After calling the dialog window "Transport" the following input window appears:

 

Equation solver

For solving the equation system there are an iterative PCG solver and a direct Cholesky solver. For meshes of about 500 nodes or more, you should always choose the iterative one, because it is much faster. The error due to the iterative solution is always much smaller (less than 3%) than the other errors (e.g. measurement error). This can be verified with the help of the mass balance printed to the output file.

 

Equal concentrations for GLEI

This determines whether at nodes with the attribute GLEI also the equal concentrations should be calculated.

For nodes at which the equal potential heads have been defined, in transport calculations can be selected if the concentrations at this node are to be equated as well or if this is not desired. Equal concentrations at equal potential heads are useful at perfect wells (potential heads are equated over the height).

If there are large open water areas (lakes, with the equal potential heads) in the transport model, then the equating of the associated concentrations are interpreted as follows:

The incoming concentrations at the inflow boundary of the lake are transported directly to the outflow boundary of the lake without delay. If the concentrations are not equated, a transport takes place inside the lake. Since the velocities calculated in the elements within the lake is close to 0, this approach will lead to large numerical problems.

Basically, a transport model with a large open water area in the range of an expected mass spreading is only calculable with the present calculation methods under simplifying assumptions. That is, a flow and transport model for an aquifer is not suitable for the calculation of flow in surface waters.

 

Boundary conditions at intermediate point in time

If the calculation is done with a fixed time step size or diminished time steps of the transient input file, it is possible at the intermediate time steps, which are not regulated by the transient input file to interpolate transient boundary conditions for the concentrations.

 

Initial conditions

Here is defined with which initial concentrations the transient transport calculation is started:

No initial concentrations: The iteration is started with initial concentrations c₀= 0.0.

Using initial concentrations: The initial concentrations of the model file (attribute AKON) are used.

The transient calculation can be continued, if the corresponding null-file from the previous calculation exists (warm start). If the user wants to continue the actual calculation, the program has to create the corresponding file called out66. This is specified in the choice of output parameters (Save for continuing (out66) ).

 

Diffusion constant

Defining the molecular diffusion coefficient d_m in [m²/s].

 

Dispersivities

Defining transversal-horizontal (α_TH) and transversal-vertical (α_TV) dispersivities [m].

The scale refers to the longitudinal dispersivity, which is defined in the model file using the attribute DISP.

 

Extended: Adsorption