A Comparative Analysis of CFD and the Potential Flow Method for the Pure Loss of Stability in Following Waves

Improving the cognition and numerical accuracy of stability failure is urgent for carrying forward the direct assessment stability of the new-generation performance-based criteria for intact stability issued by the International Maritime Organization (IMO) in 2020. Firstly, the CFD method utilizing commercial software is developed for predicting stability failure in following seas. The CFD method employed overlapping grid techniques to achieve coupled motion calculations with a free-running model. The actual propeller rate, the implemented auto polite course-keeping, the coupled effect of the ship hull-propeller-rudder, and the instantaneous wet hull are considered in the CFD method. Secondly, a comprehensive 6-DOF mathematical model, employing the MMG framework and potential flow theory, is utilized to predict stability failure in the following waves. The radiation and diffraction forces are calculated around the mean wet hull using an enhanced strip method, and the FK and hydrostatic forces are calculated around the exact wet hull in waves. Thirdly, the occurrence of pure stability loss and subsequent large roll motions or capsizing for the ONR tumblehome ship are simulated by the time domain CFD and potential flow method. Finally, the computed results are cross-referenced with the available experimental data, and the trends of maximum roll angle are found to be consistent with the test data. Additionally, the alterations in thrust and torque exerted by the twin rudders and propellers are assessed across various sailing speeds, as well as the characteristics of the flow field distribution around the hull and appendages during capsizing at the critical sailing speed, which are newly analyzed by the CFD method.