Numerical And Experimental Study On The Hydrodynamic Performance Of Ship Under Trim Condition

Since the concept of " The Green Ship" was put forward in the 90 s of last century,the technology of energy saving and emission reduction has been paid more and more attention by the international shipping industry,and the relevant green ship regulations have been implemented in china.At present,the most common ways of energy saving and emission reduction are energy saving appendages,sail assisted,new energy,trim optimization,etc.Compared with other energy saving technologies,trim optimization technology is a kind of green technology with remarkable energy-saving and low cost.Therefore,it is necessary to study the hydrodynamic performance of the ship under the condition of longitudinal inclination.Now most of the researches on trim optimization only consider the resistance performance of the naked hull,the detailed descriptions of the energy saving mechanism are not provided,the varieties of the ship's floating condition and the effects of the coupling of ship and propeller on the propulsion are ignored in the process of numerical prediction.These factors make some errors.In this paper,the model test of the physical towing tank and CFD numerical analysis are used to study the hydrodynamic performance of standard ship model KCS(KRISO)under different draft(design,ballast,overload)and trim angle.The ship model resistance,heave and trim angle are measured in the model test,the influence of the change of the trim angle on the ship model resistance and floating are compared and analyzed,and it provided experimental support for numerical prediction.The numerical analysis method was based on the constraint model and the free model respectively,and the finite volume method was adopt as the discrete method,RNG k-? as the turbulence model,and method of VOF was used to capture the free surface,the initial trim angle was adjusted by overlapping grids,and the relationship between the initial trim angle and the center of gravity was determined by Solidworks.Compared the fixed model and free model values with the test value,the results show that the free model can better capture the hull gesture and resistance under the condition of variable pitch,and it is suitable for trim optimization numerical study.Two dimensional method was used to divide the resistance into the frictional resistance and the residual resistance in the trim optimization mechanism research of the naked hull.Taking hull gesture into consideration,and considering the influence of the waterline length and wetted surface area on frictional resistance,the effects of bow and stern wave,hull surface dynamic pressure and stern flow field on the residual resistance of naked hull,the change of the frictional resistance and residual resistance between trim condition and even keel condition are compared and analyzed.The model of DFBI Superposed Rotation superimposed rotation was increased in the self-propulsion forecasting of the KCS,taking the hull-paddle coupling system and the change of trim angle into consideration,which ensured that the propeller can be attached to the hull under the condition of pitching and heaving.Based on the conditions of the naked hull at the degree of 0 and 0.25 under the design draft,compared the resistance of hull and propeller,the changing of sailing posture,free surface and coupling flow field between self-propelled condition and naked hull condition and variation of thrust and torque,trim optimization of the hull-paddle coupling system based on KCS ship is studied.