Machinery - Repository of the Faculty of Mechanical Engineering, University of Belgrade
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Integrated Adaptive Microlearning System for Healthcare Professionals
No full textA microlearning system providing up-to-date and on-time information relevant to the current work of the (bio)medical professionals was developed. The system uses a microlearning approach and adapts to the working procedure of the medical professionals. The microlearning system for healthcare professionals is built in Java programming language and Spring framework and supports three different (bio)medical knowledge sources: clinical practice guidelines documents, classification data from databases, and prepared content for specific diseases and drugs. Microlearning system enables the integration of the learning process into the (bio)medical working procedure. It aims to help medical workers gain additional information about a patient and his condition or prescribed medication. Unlike existing microlearning systems for healthcare professionals that are mostly used outside the working hours and mobile-based, the microlearning system developed in this research is designed to be used during the consultation with the patient within the (bio)medical professional’s workflowContract no. 451-03-136/2025-03/20021
Numerical Simulations for the Optimization of the Position of the Regenerative Burner System for Tundish Preheating
No full textDETERMINING THE WORKING CHARACTERISTICS OF MECHANICALLY DRIVEN CENTRIFUGAL COMPRESSORS N-46-6
No full textThe paper presents a mathematical model and research methodology, i.e., determination of working characteristics of mechanically driven centrifugal compressors used in the process of supercharging special purpose high power diesel engines (780 HP) with intake air. A special research labor-atory installation was created for research with the aim to check and adapt compressors to the needs of the operating cycle of new or generally overhauled special purpose diesel engines. The paper provides a complete testing methodol-ogy and presents a mathematical model that can be very interesting and useful to other researchers in similar appli-cations of this compressor type. After determining the com-pressor operating characteristics on the research installa-tion, the compressor is then installed on the engine and the declared engine output parameters are monitored on a special research installation for engines
Application of Model-Free and Model-Based Kinetic Methods in Evaluation of Reactions Complexity during Thermo-Oxidative Degradation Process: Case Study of [4-(Hydroxymethyl)phenoxymethyl] Polystyrene Resin
No full textThis work examined the possibilities and limitations of model-free and model-based methods related to decrypting the kinetic complexity of multi-step thermo-oxidative degradation processes (as a testing system, a [4-(hydroxymethyl)phenoxymethyl] polystyrene resin was used), monitored by thermal analysis (TGA-DTG-DTA) techniques. It was found that isoconversional methods could successfully determine the correct number of process stages and presence of multiple reactions based on derived Ea(α) profiles and identify the negative dependence of the rate constant on the temperature. These methods could not overcome the problem that arose due to mass transfer limitations. The model-based method overcame more successfully the problem associated with mass transfer because its calculation machinery had capabilities for the correct solution of the total mass balance equation. However, a perfect fit with the experimental data was not achieved due to the dependence on the thermal history of the contribution (ctb.) of a given reaction step inside a fitting procedure cycle. On the other hand, through this approach, it was possible to estimate the rate-controlling steps of the process regarding the influence of the heating rate. It was found that for consecutive reaction mechanisms, the production of benzaldehyde and gases in high yields was controlled by the heating rate, where low heating rates were strongly recommended (≤10 K/min). Also, it was shown that the transport phenomenon may be also the rate-determining step (within the set of “intrinsic” kinetic parameters). It was also established that external heat transfer controls the overall rate, where the “pure” kinetic control regime had not been reached but was approached when lowering the temperature and size of the resin particles
Hydrogen production by thermal cracking of natural gas - test facility
No full textHydrogen is an energy carrier which makes a decisive contribution for future energy transition. Over 90% of H2 is produced currently from primary fossil fuels with high CO2 emissions. Methane cracking is intensively developing, as the storage or using of solid carbon is easier and more attractive than carbon capture and storage. The process without catalysts is simpler, but requires higher temperatures. Main objective of the test was to show the viability for industrial applications. The test facility consists of two columns (for reversible operation) filled with pebble-bed and a connecting horizontal part. The cracking process takes place at the highest temperature zone, which is the upper pebble-bed and the connecting pipe. The required reaction energy is supplied by adding oxygen to burn small amount of H2. Sensible heat of product gas is stored in the pebble-bed and cold gas goes out. The product gas is further cooled and the condensate flows in a drain vessel. The capacity of the facility was 2-4 m3STP per hour of CH4, with corresponding residence time between 0.5-2 seconds. To compare the quality of those results, the H2 yield was evaluated. The highest yields have been achieved at temperature above 1500°C, with a maximum value of 94.9%, what is considerably better than results achieved in other test facilities for cracking using catalysts (yield 78% at 1175°C). The comparison shows important advantages of high temperature processes without catalyst. The cracking process at 1500°C is a simpler and more effective way to reach industrialization of that technology
INTEGRATION OF ADDITIVE TECHNOLOGY AND MECHANICAL TESTING FOR THE ANALYSIS OF AUXETIC STRUCTURE CHARACTERISTICS
No full textThe Materials with a negative Poisson’s ratio are recognized as Auxetics materials. Compared to conventional materials it has the counter-intuitive property that during the compression the structure tends to contract and stretch when it expands. These particular attributes identified in the literature have encouraged further research on this topic. The flexible photopolymer resin is used for the test specimens, which have a cylindrical-shell based Auxetics structure. The test specimens are printed on an LCD printer with resin which gives structure
