Ahmed Elhanafi

Effect of RANS-based turbulence models on nonlinear wave generation in a two-phase numerical wave tank

Ocean waves are the most important exciting source acting on marine structures such as ships, offshore platforms, wave energy converters and wavebreakers. In order to efficiently design the aforementioned structures, accurate modelling of these waves is of importance. In this paper a two dimensional Numerical Wave Tank (NWT) has been established based on the Reynoldsaveraged NavierStokes (RANS) equations for viscous, incompressible fluid and Volume of Fluid (VOF) method and a commercial software code ANSYS FLUENT (Release 15.0) has been used to numerically investigate ocean wave generation. Impact of different turbulence models such as standard k-ɛ, realizable k-ɛ, Shear Stress Transport (SST) and Reynolds Stress Models (RSM) on the generated ocean surface waves were investigated. With all uncertainties associated with various numerical setting aspects, experimental wave measurements over a wide range of wave conditions covering intermediate and deep water regimes have been conducted in a physical wave basin to validate the numerical results. The excessive generation of eddy viscosity resulted from using eddy viscosity turbulence models especially at the free surface interface, leads to a significant unphysical damping on the generated waves. Good numerical agreement with both experimental measurements and analytical wave theory was successfully achieved either with the RSM or implementing artificial turbulence damping at the airwater interface with the SST model.

Reliability analysis of novel stiffened panels using Monte Carlo simulation

ABSTRACT The present study aims to perform reliability analyses using Monte Carlo simulation to compute and compare the time-invariant reliability indices of stiffened panels with either conventional T-stiffeners or novel Y (Hat + Tee/Angle) stiffeners profiles in a double hull oil tankers bottom and deck panels under axial compressive loads. The ultimate strength and the applied axial compressive stress formulations used in the limit state functions are obtained based on the International Association of Classification Societies-Common Structural Rules for oil tankers considering the following failure modes: unstiffened plate buckling, stiffener beam-column buckling, and stiffener torsional/flexural buckling (tripping). With the Y-stiffeners profile, a considerable improvement in the panels’ reliability index throughout the vessel lifetime is achieved.