Machinery - Repository of the Faculty of Mechanical Engineering, University of Belgrade
Not a member yet
8397 research outputs found
Sort by
Experimental and Numerical Research on Swirl Flow in Straight Conical Diffuser
No full textThe main objective of the current study is a detailed (both numerical and experimental) investigation of the highly unsteady and complex swirl flow in a straight conical diffuser (with a total divergence angle of 8.6°) generated by an axial fan impeller. Pressure, and axial and tangential velocity profiles along several cross-sections were measured by original classical probes in two different flow regimes at the inlet: the modified solid body type of moderate swirl and the solid body type of strong swirl and reverse flow; they were additionally confirmed/validated by laser Doppler anemometry measurements. Computational studies of spatial, unsteady, viscous, compressible flows were performed in ANSYS Fluent by large eddy simulation. The fan was neglected, and its effect was replaced by the pressure and velocity profiles assigned along the inlet and outlet boundaries. The two sets of data obtained were compared, and several conclusions were drawn. In general, the relative errors of the pressure profiles (2–5%) were lower than the observed discrepancies in the axial velocity profiles (5–40% for the first and 15–50% for the second flow regime, respectively). The employed reduced numerical model can be considered acceptable since it provides insights into the complexity of the investigated swirl flow
Renewable Energy and Ai Implementation as Sustainable Strategy for Agriculture Resilience to Climate Change
No full textClimate change has a major impact on all human activities. One of the most important is agriculture from the point of view of food production, as the starting point of survival on the globe. The negative consequences of climate change are reflected in increasingly pronounced droughts and catastrophic floods, and are also reflected in the increase in the frequency of these extremes. Multidisciplinary teams of engineers and scientists are engaged in the development of sustainable strategies, with the aim of increasing the resilience of agriculture to climate change. The application of renewable energy sources and artificial intelligence plays a significant role in the management of sustainable strategies for the protection and improvement of smart agriculture. Wind turbines and photovoltaic panels raised above agricultural land at an appropriate distance form a synergy of agricultural development and renewable energy. Their implementation in itself reduces the emission of greenhouse gases and contributes to mitigating climate change. At the same time, this energy can be used both in the system and locally for pumping water for irrigation. Hydropower and the construction of water acumulations also provide increased opportunities for solving droughts and floods and thereby improving and stabilizing agricultural production and higher resilience of agriculture to climate change. Agricultural residues can be used as a resource for renewable bioenergy. Artificial intelligence, supported by contemporary solutions of sensor technology, helps us in the optimal management of all these complex processes. This research also contains a positive case studies from international practice on the implementation of renewable energy sources and artificial intelligence and their concrete contribution to increasing the resilience of agriculture to climate change
Reconfigurable control system for machine tools with a switchable kinematic and variable execution flow of the kinematic algorithm
No full textThis paper introduces the development of a control system for reconfigurable machine tools, featuring switchable kinematics and a variable execution flow of kinematic algorithms. The research highlights the importance of a low‐cost, adaptable solution for retrofitting aging CNC machinery, enhancing their flexibility and modularity. By leveraging open‐architecture platforms like LinuxCNC, the system incorporates direct and inverse kinematic functions designed to support multiple kinematic configurations without necessitating axis reinitialization or workpiece repositioning. Validated through real‐world experiments, the proposed system offers significant benefits for both educational and research purposes.Editor of chief: Assistant Professor Dejan Branković, PhD
Executive editor: Milivoj Stipanović, BsC
COBISS.RS-ID 14261145
Influence of dynamic behavior of excavator steel structure on correction of human vibrations: operator cabin case study
No full textIn this paper, the investigation and the influence of the dynamic behavior of the
structure of the structural part on the correction of human vibrations of the cabin of the unloading
boom of a bucket wheel excavator are performed. Diagnostic analysis using the finite element
method influenced the reconstruction of the local part of the structure to increase the first natural
frequency of the given structure, i.e. to reduce the human vibrations of the unloading boom booth.
