Machinery - Repository of the Faculty of Mechanical Engineering, University of Belgrade
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Parameter-dependent fractal spectra in quasiperiodic metastructures with elastic and rigid segments
No full textPeriodic structures exhibit unique dynamic behaviors that are strongly
influenced by their structural organization. The structural periodicity
leads to wave phenomena similar to those in crystallography,
including Bragg scattering and band gap formation. These engineered
systems, known as metastructures, allow enhanced control over
mechanical wave propagation and have been widely studied for
applications such as vibration suppression, energy harvesting, and
non-invasive testing. By carefully designing and tessellating unit
cells, advanced effects can be achieved. Notably, these dynamic
phenomena remain robust despite small structural irregularities. This
robustness enables the introduction of deterministic disorder through
controlled variations in design parameters, creating quasiperiodic
structures. Such systems often show spatial localization of vibrational
modes, confining energy to specific regions. This tunable behavior
supports the development of intelligent structures, offering innovative
solutions in various engineering domains.No. 451-03- 137/2025-03/200105 from 4.2.2025
INFLUENCE OF INFILL DENSITY ON THE TENSILE STRENGTH OF 3D-PRINTED PLA SPECIMENS
No full textAdditive Manufacturing (AM), widely known as 3D printing, has significantly evolved, transitioning from model prototyping to the production of functional components. Fused Deposition Modeling (FDM), one of the most commonly used AM technologies, enables the fabrication of parts with varied m echanical properties depending on printing parameters. This study investigates the influence of infill density on the tensile strength of 3D printed PLA (Polylactic Acid) specimens. A series of specimens were designed in SolidWorks, prepared for printing u sing Wanhao Cura 18.04 software, and fabricated on a WANHAO Duplicator 6 printer. All samples were printed under controlled conditions, maintaining constant parameters such as layer height, shell thickness, and printing speed. The study focused on differen t infill densities (20%, 60%, and 100%). Tensile strength tests were performed following standardized procedures to evaluate the mechanical
properties of the specimens. The results demonstrate a direct correlation between infill density and tensile
strengt h, with higher densities exhibiting superior load carrying capacity. The findings contribute to the
optimization of 3D printing parameters for applications where mechanical performance is critical. Future
research may explore the effects of other factors s uch as build orientation, material, infill patterns, and layer
height to further enhance the mechanical properties of 3D printed components.Grant number 51 03 137/2025 03/ 20010
CFD-based insights into KCA propellers for high-speed vessels
No full textThis study focuses on the development and application of Computational Fluid Dynamics (CFD) methodology for analyzing hydrodynamic characteristics of KCA propellers. The research emphasizes the verification of CFD methodology using existing experimental data for three-bladed propellers of KCA series and
Potsdam propeller CFD benchmark. Following the validation of the methodology, a series of simulations
will be conducted for four-, five- and six-bladed propellers, analyzing key hydrodynamic characteristics
such as thrust, torque and efficiency coefficients. This approach aims to establish a foundational database
for segmental section propellers with more than three blades. This research is particularly significant for
high-speed vessels, which are currently exempt from certain regulatory frameworks but are expected to
contribute to global efforts to mitigate the environmental impact of maritime transport. The developed
methodology and CFD results provide a foundation for more efficient KCA propeller case-by-case designs
in the early stages of development, while the expanded database creates opportunities for further studies
and applications. The proposed approach contributes to modernizing the initial propeller design process in
line with contemporary technologies and energy efficiency improvements
Fast response aerodynamic multihole probe – mechanism for calibration and possibilities for measurements
No full textSimultaneous measurements of 3D velocity field and pressure is of great importance. Complex air flows exist in nature, as well as in numerous technical systems. These flows exhibit high levels of turbulence, requiring high sampling rates for accurate measurement. Analyzing such flows is possible using optical methods (laser Doppler velocimetry or particle image velocimetry), hot-wire anemometry or spatial probes. The advantage of multihole probes is simultaneous measurement of 3D velocity field and pressure.
