Machinery - Repository of the Faculty of Mechanical Engineering, University of Belgrade
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MOTION ANALYSIS OF A VIBRATORY CONVEYOR’S TROUGH DURING ITS OPERATION
No full textThis study investigates the dynamic behavior of a trough of a vibratory conveyor. The main focus is on modeling the motion of the trough, analyzing the forces acting on the system, and assessing the spring stiffness and deflections under operational conditions. Using theoretical modeling based on the theory of elasticity and rigid body mechanics mechanics, the dynamics of the system are described, and the differential equations of motion for a single-degree-of-freedom oscillator are derived. A finite element analysis inside Solidworks Simulation package is performed to observe the motion of the vibratory trough. Orthogonal displacements of the centre of mass of the vibratory trough were observed. Simulation results are provided and discussed accordingly at the end of this paper. The findings suggest that the axial displacement of the trough is couple orders of magnitude smaller than its transversal displacement, allowing for a simplification in further modeling. This study provides valuable insights into the design and operation of electromagnetic vibratory conveyors, contributing to the optimization of spring stiffness and system stability for industrial applications.451-03-137/2025-03/200105 from 04.02.2025;
451-03-136/2025-03/200034 from 04.02.2025
INVERSE KINEMATICS SOLUTIONS OF ROBOTIC MANIPULATORS USING PADEN-KAHAN SUBPROBLEMS AND SCREW THEORY
No full textIn this paper, we used the Paden-Kahan subproblems and their extensions in the context of screw theory to solve the inverse kinematics of common robot manipulators: RR, RRR, RPR planar, and RPP spatial robot models. The inverse kinematics problem of a robot is fundamental to determining a robot’s mechanics, and among the different ways to solving it, we chose the Paden- Kahan subproblems approach for its effectiveness and simplicity. The canonical subproblems have been significantly extended and of particular interest to us are the inclusion of solutions to parallel screw axes for the second subproblem and prismatic joints instead of only revolute joints, also known as Pardos-Gotor subproblems, After solving the inverse kinematics of each robot model and representing the solutions via graphs, we then proceeded to demonstrate the correctness of our solutions against the desired configuration and found that the orientational and positional errors between the desired configuration and our solution were in the range of floating-point arithmetic errors. Taking into account the simplicity during solving the inverse kinematics and the number of operations performed, we concluded that, at least where applicable, the Paden-Kahan subproblems and their extensions provide significant advantages to other methods.No. 451-03-137/2025-03/ 200105 from 04.02.2025
KINEMATICS MODELING OF COMPLIANT AND EXTENSIBLE STEWART-LIKE PLATFORM
No full textLabor shortages, sustainability challenges, and the limitations of conventional robotic systems
for delicate tasks like crop harvesting drive the need for innovative solutions. This paper
introduces a low-cost, modular robotic platform that combines passive compliance with
extensibility, enabling safe human–robot collaboration and scalable operation in dynamic
agricultural, medical or industrial environments. The proposed hybrid Stewart-like platform
(SLP) integrates a parallel kinematic structure with scissor mechanisms, using lightweight, 3Dprinted components for rapid prototyping. This study provides detailed design and kinematic
analysis.No. 451-03-137/2025-03/ 200105 from 04.02.2025
Analysis of the effect of piezoelectric sensor ageing on indicated parameters
No full textThe research examines the ageing behavior of piezoelectric pressure sensors for internal combustion engine studies while concentrating on their declining sensitivity as time progresses. Reliable measurement of in-cylinder pressure demands precise monitoring of sensor performance to support both thermodynamic analysis and evaluation of engine performance. Research experiments performed with a single-cylinder research engine (SCRE) determine how the working cycle operational parameters relate to sensor properties, especially the indicated mean effective pressure (IMEP) and polytropic coefficients of the compression/expansion phase of the engine working process. The study demonstrates that monitoring polytropic coefficients provides an efficient technique for detecting sensitivity degradation without needing continuous pressure sensor recalibration, improving both accuracy and efficiency during prolonged engine testing. The approach allows researchers to detect sensor degradation on time, which helps maintain data integrity throughout lengthy research campaigns
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
Extension of the Throughflow Solver for Predicting the Aerodynamic Performance of Fans With Inlet Distortion
No full textNext-generation aircraft with boundary layer ingesting (BLI) engines can reduce fuel consumption but pose challenges for fan and compressor operation due to inlet distortion. To optimize the design of such engines, it is essential to assess the impact of nonuniform inlet flow on stability and performance, with the final result of a distortion-tolerant machine. One of the first steps in this process is estimating the aerodynamic performance using fast but reliable mathematical models. This paper presents an extension of the existing throughflow solver that predicts the effects of the upstream distortion. The proposed method, based on the parallel compressor theory, introduces multiple planes to accurately define and track the circumferential distribution of parameters as they advance through the machine. It applies to all types of distortion: total pressure, total temperature, and swirl. The model is demonstrated for a high-pressure, low hub-to-tip diameter ratio fan with nonuniform total pressure at the inlet. Flow physics associated with distortion is analyzed using results from full annulus unsteady RANS simulations for three operating points: near stall, design, and near choke. The flow field results are compared with the CFD data at the design point. The overall performance is evaluated against a clean inlet case
