جلیل فریدونی

In this article, the most important specifications of hydrofoil floats, i.e. their seakeeping under regular and irregular waves under different encounter angles of wave, has been investigated. Numerical simulation has been done using STAR CCM+ software. Surge, heave, roll and pitch motions are kept free at the same time and their effects on each other are taken into account. USV01 model, whose laboratory test results are available, was used to validate the simulation. The results show that the increase and change in the regular wave components and speed of the craft, cause less changes in the movements of the hydrofoil craft compared to the planing craft, except in the following sea, where planing craft performs better overall. Therefore, it should be said that the most dangerous situation for a hydrofoil craft is encounter angles less than 90 degrees, especially zero-degree encounter angle, i.e. following sea.

Among the air-to-water projectiles, the gyroscopic stabilizes ones, have economic and operational advantages over other types. The air stability of such projectiles can be achieved with the gyroscopic effect of the spin. However, maintaining stability of the projectile inside the cavity, is a challenging effect from design and practical point of view. Therefore, it will be important to figure out parameters which effects on the underwater projectile stability. It should be noted that experimental study of the underwater projectile dynamics requires a very precise and expensive equipment. Hence, the numerical approach can be used in the design process. The first section of the study, proposed a dynamic model of an air-to-water supercavitating cylindrical projectile. The 6DOF dynamics of the projectile investigated using the Star-CCM+ commercial code. The model's ability to simulate the water entry physical phenomena validated via within literature experimental results and both are in good agreement. Then, the water entry of the projectile was simulated in two situations of having spin and without spinning dynamic, and the results were compared. The results of this study show that, in the oblique water entry process, the existence of circular motion will not have a significant effect on the dynamic and kinematic behavior of the cylindrical projectile. This research proves that, the high-speed oblique water entry dynamics of a supercavitating projectile can well approximated with planar motion in the x-y plate. Proof of this assumption can lead to significant simplifications in laboratory and numerical modeling of such dynamics in the future.

Nowadays, designers have always been interested in the use of motion stabilizer systems, such as the interceptor and trim tab, especially for planing vessels. These systems can improve crew comfort and reduce fuel consumption with favorable effects on the hydrodynamic performance of these vessels, such as reduced resistance and trim angle. In the present study, the effect of the interceptor on the hydrodynamic performance of model scaled "1/15" a monohull vessel with 11 m long that was tested in the towing tank of Sharif University of Technology compared with numerical simulation by software STAR-CCM+. The results show that the installation of the interceptor on the vessel reduces the resistance to a maximum of %9.4 when the vessel is in planing mode and in particular the dynamic trim due to the shift of the center of pressure to the transom. Keywords: motion stabilizer systems؛ interceptor؛ planing vessels؛ hydrodynamic performance؛ resistance reduce؛ trim angle؛ numerical modeling؛ software STAR-CCM+

In this article, we extracted the forces and moment of a supercavtation projectile according to the former experimental work that is exist within literature. regards to the projectile high-speed and the illustration technique, it's safe to say that this experiment is one of the most attractive examples which is exists in the literature. In this test, projectile after leaving the launcher and moving a short path in the air, enters at a low angle to the free surface of the fluid (water). Due to the availability of the experiment test multimedia and thank to the image processing techniques in this paper, speed and acceleration values of the projectile were extracted. In the next step, forces, moments and hydrodynamic coefficients of the projectile were evaluated. The results in this study show that the value of the drag coefficient (C_D) are in good agreement with existing predictions, but the results related to the values of the lift and moment coefficients (C_L and C_M), contain new and important information in which it will change some of the former assumptions in the literature. The present study also provides useful information about projectile angular velocity which is used in the study of the stability of motion of such devices

To analyze the behavior of fluids around obstacles cylinder to reduce costs, reduce the time to achieve the results and analysis of boundary conditions to the numerical simulation using FLUENT software Rvym.dr paper, Unsteady Flow, two-dimensional, incompressible intended for each Reynolds static pressure contours, Vorticity, flowing lines and speed has been obtained.It can be seen that the rectangular cylinder pressure at the inlet of the circular cylinders and more triangular and wherever is made of vortices And in which the pressure Darym.dr least the low pressure flow lines will be able to lose your makeup.Also generally at high Reynolds numbers for all cases, and in this case also during the more turbulent flow vortices more.The main gates of the high-pressure occur at these points there is no vortices and flow irregularities.It is known that the contours pressure cylinder with a rectangular cross-sectional area drag to endure more.