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Influence of the Involute Gear Teeth Profile Shape and Running-In on Surface Load Capacity of Cylindrical Gear Pairs
No full textIn this article, the simultaneous influence of profile shape variation and running-in of the involute gear teeth on the surface load capacity of cylindrical gear pair was examined. Experimental investigations were carried out on spur gears in laboratory conditions, using a back-to-back gear test rig. Different involute profile shapes are achieved by varying the gear teeth pressure angle. Different running-in regimes were achieved by varying the torque of the gear pair in the initial period of operation. By modifying the profile and adequate running-in in short period of time, the following are reduced: the intensity of wear, the amount of surface damage, and friction on the contact surfaces of gear teeth. Greater benefits of a higher pressure angle and running-in were observed with driven gears. It is shown that the negative sliding on the dedendum of the driving gears teeth has a greater effect on the generation of surface fatigue compared to the driven gears
teeth, due to the direction of the friction force. The obtained results indicate that by varying the shape of the involute profile and running-in parameters, the surface load capacity of spur gears can be significantly improved, such that a longer operational life and greater efficiency of the gear drive in exploitation can be achieved.451-03-137/2025-03/20010
Structural optimisation of planetary gearbox components
No full textThe high-speed reduction in a relatively small space, coupled with a torque load capacity larger than that of any other standard transmission, positions planetary gear systems as one of the most vital components in gearing applications today. Structural analysis of a gear train is conducted using CATIA software, employing strain full tensor distribution analysis through Finite Element Method (FEM). The analysed natural frequencies and vibration modes of each component provide essential information for fine-tuning resonances away from the assembly's operating speeds. Based on these results, component dimensions are optimized using CATIA's optimizer module to achieve a structurally compact gearbox design. The minimization of gearbox mass serves as an objective function, with gear dimensions as variable parameters constrained by ultimate bending tooth root stress, safety factors, and critical frequencies expressed as inequalities. Structural optimization results are presented in tables, comparing initial natural frequencies with those obtained from the optimized solution. The final optimized design for each gear train component is also presented and discussed in the paper's concluding section. In conclusion, the paper outlines its primary objectives, summarizing key findings and proposing new ideas for further research to
enhance and optimize planetary gear transmissions in practical applications
Cavitation Erosion of Protective Coating Based on Cordierite Filler and Epoxy Matrix
No full textThe goal of this study is to investigate the surface morphology changes induced
by the cavitation erosion of a coating based on cordierite with an epoxy matrix for an
aluminum substrate. The literature review shows a certain lack of knowledge regarding
the coating’s resistance to wearing induced by water flow, which is a highly important
property of the material immersed in or in contact with water streams. The main idea
behind the investigation is that such a protective coating will also improve the cavitation
erosion resistance of metal substrates. The protective coatings were based on cordierite filler
(88 wt.%) and epoxy resin (7 wt.%). The filler, made of a mixture of kaolin, alumina, and talc,
is obtained by a sintering procedure that took place at 1350 ◦C. X-ray diffraction analysis
and scanning electron microscopy were employed in the characterization of the produced
filler. The adherence of the obtained epoxy-based protective coating and resistance to
water flow were tested by the ultrasonic vibration method (i.e., cavitation erosion testing).
Scanning electron microscopy was used for analysis of the coating’s morphology upon
cavitation erosion. Based on the value of the cavitation erosion rate and the analyzed
final surface damage, it was assessed that the investigated protective coating is resistant to
cavitation erosion
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
DESIGN AND EXPERIMENTAL VERIFICATION OF THE COMPOSITE BLADE OF THE MAIN ROTOR OF AN UNMANNED HELICOPTER
No full textThe increasing use of unmanned aerial vehicles (UAVs) across various industries worldwide dictates new design rules and standards for their structures and systems. The reliability and durability of these structures are achieved through the application of advanced materials. Each structure must be designed in accordance with mission requirements to withstand the necessary aerodynamic and mechanical loads. The development of an unmanned helicopter presents a significant engineering challenge, particularly in the design of the main rotor, which requires a multidisciplinary approach and the coupling of aerodynamic, aeroelastic, and structural phenomena. This helicopter has a maximum takeoff weight of 750 kg, classifying it as a light helicopter. This research presents a comprehensive approach to the design, numerical analysis, and experimental validation of a composite helicopter rotor blade, in accordance with predefined operational requirements. The key specifications include maintaining an identical geometry compared to an existing model, precisely defining the blade mass at 11.5 kg, utilizing composite materials, and ensuring that the blade root can withstand an axial load of 40 tons. Additionally, aerodynamic efficiency is optimized by maintaining the LOCK number within the range of 5–7.
