Contraction

**Figure:** Geometry of a contraction
$\begin{figure}\epsfig{file=Channelcontraction.eps,width=9cm}\end{figure}$

The geometry of a contraction is shown in Figure (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 b_1
the slope S_0 (if S_0<-1 zero is taken)
the length L (if L \le 0 the length is calculated from the coordinates of the end nodes belonging to the element)
the downstream width b_2 \le b_1

Example files: channel9, channel11.