Time-domain simulation of large amplitude ship roll motions by a chimera RANS method

A Reynolds-Averaged Navier-Stokes (RANS) numerical method has been employed in conjunction with a chimera domain decomposition approach for time-domain simulation of large amplitude ship roll motions. For the simulation of arbitrary roll motions, it is convenient to construct body-fitted numerical grids for the ship and ambient flow domain separately. The ship grid block is allowed to roll with respect to its center of rotation under either forced or free roll conditions. The roll moments are computed every time step by a direct integration of the hull surface pressure and shear stresses obtained from the chimera RANS method. The simulations for prescribed roll motions of a full-scale motor vessel clearly show that the bilge keels at the mid-ship produced large roll damping but generated very little waves. On the other hand, the ship skag acts like a wavemaker during the roll motion and produced large wakes in the stem region. Time-domain simulations were also performed for a free-floating pontoon barge in free decay motions and under large amplitude incident waves. The simulation results successfully predicted the roll resonance when the incident wave coincides with the free decay period of the barge.