Research On Antifouling Mechanism Of Coral-like Tentacle Bionic Structure

Marine biofouling has serious harm to the shipping,industry and aquaculture in the ocean,causing huge economic losses and seriously restricting people's exploration and development of marine resources.With the deepening of environmental protection awareness,traditional antifouling coatings with serious environmental pollution are gradually banned.In order to deal with the harm caused by marine biofouling,the development of new environmentally friendly antifouling coatings has important economic value and strategic significance.Sarcophyton trocheliophorum is a long-term fixed growth in the ocean organisms,they cannot hinder the attachment of fouling organisms through the fluid shear force generated by the movement of animals such as sharks and dolphins,but their surface can maintain clean.Through the observation and experiment of soft coral,it is found that the " harmonic motion " response of coral tentacles under the excitation of fluid medium plays an important role in preventing the adhesion of microorganisms.Inspired by this phenomenon,this paper designs a bionic structure of coral-like tentacles.Based on the similarity principle,the designed tentacle-like structure is a cylinder with a diameter of D = 1 mm,a height of 7D,and a tentacle-like spacing of 3.5D.The rigid tentacle-like structure of white resin was fabricated by 3D printing,and the silicone rubber was prepared by the template method flexible tentacle-like structure.In order to explore the antifouling performance and antifouling mechanism of the bionic structure of coral-like tentacles,this paper uses the common pantrophic paracoccus in the ocean as the fouling bacteria.Through the water tank experiment and numerical simulation,the comparative experiments of single,multiple rigid tentacle structures and single flexible tentacle structures are carried out in the velocity range of0 – 5 m/s,and the experimental results showed that:(1)Rigid tentacles do not respond to fluid excitation.Under fluid excitation,the flexible tentacle structure not only bends in the direction of water flow,but also swings in the direction perpendicular to the water flow.The bending angle,swing frequency and swing amplitude increase with the increase of flow rate.(2)The distribution of bacteria on different tentacle structures is similar,mainly concentrated in the windward area,with little bacterial adhesion in the leeward area,and almost no bacterial adhesion in the lateral area;(3)The adhesion amount of bacteria on a single rigid tentacle decreased first and then increased with the increase of flow velocity,and the adhesion amount was less in the range of 1.5-3 m/s flow velocity.(4)At the same flow rate,there are significant differences in the amount of bacterial adhesion between different tentacle structures and different parts: the single rigid tentacle structure,the parallel double tentacle structure and the tandem double tentacle structure front tentacle have the most bacterial adhesion;the rear tentacle of the tandem double tentacle structure was the second;and the single flexible tentacle structure had the least amount of bacterial adhesion.Through the above antifouling performance test results combined with numerical simulation,it is found that the "harmonic" response of the fluid medium excitationtentacle-like structure is the main mechanism to prevent bacterial adhesion,the mechanism of fluid medium excitation-coral-like tentacle structure interactionbacterial adhesion/desorption is as follows:(1)The interaction between the tentacle-like structure and the fluid medium affects the distribution law of bacterial adhesionThe increase of the tangential flow velocity in the side area of the tentacle cylinder hinders the adhesion of bacterial particles,and the bacterial adhesion in this area is the least;in the leeward area of the tentacle,there is a phenomenon of de-vortexing,and the unstable flow field is not conducive to the retention of bacterial particles,and only a few bacteria adhere to the tentacle wall during reflux;while the fluid flow in the windward area of the tentacle structure is poor,forming a low-velocity area where bacteria and other pollutants are easy to accumulate,which is the most seriously polluted area of the tentacle structure.(2)The flow velocity changes the thickness of the boundary layer and the kinetic energy of bacteria,thereby affecting bacterial adhesionThe low normal flow velocity in the boundary layer forms a "water film" near the tentacles,preventing bacterial particles from approaching the tentacle wall,and as the flow velocity increases,the tangential flow velocity in the boundary layer increases,forcing bacterial particles to leave faster,lead to a decrease in the amount of adhesion;However,with the further increase of the flow rate,the boundary gradually becomes thinner,and the normal kinetic energy of the bacterial particles is increased,so that the bacterial particles quickly penetrate the boundary layer "water film" and adhere to the tentacle-like wall surface,lead to an increase in the amount of adhesion.(3)Tentacle-like flexible features and their arrangement eliminate low flow areas and reduce bacterial adhesionThe flexible tentacles bend along the incoming flow direction and swing perpendicular to the incoming flow direction under the excitation of the fluid medium,the superposition of the two motions disturbs the low-velocity area around the tentacle,making it difficult for bacteria to accumulate on the tentacle wall;The rear tentacles in the tandem double tentacle structure are affected by the vortex street shedding generated by the front tentacles,and the incoming flow on the windward side of the tentacles becomes no longer fixed,eliminating the influence of the low flow rate area,and it is difficult for pollutants such as bacteria to gather in the unstable flow field,The antifouling performance of the tentacle structure is improved.In this paper,the antifouling mechanism of the coral tentacle-like bionic structure is revealed by the combination of water tank test and simulation test,which provides theoretical guidance for the design of the tentacle-like bionic antifouling surface and new ideas for the research of new antifouling coatings.