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Тablice za proračun protoka vode kroz hidrantsku mlaznicu
No full textU nizu merenja koja su izvršena u Centru za protivpožarnu tehniku Mašinskog fakulteta u Beogradu je pokazano da se protočne karakteristike mlaznica koje se danas prodaju na našem tržišu i koje ispunjavaju uslove propisane standardima SRPS EN 671-1:2015 i SRPS EN 671-2:2015 bitno razlikuju od protočnih karakteristika koje se dobijaju prema standardima SRPS Z.C1.050:1989 i DIN 14 200:1979. U okviru ovog rada biće predstavljene tablice u kojima je protok vode na mlaznicama prečnika usnika 12 mm i 16 mm u funkciji od pritiska, za različite protočne karakteristike.На првој страни су погрешно одштампана имена аутора.
Тачна имена су на последњој страни
Notch vs. crack effects on impact toughness and fracture behavior of a duplex steel weldments
No full textThis paper presents the effect of stress concentration due to notch or cracks on the impact toughness of duplex steel S32750. This analysis is based on the results obtained by Charpy instrumented pendulum, enabling the separation of total energy into crack initiation, Ei, and crack propagation energy, Ep. The crack sensitivity factor (CSF) was determined, defined here as the ratio of total impact energy (KV value), obtained by testing standard ISO- V specimens, and KV1 value, obtained on a same type of specimen but with 1- mm long fatigue cracks: CS = KV/KV1. Testing was conducted in accordance with standard EN ISO 148- 1:2017 at different temperatures: +20°C, −40°C, −60°C, and −80°C. Fatigue crack lengths ranged from 1 to 5.5 mm, as measured from the notch root on ISO- V specimen. Based on KV vs. crack length diagrams, KV1 values are obtained by interpolation of all results, providing data for CSF determination. Fractography was also done to clarify the fracture behavior of notched and cracked specimens under impact loading and different temperatures.Naveden je glavni i odgovorni urednik časopisa FFEMS (Fatigue & Fracture of Engineering Materials & Structures)
CAVITATION EROSION PARAMETERS OF LASER SINTERED MS1 STEEL TESTED ACCORDING TO ASTM G32 STANDARD
No full textThe paper analyses data obtained from cavitation erosion testing of MS1 tool steel. The testing samples, cylindrical in shape with a height of 5 mm and a diameter of 10 mm, were fabricated using Direct Metal Laser Sintering (DMLS), a 3D printing technique. The samples were subjected to cavitation erosion testing in accordance with the ASTM G32 standard for a total duration of 4 hours. Mass loss measurements were recorded every 30 minutes. Based on the collected data, key parameters such as Cumulative Mass Loss, Cumulative Volume Loss, Mean Depth of Cavitation Erosion (MDE), and Mean Depth Erosion Rate (MDER) were determined and analyzed. Understanding material behaviour under cavitation conditions is crucial for its potential application in manufacturing mechanical components, particularly gears, bearings, and valves, where cavitation-induced damage is a common issue in operational environments. Given that the specimens were produced by metal powder-based 3D printing, it is especially relevant to assess the performance of such material under these conditions. This insight is particularly valuable for the geometric optimization of components to minimize erosion, where additive manufacturing offers significant advantages over conventional production technologies.Contracts: 451-03-137/2025-03/ 200105 and 451-03-136/2025-03/20013
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
Carnot battery with steam accumulator and pebble bed thermal energy storage
No full textCarnot batteries can store excess electricity from intermittent renewable solar or wind sources and generate power in periods of peak consumption. A novel design of the Carnot battery is proposed based on thermal energy storage by the combination of a steam accumulator and a pebble bed in a series configuration. During the Carnot battery charging, steam is generated by high temperature heat pumps with CO2 compression cycles, pressurized and superheated by electrically driven steam compressors. The obtained superheated steam flows through the pebble bed porous structure and transfers heat to alumina balls in direct contact. Steam from the pebble bed inflows the steam accumulator. During the Carnot battery discharging phase, the steam outflows the steam accumulator, superheats in the pebble bed and expands through the steam turbine, which is connected to the electric generator for power production. The advantages of the studied Carnot battery are a simple design and operation of the steam accumulator as the thermal energy storage unit, the accumulated steam directly serves as working fluid in the steam turbine and the coupling of the pebble bed with the steam accumulator enables steam superheating that is required for an increased steam turbine efficiency in power generation. Water is low-cost
and more convenient in respect to safety, plant engineering and operational aspects in comparison with other working fluids. In addition, there is no need for additional heat exchangers for the heat transfer between the working fluid and the storage medium. Maximum temperature and pressure of the thermal storage medium are 303 ◦C and 0.7 MPa, respectively. The temperature and low-pressure values enable application of mature technology and lower investment costs, where the capacity specific cost of 471 €/kWhe is reached. The presented
Carnot battery design is supported with numerical simulations of thermal energy charging and discharging transients in the pebble bed and the steam accumulator with own original and validated modelling approaches.
