Optimum Design Method of Superstructure Vibration by Database Method

Abstract

In vibration check design for fore and aft vibration of superstructure, it is an important technology to estimate accurate natural frequency and to avoid it from critical resonant region of blade or cylinder frequency when it falls into resonant region unfortunately. In this paper, authors represent a practical design method to change natural frequency of superstructure. Mass-spring system of multi-degree of freedom with rotational spring at base of superstructure is adopted as an analytical model of superstructure. Unknown quantities required to calculation can be estimated, if necessary, by database made up of actual ship data. Most effective structural member and place can be found out from calculated figures of strain energy or kinematic energy distributions obtained for fundamental mode shape. Design values necessary to structural improvement are given by sensitivity relations between design parameter and natural frequency. Optimum design to avoid critical resonant region can be attained successively by this procedure.