Analysis Of Hull Resistance And Propulsion System Efficiency Considering The External Navigation Environment

Nowadays energy conservation and efficient operation have been reported frequently in shipping industry.Concerned the effect of external navigation environment including hull surface roughness,fouling,and wind to ship resistance,power efficiency and energy efficiency operation indicator(EEOI)of propulsion system and their relationship with sailing speed are analyzed.Basic resistance is calculated by using model testing method and Computation fluid dynamics(CFD)method.The results in two different ways reveal that the turbulence k-e RNG model is suitable for simulating the flow field around the hull with high Reynolds number.Accuracy of numerical simulation is acceptable.Effects of surface roughness,fouling,and wind on ship resistance are analyzed also by numerical simulation.It shows that different surface conditions have different impact on resistance.On the condition of surface roughness(including mild fouling)and moderate fouling,the increased resistance is mainly frictional resistance which can be dealt with the empirical incremental resistance coefficient,however,there is not the same under the condition of heavy fouling that viscous pressure resistance,wave resistance increase more than frictional resistance,the recommended coefficient is not applicable to the reality situation.Moreover,wind has a greater influence on ship resistance and larger sensitivity to the ship speed.With the raise of the wind,the relationship between increased resistance and ship speed is from the linear to power.Frictional resistance plays a major role at low ship speed,whereas residual resistance becomes main part at high ship speed.The simulation results are reference to calculate target ship's increased resistance due to hull surface condition and wind.Propulsion system simulation model of the target ship is established in MATLAB / Simulink platform.Ship speed,hull surface conditions and wind as input parameters while power efficiency and energy efficiency operation index are output results.It indicates that the ship energy efficiency operation index is sensitive to ship speed.Energy efficiency operation index can be remained in low level when speed below a critical value but it will increase once speed over the value under the same external environment condition.Both poor hull surface conditions and wind make propulsion efficiency reduction and energy efficiency operation indicator raise.Furthermore,the effect of wind is more obvious,and the critical value of the speed is gradually reduced with the wind raise.