Internality of Two-Measure-Based Generalized Gauss Quadrature Rules for Modified Chebyshev Measures II

Gaussian quadrature rules are commonly used to approximate integrals with respect to a non-negative measure ������������̂ . It is important to be able to estimate the quadrature error in the Gaussian rule used. A common approach to estimating this error is to evaluate another quadrature rule that has more nodes and higher algebraic degree of precision than the Gaussian rule, and use the difference between this rule and the Gaussian rule as an estimate for the error in the latter. This paper considers the situation when ������������̂ is a Chebyshev measure that is modified by a linear factor and a linear divisor, and investigates whether the rules in a recently proposed new class of quadrature rules for estimating the error in Gaussian rules are internal, i.e., if all nodes of the new quadrature rules are in the interval (−1,1) . These new rules are defined by two measures, one of which is a modified Chebyshev measure ������������̂ . The other measure is auxiliary

Evaluation of Aerodynamic Coefficients of Supercritical Airfoil NASA sc(2) 0712: A Comparative Study of 2D and 3D Flow Models with Experimental Validations

This study presents a comparative numerical analysis of 2D and 3D compressible, turbulent flows around the supercritical airfoil NASA sc(2) 0712 at Mach number M = 0.5 using the finite volume method implemented in ANSYS Fluent, focusing on the estimation of drag coefficients in relation to existing experimental data. In addition, different types of computational grids and turbulence models are tested. The investigation aims to highlight the discrepancies observed between the two modeling approaches and their implications for aerodynamic performance predictions. Through rigorous numerical simulations and validation against experimental results, we demonstrate that 2D models often yield overestimated drag values due to simplified flow assumptions. In contrast, 3D simulations provide a more accurate representation of fluid behavior, resulting in closer alignment with experimental findings. By performing spatial computations of turbulent flow around a supercritical airfoil, it is possible to reduce the relative error of drag coefficients by less than 10%

Experimental and Numerical Research on Swirl Flow in Straight Conical Diffuser

The main objective of the current study is a detailed (both numerical and experimental) investigation of the highly unsteady and complex swirl flow in a straight conical diffuser (with a total divergence angle of 8.6°) generated by an axial fan impeller. Pressure, and axial and tangential velocity profiles along several cross-sections were measured by original classical probes in two different flow regimes at the inlet: the modified solid body type of moderate swirl and the solid body type of strong swirl and reverse flow; they were additionally confirmed/validated by laser Doppler anemometry measurements. Computational studies of spatial, unsteady, viscous, compressible flows were performed in ANSYS Fluent by large eddy simulation. The fan was neglected, and its effect was replaced by the pressure and velocity profiles assigned along the inlet and outlet boundaries. The two sets of data obtained were compared, and several conclusions were drawn. In general, the relative errors of the pressure profiles (2–5%) were lower than the observed discrepancies in the axial velocity profiles (5–40% for the first and 15–50% for the second flow regime, respectively). The employed reduced numerical model can be considered acceptable since it provides insights into the complexity of the investigated swirl flow

Energy and exergy analysis of a hybrid ORC power plant

Organic Rankine cycles (ORCs) are highly recommended technology to generate electricity from low-temperature sources such as geothermal sources. The performance of the cycle mostly depends on operation conditions, installed equipments and selection of working fluid. This paper presents a comparative energy and exergy analysis of a geothermal-biomass Organic Rankine cycle (ORC) for three working fluids: R113, R245fa, and R600a. In addition, analyzed ORC is compared with the Rankine cycle that runs on Serbian lignite from the aspect of equivalent CO2 emission and necessary primary energy. The analyzed system is an ORC power plant with two heat sources – geothermal water from Vranjska Banja and wood biomass. The results revealed the highest thermal and exergy efficiency with R113, 14.53%, and 41.64%, respectively, as well as the turbine power output of 4.21 MW with 73.20 kW pump power input. Exergy analysis showed the highest exergy destruction rate in the heat exchanger with flue gases made by wood combustion (80-89%) and the highest obtained exergy efficiency of 41.64% in the case of R113. If the power plant used Serbian lignite as a fuel for the same thermal power input, it would need between 133-169 kt/year of lignite, which would result in CO2 emission of around 63-80 kt/yea

