Machinery - Repository of the Faculty of Mechanical Engineering, University of Belgrade
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SCALING OF HORIZONTAL STEAM GENERATOR BASED ON THREE-DIMENSIONAL THERMAL-HYDRAULIC SIMULATIONS
No full textThermal-hydraulics of horizontal steam generator (HSG) is numerically simulated and analyzed for the full-scale real HSG at the nominal 100% power built in the 1000 MWe nuclear power plant with the pressurized water reactor and for the scaled-down HSG design with all characteristic dimensions reduced to 50% of the full dimensions and operating at 12.5%, 15.7% and 18.7% of the 100% power of the real HSG. The scaled-down HSG designed is considered with the aim to investigate a design that suits the needs of a nuclear power plant with small modular reactor (SMR), which components should be manufactured in a factory and transported to and assembled at the power plant location. The several power levels of the scaled HSG are applied in the performed simulations in order to obtain steam void and water and steam velocities fields that should provide operating parameter values close to the proven safe and reliable values of the 100% full-scale HSG with mature operating experience. The simulations are performed with an in-house code based on the three-dimensional two-fluid model of two-phase flow and appropriate closure laws for the prediction of interface transport processes, such as vapour-liquid interface friction, vapour and liquid wall friction and liquid evaporation rate under thermal non-equilibrium conditions. The obtained results show a difference between geometry and power scaling. The 50% geometry reduction leads to about 80% of HSG power reduction
WAVES IN BEAM METASTRUCTURES WITH RIGID BODIES ON INERTER-BASED FOUNDATIONS
No full textThis research explores the dynamic behavior of structures encountered in various engineering
fields by modeling them as a series of elastic beams interconnected with rigid bodies and supported on an inerter-based elastic foundation. The analytical framework employed enables the derivation of a continuous-mass transfer matrix for arbitrary unit cells, which are tessellated to form a periodic structure (metastructure). Emphasizing the core design of a rigid body suspended
between two elastic beams, the study employs Timoshenko beam theory to model the beam
segments and performs a thorough analysis of rigid body motion. Dynamical properties of such
structures are evaluated by creating band diagrams and analyzing their dispersion properties. The
dispersion properties of a supported unit cell are compared to those of a unit cell with free-free
boundary conditions, not resting on any foundation. The presence of an elastic foundation increases the system's stiffness, causing the dispersion curves to shift to lower frequencies. This effect is more pronounced with an inerter-based foundation due to inertia amplification
Deep Learning-based Visual Servoing Algorithm For Wheeled Mobile Robot Control
No full textProduction-oriented companies that aspire to the concept of Industry 4.0 primarily focus on the increasing
flexibility and reconfigurability of the entire manufacturing system. By integrating a robotic material
transport/handling system that features a high level of efficiency, flexibility, and intelligence, the entire manufacturing
system reaps the benefits. With that in mind, the authors propose a deep learning-based visual servoing algorithm for
the intelligent control of a wheeled mobile robot. By utilizing a visual servoing algorithm, mobile robotic systems can
flexibly and efficiently adapt their trajectories to real-world conditions. Moreover, deep learning algorithms allow
mobile robots to learn robust visual features that make visual servoing even more applicable. The authors utilize
state-of-the-art deep learning models to train the mobile robot to perform visual servoing even without distinct
features that are necessary for such a system to function properly. Experimental evaluation with the own developed
mobile robot RAICO – Robot with Artificial Intelligence based COgnition has shown the benefits of the proposed
visual control algorithm
Radau- and Lobatto-type averaged Gauss rules
No full textWe describe numerical methods for the construction of interpolatory quadrature rules of Radau and Lobatto types. In particular, we are interested in deriving efficient algorithms for computing optimal averaged Gauss–Radau and Gauss–Lobatto type javascript:undefined;quadrature rules. These averaged rules allow us to estimate the quadrature error in Gauss–Radau and Gauss–Lobatto quadrature rules. This is important since the latter rules have higher algebraic degree of exactness than the corresponding Gauss rules, and this makes it possible to construct averaged quadrature rules of higher algebraic degree of exactness than the corresponding “standard” averaged Gauss rules available in the literature
THE EFFECT OF MOISTURE CONTENT ON THE HARDGROVE GRINDABILITY INDEX OF COAL FROM THE KOLUBARA BASIN
No full textIn order to obtain data on the effect of moisture content on the grindability of coals, experimental research was conducted. The experiment included six samples of coal from the Kolubara basin. The samples were selected based on experimentally obtained values of their Hardgrove grindability index (HGI), in order to cover the entire range of experimental HGI values. In addition to determining the HGI, proximate, and petrographic analyses were performed on all samples.
