海水摩擦抵抗を低減する船舶用塗料の基礎技術の研究開発

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A project has started in order to develop a prototype paint for reducing frictional drag of a ship. The paint releases polymer additives from the surface of ship's hull to reduce the friction by Toms effect. The development target of the prototype paint is to reduce the surface frictional drag by 10 %, which is confirmed by two lab-scale experiments. The results of the project are summarized as follows : i) Mechanism of polymer effect : The measurements of turbulent drag reduction by polymer aqueous solutions have been carried out with a circulating water channel system with a porous plate wall for blowing polymer solutions into the stream. The blowing polymer solution test, simulating the release of polymer additives from painted ship hull surface, has also shown a high surface frictional drag reduction by 15 %, demonstrating that supplying the polymer from the wall surface reduces the turbulent drag. Direct numerical simulation of the turbulent boundary layer flow in an inhomogeneous polymer solution has also confirmed this conclusion, and has suggested that the polymer additives would stay near the wall and reduce the turbulent drag. ii) Drag reduction characteristics of polymers : Frictional drag reduction characteristics of the polymer solutions have been examined by measuring pressure drop in their tube flows. The molecular weight of polymers in the solution has been measured by GPC'MALS system. The results imply that the drag reduction rate significantly depends on the molecular weight, suggesting that the 10 % reduction of the frictional surface drag would need molecular weight greater than several millions g/mol and that the solution concentration should be higher than 0.2 ppm. iii) Evaluation of prototype paints with polymer additives : Several paints containing polymer additives have been prepared for elution examination for measurement of the frictional drag reduction. As a result of the examination, the some prototype paints are selected for the precise investigation using the concentric cylinder test unit. From the investigation, the selected paints are characterized by a physical property of controlling the amount of polymer release from the surface. Selected prototype paints, which are self-polishing type paints with poly (ethylenoxide) with fine particle size, have exhibited a significant frictional drag reduction more than 10 % by measuring with the concentric cylinder equipment. iv) Towing tank techniques for frictional drag measurement : The proposed method using a couple of flat panels, one coated with the developed paint and the other with a conventional one, has shown successfully good reproducibility and accuracy where the error in drag measurement would not exceed 1.0 %. The effective prototype paint was measured the performance of frictional drag reduction in the external flow by this measurement apparatus. As a result of the performance test, the best prototype paint has shown 27.2 % of maximum drag reduction compared with the conventional paint and obtained 6.6 % of stability drag reduction, which corresponds to approximately 18.4 % reduction for a 100m ship estimated by considering the polymer accumulation along the ship's hull from fore to aft.
2010-12-28

海水摩擦抵抗を低減する船舶用塗料の基礎技術の研究開発

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