Unsteady RANS method for surface ship boundary layer and wake and wave field

Abstract

SUMMARYResults are reported of an unsteady Reynolds-averaged Navier -Stokes (RANS) method for simulation of the boundary layer and wake and wave field for a surface ship advancing in regular head waves, but restrained from body motions. Second-order finite differences are used for both spatial and temporal discretization and a Poisson equation projection method is used for velocity -pressure coupling. The exact kinematic free-surface boundary condition is solved for the free-surface elevation using a body-fitted/freesurface conforming grid updated in each time step. The simulations are for the model problem of a Wigley hull advancing in calm water and in regular head waves. Verification and validation procedures are followed, which include careful consideration of both simulation and experimental uncertainties. The steady flow results are comparable to other steady RANS methods in predicting resistance, boundary layer and wake, and free-surface effects. The unsteady flow results cover a wide range of Froude number, wavelength, and amplitude for which first harmonic amplitude and phase force and moment experimental data are available for validation along with frequency domain, linear potential flow results for comparisons. The present results, which include the effects of turbulent flow and non-linear interactions, are in good agreement with the data and overall show better capability than the potential flow results. The physics of the unsteady boundary layer and wake and wave field response are explained with regard to frequency of encounter and seakeeping theory. The results of the present study suggest applicability for additional complexities such as practical ship geometry, ship motion, and maneuvering in arbitrary ambient waves.

An unsteady single‐phase level set method for viscous free surface flows

“…The grid deformation process to fit the grid to the free surface works well and is robust as long as the free surface slope remains small. Examples of successful applications for free surface ship flows include resistance computation without [5] and with propellers [6], forward speed diffraction [7,8], roll decay motion [9] and pitching and heaving motion in regular head seas [10]. Unfortunately, as the deformation of the free surface increases it is difficult to prevent grid quality deterioration and computation breakdown.…”

Prediction of wave resistance by a Reynolds-averaged Navier–Stokes equation–based computational fluid dynamics approach

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Polydispersed bubbly flow model for ship hydrodynamics with application to Athena R/V

“…In surface-tracking methods the computational grid is fitted to the free surface and follows its motions. Examples of early applications using this technique include resistance computations (Wilson et al, 2001;Burg et al, 2002), forward speed diffraction (Wilson and Stern, 1998; Rhee and Stern, 2001) and pitch and heave in regular waves (Weymouth et al, 2005). Unfortunately, as the deformation of the free surface increases the grid quality deteriorates and eventually computations break down.…”