Numerical simulation of wave-induced scour and backfilling beneath submarine pipelines David R. Fuhrman1, Cuneyt Baykal1, B. Mutlu Sumer1, Niels G. Jacobsen2, Jørgen Fredsøe1 1 Technical University of Denmark 2 Deltares
Outline Model description Simulation of wave-induced scour Simulation of wave-induced backfilling Conclusions
Model description 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 Engelund-Fredsøe bedload transport method Turbulent-diffusion equation for suspended sediment concentration Engelund-Fredsøe reference concentration Reference level: b=3.5d (similar to Liang & Cheng 2005)
Model description (2) Morphological model Sediment continuity (Exner) equation Instantaneous bed updating (no smoothing) Sandslide model of Roulund et al. (2005)
Model description (3) Model domain 40D x 10D Frictionless rigid lid at top boundary Wave conditions (oscillatory flow) introduced at left boundary
Outline Model description Simulation of wave-induced scour Simulation of wave-induced backfilling Conclusions
Wave-induced scour 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 10T KC=UmTw/D T (s) Um (m/s) qmax 5.6 1.10 0.153 0.13 11 1.22 0.240 0.19 15 2.50 0.177 0.10 19.6 3.00 0.196 0.092 21.1 2.64 0.239 0.12 25.3 3.51 0.216 0.094 30 3.50 0.257 0.11
Scour (KC = 5.6)
Scour (KC = 30)
Summary of scour profiles
Summary of scour time series
Scour (KC = 11) Features develop matching natural vortex ripple length (Brøker 1985):
Summary of scour results Equilibrium scour: Time scale:
Outline Model description Simulation of wave-induced scour Simulation of wave-induced backfilling Conclusions
Backfilling (KC = 30 to 5.6)
Backfilling time series to KC = 5.6: To KC = 15:
Backfilling profiles Backfilling to KC = 5.6: Scour with KC = 5.6:
Backfilling summary Equilibrium scour: Time scale:
Remarks on practical application Utilize the time scalings: Taking the grain size as already full scale, model and full scale morphological times may be related as: Combining simulated scour/backfilling times give:
Outline Model description Simulation of wave-induced scour Simulation of wave-induced backfilling Conclusions
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 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. Fuhrman1, Cuneyt Baykal1, B. Mutlu Sumer1, Niels G. Jacobsen2, Jørgen Fredsøe1 1 Technical University of Denmark 2 Deltares