| During the voyage of ships, the fouling on the hull will increase the resistance ofthe ship. it is therefore of great significance to take anti-fouling measures to lower thedead weight of ship，to reduce the frictional resistance, to implement energyconservation and emissions reduction in shipping industry. For these reasons, a lot oftheoretical and experimental study have been done over the past years and manykinds of drag reduction technology have been developed such as: ship surface withanti-fouling and drag reduction ability, antifouling coating, anti-fouling and dragreduction agent, low-energy surface and so on. Owing to the negative impact ofsurface coating on the marine environment and its short functional life circle，the dragreduction effect is far from satisfying for the practical engineering application.There are a lot of biological structure and various functional surface in naturewhich have special functionality of drag reduction, antifouling and self-cleaning.Based on the principle of bionics, the non-smooth surface of shell is taken as thebionic prototype for the design of ship antifouling-drag reduction synergetic surface.The resistance performance of antifouling shell was discussed in this thesis. Firstly,the simplified form and size of bionic microstructure surface was determined. and thephysical model and geometric model was constructed. Secondly, the numericalsimulation method was selected to calculate the frictional resistance coefficient of flatplate. Thirdly the flat plate model calculation results was compared with the empiricalformula calculation results, and the calculation error is within the range ofengineering calculation, the results can ensure the rationality and accuracy ofnumerical simulation method.The wall shear stress of the bionic non-smooth surface, the velocity distribution,turbulent kinetic energy and turbulence intensity distribution and the flow velocityvector of near surface area have been analyzed. Results show that high shear stressarea at the tip of riblet is very small, however, the shear stress number is low on theriblet valley area and the area is big. In that case, the riblet surface has a smallernumber compared with flat surface on the total resistance. Ribelt surface can alsoreduce the velocity gradient of the near wall area which leads to the reduction of wallshear stress on the riblet surface. And the low speed of secondary vortex pair is found in the valleys by the analysis of velocity vector diagram. These vortex pairs push thehigh shear stress region away from the wall, just like the effect of the rolling bearing,changing the solid-liquid contact friction into liquid-liquid contact rolling friction toreduce the friction.In this thesis, the resistance calculations of the riblet surface under differentReynolds numbers have been carried out. The results show that for the same kind ofriblet (V riblet) with the dimensionless size s+and h+being equal to16.49, the dragreduction effect is the best. Comparing the resistance performance of five differentsimplified form riblet surface, the calculation results show that L riblet surface has themost outstanding performance on spanwise flow restriction and flow fieldstabilization which leads to the best drag reduction effect (drag reduction rate was5.636%). The drag reduction effect of U, V and spacing of v-shaped riblet surfacesare3.122%,5.135%and1.926%respectively. But L riblet surface has a poorerdurability than other surfaces (more vulnerable), therefore U, V and spacing ofv-shaped can be more easily applied to the practical situation. At the same time, thetrend of resistance of different shape riblet surface has also been forecasted andevaluated.The resistance are calculated and compared for apex Angle of60°,90°andapex Angle of chamfering V riblet surface. The results show that the turbulent kineticenergy and eddy quantity near the surface of60°apex Angle riblet surface are thelowest, namely the quantity of the fluid kinetic energy dissipation is the lowest whichleads to the best drag reduction rate3.405%. The apex Angle of chamfering ribletsurface has a weaker ability of blocking spanwise flow, so the resistance performanceis poorer. The riblet surfaces with different riblet spacing has also been calculated, theresults show that the riblet spacing cannot be too big to allow the vortex rush into theriblet valley and it also cannot be too small to make the surface area increased somuch which leads to drag increase. For the spacing of transverse riblet, the resultsshow that when the spacing distance d is equal to s, the drag reduction effect is thebest. |
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