The obtained Carnot battery charging electric power is 9.5 MWe for 6.9 h, while discharging power is 2.3 MWe for 9.4 h, which is suitable for the electric grid power control on a daily period
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
Artificial intelligence as a tool for item reduction in an organizational resilience questionnaire
No full textObjectives. Considering that there is no standardized questionnaire for safety climate and resilience assessment, authors usually review a large number of questionnaires from the available literature, which results in a high number of questions distributed to respondents. As the questionnaire length increases, resistance from the respondents increases. Artificial intelligence (AI) tools until now have not been used for item reduction, besides the need for selecting and retaining only the most relevant and informative questions in the questionnaire with adequate accuracy. Methods. AI tools such as multiple linear regression analysis (MLRA) and the multilayer perceptron artificial neural network (MLP ANN) are used in the development of a model able to cluster respondents’ ratings and to predict values of organizational resilience based on the respondents’ ratings of the specific questions. Results. AI could be used as a valuable tool for item reduction, since the prediction accuracy for MLRA tools is 70.4–71.5% and for the MLP ANN it is 76.4%. Conclusions. This research proves that machine learning algorithms can be used to build predictive models that determine which survey questions are the most predictive for organizational resilience index calculation using safety climate factors
Improving Steam Turbine Plants Performance Through Advanced Testing and Simulation
No full textAbstract
The prolonged operation of thermal power plants inevitably leads to component aging and a gradual decline in performance. This deterioration increases the gross heat rate and reduces electrical output, resulting in higher fuel consumption and lower electricity production. Consequently, these issues can cause significant financial losses and threaten the plant’s competitiveness. This paper presents a comprehensive methodology for improving the performance of existing plants. The methodology consists of two crucial elements: steam turbine testing and numerical simulation of the process. The tests should be comprehensive to ensure accurate measurements and reliable conclusions. The developed method for process simulation enables the calculation of overall performance, like specific heat rate and thermal efficiency, as well as the performance of individual components under various operational conditions. Comparing numerical results with experimental data can effectively identify operational problems. Based on these findings, targeted overhauls and other corrective measures can substantially improve the plant’s thermal efficiency and financial performance. The system was demonstrated through a case study of a 120 MW coal-fired steam turbine. The test revealed that it consumes more than 10% additional heat compared to its original design specifications. The analysis identified operational issues and recommended improvement measures, focusing exclusively on the steam turbine set while excluding the boiler
Nexus between geometry and thermal-hydraulic scaling of horizontal steam generator
No full textMature technology of large-scale nuclear power plants is a strong basis for the development of small modular and medium size reactors. Therefore, it is important to study the nexus between geometry and thermal-hydraulic scaling with the aim to take advantage of large-scale plants to develop safe and reliable scaled-down plants. The present study investigates the thermal-hydraulics of a large-scale Horizontal Steam Generator (HSG) built in the WWER 1000 type nuclear power plant, and a thermal-hydraulics of its replica with the 50% scaled-down geometry. Unlike most previous studies, which primarily relied on the similitude concept for scaling analysis, this work employs numerical simulations with an in-house computational code based on a three-dimensional two-fluid model approach and closure laws for the prediction of interfacial transport phenomena. Obtained results show that a uniform linear reduction of HSG dimensions in three-dimensional space leads to strong non-linear changes of thermal-hydraulic parameters. Nearly the same ranges of void fraction and two-phase flow velocity changes along vertical and horizontal directions of tube bundles are obtained in the full-size HSG and in the HSG with 50% scaled-down geometry if the tube bundle volumetric heat flux in the 50% scaled-down HSG geometry is two times greater than the full-size HSG value. It is shown that a significant increase of the volumetric heat flux is achievable with a reduced diameter of tubes in the bundle and a corresponding increase of the primary side reactor coolant flow rate, although the HSG primary and secondary fluid inlet and outlet temperatures and pressure levels are kept constant. Therefore, the scaled-down HSG geometry enables significant increase of heat power per unit of tube bundle volumes, while the preserved similarity of the thermal-hydraulic conditions ensures that the scaled-down HSG operates within safe and reliable limits comparable to the full-size HSG. The findings contribute to an understanding of HSG scaling effects and support the development of small modular and medium size reactors
Sustainable Aviation Innovations, Advancements, and Destinations
No full text- Discusses future strategies and priorities in the field of aviation sustainability
- Addresses a broad range of aviation topics with an emphasis on environmental issues
- Provides access to the complete ISSA 2024 proceeding