Abstract
This paper presents some results of the calculation on the forced response of lateral vibration in the line shafting of twin screw ships. The calculation, by means of the transfer matrix method, takes into account of the mass and stiffness of ship structure, the gyroscopic action of the propeller and the stiffness and damping of oil-film in bearings.In the case of the ships' line shafting, the oil-film stiffness in bearings can approximately be considered as rigid, since the relative deflection between bearing and journal is very small. The oil-film damping, existent as it is, is less than the damping of the propeller.In the case where the ship hull is assumed to be rigid, the orbit of shaft centre is nearly circular, which means considerable whirling. In the case of the bossing-type hull structure, however, the orbit changes to ellipse with very high eccentricity ratio, which means that the vibration is practically unidirectional and that the precessional direction such as forward or backward of orbit may be insignificant.Also, the authors present an approximate calculation method based on the modal analysis for covenient use in primary planning of ship hull and/or line shaft system designers. The resonant response amplitude by this method shows good agreement with the one by the transfer matrix method mentioned above.
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