فهرست مطالب saeid niazi

 one of the main reasons for fuel consumption in ships and vessels is to produce the power for their movement. In order for a ship, this force must overcome the resisting forces, most of which are applied by the water fluid, especially to the body and the underwater appendages, such as the ship’s rudder. Which is called drag force.Frictional resistance force has a direct relationship with the area of the wet surfaces . On the other hand, the occurrence of some fluid phenomena such as separation, eddies near the surface, can play an essential role in increasing or decreasing the amount of drag, studies are inspired by the skin of some high speed marine animals show their skin is not very smooth and polished, contrary to what was imagined. And it has micron-sized riblet. These grooves cause a delay in separation phenomenon and also keep the high-speed eddies away from the sub-layer near the surface, so the drag force will be reduced, we know that the increase in the wet surface, increases the drag force, so the aim of this research was to find an optimal point for the dimensions and size of the riblet, in such a way that in exchange for the increase, the drag is reduced the most to have The criterion that shows the reduction of the drag force is the drag coefficient, the changes indicate the impact of the size of the riblet.In this research, sawtooth riblets with a height of 300 microns were used, and by using chimp meta-heuristic algorithm and numerical simulation of the drag force, the ratio of the height to the distance of each riblet was obtained as 0.49 mm, which shows reduced in the the drag coefficient about 5.5%..

The present study examined the pool boiling process in a specific geometry by designing, constructing a laboratory complex and Providing Empirical Relations. Investigation of pool boiling process, electrical resistance, critical heat flux, heat transfer coefficient, bubble growth and departure, bubble growth frequency, and nucleation site density by applying heat flux to critical heat flux was carried out on wire mesh element in deionized water at different temperatures. According to the results, increasing the size of mesh and fluid temperature decreased the critical heat flux. In the case of a wire mesh with a constant size of mesh, a fluid with a constant temperature, and the use of heat flux values less than the critical heat flux, the wire temperature increased, but it decreased in the case of increasing the size of mesh, a fluid with a constant temperature and applying critical heat flux values. In the case of a constant size of mesh, the heat transfer coefficient was constant by increasing fluid temperature at values of heat flux less than the critical heat flux, but the heat transfer coefficient was increased with increasing values of heat flux less than the critical heat flux and decreased at critical heat flux values. By increasing 4 times the mesh size in the fluid at 30, 70 and 100°C in the critical heat flux, the heat transfer coefficient decreases by 0.7%. The maximum bubble growth frequency is related to the 0.5 mm wire mesh in 100°C fluid with 0.0763 bubbles per millisecond.

The energy and environmental crisis pose significant challenges to humanity, necessitating solutions to reduce energy consumption. In the marine transportation industry, where over 90% of global transportation occurs, addressing resistance forces acting on vessels and their components in water is crucial for efficient design.Researching the state of drag reduction in accessories usually receives less attention from researchers. It is one of the important things that should be considered in the design of the float. The rudder, an essential underwater accessory in marine vessels, plays a vital role in drag reduction, leading to improved fuel efficiency and performance. This research focuses on investigating the reduction of drag force exerted by water on a rudder with NACA0025 section. Riblets of varying dimensions are implemented on the rudder hydrofoil, and the resulting drag force is calculated using simulation in STAR CCM software. The findings reveal that a riblet height of 100 microns and a distance of 200 microns yield the maximum drag reduction of 12.5%.

The present study examined the pool boiling process in a specific geometry by designing and constructing a laboratory complex. Investigation of pool boiling process, electrical resistance, critical heat flux, heat transfer coefficient, bubble growth and departure, bubble growth frequency, and nucleation site density by applying heat flux to critical heat flux was carried out on a ring wire in deionized water at different temperatures. According to the results, increasing the number of rings and fluid temperature decreased the critical heat flux. In the case of a ring wire with a constant number of rings, a fluid with a constant temperature, and the use of heat flux values less than the critical heat flux, the wire temperature increased, but it decreased in the case of increasing the number of rings, a fluid with a constant temperature and applying critical heat flux values. In a ring wire with a constant number of rings, the heat transfer coefficient was constant by increasing fluid temperature at values of heat flux less than the critical heat flux, but the heat transfer coefficient decreased at critical heat flux values. The diameters of the produced bubbles were enhanced by increasing heat flux and they separated from the rings when combined. At the beginning of the reddening of the ring wire, a critical heat flux occurred, and considering 110% of the time required for the critical heat flux, the images of the state of the ring wire after the critical heat flux are presented.

In this study, we investigated the flow of blood plasma in which white blood cell, erythrocyte and platelet nanoparticles were suspended with a percentage of actual concentrations inside a three-dimensional rectangular micro channel. The chamber rotates around the vertical axis at constant angular velocity and is affected by electrical double layer .The numerical results on white blood cell, erythrocyte and platelet nanoparticles were extracted in plasma at different angular velocities and the movement of suspended particles in the blood was studied that was observed that in the angular velocity increases, the pressure decreases along the channel and along the axis of rotation of course the velocity has the maximum amount in the center of channel. Numerical studies of the velocity and distribution of particles also show that the velocity variations are the same in all particles and the velocities of white blood cells, erythrocytes and platelets at the end of the channel are more than another place and the streamlines more compact.

The Steger and Warming flux vector splitting implicit scheme is used to numerically solve two dimensional Reynolds Averaged Navier–Stokes (RANS) equations governing the vortex induced vibration of a flexible riser laterally supported by a spring and a damper. The k–ε model is used as turbulence model to simulate the turbulent flow in the wake of the riser. To update the new position of the riser, the lift coefficient obtained from the previous RANS iteration is coupled by the body motion equation. The proposed numerical solution is able to provide fair results in terms of lift coefficient, amplitude of oscillation and the effect of reduced velocity on it. The numerical results are compared with the available experimental and computational data where fairly good agreement even at the lock-in regime has been obtained. Taking wider external boundary, using conservative form of the equations, applying k-ε turbulence model for the separated flow and finally using the variable time step as the lock-in region approaches, are main features of the proposed numerical model.