|Groundwater modelling with MicroFEM • Lesson 7A: Marking nodes and Heterogeneity|
When you are working with a word processor and you want to perform an action with part of the text, e.g. copy that text, you first have to select that part of text and then execute the action. MicroFEM works the same way. When you want to perform an action with only part of the model, e.g. assign values to a parameter or compute the water balance, you first have to mark that particular part of the model and then execute the action.
When you start with a model, no nodes are marked. Nodes can be marked either one by one, along a line, or in some area. In previous lessons we have been marking nodes a few times: the model boundary (lesson 1b), all nodes (lesson 3A) or only a single node using the Auto-marker [F10] (lesson 5B).
Another useful command in Walking mode is [Line marker (F11)]. It will mark all nodes on a line between nodes that are clicked. First switch [F11] on and then click two nodes in order to obtain a marked line. When there are many nodes between the two clicked nodes and the grid is irregular, it is not always obvious which path will be chosen. When you have a particular path in mind, make regular clicks. Also, don't forget to switch off the line-marker once you have finished marking the required line of nodes.
We will use the line-marker to mark the northern part of the model and assign a low transmissivity for the upper aquifer. We will make this "Northern area" equal to the Northern quadrangle that we used when we created the grid.
Load the "Lesson 6" model.
[Line marker (F11)] / Click on the most NE-boundary node / Click on a node somewhere halfway on the straight line that connects to the Inner area / + + / continue with marking the straight line until the Inner area is reached.
When zooming (keyboard + or – , or zoom buttons [+] or [-]) the model is also shifted to place the current node in the centre of the map (unless the current node is so close to the model boundary and shifting will only reduce the visible part of the model). A [+][-] or [-][+] sequence shifts the current node to the centre, keeping the scale unaltered.
Continue with the Line-marker and follow the Inner area northern boundary to the left until its NW node, then follow the straight line to the most NW boundary node / [F11]
Click on one of the unmarked nodes in the northern quadrangle / [Mark up to marked (F8)]
All nodes of the northern quadrangle are now marked.
[Input mode] / Select Label 1 / Enter "Northern area" / [Marked nodes (F3)]
Select T1 / 200 / [F3]
We can mark any part of the model and then assign a value to the marked nodes for some parameter using [F3]. We can also assign to all non-marked nodes using [F4] or to all nodes with [F5]. The position of the current node is not important in those cases. When we assign only to the current node, we use the Enter-key.
First remove all marks, and then do the same marking procedure for the southern area. Assign the label "Southern area", a T1-value of 1800 m2/d and a C1-value of 100 days.
When you draw contours of Label 1, the resulting lines show 4 separate areas: "Northern area", "Southern area", "well" (a single node only) and the area in between without a particular label. To mark the north area again, place the cursor on one of its nodes, select Label 1, [Input mode] / [Ins] / [Del] / [Mark data or labels (F2)] / [OK].
In this case the word "area" is part of both labels. That allows us to mark the north and the south area at the same time.
Select Label 1 / [Input mode] / [Ins] / [Del] / [Mark data or labels (F2)] / "area" / [OK].
This trick only works when there exists no label "area". So, MicroFEM first looks at all nodes to see whether "area" exists, and when none is found it starts all over and marks all nodes that have "area" as part of their label. The same trick works in this case when we enter "thern" or even "o".