Machinery - Repository of the Faculty of Mechanical Engineering, University of Belgrade
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COMPARISON OF NOISE SPECTRA OF THE FLOW PAST A CYLINDER COMPUTED BY DIFFERENT TURBULENCE MODELS
No full textAero-acoustic features are a contemporary and important topic for many mechanical systems,
and include various flow phenomena, such as “singing” of wires, cables, metal rods, antennas,
etc. as well as wake shedding from different kinds of blades. The aim of the current
computational study is to compare and estimate the reliability of available turbulence and acoustic
models in ANSYS FLUENT. A spatial, incompressible, transient flow around a cylinder at
relatively low Reynolds number Re = 90000 and Mach number M = 0.2 is used as a benchmark
and investigated in detail. Both unsteady Reynolds-averaged Navier-Stokes (URANS) and
filtered Navier-Stokes (large eddy simulation, LES) equations are solved and resulting flow fields
are compared. In both cases, Ffowcs-Williams and Hawkings (FWH) acoustic model is
employed. The presented results include oscillating aerodynamic coefficients, instantaneous and
averaged flow field visualizations, noise spectra and overall noise levels. Comparisons between
the tested turbulence models confirm that the simpler, computationally less expensive URANS
approach captures fewer flow features than LES, as well as the resulting noise frequency
components, but is applicable for initial studies. On the other hand, both tested turbulence models
underestimate the generated noise by roughly 25%. In can be concluded that the agreement with
the corresponding, available experimental data seems acceptable for preliminary analyses.
Aerodynamic coefficients can be estimated with more reliability than acoustic quantities
A Short Discussion on the Circulation in the Turbulent Swirling Flow in the Axial Fan Jet
No full textIn this paper is analyzed distribution of the circulation in the turbulent swirling flow in
the axial fan jet. Experimental results are obtained by use of the three component LDV system.
Development of the circulation profile in the central zone, up to r = R obeys hierarchical
distribution downstream, while this is not a case in the outer zones. Positions of the circulation
extreme values are also discussed, as well as its gradients.Ministry of Science, Technological Development and Innovation of the Republic of Serbian, for scientific research work of teaching staff at accredited higher education institutions in 2025, no. 451-03-137/2025- 03/200105
Extended abstract, M34
https://sdm.org.rs/congress/2025/docs/proceedings.pd
WHOLE-BODY VIBRATION MEASUREMENT AT THE MINING MACHINERY OPERATOR’S WORKPLACE IN SMES
No full textIncreased mechanization in mining results in a larger number of workers being
exposed to longer durations of whole-body vibration (WBV). Occupational exposure to vibration is associated with an increased risk of musculoskeletal pain in the back, neck, hands, shoulders, and hips; the development of peripheral and cardiovascular disorders and gastrointestinal problems; and it may even increase the risk of developing certain cancers. In that aim, in this survey, whole-body vibration exposure levels were measured during the shift at 22 mining machinery operators’ workplaces in 3 surface mining. A triaxial accelerometer V31 was used to measure vibration exposure. Measurements were conducted in accordance with the procedures described in applicable standards in the field. The results indicate that the observed workplaces exceeded the action limit values according to the EU Directive 2002/44/EC, as well as the lower limit values of health risks according to the ISO 2631 standard. The lower limit value of health risk according to the ISO 2631 standard was exceeded at 50% of machines. The action value of WBV according to the EU Directive 2002/44/EC was exceeded in 36% of machines. The dominant vibrations were indicated along the X and Y axes. Operators on bulldozers and loaders are most often exposed to the harmful influence of WB vibrations. Research indicates that there is a risk of harmful impact of WBV that needs to be prevented and highlights the need for further research to identify the most critical risk factors and develop effective prevention and protection strategies for mining machinery operators’workplace risks caused by vibrations
EFFECT OF APPLICATION A MIXTURE OF REFRACTORY FILLERS AND ORGANIC ADDITIVES ON THE QUALITY OF PROTECTIVE COATINGS
No full textThe paper presents the results of research on the effect of a mixture of different fillers: based on cordierite and talc, cordierite and mullite, as well as cordierite and zirconium silicate on the cavitation resistance of protective coatings. Various coating compositions and production procedures were investigated. Special emphasis in the research was given to the influence of organic additives on the sedimentation stability of the coating. The quality of the coating was tested using the ultrasonic vibration method according to the ASTM G32 standard. Formation and development of surface damage were monitored by scanning electron microscope. Based on the loss of mass and the change in the morphology of the coating surface, the possibility of applying this type of coating for the protection of metal structures in metallurgy and mining was assessed. The special importance of these coatings is their non-toxicity and application of water-based solutions
History of Bucket Wheel Excavators: From the First Construction to the Guinness World Record for the Heaviest Land-Based Vehicle Ever Built
No full textA bucket-wheel excavator (BWE) is a large heavy equipment machine used in surface mining. The history of heavy equipment and excavators reaches even earlier times. Earth-moving tools and bucket wheels go back to ancient times, while the first known excavator design came in around 1420. Before the use of BWE, the first documented use of a bucket chain excavator was in 1859 by Alphonse Couvreux, a French entrepreneur. This paper presents some notes on the history of BWEs, starting from the first construction of the rail-mounted BWE, which was first put into operation in 1916, in the surface mine Bergwitz in Germany to the Guinness World Record for the heaviest land-based vehicle ever built: The gigantic Bagger 293 weighting 14,200 tones, a BWE built in 1995 used for strip-mining operations. This heaviest earthmoving machine, with the digging output of 240,000 m3 per day, is capable of moving under its own power. Historical development and evolution of BWEs led to the enormous increase of the output of those machines over the next years
