Experimental Investigation on Viscous Resistance Components of Full Tanker Models Having Normal, U- and V-shape Sterns

Abstract

In the preliminary experiments with small model ships (L=1.25 m), the stern forms of small viscous resistance are explored. One U- and one V-shape sterns are obtained (Figs.3, 4 and 5) In the next step, it is tried to separate the viscous resistance of the models into two components; the frictional and the viscous pressure resistance. It is also tried to evaluate vortical resistance caused by stern vortices. The length of the models used is 4.5 m. They have the same fore-bodies but different aft-bodies: normal, U- and V-shape sterns. (Figs 1, 2 and 6 and Tables 1, 2 and 3) To clarify the nature of the components of viscous resistance of the model ships, the following experiments are carried out in the towing tank of Hiroshima University: i) resistance tests (Figs.7&sim;11) ii) hull-surface pressure measurements (Figs.12&sim;18) iii) survey of the flow velocity fields around and behind shipe (Figs.19&sim;24, 27&sim;31 and Table 4) iv) flow observations (Figs.25 and 26) Following conclusions are obtained: i) For every model, the frictional resistance is slightly higher than that of equivalent flat plate. ii) It can be concluded that the form factor K represents almost the pressure resistance of model ships and the difference of K values between the normal stern and the U- and V-shape stern is mainly caused by the resistance of stern votices. iii) The vortices of the normal stern damp very rapidly and the vortical resistance is estimated from the velocity field measured at several sections behind a ship. iv) The fullness limit of the aft-body of a ship, where the increase in viscous resistance would be tolerable, is found to be C_<B(AFT)=0.83, although it is very difficult, in any loaded condition, to point it precisely. v) Not only the three dimensional separation but some two dimensional separation are observed in the stern part near the water surface of model ships. It is important to decrease the resistance by removing such a two dimensional separation.