Comprehensive Kinetics and Thermodynamics Analysis of Salix psammophila Biomass Pyrolysis Using Multicomponent Modeling
No full textMulticomponent deconvolution enables precise peak separation and accurate determination of kinetic parameters and improves identification of the underlying mechanisms of biomass pyrolysis. In the present study, the multicomponent kinetics and thermodynamics of Salix psammophila pyrolysis were investigated to evaluate its bioenergy potential. Thermogravimetric analysis coupled with peak deconvolution revealed three stages involving four components (pseudoextractives/PS-EC, pseudohemicellulose/PS-CL, pseudocellulose/PS-CL, and pseudolignin/PS-LG) with the corresponding peak temperatures of 246.83–270.83, 291.59–315.59, 335.26–359.26, and 386.14–410.14 °C, respectively. Pyrolysis gas chromatography/mass spectrometry analysis indicated dominant products of acids, phenolics, and alkanes. Activation energies for each pseudocomponent from four isoconversional methods were comparable, following an order of PS-EC (134.96 kJ mol–1) < PS-HC (151.59 kJ mol–1) < PS-CL (166.93 kJ mol–1) < PS-LG (239.65 kJ mol–1). Master plot analysis suggested an order-based reaction mechanism. Positive enthalpy changes (127.83–227.33 kJ mol–1) and Gibbs free energy changes (144.73–193.03 kJ mol–1) indicated higher energy barriers, especially for PS-LG, and limited spontaneity of conversion. These findings highlighted the potential of S. psammophila as a viable feedstock and offered critical insights into reactor design and process optimization for industrial applications
Neural Network-Based Visual Servoing of Wheeled Mobile Robot with Fish-Eye Camera
No full textIn the era of rapid technological invitation, artificial intelligence techniques have become a driving force in the evolution of various fields, and the
robotics domain is no exception. One of the areas where AI has proven to be
especially influential is in robotics vision, where machine learning algorithms,
particularly artificial neural networks, are revolutionizing how robots perceive
and interact with their environment. Therefore, in this paper, we examine the use
of artificial neural networks in the context of mobile robot visual servoing. Differential drive mobile robot RAICO equipped with a fish-eye lens camera is utilized.
The fish-eye lenses have a significant advantage regarding their wide-angle field
of view; however, they also introduce significant optical distortions that can affect
the accuracy of the robot’s perception and, therefore, 3D pose estimation, which is
paramount for visual servoing. Position-based visual servoing based on the ArUco
marker is employed within the 3-step switching mobile robot controller. Given the
pose estimation errors inherited by distortions in the fish-eye lens, the accuracy of
pose estimation is enhanced by utilizing neural networks. The experimental results
show a high level of final pose accuracy achieved by RAICO with the proposed
control algorithm
Editorial of the 12th Annual Conference of Society for Structural Integrity and Life (DIVK12) conference
No full textThe 12th Annual Conference of Society for Structural Integrity and Life (DIVK12), organized between 17th and 19th of November 2024, at the Faculty of Mechanical Engineering of the University of Belgrade, Serbia, gathered more than 160 participants (both in person and on-line) from all over the world, with more than 25 nationalities demonstrating the vitality and importance of this new event. This Special Issue gathers the 71 papers presented at the conference, including some keynote lectures and regular presentations. Awards for special contribution in certain topics were delivered attributed during the conference. The Organizing Committee of the DIVK12 conference sincerely thanks all contributing authors for playing a significant role in the overall success
of this event, with their exciting presentations. The members of the International Scientific Committee are also fully acknowledged for their support of the DIVK12 event. Special thanks to the Keynote Speakers for their dedication and knowledge and energy brought to this event. The Organizing Committee would also like to express their gratitude to the sponsors for their support without which the conference would be impossible to organize. Finally, chairmen sincerely thank the tireless efforts of Organizing Committee members, as well as Faculty of Mechanical Engineering, IMS institute and Innovation Center of Faculty of Mechanical Engineering staff
Comprehensive Method For Predicting Gas Turbine Cycle Performances Considering The Impact Of Various Fuels
No full textGas turbines have advanced significantly in recent years, particularly in compressor and turbine efficiency because of aerodynamic breakthroughs based on numerical flow simulations. Additionally, modern energy demands have driven the adoption of alternative, environmentally friendly fuels such as hydrogen, ammonia, and methanol. These fuels significantly influence combustion gas composition, turbine inlet temperature, mass flow, blade cooling, and overall performance. Traditional cycle performance tools often rely on 0D maps for compressors and turbines, which have limitations in simulating these recent advancements. The proposed method replaces such maps with a 2D approach, utilizing detailed flow calculations for compressors and turbines at each operating point. It integrates combustion processes and secondary air systems and iteratively determines the turbine inlet temperature for precise predictions. This method accurately simulates air bleeds, cooling injections, and adjustments in inlet guide and stator vanes while accounting for the effects of fuel composition on performance. This paper demonstrates the methodology using an industrial gas turbine in which natural gas, hydrogen and hydrogen carriers are used as fuels. It shows the consequences of this for several components as well as the main thermodynamic operating parameters. The approach is fast and effective, enabling the optimization of diverse designs throughout development