表面粗度による抵抗増加の研究 (第2報)

概要

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In the previous paper, the hydrodynamical characteristics of sand roughened surface and painted one were discussed and it was found that the differences of characteristics between two types of roughness were remarkable. Trying to explain these differences, the simple wavy roughened surfaces are investigated experimentally in this report. The main conclusions obtained are as follows ; (a) In the fully developed state, the resistance curves of wavy roughened surfaces are nearly parallel to that of smooth one (Fig.2 ; W-1,2,4,5,6,7), and these features are the same as painted surfaces. (b) However, the wavy roughness having steeper slope than about 1/10 shows the sand roughness characteristics (Fig.2 ; W-3) and the slope seems to be a critical value (Fig.2 ; W-2, 3) . (c) In the fully developed region, the roughness functions of wavy roughened surfaces take constant values (Fig.5, Fig.6), whose magnitudes are nearly in propotion to the roughness heights (Fig.7). (d) The empirical equations of roughness functions are introduced (Eq. (5), (6), (7)). ( e) For three dimensional wavy roughened surface, only one case is tested and the result is shown in Fig.3. Finally, as an application the C_F of a tanker whose skin plates are covered with various roughnesses are calculated (Fig.9).