艦船の横動搖試験成績の新解析法
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概要
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The rolling of a ship up to large angles of inclination in still water may nearly be expressed by [numerical formula] where λ_<s^2>=Wh/I ; W=the displacement ; h=the me acentric height ; I_s=the apparent moment of inertia at any amplitude ; k=the metacentric factor ; [numerical formula] the actual energy lost per swing. Let [numerical formula] E_i being the dynamical stability at an inclination θ_i, then we obtain [numerical formula] If we know the successive amplitudes and the corresponding periods by experiments, we shall have the variation of the apparent moment of inertia in terms of amplitude by the formula [numerical formula] where I_o and T_o are the apparent moment of inertia and the period of a single roll respectively when the ship rolls to very small angles. It was found from the experimental results that the apparent moment of inertia increases with the amplitude even though the period of roll decreases, and that no theoretical formulae neglecting its variation give a correct value of perid for any specified amplitude, particularly for ships fitted with deep bilge keels. As the rolling of a ship among waves is, in general, accompanied with other oscillations such as heaving, pitching, yawing, etc., the righting moment contained in the ordinary differential equation of rolling should be modified on account of the changes in the virtual weight of ship, the buoyancy, the metacentric height, etc. The wave structure is disturbed by the presence of the ship, especially in the case of synchronism, and consequently water particles, exerting an impulsive force upon the ship, affect her oscillations. When all these periodical dynamic effects on the rolling are represented by an additional resultant couple, the equation of motion may be written as [numerical formula] where λ_<w^2>=Wh/(I_w) ; I_w=the apparent moment of inertia of the ship rolling among waves. The effective coefficient of resistance α_w should be determined such as the loss of energy per roll among waves is equal to that when the ship rolls in still water with the same periol as waves. The rolling near synchrouism is approximately shown by taking the first terms from the two series in the above equation, where the reduction coefficient γ_1 for the effective wave surface may be calculated from Dr. Watanabe's formula and γ_<1'> and η_1 are decided in accordance with the actual amplitude and plase difference. From the results of the the rolling tests of a ship-model with the moment of inertia and the period varied but with the displacement and the metacentric height kept constant, it was concluded that the coefficients of resistance α and β depend upon the period of roll or waves, and that the moment of resistance for this model is expressed in the form, Moment of resistance [numerical formula] where α_0,α_1,α_2,β_0 and β_1 are constants independent of the amplitude of roll and the period of waves.
- 社団法人日本船舶海洋工学会の論文
- 1936-08-20
著者
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