Computational Mechanics Research and Support for Aerodynamics ...

More documents

Recommendations

Info

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
conditions from Example 1 defined in the new HEC-18 update was adopted here with the following given parameters: Upstream channel width and bridge opening width (W)= 40 ft (12.2 m) Total discharge (Q) = 2800 ft 3 /s (79.3 m 3 /s) Upstream channel discharge (Q 1 ) = 2000 ft 3 /s (56.6 m 3 /s) Upstream floodplain discharge = 800 ft 3 /s (22.7 m 3 /s) Upstream channel flow depth (h u )= 10.0 ft (3.0 m) Bridge opening height (h b ) = 8.0 ft (2.4 m) Deck thickness (T) = 3 ft (0.91 m) Bed material D 50 = 15 mm (V c = 6.0 ft/s, 1.8 m/s, V c is the critical velocity for the sediment size) Upstream channel velocity (V=Q 1 /(W hu )) = 2000/(40 x 10) = 5.0 ft/s (1.5 m/s) Figure 2.4 presents Equations 2.2 and 2.3 for several different upstream velocities and other quantities defined as above. It was noted that the initial fit allows for separation zone thickness significantly greater than zero for the cases where the water level was just slightly above the bottom line of the bridge superstructure ( . Although Equations 2.2 and 2.3 fit to the experimental scour data well, creation of a significant separation zone when the water is at a level that just touches the superstructure is counterintuitive. Also there was a discontinuity introduced between the two regions described by the curves – before overtopping and after overtopping. Figure 2.4 Initial fit based on Equations 2.2 and 2.3 TRACC/TFHRC Y2Q2 Page 14
Page 1 and 2: ANL/ESD/12-27 Energy Systems Divisi
Page 3 and 4: ANL/ESD/12-27 Computational Mechani
Page 5 and 6: List of Figures Figure 2.1: Bridge
Page 7 and 8: Figure 2.35: Two different transiti
Page 9 and 10: 1. Introduction and Objectives The
Page 11 and 12: 2. Computational Fluid Dynamics for
Page 13: flat surface assumption is good exc
Page 17 and 18: scour rate is initially highest nea
Page 19 and 20: Figure 2.6 Dividing streamline posi
Page 21 and 22: 2.1.3. Resolving Issues of the Seco
Page 23 and 24: educe the rate of increase for y wh
Page 25 and 26: Design Scour Depth 0.400 0.350 0.30
Page 27 and 28: extend the impact of the findings t
Page 29 and 30: Table 2.2 Contour plots comparing C
Page 31 and 32: Figure 2.14 Comparison of CFD and P
Page 37 and 38: consistent with the lab test setup,
Page 51 and 52: RMSD area area ( V1 V2 ) n area 2
Page 53 and 54: 2. Marian Muste, Hao-Che Ho, Daniel
Page 55 and 56: Honeycomb Streamline Trumpet Unifor
Page 57 and 58: (a) Streamline trumpet transition c
Page 59 and 60: 2.6. Training and Technology Transf
Page 61: Figure 2.40: Announcement for CFD t

Computational Mechanics Research and Support for Aerodynamics ...

Create successful ePaper yourself

Delete template?

Save as template?