احمدرضا کهنسال

In this study, the effect of hydrofoil stabilizer location on the porpoising instability of a mono-hull planing craft and also its optimal location have been investigated. The craft used in this project was a planing mono-hull one which was longitudinally unstable in the sea test. More precisely, it should be said that the craft entered the longitudinal instability stage at a speed of 30 knots and severe changes in its pitch and heave movements were observed. Numerical simulation which was based on computational fluid dynamics (CFD) techniques was done to simulate a three-dimensional geometric model in the fluid Eulerian two phases flow. A validation study was carried out by comparing the numerical results with the experimental data of the planing hull without the hydrofoil stabilizer. To study the effect of the installation position of the hydrofoil stabilizer, three parameters include depth of the hydrofoil relative to the transom bottom, the longitudinal distance of hydrofoil from the transom and the angle of attack were selected. The effects of changes in each of these parameters were investigated separately. Finally, the most suitable installation parameters that provide the best performance of the hydrofoil stabilizer and reduce the porpoising influence were selected. From the results of this study, it was observed that by increasing the depth of the hydrofoil from the transom and also by increasing the angle of attack of the hydrofoil, the amplitude of heave and pitch diagrams has decreased. The longitudinal distance of the hydrofoil to transom has not significant effect on porpoising instability. However, the results showed that the proper position for the hydrofoil stabilizer should not be under the hull bottom.