Vojnotehnicki glasnik / Military Technical Courier

38-50

Authors: Grečihin Ivanovič Leonid

This paper developed a mathematical model of gas dynamic fluid flow for a flat plate during its movement with positive and negative angles of attack. It is shown that at low velocities, the lifting force and the frontal resistance are determined by gasdynamic air flow in the fluid flow exit areawhile at velocities close to the speed of sound the decisive role is played by a mutualeffect of the pplate coliding with molecules of the surrounding environment in the fluid flow incidence field. The airflow behind the plate does not appear at low velocities. The conditions when the frontal resistance and the lifting force change the sign are determined.

56-73

Authors: Janković Bojan Ž.

The kinetic study of the crystallization process of the α-Fe phase from the amorphous Fe81B13Si4C2 alloy was investigated by DSC and XRD techniques. The kinetic parameters (lnA, Ea) of the investigated process were determined using the Kissinger and isoconversional (model-free) methods. It was established that the α-Fe crystallization process can be described by the JMA (Johnson-Mehl-Avrami) kinetic equation. In accordance with the XRD analysis and the calculated crystallization parameters (n = 4; m = 3), it was concluded that the crystallization stages of the considered process can be described by the bulk nucleation and the three-dimensional (3D) growth of nuclei.

72-88

Authors: Ryabtsev Anatoliy D., Troyanskyy Oleksandr A., Pashynskyi Volodymyr V., Snizhko Olga A.

The paper presents the results of alloying titanium by oxygen in the process of chamber electroslag remelting. As an oxygen-containing ligature, we used the electrodes-satellite from the reaction mass residues mixture from the retort lid for magnesium thermal reduction of a titanium sponge, a specially prepared gaseous argon oxygen mixture containing 30% oxygen applied directly to the melting space, microsize (10-15 mm) powder particles of titanium oxide and titanium oxide nanopowder with a particle size of 21 ± 5 nm. The structure and the properties of titanium alloyed by oxygen from the oxygen-containing ligature, gas phase and titanium oxide powder during chamber electroslag remelting of the titanium sponge are investigated. It was found that at the oxygen content of 0.053%mas. to 0.22%mas. in the metal formed a homogeneous single-phase structure typical for commercial titanium formed by polyhedral grains of the α-phase. The increase of the oxygen concentration in titanium for more than 0.22%mas. leads to the formation of the microstructure with a typical needle structure, which allows it to be classified as the α ׳-phase.

104-119

Authors: Petreski Drage T., Iliev Andrej P., Gjurov Lazar M., Petreska Aleksandra D.

Logistics is a set of activities for planning and implementing the relocation of materials. Since sources of raw materials, factories and outlets are not usually in the same location it is therefore necessary to conduct a series of logistics activities for supplying products or services to end users. Logistics manages the flow of data from suppliers, movement of materials through various operations within the organization as well as the flow of materials to final customers. Integrating these logistics activities is performed through supply chains which provide opportunities for cost saving and offering better services to customers. The supply chains in the Macedonian Army are an important factor in the planning and implementation of logistics support.

141-154

Authors: Lukovac Vesko M., Pejčić-Tarle Snežana A., Popović Milena J., Pamučar Dragan S.

It is difficult to achieve rational engagement, directing and developing, motivating, rewarding, and improving organizational efficiency, without the evaluation of the quality of job performance of employees. In management literature, this technique is known as 'employee performance evaluation'. Performance or productivity may be either a measurable result that has been achieved, or behaviour or personal characteristics necessary for performing certain activities in a defined period of time. Recently, a special management approach 'performance management' has been developed, in order to integrate the performance evaluation and the use of assessment results in management, aimed at improving performance. Since the employee performance evaluation is most often the result of subjective judgment of an evaluator about the quality of his/her work, one has to take into account possible errors that characterize such a way of judging. There are several types of errors that an evaluator can commit during the performance evaluation process, and in this paper, an approach to the identification and reduction of distribution errors of evaluators, most widely spread in organizations with a large number of employees, has been presented.

168-186

Authors: Arsić Slaviša N.

The process of professionalisation of the Serbian Army has caused qualitative and quantitative changes in the personnel structure and has led to the reduction in the numerical strength of its members. The restaurant at the Military Academy has faced infrastructural and organisational ballasts in its capacity for food preparation and distribution thus making the Military Academy food system uneconomic. The capacities of the restaurant are designed to allow for the preparation and distribution of 40% more meals than the actual needs, which, in the economic context, places unnecessary financial burden on the limited amount of funds allocated for this purpose. In terms of economic principles, it is possible to reduce or completely eliminate the negative effects through employing redundant workforce or finding alternative ways to organise the food system at the Military academy in a more rational way. The article represents a 'pro et contra' analysis that places an emphasis on some relevant facts in finding expedient solutions. The food system at the Military Academy was analyzed through the causeeffect relations of the factors within and outside the system and through the efforts to improve the system functioning from organizational, economic, technological and nutrition security aspects, based on current scientific knowledge and domestic and foreign experience.

