The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL Fluid Dynamics with Erosion Brandon Lloyd COMP 259 May 2003
Dec 16, 2015
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
Fluid Dynamics with Erosion
Brandon LloydCOMP 259May 2003
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
Overview
• Sediment transport in open channels Bed-load transport Suspensed transport
• Sediment transport models• Model used for this project• Implementation issues• Future work
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
Sediment Transport
• Bed-load transport: sliding, rolling, saltating
• Suspended transport: sediment moves through the fluid
Sediment
Suspension
Bed-load
Bed
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
Bed-load transport
Once the forces actingon particles are strongenough to intiate motion…
… particles slide, roll, and saltate down the river bed at a steady rate.
Figure from Chanson, p. 180
Figure from Chanson, p. 200
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
Suspended Transport
Suspension occurs here
• Particles entrained at the bed-load layer
• Transported by convection, diffusion, and turbulence
Figure from Chanson, p. 200
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Sediment Transport Models
• Difficult problem – most models are empirical.
• Usually make simplifying assumptions about flow.
• Many different formulas exist.
Table from Chanson, p. 198
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
My Model
• Simplified version of model used in [Haupt et al. 1999]
• Transport occurs above critical velocity.
• Fluid has a transport capacity related to velocity.
• Concentration of sediment relative to capacity determines change in terrain
height :
porosity :
ionconcentratsediment :
constants:
velocityfall:
velocitycritical :
velocityfluid :
erosion
accretion
1
,
0
0
2
2,
2
21
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P
c
C
w
v
v
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qc
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w
vvCqwCv
s
i
s
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ss
ssbed
s
scssc,s
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
Implementation Issues
• Semi-Lagrangian advection causes mass loss in the presence of eddies.
• What to do at boundaries?
zero concentration
backward tracing doesnot see wall mass loss.
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
Implementation Issues
• Semi-Lagrangian advection causes mass loss in the presence of eddies.
• What to do at boundaries?
Recycle concentration(limits the time-step)
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
Results
• Nice swirls of sediment with erosion and deposition at interactive rates (on a fast machine .)
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
Future Work
• Add bed-load transport• Add instability based on slope• Add variable material properties• Fix spikes and improve robustness• Better handling of velocities near
heightfield.• Experiment with and compare different
fluid/advection models• Add a free surface• Implement on GPU
The UNIVERSITY of NORTH CAROLINA at CHAPEL HILL
References
CHANSON, H. 1999. The Hydraulics of Open Channel Flow: An Introduction. Arnold.
HAUPT, B. J., SEIDOV, D. AND STATTEGGER, K. 1999. SEDLOB and PATLOB: Two numerical tools for modeling climatically forced sediment and water volume transport in large ocean basins. In Computerized Modeling of Sedimentary Systems. Springer-Verlag, Berlin.
WU, W., RODI, W. AND THOMAS, W. 2000. 3D numerial modeling of flow and sediment transport in open channels. Journal of Hydraulic Engineering, 4-15.