ductile properties during the compression test. Using an industry camera the dimensional changes are captured for further research. With Digital Image Correlation method experimental results show different scenarios in varying the dimensions of the structure. Analyzed results give a foundation for future research, giving it a special focus on improving the quality of future tests and giving a perspective of potential applications and manufacturing variations of Auxetics structures
DEVELOPMENT OF METHODS OF TESTING THE RESISTANCE OF MATERIALS IN HYDRODINAMIC CONDITIONS
No full textThe paper presents the results of cavitation resistance testing of different types of materials (metal, ceramic, polymer, composite). Methods of characterization of materials in hydrodynamic conditions of exploitation are defined-ultrasonic vibration method with a stationary sample, scanning electron and optical microscopy, methods of testing mechanical properties. The change in the mass of the material as a function of the cavitation time was monitored and the cavitation speed was determined as an indicator of the resistance of the material. The cavitation resistance of the material was determined based on the value of the cavitation speed and the analysis of the morphology of the surface damage. The formation and development of damage to the surface of the material is monitored using a scanning electron microscope. A comparative overview of test results is presented as a basis for material selection in hydrodynamic conditions. Based on the test results, the correlation of the mechanical properties of the material, primarily strength and hardness structural characteristics (grain size and shape) and properties of the material's resistance to the effect of cavitation was determined. It has been shown that the applied methods are suitable for the quick determination of resistance properties and the selection of all types of materials under cavitation conditions
Theoretical Assessment of Agro-Waste for Biogas Production Based on Novel Methodology Related to Biochemical Potential
No full textAgricultural and waste biomasses present viable solutions for utilization in the energy sector, achieving sustainable and long-term transformation into energy and fuel. However, it is important to carefully evaluate the competing applications for these feedstocks, considering both short- and long-term stability. Biomass for biogas production in agriculture and waste management is used due to its availability and ease of handling. Considering everything mentioned, evaluating the most suitable raw materials for biogas production is crucial for meeting sustainability criteria and promoting biomass as an energy source. In this paper, an examination of different biomass sources as possible feedstock to produce biogas by applying a theoretical approach to the proximate and final analysis results of those materials is presented. Based on data from the raw material analysis, the theoretical biochemical methane potential (TBMP) for the considered samples was calculated. Furthermore, the mass and energy balance for the case study biogas plant was also performed. According to the obtained results, the considered feedstocks show the validity of their use for biogas production considering the fulfillment of the raw material minimum quantity, mandatory residue arrangement, and achieving higher efficiency of the energy conversion process
A View of The Influence of Constrained Torsion on Behaviour of Thin-Walled Cantilever Channel-Section and Z-Section Beams
No full textA thin-walled cantilever beam with an open channel-section and a Z-section subjected to bending and constrained torsion is studied. The beam mass of structural thin-walled beam elements for given loads, material and geometric characteristics is minimized. The area of the cross-section is assumed to be the objective function. Stress constraints are introduced. The Lagrange multiplier method is applied to the problem. The equations, whose solutions represent the optimal values of the ratios of the parts of the chosen cross-section, are derived. As a result of the calculation the modified constrained functions are derived as polynomials of the fourth and eighth order with the coefficients derived in this paper. Illustrative examples are given. The Finite Element Method is applied to the obtained results for numerical calculations
Modification and experimental validation of the Forrestal-Warren Perforation Model for high hardness armor steel plates of intermediate thickness
No full textThis paper proposes a modification of the Forrestal-Warren perforation model aimed at extending its applicability range to intermediately-thick high-hardness armor steel plates. When impacted by armor-piercing projectiles, these plates tend to fail through adiabatic shear plugging which significantly reduces their ballistic resistance. To address this effect, an approach for determining effective thickness was defined and incorporated into the predictive model. Ballistic impact tests were performed to assess the modification’s validity, in which ARMOX 500T steel plates were subjected to perpendicular impacts from 7.62 mm×39 mm steel-cored rounds under various velocities. Frequent target failure by soft plugging was observed, as well as the brittle shatter of the hard steel core. Key properties of the recovered plugs including their mass, length and diameter were measured and reported along with the projectiles' residual velocities. Additionally, independent data from the open literature were included in the analysis for further validation. The original Forrestal-Warren model and the novel effective thickness modification were then used to establish the relationship between impact and residual velocities, as well as to determine the ballistic limit velocity. The comparison revealed that the proposed approach significantly improves the model's accuracy, showing a strong correlation with experimental data and reducing deviations to within a few percent. This enhancement highlights the potential of the effective thickness term, which could also be applied to other predictive models to extend their applicability range. Further exploration into other armor steels and impact conditions is recommended to assess the method's versatility