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1

Influence of window roller blinds on energy consumption in residential buildings in Serbia

Djoković Jelena M., Nikolić Ružica R., Bokůvka Otakar, Pastorková Jana

System Safety : Human - Technical Facility - Environment

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2023

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Vol. 5, iss. 1

75--82

EN

Roller blinds are devices that are retracted and wrapped in a box above the window opening and are used to protect against the solar radiation. Those are the well-known devices with distinct advantages over the fixed external dimming elements. The influence of external blinds on the internal thermal environment in climatic conditions in the Republic of Serbia, the city of Kragujevac, was considered in this research. An external blind was installed in the test room and its influence on the internal temperature was compared with the internal temperature of the room without the blind. Real-time monitoring was carried out in February and August 2023. The results presented in this paper show that the blind reduces the temperature in summer by 3.57ºC and increases it in winter by 1.76ºC. The cooling load can be reduced by about 20%, and the heat load by about 15%.

2

How to replace the original material for the welded structure manufacturing

Ivković Djordje, Arsić Dušan, Cvetković Radica Prokić, Popović Olivera, Nikolić Ružica R., Bokuvka Otakar

Production Engineering Archives

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2023

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Vol. 29, Iss. 4

369-378

EN

Due to difficult pandemic situation with COVID-19 decease, as well as due to current geopolitical circumstances in the world, we are facing the shortage of steel and therefore the impossibility of delivering the contracted products within the agreed deadlines. It is thus necessary to find suitable steel for replacement. The procedure for selecting one such steel for substituting the deficit steel 25CrMo4,for the purposes of producing a responsible welded assembly, is described in this paper. After the careful analysis, the steel 42CrMo4 was taken into consideration as a possible substitute material. Prior to applying the new selected steel, it was necessary to perform the following tests: analyze its chemical composition, determine its most important mechanical properties and evaluate its weld ability. Then, the optimal welding and heat treatment technologies were determined, so that the quality of the responsible welded structure would meet all the requirements, as the structure made of originally used steel. For the new steel, all the mentioned and some additional tests were conducted and the appropriate welding technology was prescribed. To verify the selected technology, appropriate tests were conducted on the model welded samples, the results of which are presented in this paper. Based on the analysis of the obtained results, it was concluded that the 25CrMo4 steel can be replaced by the 42CrMo4 steel, however, with the mandatory application of appropriate supplementary measures.

3

Prediction of the work-related injuries based on neural networks

Ivaz Jelena, Nikolić Ružica R., Petrović Dejan, Djoković Jelena M., Hadzima Branislav

System Safety : Human - Technical Facility - Environment

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2021

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Vol. 3, nr 1

19--37

EN

Artificial neural networks (ANN) are a powerful tool in the decision-making process, especially in solving the complex problems with a large number of input data. The possibility to predict the work-related injuries in the underground coal mines, based on application of the neural networks, is analyzed in this work. the input data for the network were obtained based on a survey of 1300 respondents. After analyzing the input data influence on the network output, 14 most influential inputs were selected, with help of which the network correctly predicted whether the worker would suffer the work-related injury or not, with 80% precision. The two models were developed, based on the multilayer perceptron (MLP) and radial basis function (RBF) networks. The two models' results were compared to each other. The sensitivity analysis was used to select the most influential parameters, like mine, age of miners, as well as their work experience. The parameters were further analyzed by use of the descriptive statistics. The selected parameters are direct indicators of problems that can cause injuries. The obtained results point to the fact that the work-related injuries can be successfully predicted by application of the artificial neural networks. The proposed models' importance is reflected in the clear indicators for enforcing the stricter occupational safety and organizational measures in order to reduce the number of work-related injuries in underground mines.

