RD CARD: Automatic Roughness Coefficient
Assignment by Depth
HN and/or RD is required if an HS card is used and MSC = 2 or 4
Card Description: Provides for real time adjustment of the bottom roughness
coefficient. Automatically changes the Manning's n-value of a node depending upon
the water depth at each node. Generally, the deeper the water, the lower the
roughness value.
Field
Variable
Value Description
0, C 1-2
IC1
RD
Card group identifier.
0, C 3
IC3
Card type identifier.
Specifies Option 1: Global assignment for element
b
/
numbers ≥ ISTART.
(blank)
Specifies Option 2: Set n-value by element
T
material type (IMAT).
Specifies Option 3: Set n-value by element
E
number.
If Option 1: Code the first element number for
1
ISTART
+
global assignment to begin.
If Option 2: Code the element material type.
If Option 3: Code the element number.
On/Off switch for auto Manning's n-value
2
IRUFF
-, 0, +
calculations based upon an average depth (AVEDEP
in the equation) of the element. A positive value
turns the option on and sets defaults as in the table
on the next page. A negative value or zero will turn
the auto option off for those nodes.
Maximum Manning's n-value for non-vegetated
3
RDR0
0, +
water (a positive value will override the default).
Depth at which vegetation effects roughness
4
RDD0
0, +
(a positive value will override the default).
Manning's n-value for vegetated water
5
RDRM
0, +
(a positive value will override the default).
Roughness by depth coefficient
6
RDCOEF
0, +
(a positive value will override the default).
Minimum allowed roughness, default n-value = .01
7
RDMIN
+
(a positive value will override the default)
Maximum allowed roughness, default n-value = .20
8
RDMAX
+
(a positive value will override the default)
NVALUE = RDR0 / (AVEDEPRDCOEF) + (RDRM * EXP(-AVEDEP/RDD0))
Note: If convergence instability occurs in the 1D sections of the mesh, set the
parameters to achieve a more constant n-value in the 1D sections. See the "1D trick"
suggestion in the table below.
It is recommended to use the same RD-Card parameters from the RMA2 simulation,
but you must convert the RDD0 variable to metric units. There are minute
differences in auto roughness: RMA2 used gauss points, while SED2D used the
nodal values. Computed n-value are assigned to the SED2D array XNVALU(i).
Run Control RD Card 113
Users Guide To SED2D-WES
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