Machinery - Repository of the Faculty of Mechanical Engineering, University of Belgrade
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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
Fractional-order Iterative Learning Control Enhanced Intelligent PID for Articulated Robots
No full textIn the ever-changing landscape of technological advancements, robotics plays a significant part in meeting growing industry demands. Considering the nonlinear, coupled nature and uncertainties of multi-body robotic systems, the ability of articulated manipulators to successfully track the trajectory imposed by a given task is a hallmark of a well-designed control system and remains a crucial aspect of robotics research. Motivated by the potential of control strategies based on the ultra-local models with regard to application in modern robotic systems and recognizing the potential of iterative learning control (ILC) in addressing the repetitive nature of robot manipulation tasks performed by articulated robots, this study proposes a novel control scheme combining an intelligent PD (iPD) controller and a fractional-order iterative learning controller (FOILC). Simulation results with comparative analysis are presented to illustrate the performance improvement and robustness of the proposed controller for the 3-DoF articulated robot
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
The shift to 3D education in mechanical engineering: Adapting to generation Z visualization needs
No full textThe generational shift toward digital environments has significantly impacted how students
in mechanical engineering education interpret technical representations. This
study investigates the challenges students from Generation Z face when working with
traditional 2D technical drawings, revealing a growing comprehension gap. A novel textbook
with 3D interactive models was introduced, with students accessing these models
via QR codes embedded in the textbook. The 3D models, viewable on mobile devices,
allow for rotation, zooming, and cross-sectional analyses, providing an immersive learning
experience. The study involved students, from each undergraduate academic year,
who were tasked with solving comprehension exercises using both 2D and 3D methods.
Results indicated that students demonstrated significantly higher accuracy and confidence
when using 3D models, with the most pronounced improvements observed
among first-year students. Furthermore, time efficiency and engagement levels were
substantially better when 3D tools were employed. These findings underscore the
need for a paradigm shift in engineering education, moving toward integrating 3D technologies
alongside traditional methods. By aligning teaching strategies with students’ cognitive
preferences, educators can bridge the comprehension gap, enhance learning
outcomes, and better prepare graduates for modern engineering practices. The study
advocates widespread adoption of 3D tools, emphasizing their role in creating an
engaging and effective educational environment
Finite-Time Stability of a Class of Nonstationary Nonlinear Fractional Order Time Delay Systems: New Gronwall–Bellman Inequality Approach
No full textThis paper aims to analyze finite-time stability (FTS) for a class of nonstationary
nonlinear two-term fractional-order time-delay systems with α, β ∈ (0, 2). Using a new
type of generalized Gronwall–Bellman inequality, we derive new FTS stability criteria for
these systems in terms of the Mittag–Leffler function. We demonstrate that our theoretical
results are less conservative than those presented in the existing literature. Finally, we
provide three numerical examples using a modified Adams–Bashforth–Moulton algorithm
to illustrate the applicability of the proposed stability conditions.No. 451-03-137/2025-03/200105 from 04.02.202
Artificial Intelligence-Supported Shape Optimization of an Automotive Rubber Bumper
No full textIn rubber bumper design, the most important mechanical property of
the product is the force-displacement curve under compression and its
fulfillment requires an iterative design method. Design engineers can
handle this task with the modification of the product shape, while the
axisymmetric finite element model of the rubber product is an
efficient way to evaluate the working characteristics. Using an
optimization process in place of a trial-and-error-based mechanical
engineering design method can help a company stay competitive in
the market if the iteration process can be automated
Device for increasing pressure in water supply systems with measurement of accumulated drinking water quality
