| When underwater vehicle (such as submarine and torpedo) goes through in water, it will produce the impulse of speed and pressure to form the flow drag and noise, furthermore to reduce the speed of the vehicle. So research and development of drag-reducing coating has an important role in enhance the properties and strength the capability of national defence.Spray Polyurea Elastomer (SPUA) Technology is a kind of film forming one to prepare elastomer via high temperature, high pressure and impingement mixing equipment with the mixture of compound A and B. The polyurea composite drag-reducing coating prepared by SPUA is consisted of soft skin and fatness coating, which their mechanical properties are similar to dolphin's.The quasi-prepolymer A of the soft skin drag-reducing coating is synthesized by MDI-50 and polyol (Acclaim?4200 and 330) with NCO content at 13～14%. Compound B consists of sterically hindered amine (JefflinkTM754), hard block content at 36%. The final soft skin drag-reducing coating can be used in seawater while temperature range in 0～40℃with tensile strength 5.4MPa, elongation 796%, 100% modulus 2.18MPa and loss factor over 0.3. The density of the cured coating is 1.00～1.05g/cm3, it meet the need of density near and impermeable to water.The quasi-prepolymer A of the soft fatness coating is also synthesized by MDI-50 and polyol (Acclaim?4200 with NCO content at 11～12%. The isocyanate index is controlled at 0.9. Compound B consists of long chain amine terminated polyether, polycaprolactone (CAPA3091), sterically hindered amine (JefflinkTM754) and auxiliaries. The final fatness coating is characterized with tensile strength 3.4MPa, elongation 906%, 100% modulus 1.92MPa. The above skin coating is sprayed on the surface of the fatness coating to form a composite one like dolphin's skin function.Either the soft skin drag-reducing coating or the soft fatness coating, the optimal synthesis condition of compound A is①polyol must be dehydrated below the water content at 0.05%,②synthesis temperature is 80℃and reactive time is 4 hours,③the viscosity of quasi-prepolymer is 1500～1600 mPa.s at 25℃,④the amount of diluent agent is less 10%. The optimal spray parameter is liquid pressure 65Kg/cm2, temperature 65℃, output 0.6～1Kg/min and gun moving rate 0.3～0.5m/s.This coating is characterized with non-toxic, non-odor, easy application and seamless.The drag-reducing rate of the soft skin drag-reducing coating is 12～15% at the flow speed of 4m/s and reach a high level at home. The drag-reducing effect of the composite coating is 6.84% than that of the single soft skin coating 5.18% by flow test. It is shown that the composite coating is much better than the soft skin drag-reducing coating in inhibition of pressure impulse, maintenance of the stability of laminar flow and drag-reducing in some flow speed.The models with the composite drag-reducing coating was towed and transported to test for several times. The result shows that the strength of the composite coating is good enough to resist to the high-speed flow and exterior impact. This achievement can meet the need of drag-reducing and strength of the coating.In order to develop a new underwater vehicle SPUA drag-reducing coating, the specific size of mini-fluctuation of designed geometry for vortex street traveling wave on the surface of material has been computed numerically by CFD (Computational Fluid Dynamics), which simulates the dolphin's skin and can assure mini-vortex entrapment and will not permit the vortex to escape and be washed downstream. At the same time, an experimental study on the soft drag-reducing material combined with bionics technology, compliant walls, travelling wave drag-reducing is discussed by testing effect. Liquid ball bearing effect is shown in CFD with drag-reducing.The collaboration effect of the traveling wave and the composite coating will be further researched in the future.
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