solver maximum iterations*– Maximum number of flow solver iterations, defaults to 2000.*Flow solver convergence criteria*– Flow solver convergence tolerance.*Flow solver detail*– Controls the level of detail of the solver performance. This defaults to 0 – no information, but can also be set to 1 – full information.

## Variably Saturated Flow Tab

The *Variably saturated flow* tab in the *Simulation Control* dialog of the HydroGeoSphere model is where the factors determining relative permeability are set. HydroGeoSphere defaults to the upstream weighting scheme with a factor value of 1.0.

*Upstream weighting factor*– Defaults to 1.0. This value should be in the range of 0.5 (central weighting) and 1.0 (upstream weighting).**Newton iteration parameters***Remove negative coefficients*– Forces negative inter-nodal conductance to zero.*No nodal flow check*– Turns off nodal flow check, which is on by default.*Nodal flow check tolerance*– Defaults to 10^{-2}. This is used to set constraints to the nodal flow error.*Underrelaxation factor*– Factor for the Newton iteration. This defaults to one, but can range from zero to one.

## Time Stepping Tab

The *Time stepping* tab of the *Simulation Control* dialog is where the time step values for the HydroGeoSphere model can be modified.

**General timestep settings***Initial time*– Defaults to 0. This can be used to index the times from an earlier run if the simulation needs to be restarted.*Initial timestep*– Used to assign a new value for the initial time step, which normally defaults to 0.01.*Maximum timestep*– Used to assign a new value as the maximum size for a time step. The maximum timestep defaults to 10^{25}.*Minimum timestep*– Used to assign a new value as the minimum size for a time step. This defaults to 10^{-10}. If the time step size is smaller than the default, HydroGeoSphere will stop.*Time varying maximum timestep*– This allows the creation of a table to create a dataset where the maximum time step will vary depending on the time unit.*Target times*– Allows for the creation of a list of target times to add to a current list of target times.*Minimum timestep multiplier*– Used to assign a new value for the minimum time step multiplier, which defaults to 0.5.*Maximum timestep multiplier*– Used to assign a new value for the maximum time step multiplier, which defaults to 2.*Jacobian epsilon*– The shift in the pressure head used to numerically compute the derivatives in the Jacobian matrix.*Minimum relaxation factor for convergence*– Defaults to 0.95. Convergence of the Newton iteration can only be achieved when the computed relaxation factor is larger than the minimum value.*Newton maximum iterations*– Defaults to 15. If this number is exceeded during a time step, then the current time step length is reduced by half and a new solution is attempted.*Newton minimum iterations*– Defaults to 0. Convergence of the Newton iteration can only be achieved only after it has performed the minimum number of iterations.*Newton absolute convergence criteria*– Defaults to 10^{-5}. Convergence of the Newton iteration in achieved when the maximum absolute nodal change in pressure head over the domain for one Newton iteration is less than this value.*Newton residual convergence criteria*– Defaults to 10^{-8}. Convergence of the Newton iteration is achieved when the maximum absolute nodal residual over the domain for one Newton iteration is less than this value.*Newton maximum update for head*– Defaults to 1.0. This value is used to calculate the underrelaxation factor in the equation.*Newton maximum update for depth*– Update equations are the same as those for "Newton maximum update for head", but are applied to water depth.*Newton absolute maximum residual*– If after any iteration of the Euclidean norm of the Newton residual exceeds this, then the Newton iteration is restarted with a smaller time step. by default this tolerance is set to zero, which is treated the same as infinity.*Newton maximum residual increase*– Defaults to 10^{30}. If after any iteration the Newton residual increases by a factor of more than this, then the Newton iteration is restarted with a smaller time step.

**Adaptive timestep settings***Head control*– Maximum allowed change in nodal head during any time step.*Water depth control*– Maximum allowed change in surface water depth during any time step.*Saturation control*– Maximum allowed change in nodal saturation during any time step.*Newton iteration control*– Maximum allowed change in Newton-Raphson iterations during any time step.

## Output Tab

The *Output* tab of the *Simulation Control* dialog is where a set of output times are added so that the HydroGeoSphere model knows to include them as part of the target time list.

*Output times*– listed items are added to the current set of output times.

## Zones Tab

Zones are used to assign material properties to elements in. Each element is assigned an ID number corelating with a specific zone. The *Zones* tab of the *Simulation Control* dialog is used to import data that contains certain element zone numbers for use in the HydroGeoSphere model.

*Read porous media zones from file*– Import a data set containing the element zone numbers for the porous media domain.*Read surface flow zones from file*– Import a data set containing the element zone numbers for the surface flow domain.*Read ET zones from file*– Import a data set containing the element zone numbers for the ET domain.

## Initial Conditions Tab

The *Initial conditions* tab of the *Simulation Control* dialog is where the initial head values for the HydroGeoSphere model are assigned. The iterative solver uses initial head values as a starting point for both steady-state and transient problems.

**Head***Initial head**Initial head depth to water table**Initial head surface elevation**Initial head from file*– Import an initial head value set from a file.

**Water depth***Initial water depth**Initial water depth from file*– Import an initial water depth value set from a file.