Using numerical method to predict the ships' maneuverability is indispensable for the true understanding and evaluation of ship's performance during its operation and service period. This paper presents the numerical investigation results of modified DTMB5415 model's maneuvering motion. The numerical solver includes 6-DOF model to analysis the motion of the ship, the single phase level set method was applied to capture free surface flow around ship, the overset grid technique to simplify the rudder angle and ship rotating motion under the force of the rudder and a prescribed body-force propeller model is adopted instead of the real propeller. Solving URANS equation with above models, two types of maneuvers are simulated: steady turn and zigzag. Simulation of steady turn at 25°rudder deflection and zigzag 20/20 maneuvers for Fr=0.232 using constant RPM propulsion are compared with experimental time histories of velocity, roll, and trajectories. To validate the numerical simulation results, the maneuvers experiments of full appendages ship model with real propeller was carried out in maneuvering tank. Difference between CFD and experiments are mostly within 20% for both maneuvers. The numerical study matched well with experiment result which means the numerical method used in this paper is effective and feasible in analyzing the navigation attitude of ships in maneuvers motion.
Ship maneuverability is the ability of a ship to keep or change its state of motion under the control action i.e. to keep the straight-ahead course with constant speed, or to change the speed, the course and/or the position of the ship, according to the intention of the helmsman. It relates to security and economy of ship closely.
The traditional tools use empiric descriptions of the forces and moments on ship's hull and are generally based on regression analysis of captive maneuvering test data for a preferably wide range of ships. Kuniji Kose and Wojciech Misiag found empiric formulation can provide a convenient and efficient method to predict ship maneuverability. Due to the lack of resolution of hull details or application outside the range of the regression database, the prediction of the maneuverability may be unreliable. The free running model maneuvering test is another common method to predict ship maneuverability by measuring motion trail and relative parameters of ship model in the maneuvering basin. It will produce some inevitable error because of the scale effect.