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MATHEMATICAL MODELLING AND SIMULATION OF AN ELECTROMAGNETIC VIBRATORY ACTUATOR
No full textThis paper presents a mathematical model of an electromagnetic vibratory actuator (EVA) used to drive vibratory conveyors. The model captures the fundamental aspects of electromechanical energy conversion by accounting for key energy-storing elements. The system is described by three state variables: the displacement and velocity of the actuator armature, and the current through the excitation coils. Numerical simulations were conducted for a representative vibratory conveyor configuration. To validate the accuracy of the proposed model. experimental measurements were performed using a laboratory prototype. The experimental results show strong agreement with the simulated data, confirming the validity of the nonlinear dynamic model
Top and middle management organizational level resilience modelling in mining companies
No full textTo assess organizational resilience at different organizational levels in mining companies in Serbia, a questionnaire was created based on previous research. Total of 148 respondents, with different qualifications, whose jobs are at different organizational levels (Top/Strategic Manager Level, Middle Manager Level, First Line Managers, Transport and Mining Machine Operators and
Other Workers) were surveyed. Descriptive statistics, Statistical tests Kolmogorov and U* Mann Whitney are used to test the differences between organizational levels (operative, tactical and strategic). Aspects of organizational resilience later on have been modelled by Analytic Hierarchy Process (AHP) method. The weight coefficients obtained with the AHP model, were used to calculate the resilience index. In that aim a new software tool based on the AHP method was designed - the ResOrg software. Finally, results and conclusions are presented
Experimental and Numerical Research of 3D DLP-Printed Solid and Voronoi PLA Resin Specimens Under Tensile and Bending Loads
No full textAdditive manufacturing (AM), especially vat photopolymerization processes
such as digital light processing (DLP), enables the production of highly detailed and complex
geometries with precise material structure control. In this study, the influence of
internal structure on the mechanical properties of PLA resin specimens produced using a
DLP 3D printer is investigated. Two designs were analyzed: a fully solid structure and a
shell with a Voronoi pattern. Tensile and bending tests revealed that solid specimens exhibited
higher strength, while Voronoi structures performed better under bending loading
despite lower load-bearing capacity due to their porosity ratio. The developed numerical
model, analyzed through different numerical simulations using the Ansys 2025R01 Software
package and validated by experimental results, showed a strong correlation between
experimental and numerical results that confirmed the reliability of the developed models
for preliminary design verification. These models hold significant potential for the design
of mechanical and biomedical components, including orthopedic immobilization devices.
Microscopic analysis revealed brittle fracture in solid specimens with striations and bubbleshaped
irregularities, while Voronoi specimens exhibited fragmented surfaces with clean,
brittle failure along structural voids. Based on the results obtained, this research demonstrates
how additive manufacturing enables the optimization of mechanical properties and
material efficiency through precise control of internal structures. In the future, validated
numerical models can be used to check the preliminary designs of different components,
which will significantly reduce development costs.contract No. 451-03-136/2025-03/200105; 451-03-137/2025-03/20010
Aging Effects on the Bending Performance of DLP and FDM Printed PLA
No full textThis research explores how 3D-printed PLA parts change over time, both mechanically and structurally. Two common 3D printing methods: Fused Deposition Modeling (FDM), which uses PLA filament, and Digital Light Processing (DLP-LCD), which uses a PLA-like resin are compared. Test specimens were examined right after printing, then again after one and two months of aging under everyday indoor conditions that included regular cleaning to simulate real-world use. To observe changes, three-point bending tests were used to assess flexural strength, stiffness, and strain, and microscopy helped reveal structural changes inside the materials.
Specimens made with FDM printing showed minimal changes over time. Their stiffness (flexural modulus) remained mostly unchanged, strength dropped slightly (by up to 9%), and flexibility (strain at failure) increased moderately (up to 17%). This suggests the material stayed strong and elastic, with a slight shift toward being more ductile.
In contrast, the PLA-like resin specimens printed with DLP-LCD technology showed a clear decline in performance. Their stiffness and strength dropped significantly - down to about 45% and 43% of their original values—and their flexibility increased similarly. These results point to a shift in the material’s behavior: it became softer and more flexible, but at the cost of structural integrity.
In summary, FDM-printed PLA held up well over time, making it a reliable choice for parts that need to retain their shape and strength. On the other hand, the resin-based parts showed signs of weakening, highlighting how important it is to match the right material and printing method to the demands of the final application.Contract No. 451-03-136/2025-03/200105; Contract No. 451-03-137/2025-03/20010
Prediction of technical systems availability using the simulation models based on the AI techniques and statistical methods. A case study: Bucket wheel excavator
No full textThe availability of technical systems such as the bucket wheel excavator (BWE) is one of the key indicators of their
efficiency. The BWE is a highly productive machine that works 24/7 within the so-called continuous machinery
systems known as the ECS (excavator, conveyor, stacker) and ECC (excavator, conveyor, crushing plant).
Six simulation models for predicting/calculating the BWE availability are developed based on the time picture of
its work over a four-year period. The data from the first three years are used as input data for modelling, while
the data from the fourth year are used for accuracy testing of the developed simulation models.
Simulation models differ in the way they model the times between failures and repair times, i.e., the durations of
the ``UpTime'' and ``DownTime'' states. For modelling the ``UpTime'' state, theoretical distributions (ThD), the NonHomogeneous
Poisson Process (NHPP), and Artificial Neural Networks (ANN) are employed, while for modelling
the ``DownTime'' state, ThD and ANN are utilized. Furthermore, the probability distribution of BWE failures and
stoppage occurrences, as well as the quantification of their mutual relations and influences, is provided.