201-215

Authors: Tešanović Branko M., Jović Saša B.

An oven for baking bread in field conditions is assigned to units that are by their nature relatively stationary and whose size does not require a movable bakery. It is intended for baking bread in our units located in international missions with supply difficulties, since our units have a habit od consuming bread instead of biscuits. The oven is of a prefabricated type, adapted for use in all types of terrains, simple design which makes it possible to be, dismantled and easily transported.

26-36

Authors: Grečihin Leonid Ivanovič

This paper developed a mathematical model of the gas dynamic fluid flow around the sphere. There are three areas of different mechanisms of the interaction of moving spheres and stationary gaseous environment. It has been proved that shear flow plays a decisive role at sphere low velocities, while at sphere velocities close to the speed of sound the critical role is exerted by the impact interaction of the sphere with the center in the front hemisphere. The shear flow behind the sphere makes a cone with stationary gaseous environment. The principle which defines the size of the cone has been established.

59-79

Authors: Radonjić Vojkan M., Jovanović Danko M., Ćirić Milenko P.

This paper presents the results of applying the optimal model of the concept of maintenance of modern radio-relay equipment (RRE). The model, is based on condition based preventive maintenance with the control of the level of reliability, and uses a number of positive structural and technological capabilities of the machine in order to decrease overall maintenance costs while maintaining the achieved level of the required device reliability.

101-120

Authors: Regodić Miodrag D., Benić Željana Ž.

There has always been a need to directly perceive and study the events whose extent is beyond people's possibilities. In order to get new data and to make observations and studying much more objective in comparison with past syntheses - a new method of examination called remote sensing has been adopted. The paper deals with the principles and elements of remote sensing, as well as with the basic aspects of using remote research in examining meteorological (weather) parameters and the conditions of the atmosphere. The usage of satellite images is possible in all phases of the global and systematic research of different natural phenomena when airplane and satellite images of different characteristics are used and their analysis and interpretation is carried out by viewing and computer added procedures.

128-151

Authors: Pašić Muhamed H.

This paper deals with the control of presses for sheet metal stamping. The analysis will be based on the experimental setup of the ram height. The experiment will be done for five different positions, i.e.metal sheet thicknesses. The previous state of the press was such that for every change of a position, i.e. metal sheet thickness it was necessary to adjust the ram height The new solution shown in this paper, makes the process much easier and more efficient. In order to use another position, it will be enough to select a particular position and the ram will be automatically adjusted to a required height. This will speed up production and reduce scrap that would be otherwise created due to adjustment. The state diagram for the new solution is shown as well as the control program for the new solution.

165-184

Authors: Starčević Slobodan M., Gošić Aleksandar M.

In the Serbian Armed Forces, oil and petroleum products are transported primarily for military units and institutions. The route for the movement of vehicles is selected during the transportation planning process. This paper describes a methodology for the selection of a route for the transport of dangerous goods and its application on one particular case in the Serbian Armed Forces.

27-43

Authors: Grečihin Leonid I., Guščin A.L., Naruševič A.A.

The article gives a detailed molecular-kinetic theory of the Mobius propeller functioning and shows the implementation of its computer modelling in different exploitation conditions. The mechanization of the Mobius propeller can be carried out in such a way that, under certain conditions, it enables using this type of propellers as a heat pump. The developed theory of the Mobius propeller functioning has been experimentally verified in laboratory conditions.

56-73

Authors: Janković Bojan Ž.

The kinetic study of the crystallization process of the α-Fe phase from the amorphous Fe81B13Si4C2 alloy was investigated by DSC and XRD techniques. The kinetic parameters (lnA, Ea) of the investigated process were determined using the Kissinger and isoconversional (model-free) methods. It was established that the α-Fe crystallization process can be described by the JMA (Johnson-Mehl-Avrami) kinetic equation. In accordance with the XRD analysis and the calculated crystallization parameters (n = 4; m = 3), it was concluded that the crystallization stages of the considered process can be described by the bulk nucleation and the three-dimensional (3D) growth of nuclei.

96-108

Authors: Stefanović Radiša R., Srdanov Aleksa S.

