著者

大沼 覚 山本 鷹司 中野 元博 尾上 光賢

出版者

社団法人 日本船舶海洋工学会

雑誌

西部造船会々報 (ISSN:0389911X)

巻号頁・発行日

vol.38, pp.93-120, 1969

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Qualitative investigation has been carried out on the vibration of superstructure which is assumed to be a shear beam of uniform section on elastic foundation. Coupling effect with vertical vibration of main hull is also studied, and is assessed to be less than 5% on the frequency. Calculation procedure of the vibration, using electronic digital computer, is established treating the deck houses as an array of shear beams connected each other by elastic springs. The qualitative investigation mentioned above is extended in more detail by this procedure. The results show that there exists a relation among the calculated frequencies, which is similar to so-called Dunkerley's formula, i.e. (1.07/Nc)^2=(1/Nr)^2+(1/Ns)^2 where Nc, Nr and Ns are calculated frequencies and Nc; Considering finite values of both vertical-and shearing springs. Ns; Frequency in the limiting case where elasticity of vertical springs tend to infinity. Nr; Frequency in another limiting case where elasticity of shearing springs tend to infinity. Then the lowest frequency is effected predominantly by the lower one of both Nr and Ns. In the actual structures Ns has simple relation with the height of the structure, i.e.: Ns=2600-90H cpm (H: height of superstructure, excepting poop Dk house) On the contrary, Nr undergoes significant changes due to the variety of structure. Vibration experiments have been carried out on 10 ships, and the vibratory behavior of the superstructures is observed. Comparison between measured frequency and calculated value shows that the latter is higher than the former by about 30%. Thus the lowest frequency can be estimated applying the empirical coefficient (0.73) to the calculated values. Estimated frequencies of 10 ships by digital computer agree within±10% of error with their measured values. A brief discussion on the effect of designing factors on the frepuency is investigated by the procedure mentioned above. Finally the simplified method is proposed to calculate natural frequency. Estimated frequencies of 14 ships by this method agree with their measured values within±15% of error.