Machinery - Repository of the Faculty of Mechanical Engineering, University of Belgrade
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Error estimates for Gauss-type quadrature rules for variable-sign weight functions
No full textWhen the Gauss quadrature rule is applied, the weight function (or the measure) is usually assumed to be non-negative on the integration interval. In this paper, we consider a recently introduced Gauss-type quadrature formula with respect to a weight function that changes sign in the interior of the integration interval. To economically estimate the error of that formula, we propose extensions based on the Gauss-Kronrod, averaged Gauss, and generalized averaged Gauss quadrature rules. Numerical examples illustrate the accuracy of such introduced error estimates
A systematic approach of surface texture prediction during high-speed CNC turning of ARNE® (AISI O1) alloyed steel using response surface analysis and artificial neural networks
No full textThe present research reports on the application of the artificial neural networks (ANNs) for the modelling of processed surface texture parameters in turning of a high-strength, high alloyed steel. The variable input parameters of the ANN consisted of cutting speed Vc (m/min), feed rate f (mm/rev), and depth of cut, a (mm) whereas the output parameters that utilised were the average surface roughness Ra and maximum height of the measured profile, Rt. A full factorial experimental design (FF-DOE) was selected for generating the experimental data. The achieved outcomes indicated that, despite the complexity of the process and parameter interactions, the suggested ANN could be efficiently used to forecast the surface texture parameters during the hard turning process, thus confirming the production process planning
Effect of acidic media on surface characteristics of highly filled flowable resin-based composites: An in vitro study
No full textChallenges with Waste Material Obtained by 3D Printing
No full textToday, the waste material obtained by 3D printing operations presents significant challenges due to the increasing global adoption of this technology, leading to serious environmental implications. The generation of plastic waste from unsuccessful prints and end-of-life products is a growing concern, impacting the circular economy. With a 26% annual growth rate in additive manufacturing, the amount of waste is rapidly increasing, necessitating effective waste management strategies. However, 3D printing offers advantages in waste reduction compared to
traditional manufacturing methods, with only 40% waste generation compared to subtractive technologies and much of the waste being recyclable. The challenges of waste material obtained by 3D printing are numerous and require a comprehensive approach to waste management and recycling. Moreover, leveraging the abundant opportunities for reusing materials and developing sustainable composite filaments, 3D printing can contribute to environmental sustainability and the principles of circular economy
Testing of the condition and performance of coupling links from screw couplings of train
No full textThis paper presents an analysis of train screw coupling used mainly in Europe as mechanical
connection of wagons in train. An analysis of train breaks apart incidents revealed that less than
30 % of the cases were caused by elements of the screw coupling, with coupling links accounting
for only 5 % of the failures. Therefore, the investigation focused on testing the coupling links,
which are safety elements of the screw coupling. The coupling links underwent various inspections,
including visual inspection, dimensional control, non-destructive testing, examination
of chemical composition, and mechanical tests. Dimensional control found longitudinal plastic
deformations of the links. Chemical examination revealed that the links were made of different
material than recommended, but their mechanical properties generally met the recommended
values. However, variations were observed among different links, likely due to different rates of
deformation during testing and operational conditions. Overall, the analysis and inspections
provided insights into the condition and performance of coupling links in the screw coupling
system, highlighting the importance of monitoring and maintaining these elements to ensure safe
and efficient railway operations
Контекстуални адаптивни систем за митигацију ризика рада рударских машина
No full textТехничко решење решава проблем менаџмента ризиком рударских машина и омогућава одабир адекватне стратегије одржавања. Техничко решење представља искорак у односу на све постојеће концепције управљања ризиком и одржавања рударских машина, јер је засновано на моделу међузависности контекстуалних фактора описаном структурним једначинама (SEM). Примена техничког решења омогућава решавање следећих проблема тј. унапређења која директно омогућавају:
• Подизање нивоа безбедности и здравља на раду, и
• Подизање нивоа продуктивности,
а последично доводе до:
• Унапређења индустријске безбедности, и
• Смањења трошкова одржавања.
Предложена иновација може има утицај на развој свих индустријских грана у којима раде
рударске машине, и омогућава правовремено мапирање ризика без географског ограничења
примене
Mehanizam za kalibraciju sonde sa više rupica za merenje prostornog polja brzine i pritiska u ventilacionim sistemima
Get PDFFractional order time delayed acceleration feedback control of inverted pendulum system
No full textThe issue of human balancing in the sagittal plane using fractional order time delayed acceleration feedback is studied in this contribution. The problem of asymptotic stability of closed-loop fractional order neutral time delay system is solved by applying the D-decomposition approach. Stability regions in the control parameters space are determined using this method. Special attention was focused on the consideration of the influence of the time delay on the asymptotic stability of the system. Finally, simulation results are presented to illustrate the superiority and effectiveness of the proposed method
Existing Building Renovation in the Republic of Serbia Using Green Roofs toward Fulfilment of EPBD Goals
No full textThe energy consumption in buildings is constantly rising over the last decades, besides all the efforts put in the energy efficiency and CO2 emission reduction. Increased consumption is noted especially for the cooling needs due to the climate changes and constant development of urban areas. Besides the increased energy consumption and thus the CO2 emissions, the increase of urban areas contributed to the formation of heat islands and significant increase of pollution last decades. The necessity of deep building renovation and more strict criteria for the building envelope U-values is foreseen as an imperative strategy towards fulfilment of EPBD goals. The Republic of Serbia has more than 2.2 million of buildings built before the adoption of first regulations on energy efficiency of buildings, back in 2011. Thus, the potential for final energy savings just in the term of heating needs, by thermal envelope renovation goes from 55 up to 70%, while the CO2 emission can be 50% to 65% lower depending on the type of energy efficiency measures that are implemented. Additionally, if the green roofs are introduced in the renovation as well, the energy savings in primary energy for heating and DHW increases up to 6%, while the CO2 emission decrease up to 6.5%. Besides the measurable indicators such as primary energy and CO2, a lot of studies worldwide confirmed a wide range of benefits of green roofs such as higher diversity and positive impact to pollinators, decreased pollution, possibilities of usage of green areas for recreation, lower temperatures of roofs in summer period etc.Contract number 451-03-65/2024-03/200105 from 05.02.2024
Analysis of remediation of manifold line damaged by longitudinal crack in the piping elbow of oil and gas well collector
No full textThe paper deals with damage mechanisms affecting the piping and piping elements during working life of the well collector as an integral part of the upstream plant. An initiated crack has propagated in the vertical piping elbow and caused leakage. The damaged elbow has a sensitive cut, and
a new elbow is welded onto the pipe by GTAW and SMAW processes. Necessary NDE was performed after repair welding activities showing that remediation of the line is properly conducted. The line is successfully put into service.Contract no. 451-03-66/2024-03/200213;
451-03-47/2023-01/20005