A Study on Reduction of Ship Vibration, II : Attenuation of Vertcial Vibration Caused by Couple

Abstract

Ship vibrations are mainly caused by the propeller and the marine diesel engine. The author previously reported a model experiment and its theoretical study, describing how it was conducted and how it proved successful in reducing the vertical ship vibration caused by one periodic force such as the propeller-exciting force. Now, in this paper, the auther describes the results of analytical study on the reduction of the ship vibration caused by the marine diesel engine, by adding a counteracting force. Generalized formula expressing the ship vibration is introduced by using a model of a simple uniform beam. An exciting couple and a counteracting force acting on this model are numerically analysed. By selecting φ_<13> and T_<13> so as to minimize [numerical formula], [numerical formula] is the amplitude of the vibration at a distance (il)/(40) from the end of the stern, the vibration is greatly attenuated by applying a fairly small counteracting force in such a manner that the force acts on the stern. The use of counteracting force as above is far more effective than lessening the exciting couple to half in amount, for reducing the magnitude of the responese. The counteracting force (T_<13>, smaller than T_<11>)/2, a pair of T_<11> composing a couple itself, is effective enough to attenuate the vibration caused by the couple.