This way, the lifespan of structural parts is extended, but also the health of the operator and better
working conditions are affected. By monitoring the state of human vibrations in a certain time
interval, before and after the reconstruction, this correct approach was prove
Development of Corrosion Wastage Assessment Methodology for Water Ballast Tanks: An Aging Bulk Carrier
No full textVarious environmental factors, operating conditions, transport routes, the type of transported cargo, maintenance
practices, and other external and internal factors significantly influence the development of corrosion. Cargo holds and water
ballast tanks are particularly susceptible to corrosion damage. This study investigates the extent to which steel thickness
reduction due to corrosion contributes to the degradation of steel structures and whether this reduction aligns with the
adopted Common Structural Rules (CSR). The analysis is based on an aging bulk carrier and three types of ballast tanks
within the cargo hold area: top-side tanks, hopper-side tanks, and double-bottom tanks. Thickness measurements were
conducted on nine specific transverse structural locations, and a corrosion wastage assessment methodology was
developed based on a nonlinear stochastic model. The corrosion growth rate was modeled using a probabilistic approach
where the corrosion rate parameter d0 follows a Weibull distribution. The model also incorporates 95% confidence intervals
to reflect uncertainty and assess early risk exceedance relative to CSR corrosion margins. The results revealed significant
differences in corrosion behavior among ballast tank areas and identified critical zones where corrosion thresholds are
reached earlier than expected. The proposed methodology demonstrates its applicability in assessing structural degradation
patterns and validating CSR-based corrosion allowances
Temporal changes in the flexural properties of 3D-printed ABS specimens
No full textThis study investigates the environmental aging effects on 3D-printed
Acrylonitrile Butadiene Styrene (ABS) produced using Fused Deposition
Modeling (FDM) and Digital Light Processing (DLP) techniques. The
materials in filament (FDM) and resin (DLP) forms were exposed to UV
light, humidity, and temperature fluctuations over two months. Mechanical
testing via three-point bending and Fourier Transform Infrared
Spectroscopy (FTIR) were employed to assess the impact of these
environmental factors. Results showed notable mechanical strength and
structural stability differences between the FDM-printed filament and DLPprinted resin ABS under aging conditions. The filament-based ABS
exhibited superior mechanical properties, retaining its strength over time,
while the resin-based ABS degraded significantly shortly after printing.
Despite exposure to ambient environmental conditions, the chemical
composition of both materials remained stable throughout the research
period.no. 451-03-65/2024- 03/200105; no. 451- 03-66/2024-03/20002
FLUE GAS HEAT RECOVERY FROM A BIOGAS PLANT FOR INDUSTRIAL THERMAL OIL SYSTEMS
No full textThis study presents a preliminary assessment of waste heat recovery from flue gases at the biogas plant to reduce fossil fuel consumption in the automotive factory, which uses thermal oil for process and space heating. The proposed solution involves directing 435°C flue gases from the biogas boiler to a gas-to-oil heat exchanger, where thermal oil is heated up to 260–300°C and transported through a 900-meter insulated pipeline to automotive factory. The thermal oil is then partially used to heat process water during winter via an additional heat exchanger. The available thermal energy from the flue gases is estimated at 387.4 kW, which covers approximately 60% of the factory’s current demand, reducing the load on the existing 1512 kW fuel oil boiler and two 400 kW solid fuel boilers. The required thermal oil mass flow is calculated at 0.89 kg/s, and the pipeline insulation must be optimized to minimize heat losses due to the significant distance between source and consumer. The study highlights the technical feasibility and energy-saving potential of this system, including reduced CO₂ emissions, enhanced energy efficiency, and increased sustainability. To ensure optimal implementation, a detailed design project is recommended, including heat exchanger dimensioning, pipeline layout with thermal insulation, pump and control system design, and a comprehensive techno-economic analysis. Although the preliminary results are promising, exact values should be validated through detailed field measurements and engineering calculations. This project represents a rational and environmentally responsible approach to energy use, aligning with modern industrial efficiency goals
