Zorica Djordjević

A New Design of a Two-Stage Cycloidal Speed Reducer

A new design of a two-stage cycloidal speed reducer is presented in this paper. A traditional two-stage cycloidal speed reducer is obtained by the simple combination of singlestage cycloidal speed reducers. A single-stage reducer engages two identical cycloid discs in order to balance dynamical loads and to obtain uniform load distribution. Consequently, the traditional two-stage reducer has four cycloid discs, in total. The newly designed two-stage cycloidal speed reducer, presented in this paper, has one cycloid disc for each stage, that is, two cycloid discs in total, which means that it is rather compact. Due to its specific concept, this reducer is characterized by good load distribution and dynamic balance, and this is described in the paper. Stress state analysis of cycloidal speed reducer elements was also realized, using the finite elements method (FEM), for the most critical cases of conjugate gear action (one, two, or three pairs of teeth in contact). The results showed that cycloid discs are rather uniformly loaded, justifying the design solution presented here. Experimental analysis of the stress state for cycloid discs was realized, using the strain gauges method. It is easy to conclude, based on the obtained results, that even for the most critical case (one pair of teeth in contact) stresses on cycloid discs are in the allowed limits, thus providing normal functioning of the reducer for its anticipated lifetime. [DOI: 10.1115/1.4004540]

Using multi-criteria decision making for selection of the optimal strategy for municipal solid waste management.

Multi-criteria decision making (MCDM) is a relatively new tool for decision makers who deal with numerous and often contradictory factors during their decision making process. This paper presents a procedure to choose the optimal municipal solid waste (MSW) management system for the area of the city of Kragujevac (Republic of Serbia) based on the MCDM method. Two methods of multiple attribute decision making, i.e. SAW (simple additive weighting method) and TOPSIS (technique for order preference by similarity to ideal solution), respectively, were used to compare the proposed waste management strategies (WMS). Each of the created strategies was simulated using the software package IWM2. Total values for eight chosen parameters were calculated for all the strategies. Contribution of each of the six waste treatment options was valorized. The SAW analysis was used to obtain the sum characteristics for all the waste management treatment strategies and they were ranked accordingly. The TOPSIS method was used to calculate the relative closeness factors to the ideal solution for all the alternatives. Then, the proposed strategies were ranked in form of tables and diagrams obtained based on both MCDM methods. As shown in this paper, the results were in good agreement, which additionally confirmed and facilitated the choice of the optimal MSW management strategy.

Optimization of photovoltaics panels area at Serbian zero-net energy building

In this study, the possibilities to decrease energy consumption of a residential building in Serbian conditions are analyzed. The building uses electricity for space heating system, heating of domestic hot water, lighting, and for other electric equipment. The electrical energy is generated by photovoltaics (PV) system and it may be consumed by the building or may be fed-in to the electricity grid. The major aim of the optimization of PV area is to determine the avoided electricity from the grid (avoided exergy), and to minimize the consumption of primary energy. The residential buildings with variable thermal insulation thickness, hot water consumption, life time, and PVs embodied energy are investigated, in order to achieve zero-net energy building or positive-net energy building. The buildings are presented by a mathematical model, in EnergyPlus environment. Open Studio plug-in in Google SketchUp was used for building virtual design, Hooke-Jeeves algorithm for optimization, and GENOPT software for sof...

Impact of large-scale implementation of photovoltaic devices to CO 2 emissions

Our civilization faces growing prospects of climate problems. They are blamed to current consumption of fossil fuels (FF) for electricity generation in FF plants. This yields to massive CO2 release into atmosphere and environment pollution, increase in average temperature of earth and climate problems. One way to prevent this is to use photovoltaic (PV) devices instead of FF plants for electricity generation. To replace some of FF plants, one may erect PV devices. However, this uses existing electrical energy for their construction. In this research, theoretical approach is developed to calculate the yearly energy consumption and the yearly CO2 emission during implementation of the PV devices. Then, the impact of large-scale implementation of PVs to increase and decrease in CO2 emissions is studied. It is found out that there may exist an immediate high increase in CO2 emissions and after that its decrease. The magnitude of this decrease depends on CO2 payback time (TCP) for introduced PV device. Lower TCP yields very low CO2 emission for the energy system, while higher TCP may increase CO2 emission of the energy system within its life time.

An Investigation Into Hybrid Aluminium/Composite Cardan Shaft

It is a well-known fact that natural resources are becoming increasingly scarce. Consequently, whenever possible in the machine element manufacture, metallic materials should be replaced with new artificial materials. This paper studies the possibility of replacing two cardan shafts of a truck TURBO ZETA 85.14B with one shaft made of aluminium and a composite material, while the basic requirements concerning the given load transfer and fundamental natural frequencies remain satisfied.