Zigzag maneuver is one of the typical tests to estimate the ship maneuverability. Most current studies of zigzag maneuver use the simplified model, which cannot resolve the detailed flows around the maneuvering ship. Therefore, simulations of free running ship model with direct rotating propellers and turning rudders are necessary in order to reappear the realistic operational scenario. In the present work, a RANS-overset grid method is used to numerically investigate standard zigzag maneuver in waves of twin-screw ONR Tumblehome ship. Overset grids are used to deal with the complex motions of the ship hull-propeller-rudder system. Standard 10/10 zigzag maneuver in three incident waves with different wave-lengths are simulated at Fr=0.20. The open source toolbox waves2Foam is utilized to generate desired waves for the moving computational domain. Numerical computations are carried out by the in-house CFD solver naoe-FOAM-SJTU. The main parameters of the zigzag maneuver, ship motions, hydrodynamic forces and moments are presented for further analysis. Detailed flow visualizations of wave elevations and vortical structures are also illustrated. The predicted results for the zigzag maneuver in waves are compared with the available experimental measurements and overall agreement is achieved. It is found that the wavelengths can significantly affect the ship motions while the influences on overshoot angles are relatively small. Furthermore, strong nonlinear effects due to the waves can be observed through the FFT analysis of the ship motions and hydrodynamic forces.
Steering operation during ship maneuvering motion is closely related to the navigational safety. When considering ship maneuver in waves, it will further associate with the seakeeping performance, thus making the evaluation of ship maneuverability more complicated and difficult. Recently, the research of maneuvering in waves is becoming increasingly popular, consequently, a specialist committee which is responsible for maneuvering in waves is established by the 28th International Towing Tank Conference (ITTC, 2017). In general, ship maneuver in waves will experience large low-frequency maneuvering motions and high-frequency wave induced motions. Free-running ship maneuvering test in most cases is conducted by executing rudders along with rotating propellers, thus making it very complicated when evaluating the performance of fully appended ship in waves. So far, it is one of the most difficult problems in the research of ship hydrodynamics, the accurate prediction of ship maneuvering performance during free-running motion through either experimental or numerical way is still challenging.
