Study On Resistance Of Fouled Hull And Fouling Release Behavior

With the entry into force of the effective ship management index:Energy Efficiency Design Index(EEDI)and Energy Efficiency Operation Index(EEOI),energy conservation and emission reduction have become an irreversible trend.To solve the problem of ship emissions,we must start with reducing energy consumption.The increase in resistance of ships will be accompanied by the problems of excessive energy consumption and increased CO2 emissions.Therefore,we pay attention to the phenomenon of increased resistance,increased energy consumption and increased emissions due to external factors.For a certain hull in the Yangtze River Basin,we study the adhesion of the outer wall surface Analysis of the relationship between the speed,surface condition and drag caused by the changes in sailing resistance under the circumstances;based on the results of the research on increasing the resistance of the fouling,and then exploring the release behavior of different fouling,analyzing the release of the fouling The conditions are of great significance for decontamination,resistance reduction and energy consumption.Using CFD method,combined with empirical formula,to study the navigation resistance of smooth surface target ship model at multiple speeds,the results show that the RNG k-εturbulence model and VOF method are used to calculate the numerical value of the flow field around the ship with free surface is feasible.Furthermore,the resistance of the ship hull under different fouling conditions at different speeds is simulated.The results show that in the light fouling stage,the smaller the roughness,the greater the impact of increased resistance;while for heavy fouling At the maximum speed,the resistance increase in the stage III of heavy damage is more than 2.5 times that of the rough stage with a roughness of 1 mm,and the resistance increase in the stage of heavy damage can reach 36%～65%of the resistance of the smooth hull.Therefore,the effect of heavy pollution cannot be ignored.Finally,the roughness subsidy coefficient ΔCf is involved in the estimation of the resistance of the rough surface hull.Due to the different types and sizes of hull subsidy coefficients,the scale effect between the real ship and the ship model is considered,and the roughness of the target hull is calculated The degree of subsidy coefficient,and found that the empirical recommended value of the roughness subsidy coefficient is not applicable to severe pollution.Based on the severe resistance increase caused by the fouling,combined with the fluid-solid coupling theory,through numerical analysis methods,the anti-fouling performance parameters affecting the surface of the ship hull:coating thickness T and elastic modulus E,the anti-fouling attached to the silicone was studied Release behavior of "hard fouling" barnacles and "soft fouling" Ulva spores on the coating.The calculation results show that the thickness of the coating and the elastic modulus have a certain effect on the release of "hard fouling" barnacles,but the effect of a single variable is not as good as the composite variable of the coating(E/T)0.5.For coatings with a low composite variable(E/T)0.5,the barnacle can be released under a small external force due to the fouling and the weak adhesion between it,and when the coating elastic modulus is low,the barnacle The release behavior is more inclined to the peeling method,and for the coating with high elastic modulus,the release depends on the shearing method;for Ulva,when the elastic modulus of the antifouling coating is small,the spores attached to the surface are easier to release The thickness of the coating has no significant effect on the release of Ulva spores.When the adhesive pad of the Ulva spores is thick enough that the contact angle between the adhesive pad and the coating is greater than 90°,the stress singularity at the contact edge is stronger,and the Ulva spores will come into contact with the coating Release at the edge.