An Analysis of Vertical Vibration of Ships with Deck Errections

Abstract

It is difficult to calculate correctly the natural frequencies of vertical vibration of ships with deck errections such as superstructures or deck-houses. At present, applicable calculation methods are the one proposed by Johnson and Ayling and the one by one of the present authors, Matsuura. In these calculation methods, ships with deck errections are treated as beams having effective bending rigidity derived from statical strength calculation which is made in order to allow for the presence of deck errections. Although the calculated frequencies by these methods are approximately correct in the lower modes, the accuracy of those in the higher modes is questionable. In this paper, the ships with deck errections are treated as the so-called Bleich's model. Dynamical analysis is made for the vertical vibration of this mathematical model taking into account the coupling effect of main hull and deck errection. Transfer matrix method is used in the actual computation. Experimental investigations on the model ships are also made. The results show good agreement with the theoretical results.