Cryptography is as current as ever. The need to protect data and resources from unauthorised access and use has never ceased. This resulted in creating stronger protection and breaching most of those thought to be unbreachable. This paper analyses core problems and their implementation in breaching the translational cipher by using the programme language C.

121-135

Authors: Bereš Paun J.

Education on the protection of classified information should be the top priority when it comes to ensuring the protection of the vital interests of the state. Some information should not be made available to the public because it is mainly related to national security, and no one should question the need to protect this kind of data. This paper is intended for educators dealing with the protection of classified information, and especially to those who work with or come into contact with confidential information in order to inform them of our national system of protection of classified information and enable the implementation of the existing legislation applying the heuristic model of education. This article describes the legal regulations governing the protection of data and shows mandatory standards and measures for the protection of classified information.

151-165

Authors: Petrović Miloš Z., Anđelić Kristina R., Živulović-Petrović Marina G.

Protection when handling construction machinery and construction work is a significant and important factor in the whole complex process of construction. Careful handling to protect human lives and the environment as well as building materials themselves is necessary. Careful and good handling and performance can lead to financial savings and to avoiding additional costs. Protective measures to be taken are: protection from risk during construction and protection from exploitation of the danger of the object. This area is defined by strict legislation. The Law on safety and health at work prescribed measures whose implementation and enforcement ensure safety and health at work. In addition, the law governs the rights and obligations of employers and employees to allow for more complete implementation of safety measures at work. Analyses of legal provisions show that the responsibility for creating and maintaining safe work environment lies with both employers and employees, who, each in a manner appropriate to their role in the process of work, comply with the prescribed measures. In order to ensure that the provisions about health and safety at work are consistently implemented, there is the inspection of the implementation of the act, regulations made under the act, technical and other measures relating to safety and health at work, as well as the implementation of measures for safety and health at work prescribed by a general act of the employer, collective agreement or work contract. This inspection is performed by labor inspectors. In the process of inspection, the inspector should work to control safety and health at work in accordance with his jurisdiction and provisions prescribed by law which also prescribes the obligations of the employer during inspection. If it is found out during the inspection that there are reasons that have caused an injury or led to the hazard to safety and health at work, the inspector shall order taking measures and actions to eliminate these causes, or take measures which may prevent the emergence of injuries and reduce or eliminate risks to safety and health at work. Under certain conditions, for the duration of the circumstances that led to the endangerment of the safety and health of employees, specifically prescribed by law, the inspector shall ban work at employer's workplace . During the organization of a site it is necessary to take account of the place and manner of depositing building materials. The material resistant to external influences (timbering, formwork, reinforcement, concrete curbs, pipes, sand, etc.,. Is stored in the open space near the building or in the vicinity of work. In case of heavy rain, wind or frost, their protection must be provided by covering them with plastic sheets, paper or cloth. For the works performed in the open air under adverse climatic and atmospheric conditions, the employer provides the use of appropriate personal protective equipment, or equipment while performing work. A first-aid cabinet must be set up at the construction site Before sent to the place of work, construction machines must be checked in terms of their proper functioning. Mechanization is placed along the road. Security of construction equipment shall be organized through the guardian office. The operator of construction machinery powered by an internal combustion engine must be protected from the harmful effects of exhaust gases. A location for operating self-propelled construction machines must be set up so that the machine operator has a clear overview of the field in which it moves. All self-propelled construction machinery must have devices for giving audible signals. Construction processes are complex and open systems, characterized by a number of different types of resources whose interactions as well as interactions with the environment generate frequent occurrence of health and safety risks with potentially severe consequences. Risks identified at one site may only partially appear at another site in the same form and other risks must be considered again. Unlike other industries, the product of the construction process is stationary and often unique. Construction is implemented in the open area where the process is exposed to weather conditions. Construction processes are characterized by complex influences of interested parties(investor, contractor and subcontractors, government, public, etc) with their goals being often mutually exclusive which is projected on the implementation process and the aspects of the operation. When a company that performs a process of construction is of high quality, the negative impact of interested parties is more mitigated and the process of managing the work is successful. A specificity of the construction process is reflected in the process of separation of the design and the construction phase thus generating safety risks that could be avoided in the design phase. This problem is partially solved by introducing a coordinator for security and safety in the design phase whose task is to avoid or minimize any risks arising from the adopted design solutions. Also, by a stricter control and by punishing non-compliance with laws and regulations, the protection of workers, the environment and materials can be brought to a higher level.

23-41

Authors: Inđić Dejan R., Luković Zoran T., Mučibabić Spasoje D.

