電子計算機による船体固有振動数の計算法およびその精度について

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In calculating natural frequencies of a ship, the ship's hull is generally regarded as a free-free beam with variable cross sections. Although several calculation methods by the use of digital computer are available for such a stepped beam analysis, there are few investigations made into the accuracy of those methods. In this report, three methods, Myklestad-Prohl Method, Transfer Matrix Method and Finite Element Method, are chosen as representative methods to analyse ship vibration, and their applicability and accuracy due to the effect of beam properties are investigated. Morever mutual relationship among those methods and the results of their applications to actual ships are discussed. From these studies the following conclusions have been obtained. (1) As to the accuracy of the calculation methods when they are used for calculation of natural frequencies of a ship up to 8th mode, the results are as follows: (a) Transfer Matrix Method: It is possible to keep the error less than 1 per cent by taking 6 terms of Taylor's expansion of transfer matrix when the ship is divided into 20 segments and 4 terms when 40 segments. (b) Finite Element Method: The accuracy is about the same with the approximation of taking 8 terms in Transfer Matrix Method when bending displacement only is considered and 4∼5 terms when both bending and shear are considered. (2) For practical purpose, the above-mentioned two methods are applicable to the calculation of natural frequencies up to 8th mode of vertical vibration with reasonable accuracy. (3) The calculated natural frequencies by digital computer are closely agreed with experimental results in the lower vibration modes. But in higher modes the calculated frequencies are tending to be higher than those measured as ship sizes grow.
社団法人日本船舶海洋工学会の論文
1971-06-30

電子計算機による船体固有振動数の計算法およびその精度について

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