浮力中心位置の影響 : 最小抵抗船型の研究

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The effects of deviation of ship form-in brief, the effects of C.B. of ship upon the resistance are calculated theoretically, as an attempt to discover the least resistance ship form. Since Michell published his mathematical formula for ship wave resistance, the discrepancies between actual and theoretical cases have been researched by means of the model experiments by tank authorities in the world. Wigley, especially, made careful considerations for the effects of viscosity on the wave-making and he introduced an empirical allowance to the ship aft of amidships and calculated the wave-making resistance of the bow and stern separately from Michell's solution. In these cases, the ships were too slender compared with the sea-going vessels. In the broad ship, however, it is obvious that the aft ship is affected by viscosity and also by eddy-making probably. It may be very difficult to study theoretically these effects on the wave-making. The author has prepared this paper tentatively without investigating the mechanisms of wave-making in the first place. It is reasoned mathematically from Michell's formula that the least resistance ship form is symmetrical fore and aft in the perfect fluid, though this is transformed according with its speed. In general, therefore, the best ship form must be asymmetry lengthwise in actual case, this form is shown as follows, adopting two-dimensional flow for brevity, and taking axis of Ox lengthwise, Oy broadwise, and the origin O amidships, y=F_1(x^2)+F_2(x), where F_1 and F_2 are even and odd functions respectively. A form which deviate from and has same area as the best form is written as y=F_1(x^2)+F_2(x)+F_3(x). F_8 is odd function and may be small compared with F_1+F_2,supposing our present ships. It may be that the wave-making resistance of this form in actual fluid is correspondent with that of a next formula in perfect fluid, y=F_s+F_3 where F_s is an even function (the best form) and F_3 as before. In this stage, Michell's formula can be applied. The effect of F_3,the deviation from the least resistance form, can be separately calculated without considering the interferences with the main body F_s, although there are interference-phenomena in the wave syst m. A following formula was applied, [numerical formula] where k and l are parameters to change the deviation. The additional wave-making resistance due to F_3 is reduced to [numerical formula] in which [numerical formula], (c…ship speed) [numerical formula], [numerical formula]. From another point of view, this resistance is very analogous to the total wave resistance of two ships running in tandem, each ship-length being l and the space 2k, nevertheiess, the wave system of one ship of them is reverse exactly in the sense compared with the actual case. The properties of above formula are shown in Figs. 3 and 4,being further indicated the range of variation of the additional resistance by dotted lines in Fig. 3. The effects of deviation from the least resistance form, or the effects of longitudinal position of C.B. of ship are calculated for various deviatecl forms. These results are shown with each form in Figs. 5-9. As it has been expected, the additional resistance constant is swelled at lower speed according as the range of deviation is reduced (this is mainly due to Froude Number), and becomes to fluctuate more frequently as the deviation moves to ship-ends (this is mainly due to the ratio k/l, and can be comprehended from the cases of two ships in tandem).
社団法人日本船舶海洋工学会の論文
1941-02-25

浮力中心位置の影響 : 最小抵抗船型の研究

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