The blade design is based on composite prepreg materials due to their high specific strength, excellent fatigue resistance, and superior damage tolerance. The structural configuration has been developed to achieve an optimal balance of weight, strength, and aerodynamic performance
EFFECT OF ENGINE CYLINDER DEACTIVATION ON FUEL ECONOMY AND CRANKSHAFT SPEED VARIATIONS
No full textIn this paper the cylinder deactivation technique in spark ignition engines was investigated. The potential of this concept was analysed using engine working cycle simulation model AVL Boost. The engine power output regimes corresponding to the vehicle moderate constant driving speeds were considered and the results show that at that low load engine operating regimes cylinder deactivation can enable fuel economy improvement of about 6%-13% and corresponding CO2 emission reduction. The angular speed variations of engine crankshaft under cylinder deactivation conditions were also analysed and it was found that the speed variations increase several times compared to the standard operation of the engine with all active cylinders
Transient simulation on internal flow characteristics and pressure pulsation of variable speed Francis turbines during acceleration process
No full textVariable-speed Francis turbines offer the advantages of a broader operational range and enhanced stability. To investigate the internal flow dynamics and pressure pulsation characteristics during the variable-speed operation of the Francis-99 turbine, this paper employs numerical
simulations to examine the internal pressure, flow behavior, and energy loss variations over time during the acceleration process. The Hilbert–Huang Transform method is utilized to generate the corresponding time-frequency diagram of the pressure pulsation signal, thereby
enhancing the accuracy and reliability of feature extraction. The pressure pulsation signal was decomposed into an intrinsic mode function (IMF) using variational modal decomposition, and fast Fourier transform was applied to the IMF to identify the components contributing
most significantly to the pressure fluctuations. The final results demonstrate that the accelerated operation of the Francis-99 turbine positively affects the reduction of hydraulic losses and enhances operational stability. Regarding hydraulic stability, the rotor stator interference effects
must be considered. Following a change in rotor speed, the flow within the runner becomes more complex. However, total entropy production within the Francis-99 turbine decreased by 9.1% following accelerated operation. During acceleration, the dominant frequencies of pressure
pulsations at the guide vane outlet and impeller inlet remained at 30 fn and 28 fn, respectively, as speed increased. Furthermore, the peak pressure pulsations at these dominant frequencies were reduced by 83% and 76%, respectively, compared to those observed during fixed speed
operation. This study offers a valuable reference for assessing the instability characteristics of the turbine during variable-speed operation and enhancing operational efficiency
Development of the Turbulent Swirling Flow Velocity Profiles in the Axial Fan Jet
No full textTurbulent swirling flow in the jet generated by
the axial fan impeller with twisted blades is studied
in this paper. Three velocity components are
obtained by using three-component laser Doppler
velocimetry system in ten measured sections.
Downstream flow development and continual
deformation of all velocity profiles with gradients in
radial and axial directions are obvious. It is shown
that circumferential velocity significantly deforms
profile of the axial velocity which gets M-shape
with weak reverse flow region in the central flow
zone in the first two measuring sections. This
phenomenon is still not well explained, especially
from the mathematical point of view.
Derivatives of all three velocity components in
radial direction are calculated for velocity field
analysis. Axial velocity profile in the downstream
sections becomes more uniform, with the strict
hierarchy of the positive gradient of the axial
velocity in axial direction in domain 0 < r/R < 0.5.
Character of distribution of the axial velocity out of
this region shows jet expansion. Maximum of the
axial velocity doesn’t belong to the jet core. In the
jet axis vicinity profile of the axial velocity is
concave even in the last measuring section. It means
that the transformation process is not completed.Ministry of Science, Technological Development and Innovation of the Republic of Serbia under the Agreement on financing the scientific research work of teaching staff at accredited higher education institutions in 2025, no. 451-03- 137/2025-03/20010
CII Compliance for a Fleet of 50 Bulk Carriers and Tankers
No full textThis study evaluates the Carbon Intensity Indicator (CII) for a fleet comprising 25 bulk carriers and
25 tankers, focusing on their energy efficiency and environmental performance in compliance with
the International Maritime Organization's (IMO) regulations. The CII, measured in grams of CO2 emitted
per cargo-carrying capacity and nautical mile, serves as a critical metric for assessing the carbon footprint
of maritime operations. Initial assessments reveal that a significant proportion of both vessel types
are likely to fall into lower CII rating categories (C, D, or E) due to operational inefficiencies and the increasing
stringency of CII thresholds leading up to 2030. To meet the CII requirements, it is estimated that
a reduction in operational speed will be necessary for many vessels in the fleet. This speed reduction aims
to enhance fuel efficiency and lower carbon emissions per unit of cargo transported. The study highlights
the necessity for ship owners to implement corrective measures to improve their CII ratings. Furthermore,
the findings underscore the importance of developing tailored decarbonization strategies for each vessel
class to ensure compliance and competitiveness in a rapidly evolving regulatory landscape. This evaluation
not only contributes to understanding the current performance of bulk carriers and tankers but also provides
a roadmap for future improvements in carbon emissions reduction across the maritime industry
Ecological aspects and occupational safety in welding processes: Contemporary approaches and challenges
No full textWelding is one of the fundamental technological processes in contemporary industrial production, playing a key role in sectors such as automotive, aerospace, shipbuilding, and civil engineering. Despite its indispensability, welding operations are associated with significant environmental and occupational health concerns. These include the emission of toxic gases and fine particulate matter, high energy consumption, intense noise, and thermal radiation, all of which can adversely affect both the environment and the health and safety of workers. This paper explores the ecological aspects of welding processes, with special attention given to current challenges and innovative solutions aimed at minimizing environmental impact and enhancing occupational safety. The analysis includes a review of modern techniques such as laser welding, friction stir welding, and hybrid welding methods, which offer improved energy efficiency and reduced emissions. Additionally, the paper addresses the importance of proper ventilation systems, protective equipment, and continuous monitoring of air quality in workspaces. A multidisciplinary approach that combines engineering innovations, environmental protection strategies, and occupational safety regulations is necessary to meet the growing demands for sustainable and safe industrial practices. This study highlights the need for further research and cross-sector collaboration in order to develop eco-friendlier and worker-conscious welding technologies.No. 451-03-137/2025-03/200105, dated February 4, 202