In the present study, Computational Fluid Dynamics (CFD) is used to investigate the roll decay of the benchmark surface combatant DTMB-5512 ship model appended with bilge keels, sailing in calm water at different speeds (Fr = 0.0, 0.138, 0.2, 0.28 and 0.41) and with different initial roll angles. The numerical simulations are carried out using the viscous flow solver ISIS-CFD of the FINETM/Marine software provided by NUMECA. The solver uses the finite volume method to build the spatial discretization of the transport equation to solve the unsteady Reynolds-Averaged Navier–Stokes equations. Two-phase flow approach is applied to model the air–water interface, where the free surface is captured using the volume of fluid method. The closure to turbulence is achieved by making use of the blended Menter shear stress transport and the explicit algebraic Reynolds stress models. First, a systematic validation against the experimental data at medium speed and initial roll angle of 10° are performed; then, the effect of the initial roll angle and ship speed is later studied. Numerical errors and uncertainties are assessed using grid and time step convergence study based on Richardson Extrapolation method. A special focus on the flow in the vicinity of the bilge keels during the simulation is also investigated and presented in the form of velocity contours and vortical structure formations. The resemblance between the CFD results and experimental data for roll motion and flow characteristics are within a satisfactory congruence; however, some discrepancies are recorded for the over predicted roll amplitudes in the second and, sometimes, the third roll cycle, which appeared mostly in the cases with high initial roll angles.
In the present study, the vertical motions and the added resistance in waves of the KVLCC2 ship model are predicted numerically in regular head wave, for a single wave height and different wave lengths, including long and short waves. The numerical simulation is performed by making use of the ISIS-CFD solver of the commercial software FineTM/Marine provided by NUMECA, where the discretization in space is based on finite volume method using unstructured grid. The unsteady RANSE are numerically solved, while the turbulence is modelled by making use of the k-ω SST model. The free-surface is captured through an air-water interface based on the Volume of Fluid method. For validation purposes, the computed solutions are compared with the available tank test data existing in the public domain. A systematic grid convergence study based on Richardson Extrapolation method is performed for a single wave case on three different grid resolutions, as an attempt of predicting the uncertainties in the numerical solution. A thorough investigation for the free-surface topology at different encountering moments is also presented to prove not only the accuracy of the solver, but also its robustness.
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