Groundwater modelling with MicroFEM • Lesson 1A: A simple finite element grid


First a bit of explanation:


Text in bold means that your action is required.

Menu bar: Help / Info / About MicroFEM ... / [OK] means that you have to do a number of actions:
• Go to the Menu bar and click on "Help.
• Move to "Info" in the pull down menu.
• Click on "About MicroFEM ...".
• Click on the OK button to close the About box pop-up window.
This way you display the About box, so you can check the present MicroFEM version.


Any [text] between square brackets means that you have to click on a button.
Clicking means "Left clicking" (clicking with the left mouse button).



Double click the yellow MicroFEM icon.

A window opens with, from top to bottom:
– the blue title bar with the text "MicroFEM 4.10 LT"
– a Menu bar (Files, Project, View, .... etc. )
– a large black rectangle: "the Map"
– a grey Status line, with no information yet
– a Toolbar with only grey buttons, left and right
and at the right hand side: an empty Table.



Step 1: Create an extremely simple grid (mesh, network) of only six equilateral elements


Menu bar: Files / New grid ... / select Create New grid / Irregular boundary grid (FemGrid) / [OK]

Enter the Model name in the upper cell: "Lesson 1" / [OK]

Only the Model name is required, but you may enter more information (Project, Location, etc.). The pop-up window disappears and we are now in one of the two "Grid generation modes". At the right-hand side an empty table (with the tabs: Fixed nodes, Segments and Regions) has appeared. Also, in the lower left corner, a Toolbar with some coloured buttons has appeared.


Place the arrow cursor above each of these buttons one-by-one, and read the texts shown in the small yellow pop-up windows.

We call such texts the "hint" of a button. One button is much larger than the others. It shows the hint: "Next generation step (F8)".

Find the button with the text "Start with a hexagon (F5)".

I call this button "F5". Clicking on this button has the same effect as pressing the F5-key on the keyboard.


Toolbar: [F5] / [OK]

Toolbar: [F8] / [F8] / [F8] / [F8] / [F8] / [F8]

Note that each time we click on the F8 button (or press the F8 key), the text on this button changes. A simple finite element grid has been built on the map.

Click with the cursor on each of the seven nodes in the map and look at the table on the right hand side.

Click on the cells in the table and look at the corresponding nodes in the map.

How large is the grid from West to East? And from North to South?


Toolbar: [F9]

This saves all information of the generated grid to a Finite Element Network data file (a "fen-file"). We have finished with the grid in "Grid generation mode" and now can move on.


Toolbar: [F10] / [OK]

During this step we have to choose the number of aquifers of our model and accept the suggested number of aquifers = 1.






Intermission: Stop, save and start

This is the end of Lesson 1A. Suppose you would like to stop for today.


Menu bar: Files / Exit

A pop-up window appears with the question: "Do you want to save changes to Base model?".

Click [Yes]

This allows you to save a file "Lesson 1.fem". After that, a similar pop-up window will ask: "Do you want to save changes to Project? (Lesson 1.fpr)".

Click [Yes]


When you want to start again, there are different possible ways to continue:
– You can double-click the "Model 1.fpr" icon. The icon looks like a white paper with the MicroFEM logo.
– You can double-click the "Model 1.fem" icon. The icon looks similar, with a small blue 3D cube.
– You can double-click the "Model 1.fen" icon. The icon looks similar again, with a small red hexagon.

In all cases MicroFEM will be started.

The fpr-file (project file) tells MicroFEM to open all model files: in this case it is only the Base-model: "Lesson 1.fem".
A Base-model is a relatively simple model. All its data can be saved in a single file, the fem-file.
The fem-file (model file) contains data about the grid, transmissivities, heads, discharges, boundary conditions, etc. The fem-file information is always required, for any MicroFEM model.

Many MicroFEM models also require additional information, saved in additional files.
For example, transient models require Storage coefficients.

The fen-file (network file) only contains grid information. When you start with a fen-file you are asked to enter the number of aquifers of the model. A fen-file can also be used to repeat the grid generating process with modified data. In the latter case, the file must be loaded from the Menu bar:

Menu bar: Files / New grid ... / Open existing network file with / Appropriate generator / [OK] / Open

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