| As the number of large ships has increased,the risk of collisions has risen rapidly.To ensure the safe navigation of ships in shallow waters is the focus of scholars,port and navigation enterprises and pilots.The 29 th International Towing Tank Conference(ITTC)pointed out that shallow waters can increase ship handling difficulty,worsen turning ability,and reduce rudder efficiency and propeller efficiency.With the increase in the number of ships,the risk of grounding and collision accidents has also increased rapidly.Ensuring the safe navigation of ships in shallow water is a key focus of ports and pilots.The 29 th International Towing Tank Conference(ITTC)pointed out that shallow water will worsen the ship’s turning ability,reduce rudder efficiency and propeller efficiency.However,it is difficult for conventional ship model equipment to carry out shallow water test,so there are still few theoretical and experimental researches,and the understanding of maneuverability in shallow water is still insufficient.In order to explore the influence mechanism of the shallow water effect and analyze the difference of the ship’s maneuverability index in deep and shallow water,the main work of this paper is as follows:Firstly,a separate MMG 6-DOF model is constructed based on the standard tanker KVLCC2 published by ITTC,and the hull hydrodynamic and propeller-rudder interference are calculated respectively based on the empirical formula in shallow water.For the propellerrudder interference problem,although the empirical formula can reflect the influence trend,the prediction accuracy of the ship’s turning motion is poor.To solve this problem,this paper proposes an improved modified formula,which is superior to the traditional empirical formula in the prediction of the ship’s turning track,tactical diameter and other maneuverability index.It is a fast calculation method considering the loss of propeller and rudder efficiency in shallow water at the initial stage of design.However,the coupling between hull hydrodynamics and water depth is complex.The prediction error of turning motion based on empirical formula of shallow water is large,so it is necessary to conduct numerical simulation study for making a deep analysis of hull hydrodynamics.In order to establish a suitable numerical simulation program,gird independence、turbulence and motion method are carried out.The hydrodynamic derivative obtained by numerical simulation is used to simulate the standard ship maneuverability and is compared with the experimental trajectory,heading angle、overshoot angles and turning rate to verify the feasibility of the scheme.Numerical simulation was carried out under four conditions of d/H =1.2、1.5、2 and 8.3,including oblique towing,rotating arm with different drift angles.Combined with the flow field information such as surface pressure,streamline distribution and stern velocity,the variation rule and influence mechanism of hydrodynamic derivative were explained.The hydrodynamic characteristics of hull in different water depths were emphatically compared,and the maneuverability variation of ship KVLCC2 was quantitatively determined according to the heading stability index.Finally,a complete maneuvering mathematical model is constructed by using the propeller-rudder interference correction formula and the hull hydrodynamic derivative obtained by numerical simulation.Through the simulation research under different water depths,the differences of Very Large ship KVLCC2 in trajectory、speed and overshoot angle are compared,which enriches the research on maneuverability in shallow water.Combined with the meteorology of the Bohai Sea,the ship motion simulation under wind load is carried out,including the study of turning motion and heading in the wind.The simulation results have a certain reference value for guiding the prevention of maritime accidents,and help to improve people’s understanding of the ship’s hydrodynamic performance and maneuverability when sailing in shallow water... |
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