The Evaluation Method of the Hydrodynamic Frictional Resistance for the Painted Rough Surface

The present study shows a method to evaluate the performance of the paints to reduce the additional frictional resistance in full scale ship Reynolds number. Simultaneous non-linear ordinary differential equations are developed to calculate the hydrodynamic frictional resistance of flat plate based on the momentum equation and Coles’ wall wake law which is the similarity law of the velocity distribution in the turbulent boundary layer. Roughness influence of painted surface is taken into account by adding the roughness function to Coles’ wall wake law. The expression of the roughness function should be determined based on the experimental results of the additional frictional resistance for various kinds of paints. The obtained roughness function depends on the roughness Reynolds number, and it also depends on both the roughness wave height and wave length fraction to its height which are obtained FFT analysis for measured paint surface profiles. The calculated local frictional stress coefficients on the painted surfaces well agreed with the measured ones. The total frictional resistance coefficients of painted surface in the actual ship scale Reynolds number can be evaluated considering influence of surface roughness.