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### Contraction

Figure 101: Geometry of a contraction

The geometry of a contraction is shown in Figure 101 (view from above). Although a contraction is really a discontinuity, a small fictitious length an a slope have to be assigned. For the slope one can take the mean values of the slopes of the adjacent channels. The following constants have to be specified on the line beneath the *FLUID SECTION,TYPE=CHANNEL CONTRACTION card:

- the upstream width
- the slope (if zero is taken)
- the length (if the length is calculated from the coordinates of the end nodes belonging to the element)
- the downstream width

Example files: channel9, channel11.