FLOOD06499

• County: Statewide
• Basin: Statewide
• Title: Development of Generalized Free Surface Flow Models Using Finite Element Techniques
• Date: 2/1/1979
• Prepared For: US
• Prepared By: COE
• Floodplain - Doc Type: Educational/Technical/Reference Information

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Figure 8 Velocities for Spillway Q = 0, Existing Powerhouse
Q = 6500 cms (230,000 cfs), Second Powerhouse Q =
7000 cms (250,000 cfs), Slip Boundary Conditions

.

The model allows two valid types of boundary conditions
at boundaries where no flow enters or leaves the system. One
is the stagnation point where both components of velocity are
zero; the other is the slip boundary condition where the
velocity on the boundary is tangential to the boundary. The
slip condition requires use of curved-sided elements on the
boundaries. Use of curved boundaries with tangential flow is
favored. Use of stagnation points along the boundaries results
in a substantially different solution as shown in Fig. 9. Not
only is the velocity distribution altered, but calculated head
loss in the reach is about 0.21 m (0.7 ft.) g~eater than with
the slip boundary condition. Continuity performance for the
two simulations was similar, thou9h in other problems analyzed
by Resource r.anagement Associates (1977), the slip condition
was superior. Use of different boundary conditions should be
investigated in an attempt to identify under what conditions
the modeler should choose slip or stagnation point boundaries.
It is encouraging to note that the McNary study requi red
no code changes to the model. .

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