Istraživanja magnetno hidrodinamičkih strujanja i prenosa toplote mikropolarnih fluida

The basis of the doctoral thesis is the analysis of flow and heat transfer of one or two electrically conducting micropolar fluids in the presence of magnetic and electric fields. The first part of the dissertation is the development of mathematical models for described problems of MHD flow and heat transfer of micropolar fluid, where the research is conducted in inductionless approximation and for the case of coupled equations. After that, in the next chapters, the problem of walls conductivity of the channel is considered, also the effects of induced magnetic field and interface boundary conditions for the flow of two fluids. Special attention is paid to the flow of two fluids between inclined plates where one fluid is micropolar and the other one is Newtonian. Analytical solutions are given for momentum, microrotation, energy and magnetic induction equations for the problems of MHD flow of one and two fluids. Next part of the dissertation has a detailed analysis of physical phenomena that occur in MHD and EMHD flow of micropolar fluids, and comparison of analytical solutions obtained in closed form with the results obtained by numerical simulations. Using the numerical simulations the case of the flow of micropolar fluid in the horizontal and vertical channels under the influence of magnetic and electric fields are solved. At the end, within the dissertation detailed analysis of results are given for micropolar fluids, which is significant in the technical practices, for different values characteristic dimensionless numbers that describes MHD and EMHD problems of flow and heat transfer of micropolar fluids. Special attention is also given to the applicability of the research in the development of new technologies

The Rare-Earths influences on doped BaTiO3-Ceramics Microstructure and Electric Characteristics

The influence of rare-earth additive content on microstructure and electric properties of doped BaTiO3 ceramics is investigated. The concentration of Er2O3 and Yb2O3 in the doped samples range from 0.01 to 1.0at % . The samples are prepared by the conventional solid state reaction, and sintered at 1320° and 1350°C in air atmosphere for 4 hours. SEM analysis shows that all samples are characterized by polygonal grains. The uniform and homogeneous microstructure with grain size ranged from 20 to 45μm is the main low doped samples characteristics. For the samples doped with the higher dopant concentration (0.5 and 1.0 at%) the average grains size is ranged from 5 to 10μm. Dielectric measurements are carried out as a function of temperature up to 180°C at different frequencies. The low doped samples display the high value of dielectric permittivity at room temperature. A nearly flat permittivity-temperature response is obtained in specimens with higher additive content. The Curie temperature of doped samples were ranged from 126 to 130°C. The Curie constant for all series of samples decrease with increment of dopant concentration and the lowest values is mesured from samples doped with 0.01 wt% of aditive. The obtained value of γ pointed out that the specimens have almost sharp phase transition. Also, the specific electrical resistance is measured in function of temperature at the different frequencies from 100Hz to 1MHz. With increasing additives concentration, the electrical resistance decreases to the concentration of 0.5 at% and then increases

CONTROL OF MHD MICROPOLAR FLUID FLOW

In this paper, the steady flow and heat transfer of an incompressible electrically conducting micropolar fluid through a parallel plate channel is investigated. The upper and lower plate have been kept at the two constant different temperatures and the plates are electrically insulated. The applied magnetic field is perpendicular to the flow, while the Reynolds number is significantly lower than one i.e. the considered problem is in induction-less approximation. The general equations that describe the discussed problem under the adopted assumptions are reduced to ordinary differential equations and closed-form solutions are obtained. The influences of each of the governing parameters on velocity, heat transfer on the plates (Nusselt number), flow rate and skin friction are discussed with the aid of graphs

Experimental and numerical investigation of flow around a sphere with dimples for various flow regimes

