Three-Dimensional Numerical Modeling of Local Scour around a Non-Slender Cylinder under Varying Wave Conditions.

---

Nadeem Ahmad, Hans Bihs, Mohammad Saud Afzal, Øivind A. Arntsen

Tuesday 30 june 2015

14:50 - 15:05h at Mississippi (level 1)

Themes: (T) Sediment management and morphodynamics, (ST) Sediment transport mechanisms and modelling

Parallel session: 6A. Sediment - Erosion

---

The three-dimensional numerical model REEF3D is used to simulate the detailed flow field and sediment transport around a non-slender cylinder under regular waves. The location of the free surface is calculated with the interface capturing level set method. The model is used as a numerical wave tank. Waves are generated at the inlet boundary, which dissipates through a numerical beach at the outlet boundary in order to avoid reflections. The convection terms in the Navier-Stokes equations and the level set method are discretized with the 5th-order Weighted Essentially Non-Oscillatory scheme. Together with the staggered grid arrangement and its tight velocity-pressure coupling, this results in an accurate and stable prediction of the propagating water waves. The sediment transport is calculated with standard bedload formulas. The Exner equation is used for evaluating sediment continuity at the bed, giving the temporal change of the location of movable bed. For the modeling of the bed changes an Eulerian approach is taken, using the level set function for the geometric representation of the bed location. As a result, re-meshing is not required. Local scour around the cylinder is predicted for different KC numbers. The calculated scour pattern is compared with experimental laboratory measurements, which shows good agreement.