Digital twin-based numerical simulation of stress distribution in the mandible with dental implants
No full textA segment of the mandible with dental implants and natural teeth is modelled in SolidWorks® to create two digital twins: one with coupled implants and the other with separated implants. These digital twins are subsequently used to develop finite element models for calculating stresses and determine the stress distribution under various loading conditions and material configurations. The modelling process is presented here in full detail, while stress analysis results are presented in detail just for the case involving separated implants, with a porcelain veneer, and the loading applied equally at two points. All the other considered eight cases are briefly presented and discussed.contract No. 451-03-136/2025-03/200213 (from February 4, 2025
APPLICATION OF GENERATIVE DESIGN AND DIGITAL IMAGE CORRELATION FOR PART OPTIMIZATION AND MECHANICAL TESTING
No full textGenerative design has emerged as a transformative approach in engineering, enabling the creation of highly optimized components with complex geometries that are well-suited for additive manufacturing (AM). This study examines the integration of generative design, AM and digital image correlation (DIC) for iterative part optimization and mechanical performance validation. By leveraging generative design algorithms, parts can be optimized for weight reduction, material efficiency, and structural performance. The rapid prototyping capabilities of AM facilitate swift fabrication of both original and redesigned components, allowing for direct comparison through experimental testing. DIC, as a noncontact full-field measurement technique, plays a pivotal role in validating numerical models by capturing detailed strain distributions under various load conditions. This paper presents a comprehensive framework that highlights the interdependence of these technologies, reviews
challenges and advances, and outlines future directions for refining the mechanical design cycle through enhanced data-driven workflows
Functional analysis of LIDAR technology in optimizing efficiency and sustainability in construction sector
No full textThe construction is fraught with growing environmental and efficiency issues contributing a significant percentage toward the use of energy worldwide and carbon emission. Among several technologies that are now coming to light in the sustainable area of management of construction, one with good promise is LIDAR (Light Detection and Ranging). The purpose of this research is to fill a big knowledge gap regarding the direct impacts on construction project management from LIDAR, like cost, safety, environmental influence, precision, and efficiency. The results, therefore, demonstrate that there were significant improvements in different aspects of the system, which included time efficiency (0.27), cost-saving (0.126 average effect), safety (0.148), and reduction of environmental impact (0.372). Equally, the value of the predictive relevance Q2 = 0.529 further highlights the capability of the model for accurate predictions. This study supports the view that integration of LIDAR may be a strategic enabler of sustainable practice
The Influence of Al12Mg17 Compound Concentration in High-Energy Mixtures on Thermobaric Systems Characteristics
No full textThe influence of the concentration of Al12Mg17 intermetallic compound in high-energy mixtures (HEMs) on the performances of thermobaric (TB) systems is investigated. Thermobaric charges based on HEM pressed around the high explosive core were detonated in the open area. The pressure measurements of TB and trinitrotoluene reference charges were performed using eight
pressure transducers placed around the horizontally positioned charge. A high-speed camera and image processing technique were used to record a fireball evolution and quantify fireball characteristics. The highest values of overpressure peak and positive phase pressure impulse were obtained for HEM with 37 wt.% of Al12Mg17 content. The fireball image analysis shows satisfactory fireball surface area and duration time for HEM with 37 wt.% of Al12Mg17.This research was supported by funding through grants number 451-03-66/2024-03/ 200017 and 451-03-65/2024-03/200105 provided by the Ministry of Science, Innovation and Technical Development of the Republic of Serbia
Structural Optimization and Experimental Validation of a Composite Engine Mount Designed for VTOL UAV
No full textUnmanned air vehicles (UAVs) with vertical take-off and landing (VTOL) capabilities, equipped with rotors, have been gaining popularity in recent years for their numerous applications. Through joint efforts, engineers and researchers try to make these novel aircraft more maneuverable and reliable, but also lighter, more efficient and quieter. This paper presents the optimization of one of the vital aircraft parts, the composite engine mount, based on the genetic algorithm (GA) combined with the defined finite element (FE) parameterized model. The mount structure is assumed as a layered carbon composite whose lay-up sequence, defined by layer thicknesses and orientations, is being optimized with the goal of achieving its minimal mass with respect to different structural
constraints (failure criteria or maximal strain). To achieve a sufficiently reliable structure, a worst-case scenario, representing a sudden impact, is assumed by introducing forces at one end, while the mount is structurally constrained at the places where it is connected to wings. The defined optimization methodology significantly facilitated and accelerated the mount design process, after which it was manufactured and experimentally tested. Static forces representing the two thrust forces generated by the propellers connected to electric engines (at 100% throttle and the asymmetric case where one engine is at approximately 40% throttle and the other at 100%) and loads from the tail surfaces were introduced by weights, while the strain was measured at six different locations. Satisfactory comparison between numerical and experimental results is achieved, while slight inconsistencies can be attributed to manufacturing errors and idealizations of the FE model