Analysis Of Fluid Resistance Effect Of Shell Surface Texture With Antifouling Ability

Under the background of promoting energy conservation and emission reduction,the shipping industry has received great attention as a bridge for maritime transportation.When ships navigate in the ocean,the fouling organism can easily attach to the hull and corrode the hull.Then increases the ship's own weight and the surface roughness of the hull,and finally causes the rise of the ship's resistance.The raise of the ship's resistance will lower the speed and cut back the impact of the water flow,and eventually provides a more favorable condition for the adhesion of fouling organisms.Therefore,combining the anti-fouling and drag reduction of ships can effectively improve energy utilization and reduce energy consumption,and is also a powerful response to the call for energy conservation and emission reduction.A large number of previous studies on energy conservation and emission reduction mainly focused on the anti-fouling or drag reduction of ships.However,there is a synergy relationship between anti-fouling and drag reduction.It will be of great significance to ship's energy saving and emission reduction if anti-fouling and drag reduction can be combined.Many organisms in the ocean have their own characteristics of preventing the attachment of fouling organisms.Currently,there are many marine organisms such as sharks,dolphins and shells that rely on surface microstructure to keep the surface clean.Unlike sharks and dolphins swimming at high speeds and secreting mucus on the surface,shells do not secrete mucus and generally live in the sea in a relatively static state.Chlamys nobilis,common in the sea,was taken as the research object for the fouling generally occurs at low speed operation.The anti-fouling area of the surface of the scallops was studied by ultra-deep-field three-dimensional microscope and the data of the acquired features were statistically analyzed to obtain the scale range of the antifouling area.Whereafter,MATLAB was used to obtain the true cross-sectional contour fitting curve of the anti-fouling area of Chlamys nobilis.Finally,a numerical calculation model was established based on the special ribbed anti-fouling surface of Chlamys nobilis to explore the fluid resistance performance.In the meanwhile,the independence of meshing and the accuracy of the selected turbulence model were also analyzed to ensure the rationality of the numerical simulation.In this paper,a model was taken as an example and the numerical calculation results of this model were analyzed from the aspects of shear stress distribution,velocity field and turbulence related parameters,and the drag reduction mechanism of the Chlamys nobilis anti-fouling surface was expounded.The paper believes that: on the one hand,the ribbed structure of the Chlamys nobilis anti-fouling surface changes the flow field characteristics of the turbulent boundary layer.It lowers the energy loss during fluid momentum exchange and the speed gradient of the near-wall area,thus increases the thickness of the boundary layer,achieving the effect of drag reduction;on the other hand,the micro-groove structure interacts with the fluid to create a "secondary vortex" in the groove,hindering the movement of the fluid,inhibiting the assembly of low-speed fluids and high-speed fluids.Intrusion downwards stabilizes the flow field in the near wall area and fundamentally reduces the frictional resistance of the wall.By numerically calculating nine groups of the models established on the surface of Chlamys nobilis,the reasons for the effect of fluid resistance on the Chlamys nobilis anti-fouling surface were discussed.It was found that the inflow velocity,shape and size can affect the drag reduction effect.The surface resistance increases by the incoming flow rate.The higher the speed,the larger the increase.The increase of the shear stress in the high stress region at the tip of the groove is larger than that at other positions.By comparing different models,it is found that the surface groove spacing 2-3 times of the groove depth has better drag reduction effect and the drag reduction effect is worse when the groove pitch is less than the depth,and resistance may increase as the flow rate rises;The calculation results of n-shaped and m-shaped sinusoidal models with similar spacing and depth show that at low speed,the n-shaped sinusoidal model with simple surface structure has better drag reduction effect.When the flow velocity increases to a certain value,the m-shaped sinusoidal model with complicated surface structure has better drag reduction effect.For the same anti-fouling Chlamys nobilis surface,the smaller the groove spacing,the better the drag reduction effect under the condition that the groove depth is constant.However,when the groove pitch drops to a certain value,the resistance might increase.