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Abstract
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Reducing vertical motions of high-speed planing hulls in rough water is one of the most
important factors that help a boat to become more operable, and will benefit the
structure of the boat and the crew on board. In the recent decade, stepped planing hulls
have been investigated with emphasis on their better performance in calm water than
that of non-stepped planing hulls. However, there are still doubts about their performance in rough water. In this study, we investigate this problem by providing numerical
simulations for motions of a double-stepped and a non-stepped planing hull in a vertical
plane when they encounter head waves. The problem will be solved using the finite
volume method and volume of fluid method. To this end, a numerical computational
fluid dynamics code (STAR-CCM1) has been used. Accuracy of the numerical simulations is evaluated by comparing their outcome with available experimental data. The
dynamic response of the investigated hulls has been numerically modeled for two
different wave lengths, one of which is smaller than the boat length and the other which
is larger than the boat length. Using the numerical simulations, heave and pitch motions
as well as vertical acceleration are found. It has been found that at wave lengths larger
than the boat length, heave amplitude decreases by 10–40% when two steps are added
to the bottom of a vessel. It has also been observed that pitch of a planing hull is reduced
by 18–32% in the presence of the two steps on its bottom. Finally, it has been observed
that for wave lengths larger than the boat length, the maximum vertical acceleration
decreases by a gravitational acceleration of about .2–.7.
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