No full textLow pressure in water supply systems, affecting both residential and industrial facilities, is a common issue in water distribution networks. Water sourced from municipal systems or shallow wells can experience pressure fluctuations or even complete drops, particularly during summer months. Supply from rooftop or overflow reservoirs often fails to maintain sufficient pressure to adequately supply all taps and appliances. Low pressure can also disrupt household devices such as washing machines, dishwashers, and water heaters. To address these problems, pressure-boosting systems are installed, which include additional pumps connected inline with pipelines or accumulation tanks for cases when water supply is interrupted. +The simplest solutions involve hydrophore units (a booster pump combined with a pressure vessel controlled by a pressure switch). However, noise generated by water pipes or booster pumps can cause discomfort for residents, often due to improper pump selection or inadequate regulation. Older centrifugal pumps with fan-cooled motors can create system-wide vibrations, increasing overall noise levels. This paper presents a technical solution for a pressure-boosting device in water supply systems, featuring reservoirs, recirculation pumps, water quality measurement systems, pressure-increasing pumps with PID control, compact electronic pressure transmitters, and expansion tanks. The design ensures silent operation while maintaining constant pressure in the water supply network. The device has been installed and tested in the Tonanti Hotel, Vrnjačka Banja, Serbia.https://doi.ub.kg.ac.rs/10-46793-sbt30
CFD INVESTIGATION OF TURBULENT WATER FLOW IN A PIPE ELBOW: ASSESSMENT OF CAVITATION RISK
No full textIn this study, turbulent water flow in a DN65 pipe elbow was analysed at high Reynolds numbers
using the OpenFOAM software with a two-dimensional model. The research aims to determine the critical mean inlet velocity of the fluid—water that leads to a pressure drop below the saturation pressure and the onset of vapour phase formation, i.e., cavitation. Although such elbows in practice usually operate at lower flow rates, corresponding to fluid velocities that do not reach cavitation conditions, here the limiting conditions were examined for potential non-standard applications involving extremely high flow rates resulting in large velocities. After developing the turbulent flow model, the visualisation was performed in ParaView, and the data were subsequently processed in Python, where the cavitation zone areas were calculated.Ugovor: 451-03-137/2025-03/ 20010
APPLICATION OF CFD FOR SIMULATION OF TRANSITIONAL FLOW IN SMOOTH CIRCULAR PIPES
No full textThe transitional flow regime in internal pipe flow presents unique challenges for accurate computational fluid dynamics (CFD) modelling due to its inherently unstable and intermittent nature. Transitional flows in pipes are encountered in numerous engineering applications, ranging from oil and gas pipelines to biological systems and various industrial processes. Experimental studies investigating the effects of flow transition have been conducted across a broad range of scales, from large industrial setups to microscopic systems. Intermittency, as a hallmark of transition, significantly influences flow characteristics such as velocity distribution, heat transfer, and pressure loss. Capturing the intermittent nature of transitional flows in CFD remains a significant challenge. Emphasis is placed on turbulence models enhanced with intermittency functions, such as the SST Transition (γ–Reθ) model, which is capable of capturing the gradual and spatially non-uniform onset of turbulence. Here, a set of simulations were completed for the case of a straight, circular pipe, long enough to establish fully developed conditions (L/D = 200), for different values of turbulence intensity levels at the inlet and for different Reynolds numbers. Fluid is water. This simulation study highlights the importance of turbulence transition modelling in predicting pressure drop, velocity profiles, and flow development length, providing insight into optimizing fluid transport with systems that can operate within this sensitive flow regime.contract 451-03-136/2025-03/ 20010
EFFICIENCY OF SOLAR CELLS IN THE CONDITIONS OF ELECTROMAGNETIC OR NEUTRON RADIATION
No full textThe paper discusses the influence of the dose of gamma or neutron radiation on commercial silicon photovoltaic cell under operating conditions. Before the measurement, the cells were irradiated with electromagnetic gamma radiation or neutron radiation. The examination was carried out experimentally and theoretically. The experiments were performed under well-controlled laboratory condidtions. Only licenced instruments were used. The measurement uncertanty of the experimental procedure was less than 5%.MNTR 451-03-137/2025-03/20010