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TABS-MDS
SM CARD
CONTROL OF THE HORIZONTAL EDDY VISCOSITY
SM CARD
AND DIFFUSION COEFFICIENT BY SMAGORINSKY
Field
Variable
Value
Description
0,C1-2
IC1
SM
Card group identifier
0,C3
IC3
b/
Universal assignment
T
Assignment by material type.
1
NMAT
+
Material type for the Smagorinsky parameter assignment.
2
TBFACT
+,0,-
Smagorinsky coefficient for turbulent exchange.
A negative value applies the default coefficient (= 0.1)
3
TBFACTS
+,0,-
Smagorinsky coefficient for diffusion. A negative value applies the
default coefficient (= 0.1)
4
TBMINF
+,0,-
Minimum turbulence exchange factor. A negative value applies the
default coefficient (= 1.0)
5
TBMINFS
+,0,-
Minimum diffusion factor. A negative value applies the default
coefficient (= 1.0)
Note: a SM card will override EV, DF, and PE cards.
The Smagorinsky coefficient (TBFACT and TBFACTS) can vary from approximately 0.094 to 0.2. The optimum
value has been found to be approximately 0.1 for a trapezoidal channel, with higher values for more heterogeneous
systems such as estuaries (See Thomas, T.G. and Williams, J.J.R. "Large Eddy Simulation of a Symmetric
Trapezoidal Channel at Reynolds number of 430,000" Journal of Hydraulic Research, Vol.33 No. 6, 1995.)
The minimum turbulence exchange and diffusion factors (TBMINF and TBMINFS) are used to find the minimum
turbulence exchange and diffusion coefficients (Emin and Dmin) as follows:
Emin = TBMINF ρ Vmin dx / 40
Dmin = TBMINFS Vmin dx / 40
Where Vmin = 0.2 ft/sec (0.061 m/s) and dx = the square root of the surface area of the element.
Also, if |V| < TBMINF Vmin, Emin is applied, regardless of the value of the turbulence exchange coefficient
resulting from the Smagorinsky calculation. This is done to inhibit numerical instability in areas with both extremely
small velocities and high velocity gradients.
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