Computational Mechanics Research and Support for Aerodynamics ...

Figure 2.3 Vertical contraction and definition for geometric parameters.
In the approach taken by TFHRC, a dimensional analysis was used to obtain a format of the equation for
the thickness of the separation zone. Experimental data was then used to find the best parameter fit
using the least-squares method. A safety margin was also intentionally added to this formula to allow
sufficient reliability in design. The initial calibration process yielded the following two curves defining
separation zone thickness for the cases after and before the deck’s overtopping:
t
h
Where:
g acceleration due to gravity
density of water
viscosity of water
a h u - h b
t
1.
7
t
a
1.
7
V
gh
t
1.
1T
h
t
V
ga
0.
3
0.
3
0.
15
1.
2
1
Vh
t
h
b h
t
2.2
hu
hu
0.
15
1.
2
1
Va
hb
a
2.3
hu
hu
The geometrical parameters used in these equations are defined in Figure 2.3. It is important to note
that the thickness of separation zone from Equations 2.2 and 2.3 is not the theoretical separation zone
thickness defined by the boundary streamline. It is obtained from experimental data and produces the
best scour depth prediction when used with Equation 2.1. It includes compensation for errors/biases of
a number of other factors as well as needed conservatism for design. To visualize these curves the
TRACC/TFHRC Y2Q2 Page 13