Midshipに働くWave Bending Momentの近似的表示に就て

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This paper deals with the approximate expression for the wave bending moment at the midship section of a ship and clarifies the reason why many experiments hitherto executed differ so widely. According to the strip theory, vertically acting force on the unit length of a ship can be given by the formula (1). By multiplying x on the mean valne of (1) for +x and -x, and integrating over the ship's half length, we obtain the bending moment at the midship section. Now for T2-Tanker, the author assumes the ship to be symmetry fore and aft, and neglects the terms in (1) due to the forward velocity and resistance caused by the wave motion, as it is known that the bending moment is affected little by the forward velocity for Froud Number F_r<0.2 and increases gradually with F_r, and the effect of the vertical resistance due to wave motion may be considered very small. Then, it is deduced that the midship bending moment of the ship statically in equilibrium condition can be calculated by the usual standard calculation by taking the effective wave height he, h_e=C_1C_2h where h=acual wave height C_1=e^<-2π/λd_m> C_2=1-π^2C_wB/4λ λ=wave length d_m=mean draft B=ship's breadth C_w=water plane coef. The bending moment thus obtained may be considered as that at F_r=0. (actually a little greater) For the ship with forward velocity, the author took only the heaving motion into account as pitching effect is small, and assumed the distribution of the additional mass and vertical resistance due to the surrounding water along ship's length to be parabolic. Under these considerations, the midship wave bending moment is calculated and its non-dimensional expression C is given by the formula (15). It is to be noted that C is a function of r=x_g/x_w, where x_g and x_w being the distances between centers of virtnal mass and centers of area of the water plane for the fore and aft parts of the ship. Calculated results of C for T2-Tanker for λ/L=1.00 is given in Fig. 6, from which it is seen that C is greater with smaller r for F_r<0.2, the tendency being opposite for larger F_r. The results obtained at many experimental tanks agree quite well with the calculation, if the ratio=radius of gyration/ship length be taken instead of r, Fig. 6, also, coincides quite well with the results of the experiments obtained at the Mitsubishi Tank quantiatively, if corresponding valuues of r be taken. For smaller λ/L, variation of C with F_r is shown by experiments to be small which can also be verified by theoretical calculation.
社団法人日本船舶海洋工学会の論文
1962-09-20

著者

渡辺恵弘
九州大学

Midshipに働くWave Bending Momentの近似的表示に就て

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