URANS predictions of wave induced loads and motions on ships in regular head and oblique waves at zero forward speed

The paper presents predictions on the hydrodynamics of a conceptual floating liquefied natural gas (FLNG) and a liquefied natural gas (LNG) carrier in regular head and oblique sea waves using an unsteady Reynolds-Averaged Navier-Stokes (URANS) solver. Initially, a verification and validation study is performed on estimating the numerical uncertainties in the presented URANS simulations. Using the verified numerical setup, ship hydrodynamic properties including wave induced loads as well as ship motion responses are investigated for different wave conditions. The computed time history results are decomposed by Fourier Series to estimate the wave load and ship motion transfer functions. These results show good correlation with predictions from model tests and potential flow calculations. From the computations, it is observed when increasing the wave length, wave diffraction around the ship becomes less profound and the water depth starts to influence the transfer functions. Full scale computations in head and oblique sea waves are also presented and compared with model scale predictions for investigating possible scale effects. The differences are found to be close to the numerical uncertainties, indicating minor influences of scale effects on the prediction of wave loads and ship motion responses for the tested cases.