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SED2D-WES Version 4.3 Beta
when the depth tolerance was exceeded. For greatest accuracy, make DEPLIMIT as small as possible and generate
new flow fields often.
c.
Geometry cards (G1, GC,DM).
The G1 card allows the user to scale the coordinates provided in the GFGEN binary file by a constant
value. The GC card allows the user to specify lists of nodes that define channel cross-sections. The GC cards are
useful for specifying boundary conditions along cross-sections that lie on the mesh boundary. The DM cards are
used to specify the marsh porosity parameters, using the same format as RMA2. However, the user must remember
to convert the first three variables if the units are changes between RMA2 and SED2D-WES.
Timing and run length control (TZ card). The TZ card specifies the computational interval and number
d.
of time - steps to be run. Choice of a computational interval is dependent on the size of mesh cells used, speed of
the flow, effective settling velocity of the sediment, and how well the modeler wishes to resolve small - scale bed
features. It is recommended that the time interval for SED2D-WES be identical to the RMA2-WES time interval.
To obtain the number of time-steps needed to reach a given length of run, use the equation
No. of time-steps
=
Run Length
+ 1
Computational Interval
Implicitness factor (TT card). The program uses the Crank-Nicholson time - stepping scheme that
e.
employs an implicitness factor. A value of 0.66 is recommended, but variations from 0.5 (equal weighting of
this time - step and the previous time - step) to l.0 (no influence from the previous time - step) are permitted. A
higher value of Theta produces results that are more stable but numerical (artificial) dispersion of sediment is
increased.
Sediment size classes for sand (SA,SR,ST). The program requires that sediment sizes and/or their
f.
characteristics be specified. For noncohesive sediment bed problems, input allows for multiple grain sizes on the
SA card, BUT AT PRESENT THE PROGRAM CONSIDERS ONLY ONE EFFECTIVE GRAIN SIZE. (The
input reflects some changes that are planned for the SED2D-WES program, but are not currently functional). The
grain size specified on the SA card is applied to every node in the mesh. Values at specific nodes may be changed
by use of the SR and ST cards. The ST card specifies grain sizes to be used in noncohesive sediment transport
equations and the SR card specifies the effective grain size to be used in bed roughness calculations (Ackers-White
transport equations only). These two sizes will be the same only for plane beds in straight channels. Bed forms
and channel curvature introduce form roughness that causes the roughness size to be larger than the size used for
transport computations.
23
WORKING DRAFT
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