Lignites are naturally tough, soft, and greasy when in a moist state. By reducing the moisture content, lignites become more brittle. For this reason, HGI values have different values depending on the moisture content at which they are determined.
The Hardgrove grindability index of coal (HGI) has a nonlinear dependence on the moisture content of the coal. All curves have two inflection points, one minimum and one maximum value of HGI in the tested range. The minimum values of HGI are in the range of 15 – 22 [%] of the mass fraction of total moisture in coal, while the maximum values of HGI are for a total moisture content of 5 – 13 [%].
In the case of high moisture content in coal, the obtained high values of HGI may not reflect the true grindability of the coal. These values could be misleading and not necessarily indicative of the coal's inherent characteristics. Instead, they could be a result of the imperfections in the Hardgrove method used to determine the grindability index of coal with high moisture content
APPLICATION OF 2D DIGITAL IMAGE CORRELATION METHOD IN FRACTURE MECHANICS
No full textFracture mechanics, a fundamental field in materials science and engineering, deals with the study of crack initiation, propagation, and fracture resistance of materials. Traditional methods in fracture mechanics analysis often rely on analytical or numerical approaches, which may have limitations in capturing crack behavior under various loading conditions. To overcome these challenges, the 2D Digital Image Correlation (2D-DIC) method, a noncontact, full-field measurement technique, is employed to precisely quantify displacement and strain values. This paper investigates the application of the 2D-DIC method in the field of fracture mechanics. Through an experimental investigation that involves fracture toughness testing, crack growth monitoring, and fatigue crack propagation analyses, the effectiveness of 2D-DIC in capturing crack behavior is demonstrated.
The results showcase the method's ability to accurately track crack propagation, providing valuable insight into crack growth mechanisms, and offering new data for understanding fracture mechanics phenomena. This paper contributes to advancing the field by highlighting the utility of 2D-DIC as a powerful tool for studying crack behavior and improving the overall understanding of fracture mechanics
Tensile strength and stiffness properties of additively manufactured PET-G polymer-based composite plates reinforced with different weight fractions of short carbon fibers
No full textTensile properties of composite thin-plate specimens additively manufactured from two commercially available filaments composed of PET-G polymer loaded with 15 wt% and 30 wt% of short carbon fibers (SCF) are experimentally determined, together with neat PET-G specimens tested for comparison. Relatively high overall average values of ultimate tensile strength were obtained for the SCF reinforced specimens (61.6 MPa and 52.2 MPa, respectively for specimens with 15 % and 30 % of SCF), compared to the value obtained for neat PET-G specimens (43.9 MPa). Similarly, the average value of modulus of elasticity for 15 % SCF specimens (5990 MPa) was higher than the value obtained for the ones with 30 % of SCF (4752 MPa), again both being higher than the value reached with neat polymer (1694 MPa). Scanning electron microscopy (SEM) was used to analyze specimens’ fracture surfaces. SEM images of 30 % SCF specimens revealed higher presence of voids compared to 15 % SCF specimens
Sensitivity and Eigensensitivity Analysis in Structural Dynamics Using Finite Element Substructuring
No full textThis paper explores sensitivity and eigensensitivity analysis methods to optimize structural performance in the field of structural dynamics, with a focus on vibration control and resonance management. Sensitivity analysis is crucial across engineering fields, allowing assessment of system responses to variations in design parameters. Within structural dynamics, eigensensitivity analysis examines how design changes impact eigenvalues and eigenvectors, particularly when it is necessary to control resonant frequencies for improved structural safety and performance. To conduct efficient dynamic simulations, finite element analysis (FEM) is applied to complex structures. Given the computational demands of models with numerous degrees of freedom, this study introduces a substructuring approach. By dividing the structure into interconnected substructures, each analyzed separately with a reduced eigenpair set, the model achieves substantial computational efficiency while maintaining accuracy in critical vibration modes. This substructuring technique not only enhances analysis feasibility but also supports rapid adjustments in design, enabling effective resonance frequency management and optimization. The case study demonstrates the practical application of eigensensitivity analysis in dynamic structural modification, achieving targeted performance improvements with reduced computational resources. Findings underscore the potential of combining sensitivity and eigensensitivity analyses with FEM substructuring for streamlined and effective structural design.Project no. 451-03-65/2024-03/20010
