By Jason McIntosh

Continued from part 1 – Making the most of Leapfrog for Flow Modelling.

Generate and evaluate a finite element grid

Finally to generate a FEFLOW model right click ‘Flow Models’ in the project tree and select ‘New 2D FEFLOW Model’. Set the element size and boundary from either a GIS line, polyline or a GM. Next expand the grid, right click ‘grid’ and select ‘New feature’. Within the dialogue add any ‘Point’, ‘Line’ or ‘Polygon’ features you wish to refine the grid with. Select ‘Simplify Feature’ to reduce or increase the number of points used for the boundary prisms. Next double click the grid, in the ‘Features’ tab and activate any features you wish to build detail around and the number of refinement steps. Within the ‘Boundary’ tab select either a rectangular boundary or a custom boundary by selecting ‘From another object’.

2D FEFLOW grid with refined cells about the collar locations.

2D FEFLOW grid with refined cells about the collar locations.

To generate a 3D FEFLOW model select ‘New FEFLOW model’ from the flow modeling folder then select the 2D FEFLOW grid and the GM from the ‘FEFLOW Grid:’ and ‘Gridding from’ menus. Within the same dialogue open ‘Select Layer Guides’ and select the GM layers that you wish to use to cut the cells horizontally.

To apply hydraulic parameters to the 3D FEFLOW grid right click the 3D FEFLOW model and select ‘Edit Material Types’. The GM used to define the lithologies can be changed within the material editor by choosing any GM from the ‘Evaluation:’ drop down list. Only models that have been evaluated on the grid are available. To evaluate models right click ‘grid’ within the project tree and select ‘Evaluations’. Within the same dialogue it’s possible to combine evaluations by selecting ‘Combined Evaluation’. In this case I combined the refined GM with the parent GM to add the additional parameter zones. 

Within the material editor select an interpolant for each lithologies corresponding parameter from the ‘Interpolant’ drop down list. Parameters may also be defined by a single value. The prisms are evaluated on the grid cell centroids with the interpolant value at each centroid location.

Interpolated aquifer drain/fillable porosity applied to FEFLOW grid.

Interpolated aquifer drain/fillable porosity applied to FEFLOW grid.

Finally insure the correct GM is set for export by selecting ‘Set Evaluation for Export’ from the model menu, then export the grid by selecting ‘Export to FEFLOW’ from the model menu. Next import the file into FEFLOW, all the main initial conditions are assigned to the grid. All that remains to be set are the well conditions, boundary conditions and the problem settings. In this case I have run a steady state saturated unconfined simulation to set the hydraulic head initial conditions and generate a streamline visualisation. And lastly a 365 day saturated unconfined transient simulation, both simulations were run with unconstrained head.

Forward random streamline travel time In FEFLOW.

Forward random streamline travel time In FEFLOW.

To visualize the simulation output time series in Leapfrog insure it’s recorded in ASCII format prior to running the simulation. To import the results into Leapfrog simply right click ‘Flow models’ and select ‘Import FEFLOW (ASCII dac) Results’. The initial steady state parameters, Phi, Psi and Theta are viewable on the grid. The simulation output time series are contained within the ‘Simulation Outputs’ folder. The timestep slider is located in the shape properties panel when any of the simulation outputs are viewed in scene.

Transient state simulation, hydraulic head time series 39 of 365 in Leapfrog.

Transient state simulation, hydraulic head time series 39 of 365 in Leapfrog.