Machinery - Repository of the Faculty of Mechanical Engineering, University of Belgrade
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LOW-AMPLITUDE ACOUSTIC MODULATION AS A TOOL FOR CONTROLLING THE VORTEX STRUCTURES OF THE TURBULENT AXISYMMETRIC AIR JET
No full textThe roll-up of vortex structures in turbulent jets
can be influenced by low-amplitude modulations of
the nozzle exit velocity. These modulations can be
generated either by external low-amplitude
oscillations or by self-sustaining oscillations
inherent to the operation of specially designed
whistler nozzles. The aim of the experimental
investigations, mathematical modeling, and
numerical simulations carried out as part of the
project evaluation was to thoroughly investigate the
characteristics and vortex dynamics of acoustically
modulated and non-modulated nozzles. A major
focus was on identifying effective methods to control
vortex structures, as these play an important role in
improving heat transfer processes.
This paper presents the results of mathematical
modeling and numerical simulations of free and
impinging turbulent axisymmetric air jets, both
unmodulated and modified by low-amplitude
oscillations. The modeling results showed strong
agreement with experimental findings confirming
the ability to manipulate vortex structures in the jet
by acoustically modulating the nozzle exit velocity.
This study provides a basis for the development and
optimization of technological processes using air
jets, particularly in applications where improved heat
transfer is critical.Grant no. 451- 03-66/2024-03/200017 («Vinča» Institute of Nuclear Sciences, National Institute of the Republic of Serbia, University of Belgrade
Energy harvesting from topological interface states in an elastic beam array system
No full textRecent discoveries of exotic topological phenomena in mechanical phononics and metamaterials have become a prominent focus in engineering research. These findings not only expanded the functionality and potential applications of such artificial materials and structures but also went well beyond the initial identification of effects such as band gaps. In this study, we propose energy harvesting from localized interface modes in a periodic beam array system. The system is composed of elastically connected parallel beams, with bimorph piezoelectric beams considered at the interface. We derive a system of governing equations, and respective eigenvalue problems for both the full finite lattice model and a reduced-order model based on Bloch mode synthesis are defined and solved. We analyze the topological properties, eigenspectrum, frequency–voltage relationships, and steady-state responses to explore localized interface modes and their energy harvesting capabilities. Additionally, we investigate the robustness of the frequency of topologically protected interface modes in the presence of a mass defect in the lattice, demonstrating the efficiency of the proposed energy harvesting system
Ecology materials in the context of sustainable strategies and optimal resources management
No full textThe integration of ecological materials into sustainable strategies and resources management represents a fundamental approach towards environmental preservation and efficient utilization of natural and processed resources on the Globe. Ecological materials, characterized by minimal environmental footprint, recyclability, and renewability, enable implementation of circular economy principles in construction, industry, and everyday life. Their use contributes to reducing pollution, lowering energy consumption in production processes, and extending the lifecycle of products through reuse and recycling. This paper analyzes key aspects of the reuse of materials, with a focus on management strategies that ensure sustainable ecology material flows within economic systems. In particular, the role of management in designing policies that promote the transition from linear to circular models is emphasized. Sustainable strategies must include life cycle assessment (LCA) and eco-design to minimize negative impacts on ecosystems while maintaining economic competitiveness. Moreover, the selection of ecological materials affects the quality of life and health of the population, aligning environmental and social objectives with economic development goals. The results of the analysis conducted in this paper indicates that successful integration of ecological materials into resources management requires cooperation of researchers, producers, consumers, and policymakers, as well as education that raises awareness about environmental protection and responsible material use. Implementing these approaches contributes to building a resilient society based on sustainability, circular economy, and optimal resources management.Contract number: 451-03-136/2025-03/ 20021
