On the Natural Frequency of Funnel of Large Tanker

Abstract

It is due consideration for ship designer to predict the natural frequency of funnel to avoid the resonance with hull in the preliminery design stage. The natural frequency of funnel depends on the weight distribution of its body and the rigidity of the foundation on which it is positioned. In this report, the funnel body is idealized as a cantilever beam whose end is elastically supported. The weight distribution is replaced by lumped for feasible analysis. On the other hand, the structure of the foundation is assumed to be of plane grillage which consists of primary supporting members under deck. Furthermore, the correlation between fore and aft and athwartship vibration is taken into account. Based on the above assumption, a computer program is devoloped to calculate the natural frequency of funnel as well as the correlation between the regidity of the foundation and the natural frequecy. By comparing the calculated value with the measured one, the present method is proved to be fully practical, and, also, a simple formula to predict the natural frequency of funnel is proposed.