Flow over a sphere is a typical bluff-body flow with many engineering applications. However, it has not been studied in depth, as compared to flow over a circular cylinder, because of the difficulties in the experimental set-up as well as in the computational approach for studying flow over a sphere. The main challenges are to understand the flow hydrodynamics and to clarify the flow pattern around a dimpled sphere because the flow pattern complying with the dimple structure on its surface is very complicated. In this paper experimental and numerical investigations of the fluid flow around a sphere with dimples, are represented. The sphere with dimples is placed in a quadratic cross section duct (measuring section) and numerical simulation results are obtained by solving RANS equations. Furthermore, experimental measurements are carried out using a Laser-Doppler Anemometer (LDA). Experimental and numerical results of flow velocity fields were compared for three different flow regimes (Re=8×103, 2×104 and 4×104). Numerical investigation was performed for wide range of Reynolds numbers (Re=270%106). The final purpose of this paper is experimental and numerical determination of velocity field, separation point, pressure and drag coefficient, the length of reverse flow region in the wake and RANS turbulent model which gives the best results for engineering practice

EFFICIENCY OF BALL MANIPULATION IN BASKETBALL PLAYERS

Abstract. Basketball belongs to the type of sports where the skill of using one’s arms is of the greatest significance for game success. Basketball technique elements which involve the use of the ball are realized solely with the use of the arms, and this is where the name “ball manipulation” stems from. Modern basketball requires top basketball players to display the greatest level of the mentioned ability, irrespective of the playing positions within the team. The aim of this research has been to determine the situational-motor skill of a basketball player’s ball manipulation efficiency with regard to the basketball competition rank. A sample of 30 participants was analyzed, and split into two subsamples (the first subsample consisted of basketball players from the Super League, i.e. the players from the Konstantin basketball team from Nis – 15 participants, and other basketball players from the First Regional League for Men, the Junior Youth Basketball Club from Nis – 15 participants). The ball manipulation efficiency was estimated through the following tests: ball stopping, starting dribbling, ball dribbling around the body, ball dribbling through the legs and leading the ball with variants. In order to determine the inter-group differences, the Multivariate Analysis of Variance (MANOVA) was applied, while the differences between the groups were determined with the Analysis of Variance (ANOVA) for every measuring instrument separately. It was determined that the basketball players of the Super League display significantly greater values in almost all the variables, except one – ball stopping.Keywords: basketball players, ball manipulation, competition rank, differences.es

DIFFERENCES IN EXPLOSIVE STRENGTH OF LEGS BETWEEN FOOTBALL AND FUTSAL PLAYERS

Football and futsal belong to the group of polystructural activities of a complex character. From the motor aspect, both games are defined by a complex structure, comprised of various movements of the cyclic and acyclic type. Football and futsal are characterized by specific movements of the lower limbs, which are used to regulate possession of the ball (leading, passing) as well as the movement of the torso and hitting the ball with the head. The movement structure is comprised of various activities: running, jumping, turning, reception and shooting the ball. The aim of this research is to establish whether there are statistically significant differences in the explosive strength of the legs in football and futsal players. The analysis involved a sample of 37 participants, divided into two subsamples, the first being senior football players (first lineup) of FC "Radnički" from Niš – 23, and the second being senior futsal players (first lineup) of Futsal Club "Kopernikus" from Niš – 14 participants. The explosive strength of the lower limbs was estimated through the following tests: Squat Jump (SJ), Counter Movement Jump without arms swing (CMJ) and Counter Movement Jump with arms swing (CMJS). The Multivariate Analysis of Variance method(МАNOVA) was used to determine the differences between the groups, while the Analysis of Variance method (ANOVA) was used for the differences between the groups in terms of separate measuringt instruments. It has been determined that there are differences in the explosive strength of the legs between football players and futsal players

The Rare-Earths influences on doped BaTiO3-Ceramics Microstructure and Electric Characteristics