Strategic mining management in light of resource scarcity, sustainability and environmental protection challenges AND ENVIRONMENTAL PROTECTION CHALLENGES
No full textSavremeno rudarstvo nalazi se na raskršću između rastućih potreba za mineralnim sirovinama i ograničenih prirodnih resursa, uz istovremeno pojačane pritiske javnosti i regulatornih tela da se očuvaju ekosistemi. Strateško upravljanje rudarskim aktivnostima zahteva integraciju ekonomskih, ekoloških i socijalnih aspekata, kao i usaglašavanje sa principima cirkularne ekonomije. Cilj ovog rada je da se analiziraju ključni izazovi u domenu održivosti, identifikuju faktori koji uslovljavaju nedostatak mineralnih resursa i ponude strategije za dugoročno planiranje. Metodologija je zasnovana na komparativnoj analizi globalnih trendova, proceni raspoloživosti rudnih ležišta i analizi uticaja na životnu sredinu kroz indikatore kao što su emisije CO₂, potrošnja vode i degradacija zemljišta. Rezultati ukazuju na potrebu primene integrisanog upravljačkog pristupa, razvoj tehnoloških inovacija za povećanje efikasnosti eksploatacije i uspostavljanje strogih ekoloških standarda. Diskusija pokazuje da uspešna transformacija rudarskog sektora zavisi od dugoročne vizije, javnoprivatnog partnerstva i usmeravanja investicija ka istraživanju i reciklaži sekundarnih sirovina. Zaključak ističe da je samo holistički pristup, koji istovremeno tretira ekonomsku dobit i zaštitu prirodnog okruženja, u stanju da obezbedi stabilnost i prihvatljivost rudarstva u narednim decenijama.Contract number: 451-03-136/2025-03/ 20021
Experimental Assessment of PA6 Bearing Housing Pressed-Fit for Enhanced Reliability and Multiple Maintenance Process
No full textThis paper presents an experimental method for determining the suitable bore diameter of bearing housings made of polymer designated as PA6, which enables multiple bearing replacement processes. Preceded by analytical calculation, four distinct series of housing samples (each with varying production tolerances) were subjected to testing, where each series comprised three housing samples with identical tolerance specifications. The assembly and disassembly processes of press-fit joints were thoroughly monitored using a force sensor, complemented by equipment for measuring the roughness of contact surfaces. Based on the experimental findings, a recommendation is provided for an appropriate interference fit for the tested bearing housing, providing a suitable solution for multiple maintenance processes. As a summary, the idea of this research is to define the prototype solution for the interference fit of a rolling bearing installed in a PA6 housing. Methods used to examine the proposed solution were surface topography and roundness measuring of PA6 housings, while the press-fitting and dismantling tests of rolling bearings in/from PA6 housings were used to verify it.451-03-137/2025-03/200105 ;
451-03-136/2025-03/20021
A system engineering approach for robot manipulator design using game engine simulation and computational modelling
No full textModern game engine platforms are increasingly used in the field of robotics due to their built- in support for creating real-time simulation within an Extended Reality (XR) environment. This research investigates the integration of game engine platforms into systems engineering processes in the robotics domain. A novel method for the design of robotic manipulators, focusing on actuator selection, based on robot motion simulation within game engine platforms using integrated functionalities for joint torque calculation, is presented. The proposed robot model integration methodology involves the use of a CAD-based robot model, the game engine’s physics engine, and MATLAB Simscape as an intermediate modeling environment. This approach enables appropriate actuator selection, verification of component dimensioning, and accelerates the design process. The proposed approach offers a cost-effective and flexible alternative to traditional simulation environments and offers enhanced immersive visualization of robotic systems through XR technologies. The simulated joint actuator torques are verified using MATLAB Simscape for a 6-DoF articulated robot model
OPTIMIZATION OF THE DELTA 3D PRINTER STRUCTURE
