Study On Energy Efficiency Change Of Ship Main Engine And Speed Optimization Under The Influence Of Multiple Environmental Factors

Under the environment of energy saving and emission reduction,reducing fuel consumption and improving ship energy efficiency have become the focus of shipping industry.This paper takes the navigation environment factors as the starting point,studies the influence of various navigation environment factors on ship energy efficiency,and achieves the purpose of improving ship energy efficiency by optimizing ship speed.Taking 5000 PCTC(Pure Car and Truck Carrier)as the research object,this paper calculates the ship resistance under different navigation conditions by using the empirical formula for calculating ship resistance and the results of ship towing experiment,and studies the influence of wind speed,wave height and direction angle of wind and wave on hull resistance.The dynamic simulation model of ship propulsion system is built based on AMESim,and the energy flow and related efficiency of propulsion system under different environmental conditions are simulated and analyzed.The simulation results show that the output power of the main engine and the transmission efficiency of the shafting system decrease first and then increase with the increase of the direction angle of wind and wave,and reach the minimum when the direction angle of wind and wave reaches 120 °,while the value decreases gradually with the increase of the direction angle of wind and wave at higher speed.The propeller's changing trend is always contrary to that of these parameters.For ship propulsion efficiency,the value increases with the increase of ship speed under the condition that the wind power level remains unchanged.When the ship speed reaches a certain value between 13 kn and 14 kn,the propulsion efficiency begins to decline.When the ship's speed is constant,the propulsion efficiency decreases with the increase of wind level.When the wind force is less than level 5,the change range is relatively flat.When the wind force exceeds level 5,the ship propulsion efficiency begins to decrease rapidly.Propulsion efficiency varies slightly with the direction of wind and wave,and its fluctuation range is about 1 %.At a lower speed of less than 8 kn,the propulsion efficiency increases with the increase of the direction angle of wind and wave,and decreases slowly with the increase of the direction angle of wind and wave until the direction angle of wind and wave exceeds 120 °.When the speed is higher than 8 kn,the propulsion efficiency increases with the increase of wind wave direction angle.A ship energy efficiency simulation model is built based on AMESim to analyze the ship energy efficiency and optimal speed in different environments.The simulation results show that when the wind and wave direction angle and speed are constant,the energy efficiency operation index of the main engine of ship does not change much when the wind power level is less than 5.When the wind power level exceeds 5,its value suddenly changes and increases sharply.When the wind power level(0-5 wind)and the wind wave direction angle are constant,the energy efficiency operation index of the main engine of ship first decreases and then increases with the increase of the speed,and at the speed of 5 kn,it reaches the minimum value.When the speed exceeds 11 kn,the energy efficiency index of the main engine increases sharply.When the wind power level and speed are constant,the energy efficiency index of the main engine decreases gradually with the increase of the wind wave direction angle,and the larger the direction angle,the slower the change of the energy efficiency index of the main engine.Under different navigation conditions,the optimal ship speed fluctuates from 13.16 kn to 13.45 kn,and the smaller the direction angle of wind and wave,the larger the wind level,the greater the fluctuation range.