Bossing Vibration of a Twin Screw Roll-on/Roll-off Ship

Abstract

Bossing vibration for a twin screw ship was discussed theoretically. Coupled effect of two bossings and shell plating of after part of ship was investigated using a simple mathematical model. The main conclusions obtained from this study are as follows; (1) Natural frequency for symmetrical and asymmetrical mode shape of two bossings depends upon rigidity of bossing and shell plating and distance between two bossings. (2) For a twin screw container ship, the lowest natural frequency indicates asymmetrical mode shape and the second lowest symmetrical mode shape, and for a twin screw roll-on/roll-off ship vice versa. (3) The added mass for symmetrical mode shape becomes two times that for asymmetrical mode shape. (4) It was found that calculated natural frequency obtained from the present theory agrees very well with the experimental value for the roll-on/roll-off ship.