4

Influence of different hard-facing procedures on quality of surfaces of regenerated gears

Nikolić Ružica R., Marković Svetislav, Arsić Dušan, Lazić Vukić, Hadzima Branislav, Ulewicz Robert

Production Engineering Archives

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2021

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Vol. 27, Iss. 4

257--264

EN

During the process of regeneration of machine parts, certain phenomena occur that have a significant impact on the loss of their working ability. Hereditary properties are expressed by the interdependence of geometric and physical-mechanical-metallurgical parameters of gear teeth created during the technological operations of regeneration of worn teeth by hard-facing. The influence of the type of additional material (electrodes and their combinations) on the tribological characteristics of welded gear teeth was considered, whereby the so-called hard additional materials were applied. Those are the additional materials that give the required surface hardness of the teeth without subsequent thermal or thermochemical treatment. This research did not involve the regeneration of specific worn gears removed from machine systems, but the new gears were made, which were then damaged and then regenerated by hard-facing using the shielded metal arc welding (SMAW) procedure. Thus, all the tested gears were made of the same material, belonged to one batch and were machined on the same machines with the same machining regimes. The tests were performed on samples made of 20MnCr5 steel for cementation, on a tribometer by the “block on disc” method, which was designed to simulate the operating conditions of coupled teeth of concrete gears in the exploitation conditions. Based on the conducted tribological tests, the average coefficients of friction and topography of the surfaces were determined by measuring the wear trace and it was defined which additional materials give the best tribological characteristics of the surfaces of gears regenerated by hard-facing.

5

Analysis of work-related injuries in mining industry in Serbia

Ivaz Jelena, Petrović Dejan, Nikolić Ružica R., Djoković Jelena M.

System Safety : Human - Technical Facility - Environment

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2020

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Vol. 2, nr 1

158-165

EN

The mining industry in Serbia has an important place in the country's economic development. Bearing in mind that the number of injuries that occur in the mining industry is unacceptably high, occupational safety and health is a challenge that existing and future mines will have to deal with. Studying injuries in mining, it was noticed that injuries requiring an absence from work for more than three days (especially fatal ones) are diametrically different in relation to the cause and manner of events related to injuries for which an absence from work is not necessary. In this research, authors focused on injuries that were characterized as ones requiring an absence from work. The statistical analysis of work-related injuries in mining is presented, as well as analysis of the direct causes of injuries, which are described as unsafe conduct of employees, unsafe conduct of company's management and/or unsafe working environment. In relation to classification of causes of injuries, a recommendation on what needs to be changed in order to remedy this situation in Serbia is given.

6

Thermal fracture characteristics of an interface crack subjected to temperature variations

Kalinović Saša M., Djoković Jelena M., Nikolić Ružica R., Hadzima Branislav

Production Engineering Archives

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2020

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Vol. 26, Iss. 2

54--59

EN

Thermal fracture characteristics - the thermal energy release rate and thermal stress intensity factor of a semi-infinite crack at an interface between the two elastic isotropic materials, subjected to the temperature variations, are considered in this paper. Those characteristics are determined based on application of the linear elastic fracture mechanics (LEFM) concept. Expressions for obtained theoretical solutions are compared to solutions from literature and they are found to be more concise. Influence of the materials change on these two thermal fracture properties were observed, as well as the influence of the thickness ratio of the two layers constituting the interface.

7

Calculation of the thermal dynamic performance of the residential buildings' walls

Kalinović Saša M., Djoković Jelena M., Nikolić Ružica R., Hadzima Branislav

Quality Production Improvement - QPI

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2019

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Vol. 1, Iss. 1

212--221

EN

Calculation of the thermal dynamic properties of the multi-layer wall isolation of residential buildings is presented in this paper. Taking into account that the final objective is to create a building with the highest energy efficiency ratio, i.e. with the lowest energy consumption, both for heating and cooling, it is necessary to realize the good thermal characteristics of the multi-layer wall. To obtain the optimal solution for the wall's structure, various wall structures with different thicknesses of the individual layers, were analyzed. Based on results, presented in this paper, one can conclude that for walls with the same total thickness, but various thicknesses of the individual layers, that constitute the complete wall structure, the differences appear in the delay of the change of the walls outside temperature. In that way, by varying those individual layers' thicknesses, one can obtain the optimal solution for the wall structure with the highest savings of energy.