NUMERICAL SIMULATION OF WAVE-INDUCED
SCOUR AND BACKFILLING BENEATH
SUBMARINE PIPELINES
David R. Fuhrman 1 , Cuneyt Baykal 1 , B. Mutlu
Sumer 1 , Niels G. Jacobsen 2 , Jørgen Fredsøe 1
1 Technical University of Denmark
2 Deltares

• Model description
• Simulation of wave-induced scour
• Simulation of wave-induced backfilling
• Conclusions

• Fully-coupled sediMorph model (OpenFOAM)
• Jacobsen & Fredsøe (2014)
• Hydrodynamic model
•
• Incompressible Reynolds-Averaged Navier-Stokes (RANS) equations
Two-equation k w turbulence closure (Wilcox 2006)
• Sediment transport model
• EngelundFredsøe bedload transport method
•
• Turbulent-diffusion equation for suspended sediment concentration
EngelundFredsøe reference concentration
• Reference level: b =3.5
d (similar to Liang & Cheng 2005)

• Morphological model
• Sediment continuity (Exner) equation
 h
 t

1
1
 n



 q
Bi
 x i

D

E

 ,
D

 w s
 u
3
 c b
, i

1 , 2
E

   
T

 c
 x
3 x
3
 b
• Instantaneous bed updating (no smoothing)
• Sandslide model of Roulund et al. (2005)

• Model domain 40 D x 10 D
• Frictionless rigid lid at top boundary
• Wave conditions (oscillatory flow) introduced at left boundary

• Model description
• Simulation of wave-induced scour
• Simulation of wave-induced backfilling
• Conclusions

• Conditions chosen to match selected experimental conditions (Sumer & Fredsøe 1990, Fredsøe et al. 1992)
• Pipeline diameter: D = 3 cm , grain diameter d = 0.19 mm
• Warm-up period (morphology off) of 10 T
KC=U m
T w
/D
5.6
11
15
19.6
21.1
25.3
30
T (s)
1.10
1.22
2.50
3.00
2.64
3.51
3.50
U m
(m/s)
0.153
0.240
0.177
0.196
0.239
0.216
0.257
q max
0.13
0.19
0.10
0.092
0.12
0.094
0.11

Scour
( KC = 5.6
) t *
 g
 s

1
 d
3
D
2 t
S
D

0 .
1 KC

Scour
( KC = 30 )

Summary of scour profiles

Summary of scour time series

Scour
( KC = 11 )
Features develop matching natural vortex ripple length
(Brøker 1985):


D

1 .
2 a ,

1 .
2
2

KC a

2

U m

2 .
1
/ T w

• Equilibrium scour: • Time scale: T *
 t '* max 
0
S max

S dt '*
S max

• Model description
• Simulation of wave-induced scour
• Simulation of wave-induced backfilling
• Conclusions

KC = 30
5.6

• to KC = 5.6: • To KC = 15:

• Backfilling to KC = 5.6: • Scour with KC = 5.6:

• Equilibrium scour: • Time scale: T *
 t *
 max
0
S
S
0


S min
S min dt *

• Utilize the time scalings: t *
 g
 s

1
 d
3
D
2 t ,
T *

1
50 q 
5 3
• Taking the grain size as already full scale, model and full scale morphological times may be related as: t full t model



D full
D model


2 
 q full q model



5 3
• Combining simulated scour/backfilling times give: t * model

15
 t full

O

1 day


• Model description
• Simulation of wave-induced scour
• Simulation of wave-induced backfilling
• Conclusions

• Fully-coupled RANS model for simulating scour processes beneath submarine pipelines
• Hydrodynamics + turbulence description
• Sediment transport (bed and suspended load) + Bed morphology
• Accurate simulation of pipeline scour depths as well as scour time scales
• Model predicts backfilling to profiles governed by new wave climate
• Consistent with experimental findings ! (Fredsøe et al. 1992)
• Results published in:
Fuhrman, D.R., Baykal, C., Sumer, B.M., Jacobsen, N.G. & Fredsøe, J. (2014) Numerical simulation of wave-induced scour and backfilling processes beneat submarine pipelines. Coast. Eng. 94 , 10-22.

Animation of tsunami-induced scour
ASTARTE EU FP7 project: www.astarte-project.eu

NUMERICAL SIMULATION OF WAVE-INDUCED
SCOUR AND BACKFILLING BENEATH
SUBMARINE PIPELINES
David R. Fuhrman 1 , Cuneyt Baykal 1 , B. Mutlu
Sumer 1 , Niels G. Jacobsen 2 , Jørgen Fredsøe 1
1 Technical University of Denmark
2 Deltares