احمدرضا کهنسال

Change in body shape specification, is one of the ways to reduce the resistance and thereby increasing speed of the vessels. Creating the transverse steps is one of these variations. Generally transverse negative pressure gradient on the surface of vessels causes boundary layer separation and expands through body's surface to transom of vessel which reverse vortex appears that leads to resistance increasing of vessel. Hence, by creating the step in vessel's body boundary layer growth and flow separation that increased resistance would be prevented. In this thesis, a three dimensional numerical solution by using finite volume and volume of fluid method, motion characteristics of a non-step and two stepped planing hull with transverse steps in calm water, regular and irregular waves have been examined. For this purpose, the vessel is free to trim and sinkage and by using the morphing mesh approach, the numerical simulation continued in calm water and waves until the equilibrium conditions of vessel be satisfied. Resistance, lift, trim angle and wetted surface in calm water with various velocities for both vessels have been computed and compared with the available experimental results.Analysis of considered planing hulls in calm water show that the numerical solution for resistant, trim, lift and wetted surface area are relatively precise in comparison with model test data. However, both the non-step and two stepped planing hulls influenced by various regular and irregular waves and the domain motion of heave, pitch and vertical acceleration of each vessels calculated and discussed about pressure distribution and wetted surface of two stepped planing hull in various velocities. In addition the positive effects of steps to reduce the movement of vessel in waves have been observed clearly.