DEVICE FOR TESTING BOND STRENGTH BETWEEN ARTIFICIAL TOOTH AND DENTURE BASE UNDER VARIABLE LOADING ANGLES
No full textThe presented device is a technically innovative solution designed to test the bond strength between various biomaterials, with specific application in dentistry—especially in analyzing the adhesion between artificial teeth and denture base materials. Conventional bond strength testing methods typically involve uniaxial loading, which does not reflect the complex multidirectional forces acting within the oral cavity during mastication and functional jaw movements. These forces include both vertical (compressive) and horizontal (shear) components, influenced by anterior tooth relationships and incisal guidance angles—factors often neglected in standard tests. This tool is compatible with universal testing machines and allows force application at precise, adjustable angles, there by more accurately simulating physiological conditions. Its adjustable holder geometry and gripping system ensure secure positioning of samples without introducing artifacts or pre-test damage. The device enables systematic analysis of how different loading angles affect bond strength, which is crucial for evaluating adhesive systems, surface treatments, and new materials. By incorporating this device into experimental protocols, researchers can achieve more accurate, repeatable, and clinically relevant results. Its application may significantly improve the understanding and optimization of prosthetic materials, leading to increased longevity and functional reliability of dental restorations, particularly within the scope of digital and CAD/CAM prosthodontic workflows
CYCLE ANALYSIS OF A SINGLE-STAGE TRANSCRITICAL R744 SYSTEM IN SUPERMARKETS: THE IMPACT OF ISENTROPIC EFFICIENCY AND OIL
No full textCarbon dioxide is increasingly present in modern refrigeration systems,
finding significant application in commercial cooling, especially in
supermarkets. However, its application encounters many challenges due to its
unfavorable thermodynamic properties. This serves as a starting point for
numerous engineering solutions, as well as for many theoretical and
experimental analyses of various systems utilizing R744. Some analyses often
overlook the fact that, in addition to the refrigerant, oil also passes through
all the system components in a certain quantity, which subsequently impacts
heat transfer as well as the cycle itself. This paper presents a cycle analysis
of a typical single-stage transcritical CO2 system used for medium-
temperature (MT) cooling applications in a supermarket. The analysis
included the impact of oil, considering several realistic steady-state scenarios
with predicted OCR (Oil Circulation Ratio) values. In addition to the effect of
oil, the study was expanded by examining available equations for the
isentropic efficiency of the compressor. The results showed that considering a
realistic compression process leads to an efficiency reduction of 15.4% to
39.9%, while the presence of oil decreases it by 5.7% to 27.8% under varying
conditions.Ugovor br. 451-03-137/2025-03/20010
Quadratures with quasi-degree of exactness
No full textMonic orthogonal polynomials satisfy a three-term recurrence relation whose coefficients determine a symmetric tridiagonal Jacobi matrix. To efficiently compute the nodes and weights of Gauss quadrature, the Golub-Welsch algorithm, based on the observations that the nodes are the eigenvalues of the Jacobi matrix and that the weights are proportional to the square of the first components of corresponding normalized eigenvectors, can be applied. The Gauss quadrature with nodes is exact for all polynomials of degree and represents a unique optimal interpolatory quadrature rule. After choosing arbitrary points (at which the integrand is defined), we transform the given integral into a sum of an integral that does not cause a quadrature error and an integral with a property that the points are the zeros of its modified integrand. Then, we approximate the integral of the modified integrand by an -point quadrature whose nodes and weights are simply expressed in terms of the nodes and weights of associated -point Gauss quadrature. Formula is exact for all polynomials of degree with fixed zeros , but those fixed zeros should not be a disadvantage, since the modified integrand has the same zeros