Research On Drag Reduction And Ice Prevention Of Bionic Superhydrophobic Surface Of Polar Ships

Polar ships will be threatened by fluid resistance and cold environment when sailing in the Arctic passage,which will seriously affect endurance and navigation safety.Therefore,it is urgent to meet the drag reduction and anti-ice performance of the surface to improve the overall navigation capacity of the ship.Fortunately,nature can always provide inspiration when it comes to exploring drag reduction and ice resistant surfaces.Inspired by various organisms,biomimetic superhydrophobic surfaces are becoming more and more mature in drag reduction and ice prevention.The bionic superhydrophobic surface can maintain the air layer at the solid-liquid interface,which makes it has the effect of reducing drag and preventing ice.Inspired by the underwater dragon louse and cold-resistant iris plants,this thesis designs bionic porous structures and rhomboid array composite structures on metal substrate by coating method and laser processing.The performance of different bionic microstructures was tested in drag reduction and ice prevention by using relevant experiments.The details are as follows:(1)Aiming at the problems of poor air layer stability and wear in the underwater hull of polar ships.Based on the porous microstructure of the aquatic insect,the bionic porous superhydrophobic surface with ultrafast repair ability was designed and prepared.The bionic super-hydrophobic coating with irregular porous structure is prepared on stainless steel surface by using coating method and sacrificial template method.In order to cope with the actual application scenario,sandpaper wear experiments and seawater immersion experiments are designed to prove its mechanical stability.Finally,the underwater drag reduction performance of the coating is tested,and the ability to maintain the air layer are studied experimentally.In the free-fall experiment,it is found that the drag reduction performance of the bionic porous sample is significantly improved compared with the superhydrophobic surface without porous structures,and the maximum drag reduction is76%.Compared with the superhydrophobic surface without porous structures,the maximum drag reduction of the bionic porous surface is increased by 32%.Secondly,the effect of different pore sizes on the gas storage performance is investigated.It is found that the porous structure with an average pore size of 50μm can effectively delay the escape velocity of the air layer on the superhydrophobic surface.In addition,the porous structure can effectively balance the capillary force and resist wetting behavior in the edge region.(2)In order to deal with the problem that the surface of polar ships is easy to freeze in the cold and high humidity environment,a hardy plant growing near wetlands,Iridaceae,was selected as the bionic object in this thesis.The iris plant is able to make the liquid droplets on the leaves roll off quickly to effectively prevent the leaves from freezing.The bionic rhomboid array composite structure of the iris family was selected to deal with the problems such as easy icing in high humidity environment.Bionic anti-ice surface with rhomboid array composite structure was prepared on metal substrate by laser ablation and immersion method.In order to simulate the sea fog environment and the splashing of sea water,the surface condensation and droplet flow characteristics of the bionic anti-ice sample were analyzed.The experimental results show that the bionic rhomboid array composite structure sample can make the tiny droplets quickly gather and roll off the surface to prevent the droplets from freezing on the metal surface.Through the delayed freezing experiment,it was found that the bionic iris sample could prolong the freezing time of distilled water and salt water by more than 4 times,so that the droplet would roll before freezing.The delay mechanism is due to the fact that the cross-arranged rhomboid array composite structure effectively reduces the contact area between the sample surface and the droplet,thus significantly reducing the heat transfer rate.This study will provide a new idea and method for the application of superhydrophobic surface on polar ship surface.