The problem with optical methods is that they require laboratory conditions and they are not often used, except in special well prepared cases, on-site.Their advantage lies in non-invasiveness, high sampling rates and precision. On the other hand, standard spatial multiholeprobes are not suitable for measuring flows with high levels of turbulence. Newer generations of the multiholeprobes are capable of these measurements with fewer drawbacks. Integrating fast pressure transducers into the probe handles has enabled high sampling rates. These probes are known as FRAP (Fast Response Aerodynamic Probe).
In this paper is presented five hole FRAP, mechanism and installation for its calibration. The developed half-automatic mechanism for pitch-yaw calibration in the Laboratory of the Hydraulic Machinery and Energy Systems Department, at the University of Belgrade, Faculty of Mechanical Engineering is introduced. Calibration is performed by placing the probe in a known flow field in the nozzle of the wind tunnel with low level of turbulence (less than 2%). Specified pitch-yaw calibration angles should cover all the angles of attack that will encounter during application.no. 451-03-65/2024-03/20010
Numerical Simulation of Five-Hole Probe Used for Small UAV
No full textThe multi-hole probe (MHP) is extensively employed in turbomachinery, although its application in the aviation industry is relatively limited. With the recent expansion of the aviation field, especially small unmanned aerial vehicles (UAVs) and drones, there is now a variety of unmanned aircraft, each with its own specific features. The MHP provides a compact, easy-to-manufacture, and accurate way to measure flight angles while gathering real-time external data. This study presents a numerical simulation of a five-hole probe, which is compared with experimental data obtained from wind tunnel testing. The objective is to assess the feasibility of utilizing numerical simulation for the calibration of the five-hole probe, thereby reducing reliance on traditional wind tunnel testing methods
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
Sustainable development and circular economy supported by artificial intelligence tools
No full textThis paper researches how artificial intelligence (AI) can support sustainable
development and the circular economy. It focuses on the use of AI tools in resource
optimization, waste reduction, and improving manufacturing processes in line with the
principles of the circular economy. The aim is to demonstrate how AI can contribute to
sustainable practices across industries, from agriculture to manufacturing and recycling,
enabling economies that minimize environmental impact. The study analyzes current AI
technologies such as machine learning, deep learning, and data-driven optimization, and
their application in resource consumption pattern recognition, product lifecycle
prediction, and recycling improvements. While AI offers significant potential, the paper
also discusses challenges such as high implementation costs, the need for training, and
ethical concerns regarding data usage. The conclusion of the study emphasizes the need
for an integrated approach in AI tool implementation, with special attention to the social,
economic, and environmental aspects of sustainable development
Optimal Methodology for Designing and Testing Multicopter Arm Made of Composite Materials
No full textThe modern unmanned aerial vehicle (UAV) industry relies heavily on structures made of composite materials. This study focuses on designing the structure of a military-grade multicopter. This type of UAV must meet rigorous standards to prevent risks of damage or even catastrophic failure during missions. One of the most challenging parts for design is the multicopter arm since it is exposed to high-magnitude forces during flight. Understanding these forces and how to withstand them is of crucial importance for good arm design. In this research, where the goal was to define the optimal methodology of arm design, it was necessary to conduct a static propulsion test to determine maximum force acting on the arm. Then, the arm design was validated using the finite element method (FEM) in combination with static experiments held on a specially created test stand. Finally, the production process, as one of the most demanding aspects of designing the arm, was carefully planned and defined, as it required not only selecting the appropriate materials but also mastering the technologies for high-quality arm manufacture
Promising tensile mechanical properties of the flax fibre reinforced vitrimer matrix composites – seeking sustainable opportunities for automotive
No full textunder the agreement number 451-03-137/2025-03/200105
AUTHOR CONTACT
Milan Jankovic, MSc
email: [email protected]
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