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Research Papers: Offshore Geotechnics

# Three-Dimensional Numerical Modeling of Pier Scour Under Current and Waves Using Level-Set Method

[+] Author and Article Information
Mohammad Saud Afzal

Department of Marine Technology,
Norwegian University of Science and Technology,
Trondheim 7491, Norway
e-mail: mohammad.s.afzal@ntnu.no

Hans Bihs, Arun Kamath, Øivind A. Arntsen

Department of Civil and Transport Engineering,
Norwegian University of Science and Technology,
Trondheim 7491, Norway

1Corresponding author.

Contributed by the Ocean, Offshore, and Arctic Engineering Division of ASME for publication in the JOURNAL OF OFFSHORE MECHANICS AND ARCTIC ENGINEERING. Manuscript received March 10, 2014; final manuscript received March 4, 2015; published online April 6, 2015. Assoc. Editor: Dong S. Jeng.

J. Offshore Mech. Arct. Eng 137(3), 032001 (Jun 01, 2015) (7 pages) Paper No: OMAE-14-1027; doi: 10.1115/1.4029999 History: Received March 10, 2014; Revised March 04, 2015; Online April 06, 2015

## Abstract

A three-dimensional (3D) computational fluid dynamics (CFD) model is used to calculate the scour and the deposition pattern around a pier for two different boundary conditions: constant discharge and regular waves. The CFD model solves Reynolds-Averaged Navier–Stokes (RANS) equations in all three dimensions. The location of the free-surface is represented using the level-set method (LSM), which calculates the complex motion of the free-surface in a very realistic manner. For the implementation of waves, the CFD code is used as a numerical wave tank. For the geometric representation of the moveable sediment bed, the LSM is used. The numerical results for the local scour prediction are compared with physical experiments. The decoupling of the hydrodynamic and the morphodynamic time step is tested and found to be a reasonable assumption. For the two situations of local pier scour under current and wave conditions, the numerical model predicts the general evolution (geometry, location, and maximum scour depth) and time development of the scour hole accurately.

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## Figures

Fig. 5

3D model result under constant discharge showing free-surface and topography

Fig. 6

Pier numerical setup under waves

Fig. 1

Pier numerical setup under steady current

Fig. 2

Contour plot of experimental result (as in Ref. [6])

Fig. 3

Model result with k–ω model and Dey empirical formula for bed shear stress reduction

Fig. 4

Time development of scour, numerical model (REEF3D) with k–ω model and Dey empirical formula for bed shear stress reduction

Fig. 7

Contour plot of bed elevation changes under waves (experimental from Ref. [8])

Fig. 8

Contour plot of bed elevation changes under waves (model result)

Fig. 9

Time development of scour under waves using numerical model (REEF3D)

Fig. 10

Time development of scour under waves by varying relaxation factors for sediment time step

Fig. 11

3D model result under waves showing free-surface and topography

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