Process system simulation of coupled pyrolysis disposal of domestic waste in coal-fired boiler and pilot study on dioxin emission
No full textThe disposal of domestic waste has become a critical and costly problem. Incineration for power generation is currently the primary domestic waste treatment method. Due to its small capacity and low parameters, domestic waste incineration is generally uneconomical and associated with significant risks to public health and environmental safety. The coal-fired power plants are generally characterized with huge capacity and high parameters, consequently resulting in much higher power generation efficiency with lower cost emission control. This indicates that co-disposal of domestic waste using existing coal-fired units may significantly reduce its treatment costs associated with the improvement of utilization efficiency and environmental risks. Base on this, a highly-flexible coupling of pyrolysis-pretreated solid waste in pulverized coal furnace is proposed in this paper, and field tests and numerical simulations have been carried out separately according to the process route. The results show that after coupling with pulverized coal boiler, domestic waste pyrolysis pretreatment unit can operate self-sustainably without external energy supply and the process route is feasible. Furthermore, the coupled co-combustion of domestic waste pyrolysis products and pulverized coal was simulated by fluent software. Compared with pure pulverized coal combustion, mixing domestic waste pyrolysis products can promote pulverized coal combustion in the furnace and help the pulverized coal boiler to burn stably at low load. The emission concentrations of NOx at the outlet of the furnace are 530 ppm, 545 ppm and 478 ppm respectively when pulverized coal is burned purely and mixed with 100 t/d and 200 t/d domestic waste. the NOx emissions could be reduced to a certain extent by mixing domestic waste. On the basis of previous research, the field test of coupling disposal of domestic waste by pulverized coal boiler was carried out, and the dioxin concentration in flue gas and fly ash was tested emphatically. The results show that when the amount of waste is less than 4 %, the concentration of dioxin in flue gas is 0.0107 ng TEQ/m3, which meets the latest emission standard of air pollutants in Shanghai coal-fired sludge power plant of 0.02 ng TEQ/m3. Low proportion of domestic waste will not increase the production and emission of dioxins. These studies show that it is feasible and promising to treat municipal solid waste with low coupling ratio by using existing coal-fired units
First Escalators and Their Inventors Until the End of the 19th Century
No full textVery important factors in vertical transportation are escalators (moving stairways). In this historical respect the escalators and moving stairways differ from elevators, which basic principles were formulated several centuries ago, but at their beginnings they were considered as some kind of elevators and/or conveyors. Nowadays, escalators are widely used and operate in different places such as shopping centers, underground stations, airports, etc. The basic design employed has not varied from those patented more than a century ago. All crucial patents regarding the fascinating history of escalators have been developed in the second half of the 19th century, until 1900. However, some of those patents are quite different from the traditional ones. Inventors and engineers, who created the first patents and installations of escalators as we know them nowadays, can be considered as fathers” of escalators. They are: Nathan Ames, Leamon Souder, Jesse Reno, George Wheeler, Charles Seeberger, Jacques Hallé and James Dodge. Their patents and installations are described in chronological order, including some available short biographical notes on those first inventors of escalators. The formal name of moving stairways the word “escalator” was trademarked in 1900 by Otis Company and coincides with escalator debut at the Paris Exposition