The influence of rare-earth additive content on microstructure and electric properties of doped BaTiO3 ceramics is investigated. The concentration of Er2O3 and Yb2O3 in the doped samples range from 0.01 to 1.0at % . The samples are prepared by the conventional solid state reaction, and sintered at 1320° and 1350°C in air atmosphere for 4 hours. SEM analysis shows that all samples are characterized by polygonal grains. The uniform and homogeneous microstructure with grain size ranged from 20 to 45μm is the main low doped samples characteristics. For the samples doped with the higher dopant concentration (0.5 and 1.0 at%) the average grains size is ranged from 5 to 10μm. Dielectric measurements are carried out as a function of temperature up to 180°C at different frequencies. The low doped samples display the high value of dielectric permittivity at room temperature. A nearly flat permittivity-temperature response is obtained in specimens with higher additive content. The Curie temperature of doped samples were ranged from 126 to 130°C. The Curie constant for all series of samples decrease with increment of dopant concentration and the lowest values is mesured from samples doped with 0.01 wt% of aditive. The obtained value of γ pointed out that the specimens have almost sharp phase transition. Also, the specific electrical resistance is measured in function of temperature at the different frequencies from 100Hz to 1MHz. With increasing additives concentration, the electrical resistance decreases to the concentration of 0.5 at% and then increases

The Rare-Earths influences on doped BaTiO3-Ceramics Microstructure and Electric Characteristics

The influence of rare-earth additive content on microstructure and electric properties of doped BaTiO3 ceramics is investigated. The concentration of Er2O3 and Yb2O3 in the doped samples range from 0.01 to 1.0at % . The samples are prepared by the conventional solid state reaction, and sintered at 1320° and 1350°C in air atmosphere for 4 hours. SEM analysis shows that all samples are characterized by polygonal grains. The uniform and homogeneous microstructure with grain size ranged from 20 to 45μm is the main low doped samples characteristics. For the samples doped with the higher dopant concentration (0.5 and 1.0 at%) the average grains size is ranged from 5 to 10μm. Dielectric measurements are carried out as a function of temperature up to 180°C at different frequencies. The low doped samples display the high value of dielectric permittivity at room temperature. A nearly flat permittivity-temperature response is obtained in specimens with higher additive content. The Curie temperature of doped samples were ranged from 126 to 130°C. The Curie constant for all series of samples decrease with increment of dopant concentration and the lowest values is mesured from samples doped with 0.01 wt% of aditive. The obtained value of γ pointed out that the specimens have almost sharp phase transition. Also, the specific electrical resistance is measured in function of temperature at the different frequencies from 100Hz to 1MHz. With increasing additives concentration, the electrical resistance decreases to the concentration of 0.5 at% and then increases

Electro-Magnetoconvection of Conductive Immiscible Pure Fluid and Nanofluid

This paper discusses the magnetohydrodynamic flow and heat transfer in a horizontal channel whose top and bottom halves have different or the same permeability. The top half of the channel is saturated with oil and the bottom half with a water-based nanofluid. The channel is under the influence of an external homogeneous vertical magnetic field and an external homogeneous electric field perpendicular to the vertical longitudinal plane of the channel. The Darcy model is used to determine the fluid flow and heat transfer. Expressions for velocity and temperature distributions are defined and presented graphically for different values of the dimensionless parameters. The Nusselt numbers are determined and given in a table. The paper also investigates the influence of the Hartmann number, the porosity factor, the electrical load factor and the volume fraction of the nanofluid on velocity and temperature distributions in the channel as well as the Nusselt numbers. It has been shown that an increase in the volume fraction of nanoparticles leads to a decrease in the temperature in the channel. Increasing the porosity factor reduces the fluid velocity in the channel and increases the temperature. The Hartmann number increases the temperature in the channel. Higher absolute values of the load factor correspond to higher temperatures. By changing the value of this factor, the direction of fluid flow can also be changed

CONTROL OF FLOW AND HEAT TRANSFER USING SUCTION, MAGNETIC AND ELECTRIC FIELD

Flow of a viscous incompressible electrically conducting fluid between two infinite horizontal parallel porous plates under a constant pressure gradient or constant flow rate has been considered in the paper. Effects of magnetic field, suction/injection and load factor have been studied in order to control the flow rate, shear stress and heat transfer on the plates. Applied magnetic field is perpendicular to the plates, the channel plates are electrically insulated and through the plates perpendicular to the surface the fluid of the same physical characteristics as the fluid in the basic flow is injected or ejected. An exact solution of governing equation has been obtained in a closed form. The influences of each of the governing parameters on flow rate, shear stress and heat transfer are discussed with the aid of graphs