船の安定性能の簡易判定法

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The adequacy of stability qualities of a vessel in a storm can be jndged by comparing the ratio R_m of the reserve dynamical stability referred to a gust to the inclining energy with that of a critical vessel of the same type. The latter ratio that is the standard work ratio was determined by a simplified method for critical vessels selected from among those presented in anthor's previous paper. The causes which incline the vessel are limited for simple comparison to the steady wind, gust and waves. The equivalent wind moment lever L_s. which is expressed by the equation.L_s=0.78×10^<-4> c^2 v^2 (Ah)/W, is assumed to be constant for all inclinations, and the effective velocity of gusts during gales is taken as 1.25 times the average wind velocity. The vessl is supposed to be rolling among irregular waves whose mean period is equal to the natural period of vessel about the angle of heel θ_s produced by the steady wind, and struck by a gust when she rolls on the weather side as usually considered. The relative angle of roll on the weather side can approximately be obtained by the equation θ_0=0.96 θ_<a1>-γΘ cos p_a, where θ_<a1>=0.33θ_<at>+0.50(θ_m-θ_s)<0.8θ_<at> ;θ_<at>=√<(πrΘ)>/(2N) ; γ=0.74((KG)/d)^<0.85>;N=(δθ)/(θ_<at>^2=a/θ_<at>+b; pa=(BΘ)/d{0.65+5.56(θ_<at>)/(Θ^2)-0.183(θ_<at>^2)/(Θ^4)}, The period of roll of vessels which is necessary to find the maximum surface wave slope is approximately given by the following formula for passenger, passenger-cargo and cargo vessels T_s=2.01B./√<m>{0.125 (H^2)/(B^2)+ 0.020 H/(d_0)(1+3.7(d_0-d)/(d_0))+0.027 }^<1/2>, where H=D+A_e/L.The standard work ratio R_c calculated from critical vessels was found to be given by the equation R_c=1.20+f{0.38 (2.25-K_v) +0.95 (2.25-K_v)^<1.85>} on condition that R_c is taken as 1.20 when K_v is greater than 2.25. The value of the coefficient f is 1.0 for ordinary vessels and 0.20 for vessels without bulwarks such as tankers. The stability qualities of a given vessel may be judged to be suitable if the stability factor C_0 given by the ratio R_m/R_c is greater than unity. The standard wind velocity adopted in the present paper is 25 m/sec. for ocean-going vessels and 18 m/sec. for coasting vessels.Nomenclature.L : length of vessel.B : moulded breadth of vessel.D : moulded depth of vesel.d : draft of vessel.d_0 : load draft.W : displacement.A : wind area.h : lever of wind area moment, i, e., vertical distance of c. g. of A and c. g. of the area of centre line plane below water.K_v=Ah/W m : metacentric height.GZ_m : max. stability arm.e_m : angle of inclination at GZ_m.θ_r : angle of vanishing stability.v : velocity of wind.c : coefficient of velocity due to the height of c. g. of wind area.h_1 : distance of c. g. of A above water.L_s : equivalent lever of moment due to steady wind.L_a : equivalent lever of moment due to gust.θ_s : angle of heel due to steady wind.T_s : period of complete roll of vessel.T_w : period of waves.T_n : period of roll about steady heel θ_s up to mean angle θ_n.Θ : max. surface wave slope.γ : reduction coefficient for effective synchronous wave slope.N : coeffcient of extinction, the resistance being assumed to be proportional to the square of angular velocity.θ_<at>, θ_<ae> : theoretical and experimental absolute angle of roll among regular synchronous waves respectively.θ_<0e> : experimental relative angle of roll among regular synchronous waves.θ_<an> : mean absolute angle of roll about θ_s among irregular waves whose mean period is equal to the vessel's natural period.θ_<a1>, θ_<a2> : absolute angle of roll among irregular waves on the weather side and on the lee side respectively.θ_0 : relative angle of roll on the weather side among irregular waves.p_a : phase lag of absolute rolling.K : transverse radius of gyration of vessel.H : effective depth of vessel.
社団法人日本船舶海洋工学会の論文

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加藤弘
東京大学工学部

船の安定性能の簡易判定法

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