CAVITATION EROSION PARAMETERS OF LASER SINTERED MS1 STEEL TESTED ACCORDING TO ASTM G32 STANDARD

The 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

Computational Fluid Dynamics Study of Biomass Moisture Content Impact on Particle Matter Emissions

Wood combustion is a significant energy source, but it also contributes to air pollution due to the emission of gaseous and particle matter. Understanding the formation and behaviour of gaseous and particle emissions is crucial for environmental and health concerns. To simulate and analyse beech wood combustion, a mathematical model for computational fluid dynamics (CFD) simulation was developed. This model considered various parameters such as fuel properties, combustion kinetics, and fluid dynamics. The model enables the prediction of temperature profiles, species concentrations, and soot particle emissions. To validate the accuracy of the CFD model, experimental measurements were conducted on an actual beech wood combustion setup. The experimental data, including flue gas temperature, CO2 and CO concentrations, and soot particle measurements, were compared with the simulation results. The validation process was aimed to ensure the reliability and fidelity of the CFD model for predicting beech wood combustion behaviour. Furthermore, a parametric analysis was performed using the validated model to investigate the influence of different moisture content levels in the fuel on the combustion process and emission characteristics. The moisture content varied from 10 to 40%, representing a range of realistic conditions. The results of the parametric analysis provided insights into the relationship between moisture content and combustion performance. The findings contributed to optimizing beech wood combustion processes, improving energy efficiency, and reducing emissions. The study emphasized the importance of considering moisture content as a critical parameter in designing and operating wood combustion systems to achieve sustainable and environmentally friendly practices. © The Author(s), under exclusive licence to Springer Nature Switzerland AG 2024.Contract no.451-03-47/2023-01/20010

A review paper: Influence of welding defects to structural integrity of welded joints

This paper presents a review of the most notable cases involving welded joint defects and their influence on structural performance. It examines examples where imperfections such as undercuts, incomplete penetration, lack of fusion, and so on, have compromised the integrity of welded structures. By analyzing these cases, the paper highlights how such defects contribute to stress concentration, reduced load-bearing capacity, and, in severe instances, failure. The review underscores the critical importance of identifying and mitigating these flaws to ensure the safety and reliability of constructions like bridges, buildings, and industrial frameworks

Enhancing impact toughness of additive manufactured pet-g using short carbon fibers

Polyethylene terephthalate glycol (PET-G) material is used in additive manufacturing (AM) for the production of moderately loaded polyester-based parts. Scientific papers show that build orientation and printing direction angle substantially influence the mechanical properties of additively manufactured specimens. This paper explores the influence of adding short carbon fibers (SCF) to PET-G material where the effect of build orientations (flat, on edge and upright) and raster angles (0° and 90°) on the impact toughness was investigated. In this study, a low-energy instrumented Charpy Instron Ceast 9050 test was used as an experimental method to evaluate the impact behavior of those two different materials. An experimental evaluation of impact toughness in the case of AM impact specimens fabricated with different build orientations and printing angles was performed. The impact tests were carried out on five specimens per group (a total of 60 specimens for this research). The results obtained from an instrumented pendulum were compared between different specimen groups and different material to gain insight into enhancing impact toughness of additive manufactured PET-G using short carbon fibers. It was confirmed that addition of short carbon fibers enhance impact toughness but the different build orientations and raster angles have a greater influence on the final mechanical properties.under the agreement number 451-03-136/2025-03/200105, date February 4, 2025

The influence of dwell time on the collected data during linear displacement measurements of machine tools

During linear displacement measurement of CNC machine tools (MT) with laser interferometer the optical components are moved along the measured axis. At the selected measurement points of the axis the optics stops and data collection is performed. At the beginning of the stopping cycle, because of the inertion of the optics and the MT structure, vibrations occure, which spoils the collected data. To minimize the dwell time, the time needed to wait at the measurement point, the number of the collected position data needs to be minimized. In this work through an example is represented the influence of the number of collected data on the measurement values during linear displacement measurements of machine tools.Editor of chief: Assistant Professor Dejan Branković, PhD Executive editor: Milivoj Stipanović, Bs