Asymmetric ship maneuvering due to twisted rudder using system-based and direct CFD approaches

Abstract

In this study, the maneuvering ability of a 1/100 scaled model of Duisburg Test Case (DTC) hull was investigated by utilizing system-based and direct CFD methods. DTC hull has a twisted rudder generating significant asymmetry in the flow, which makes it a specific case for ship maneuvering. Resistance tests were first conducted at Ata Nutku Ship Model Testing Laboratory of Istanbul Technical University to provide a basis for the validation of numerical approach. Free surface effects were neglected in all numerical simulations due to low cruising speed of the ship (6 knots in full scale). For system-based approach; hydrodynamic derivatives, rudder and propeller parameters were determined by performing a series of numerical simulations. These parameters were then used in MMG mathematical model to estimate the turning circle and zigzag abilities of the ship under calm water condition. direct CFD simulations of turning and zigzag maneuvers were also performed adopting URANS equations with overset mesh technique that allows the deflection of the rudders while the ship moves with 3DOF motions. Noting that all the simulations involved in the system-based method consumed more time than the direct CFD method, both results were compatible with free running data. Simulation results reveal that the twisted rudder creates considerable asymmetry in the flow, leading to large discrepancies in a rudder parameter (γR) obtained for port and starboard turnings. It was also noticed that although two rudder parameters (ε and κ) are taken as constants in the literature, a strong non-linear behavior was observed in the twisted rudder case and seemed difficult to reduce to a constant.