The predicted change of the BWE availability in a one-year (test) period, for all six simulation models, is presented.
The best prediction results are yielded by the simulation model that uses the NHPP for modelling the ``UpTime''
state duration and the ANN for modelling the ``DownTime'' state duration.grant numbers 451-03-137/2025-03/200105, 451-03-136/2025-03/20012
Outlook for Air Taxis at the 2027 Expo in Belgrade
No full textThe 2027 Expo in Belgrade offers a valuable opportunity to showcase air taxis as an emerging urban mobility solution, a prospect actively recognized and supported by Serbia’s political leadership. This paper addresses the key challenges that must be overcome to take advantage of this opportunity. A comparison of several eVTOL (electric vertical take-off and landing) aircraft currently at an advanced stage of development is made, and their potential performance in the context of use at the upcoming World Expo in Belgrade is discussed
POSSIBILLITIES FOR INCREASING EFFICIENCY OF MILLING PLANT OPERATION FOR THE PURPOSE OF OPTIMIZING COMBUSTION PROCESS WITHIN POWER STEAM BOILER
No full textDuring retrofits taken on power unit “Nikola Tesla” A6 in 2011 for the purpose of increasing its overall production capacity certain modifications on milling plants have been applied. Enlargement of power steam boiler production capacities included increase in milling plant output with existing number of mills in operation. Changes made on arrangement of pulverized coal burners, geometry of mill gaseous mixture distribution elements inside mill gaseous mixture duct as well as operational rotational speed of mill impeller led to increase of milling capacity to the certain extent. Consequently, applied modifications resulted in higher primary air flow required for the purpose of regulating mill gaseous mixture temperature, thus, reducing secondary airflow in burners below recommended level which affected combustion process within boiler furnace. In this paper results of thermal calculations of power steam boiler and aerodynamic calculations of milling plant for the present operating conditions have been presented. Calculations results have been validated by use of measurements taken on site in present operating conditions. Impact on overall boiler operation made by modifications taken on milling plants has been discussed in details. In text new measures, which would reduce occurred negative effects, have been proposed. Positive effects of proposed measures, as new operating point of milling plant, are confirmed by the results of additionally performed thermal and aerodynamic calculations given in this paper
Testing Conformity with Benford's Law in Chaotic Dynamical Systems
No full textBenford's law, also known as the first digit law, gives a monotonically decreasing distribution of the first digit in the considered data set. Contrary to our intuition, which suggests that the first digit would appear with a uniform distribution, this is decreasingly logarithmic law, where the digit 1 is appearing with 30% chance and the digit 9 is appearing with 4.58% chance. The purpose of this paper is to consider whether the Benford's law can be applied on different dynamical systems (Lorenz, Hénon and Rössler). As a procedure, we analyze the frequency of the first and the second digit of the coordinates of the trajectories generated by these dynamical systems. We conclude that some trajectories follow Benford's law, while others do not, and some results depend of the choice of the parameters of the model. As the main point is that natural data generally follow Benford's law, we have shown that for some dynamical systems the distinction between the trajectories that follow Benford's law and that do not follow Benford's aw may be very small which may require much more careful consideration
FROM MODULAR LEGACY TO OPEN INNOVATION: EVOLUTION OF THE LOLA CNC SYSTEM ARCHITECTURE
No full textThis paper provides a comprehensive overview of the development, technical architecture, and
practical applications of the LOLA 30 CNC system, a landmark achievement in domestic industrial innovation in the field of numerical control. Developed in the early 1980s by the LOLA Institute, the system is examined within its historical context, with particular attention to its architectural features and its broader impact on industrial autonomy and engineering education. Special emphasis is placed on its modular design, integration with the PA512 programmable logic controller, and representative use cases. The paper also presents a comparative analysis between the LOLA 30 CNC and the modern LOLA ROSA CNC system, which is based on open-architecture hardware and software. Key technological advancements of the new system, particularly in terms of reconfigurability and distributability, are highlighted.Conference proceedings [Elektronski izvor] : 60th Anniversary of the Association of Production Engineering of Serbia
/ 40th International Conference of Production Engineering ICPES 2025 - Serbia 2025, Nis, Serbia, 18th - 19th
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Народна библиотека Србије, Београд
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Comparative Assessment of Noise Exposure in Loaders’ and Bulldozers’ Cabin in Mining Industry: A Case Study
No full textOccupational noise exposure is a significant issue in the mining industry, especially for operators of heavy machinery and it can result with serious health risks, including Noise-Induced Hearing Loss This case study analyzes the noise levels in cabins of two prevalent mining machines—bulldozer and loader, in aim to assess potential threats to operator health and to guide measures for enhancing workplace safety. Noise characteristics, such as peak sound pressure level, equivalent continuous sound level, and maximum sound level with fast weighting, were recorded during a single work shift. Descriptive statistics reviled non-normal data distribution, so the Mann-Whitney U test was applied. The results indicated statistically significant differences in all noise parameters between the two machineries (p < 0.01), with loader demonstrating elevated continuous noise levels and bulldozer exhibiting increased variability. The research underscores the necessity for specific noise reduction measures, particularly in loader cabins, to adhere to ISO 9612:2025 and ISO/11201:2010 standards and safeguard operator health. This study contributes valuable insights for occupational health assessments and serves as a foundation for future research. Subsequent
research ought to build upon these findings by incorporating diverse machinery kinds and varying operating situations in order to to mitigate noise-related health risks in the mining sector