Applied Engineering Letters

39-45

Authors: N. Petrović, N. Kostić, N. Marjanović, J. Živković, I. I. Cofaru

In truss structural optimization the most frequently optimized factor of a structure is its weight. The minimization of weight contributes not only to savings in material, but also in other aspects of the structure such as number of elements used, number of welds needed, outer surface area, etc. This research aims to show the difference in optimal solutions for four different topological cases of a typical trapezoidal roof truss looking at their effects on overall outer surface area. The truss layouts are optimized for sizing, and a combination of sizing and shape with a minimal weight objective function. In order to ensure the most practically applicable solutions the example optimized in this paper uses dynamic constraints for buckling, stress constraints, and nodal displacement constraints. The overall outer surface area for all cases is compared, as surface protection accounts for a substantial part of the total cost of roof truss construction. Optimal solutions show a lack of correlation between weight and surface area, which is discussed in the conclusion.

50-61

Authors: M. P. Vasić, B. Stojanović, M. Blagojević

The paper presents the results of testing gearboxes in coal open pit mine which have been damaged by various mechanisms. Gearboxes, as constituents of belt conveyors, bucket-wheel excavators and bucket chain excavators and spreaders, are the most loaded segments of drive units the functionality of which affects the operation of complete coal and overburden systems. Therefore, special attention has to be paid to their condition so that the analysis of relevant condition indicators could lead to correct conclusions as to their functionality, as well as point to the factors causing their fault. Tests were carried out on 95 gearboxes throughout 2017, during general repairs at Drmno mine workshop. After examination, all identified failures were illustrated with an appropriate photo, classified according to the appropriate standard, and described in the form of manifestation and cause. The research has shown that the most dominant were faults of bearings and lubrication, whether seals and cuffs or a thin hermetic layer between the housing and covers. In addition, some of the faults happened on gears and toothed and stepped shafts. Major irregularities in operation, resulting from damage to gearbox elements, are show by fault tree analysis (FTA).

68-74

Authors: B. Vujic, J. Pekez, V. Mihajlovic, Lj. Radovanovic, U. Marceta, I. Palinkas

Serbia, as a developing country and EU accession country, faces many challenges. One of the key areas identified as the most complicated problem in the negotiation process is the issues of environmental protection and improvement, including the energy sector. Since population in Serbia is concerned because of poor living standards, high unemployment rate, and other social issues it could be questioned what is their concern and awareness about climate change since it is a realistic and visible phenomenon that is hard for someone to ignore and neglect. This paper presents some of the results of a survey conducted among adults in rural and urban parts of the Autonomous Province of Vojvodina on their perception, awareness, and knowledge about climate change issues. The research/survey also examined the specific actions that respondents would take as a personal contribution to mitigating the effects of climate problems. The results indicate that respondents have a high awareness of climate change, but the knowledge on climate change is relatively low even though the respondents graduated from faculty (about 52%).