Chemical accidents are inevitable in modern technological development and they cause a number of effects on people, property and the environment. The nuclear-biological-chemical (NBC) services as well as specialized units of the Army of Serbia perform particular tasks in the elimination of the consequences of chemical accidents. This paper presents a modeling of the effects of chemical accidents and one possible method for the selection of NBC services engaged in the elimination of the consequences of chemical accidents, using the method of analytic hierarchy processes.

58-73

Authors: Tadić Marin M., Čitaković Nada M.

The sol-gel method was successfully utilized for the synthesis of the highly concentrated α-Fe2O3/SiO2 nanocomposite containing 45 wt% of hematite. TEM micrograph showed that spherical particles of 10 nm average size were evenly dissolved in glassy silica matrix. Both DC magnetization and AC susceptibility measurements indicated superparamagnetic behaviour of the system with the blocking temperature TB ≈ 65 K. Magnetization vs. field data at 300 K was successfully fitted to a weighted Langevin's curve for superparamagnetic system and the particle size obtained from this fit was in excellent agreement with the TEM results. Several features evinced in the magnetic data pointed to the presence of non-negligible magnetic interaction between hematite nanoparticles: the weak field dependence of the magnetization as a function of temperature, narrowing of the hysteresis loop at low applied field below TB, and high value of TB for hematite nanoparticles of 10 nm in size. On the other hand, features like continuous increase of the ZFC magnetization with decreasing temperature and the absence of a plateau or a peak in the FC branch showed that no strong magnetic interactions were present in the system. The AC susceptibility study showed that the Vogel-Fulcher model for singledomain inter-acting particles was applicable, while the empirical parameters C1 = 0,055 and C2 = 0,57 that lie between values for strongly interacting systems and non-interacting systems obtained have pointed to the presence of the interactions of intermediate strength. On the basis of the above listed results, we can conclude that the system under consideration consists of interacting single-domain hematite nanoparticles with magnetic properties that are located between weakly and strongly interacting systems.

89-111

Authors: Pavlović Rade M., Petrović Vladimir S.

We propose a novel method to fuse true colour images with monochromatic non-visible range images that seeks to encode important structural information from monochromatic images efficiently but also preserve the natural appearance of the available true chromacity information. We utilise the β colour opponency channel of the lαβ colour as the domain to fuse information from the monochromatic input into the colour input by the way of robust grayscale fusion. This is followed by an effective gradient structure visualisation step that enhances the visibility of monochromatic information in the final colour fused image. Images fused using this method preserve their natural appearance and chromacity better than conventional methods while at the same time clearly encode structural information from the monochormatic input. This is demonstrated on a number of well-known true colour fusion examples and confirmed by the results of subjective trials on the data from several colour fusion scenarios.

130-140

Authors: Grečihin Leonid Ivanovič

The paper presents the aerodynamics of a wing of a closed oval ellipsoidal shape, designed with the use of the molecular-kinetic theory. The positive and negative characteristics of aircraft - drones with an oval wing are described. The theoretical calculations have been experimentally checked.

167-193

Authors: Janković Bojan Ž., Janković Marija M.

The differential conversion curves of the non-isothermal NiO reduction process by hydrogen are fitted by the Weibull (non-isothermal) probability density function (Wpdf), in a wide range of the degree of conversion (α = 0.06 - 0.96). It was established that the Weibull distribution parameters (β and η) show the different dependences on the heating rate of the system (vh) (shape parameter (β) - linear form and scale parameter (η) - exponential form). Model independent values of the apparent activation energy were calculated using the Friedman's isoconversional method. It was found that the calculated apparent activation energy depends on the degree of conversion, α, and it shows a constant value in the range of the degree of conversion 0.20 ≤ α ≤ 0.60 (Ea = 90.8 kJ mol- 1). Knowing the Weibull distribution function of reaction times, it is possible to determine the density distribution function of apparent activation energies at different heating rates. It was established that the changes of the symmetry of density distribution functions may be an indication for deviations from the simple crystallization kinetics as expressed by the Johnson-Mehl-Avrami (JMA) model, and this behaviour is probably due to a more complex transformation process such as a process described by the two-parameter autocatalytic Šesták-Berggren model.

199-211

Authors: Pašić Muhamed H., Ružić Dragana R.

This paper describes the modernization by installing frequency converters, their features and benefits as well as the disadvantages of the existing solutions and the advantages of the upgraded status. The existing state was such that the motors were switched on through the contactor and were always working at full capacity. In the new solution, one motor will be switched on through frequency converters, thus working with a particular intensity, depending on the need. This will bring savings in power consumption as well as in the maintenance.