No full textIn recent years, additive manufacturing technologies have made significant progress in terms of structural solutions, printing parameters, materials, and software support. This paper presents the process of reconstructing and optimizing a damaged and non-functional Delta 3D printer, with the goal of making it suitable for use in an educational setting. A Delta 3D printer is a type of additive manufacturing system distinguished by its unique kinematic structure, where three vertical arms are arranged in a triangular base configuration and simultaneously control the printhead's position. This design enables high-speed operation, precise movement, and fabrication of models with significant height. This configuration is particularly advantageous in educational environments, as it illustrates the diversity of 3D printer mechanisms and underlying engineering principles. Using reverse engineering methods and modern additive manufacturing technologies – FFF (Fused Filament Fabrication) and SLA (Stereolithography), damaged and worn-out components were replaced and certain technical improvements were implemented. The reconstruction involved replacing key components and improving the printer’s functionality and ease of use, making it more suitable for educational purposes. After the reconstruction, the device was successfully tested and is now capable of reliably producing functional models. The printer is operated using Marlin firmware and the Arduino
Application of modern test methods and engineering practice on pressure vessels
No full textIn welding, a highly multidisciplinary field, quality assurance is crucial. Even minor deviations fromthestringent requirements set by welding standards can lead to defects in welded joints. This is especiallytrueforpressure equipment fabricated with materials for high-temperature service, where small variations inkeyparameters almost inevitably cause defects. When defects are detected and the installation of newcomponentsis not an option, a numerical simulation can be an effective modern method to assess the integrity of theweld. By interpreting the results of these simulations and combining them with sound engineering practice, thereliability and functionality of the component can be proven, minimizing the need for costlyreworkorreplacement. For example, indications were found in the superheater tubes of SteamBoiler 1, fabricatedforthe "Šoštanj" Thermal Power Plant in Slovenia. These were discovered using destructive testing methods, asconventional nondestructive testing methods, which were mandated for final inspection, failed to detect them. A detailed analysis revealed the root cause: an excessively high quality class for the welded jointswasspecified in the design, exceeding what was necessary. While the designer correctly prioritized the structural integrity and load-bearing capacity of this pressureequipment, the attempt to achieve an unnecessarily high-quality class of welds resulted in inadequatepreparation. This, in turn, made the occurrence of defects in the welded joints inevitable. To prove the load-bearing capacity of the welded joints, a numerical simulation was performed. Thissimulation demonstrated the welds' resistance to static load for several potential loading scenarios, evenwithcritical indications present at the weld root. The simulation also provided the values for the maximumpossibleloads before the onset of plasticity
STRUCTURAL MODIFICATION OF THE CARGO HOLD DOUBLE BOTTOM FOR A MULTI-PURPOSE VESSEL
No full textIncreasingly, modern maritime vessels must demonstrate sructural flexibility to accommodate the growing
need for transporting various cargo types in response to evolving industry demands. As a result, regulatory
bodies, and their respective rules, regulations and standards, require that novel structural solutions are to be
verified through advanced structural assessments, including finite element analysis (FEA). Therefore, this
study focuses on FEA-based structural assessment and optimization of the double bottom and underdeck
reinforcement structure in the two cargo holds of a multi-purpose vessel originally designed for bulk cargo.
However, the vessel now also needs to carry standard 20-foot high cube containers, imposing a significantly
different loading scenario. While bulk cargo results in nearly uniform load distribution, containerized cargo
introduces concentrated point loads. The analysis accounted for container weights, gravity, and accelerations
due to ship motion. Von Mises stress criteria were used to evaluate the structural response, according to the
rules and regulations of two major regulatory bodies: Lloyd’s Register and International Association of
Classification Societies. The results indicated that the original structure could not withstand the new loading
demands according to the regulatory standards. Consequently, structural modifications were proposed and
implemented. The study highlights that even multi-purpose vessels, which are assumed to be suitable for
various cargo types by design, require structural modifications to safely accommodate containerized cargo.
The presented solution demonstrates how targeted reinforcements can ensure compliance with modern
classification society rules while enabling operational flexibility.Project no. 451-03-137/2025-03/200105 from 4 February 202