Machinery - Repository of the Faculty of Mechanical Engineering, University of Belgrade
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Modeling Approaches to Shaped Charge Jet Penetration Depth: Numerical and Analytical Perspectives
No full textShaped charge effect have been successfully used in various fields, including defense (anti-armor projectiles and warheads) and non-military (explosive demolitions, oil and natural gas industry) applications. The shaped charge mechanism relies on conversion of explosive charge detonation energy into kinetic energy of a hypervelocity metal penetrator, known as a jet. The focus of the present research is on the jet interaction with the target material and consequent target penetration. Two approaches to the jet penetration depth determination are considered. The first is the well-known analytical model based on the virtual origin concept. The second approach is the numerical modeling of the penetration process. The commercial FEM based software Abaqus/Explicit has been used for simulations and the model formulation is described in detail. The complete process of the shaped charge jet formation and penetration is successfully simulated using the pure Eulerian approach with appropriate material models.
Through comprehensive analysis, various jet parameters – such as kinetic energy, diameter, length, velocity gradient, and effective standoff distance – are explored to assess their impact on penetration depth. The insights gained from this study provide valuable guidance for the preliminary evaluation of shaped charge effectiveness and contribute to the refinement of shaped charge projectile or warhead designs
Reverse engineering and finite element analysis of Ti-6Al-4V orthopaedic hip implants
No full textThe goal of the research presented is to combine reverse engineering methodologies with a numerical approach to analyse the structural integrity of artificial hip implants made of Ti-6Al-4V alloy subjected to different types of loads. In this way, numerical models validate the adopted methodology for obtaining implant geometry using 3D scanning, while also providing valuable insight into the behaviour of hip implants under different static loading cases. Since 3D scanning is proven as efficient and reliable for obtaining accurate geometry of various types of implants, it is applied in this research. Following a detailed development of a hip implant model geometry, involving 3D scanning and refining the obtained point cloud to a level that would realistically represent the actual hip implant, numerical models are made based on the obtained geometry. Results of these simulations using the finite element method in ANSYS® software have provided realistic values of stresses in most critical areas of the hip implant. The precise value of load that would produce plastic strain on the implant is also determined and is used as the limit criterion for selecting load cases for further analysis. This analysis would involve the assessment of fatigue life of hip implants with the same geometry and the same material while assuming the presence of a crack in the most critical area
Research of the draw gear and screw coupling failures of rail vehicles
No full textThe reliability and safety of railway vehicles are significantly influenced by the performance of their draw gear systems and screw coupling elements, which are essential for maintaining stable connections between rail cars. The draw gear component failures, especially coupling links, have raised concerns about their ability to withstand operational loads. Although failures in draw gear components are relatively rare, they can lead to severe consequences for both rail vehicles and infrastructure when they do occur. These failures often result in fractures and breakages, Fig. 1. This research analyses different cases of failure and proposes a detailed study aimed at understanding the underlying causes of draw gear failures. The planned methodology involves a multifaceted approach, combining field data collection, finite element analysis (FEA), and laboratory testing. Initially, field inspections will be conducted to identify common failure points and document the operational conditions under which these components fail. Following this, a forensic approach will be applied, selected samples of failed components will undergo laboratory analysis to assess material properties and identify signs of fatigue or other forms of degradation.
Finite element analysis will be used to simulate operational stresses and predict potential failure points under various loading scenarios. A numerical model will be developed based on experimental research and will be used for more detailed analysis of different load cases and failures of different parts of draw gear and screw coupling assembly. By systematically investigating these issues, this research aims to lay the groundwork for improved draw gear systems that contribute to safer and more dependable railway operations
On the possibilities of obtaining analytical solutions for gas flow of different levels of rarefaction
No full textAssessing green hydrogen potential and utilization for sustainable energy production in Serbia
No full textThe paper provides a comprehensive examination of resources available for the deployment of green hydrogen in Serbia. The assessment encompasses various aspects, including renewable energy potentials, technological advancements, and future projections. The evaluation considers factors such as solar and wind power capacities, which are pivotal for green hydrogen production. Additionally, the study delves into the policy landscape, addressing initiatives aimed at fostering the integration of green hydrogen into Serbia's energy matrix. The analysis combines quantitative data on energy production capacities with qualitative insights into the economic and environmental implications of green hydrogen utilization. While the nation boasts abundant renewable energy resources, challenges such as high production costs and infrastructure limitations hinder widespread adoption. However, with strategic initiatives and technological advancements, Serbia can overcome these hurdles and pave the way for a sustainable hydrogen economy. Assessing Serbia's green hydrogen potential, driven by over 24 095 MWp from solar and 10 750 MWp from wind, highlights the nation's capacity to harness renewable resources, with hydrogen production set to grow from 1915 tons in 2019 to 37 ,123 tons by 2040. The findings aim to contribute to the ongoing discourse on sustainable energy transitions and the role of green hydrogen in Serbia's evolving energy landscape.Ministry of Science, Technological Development and Innovation; Faculty of Technical Sciences, University of Novi Sad through project "Scientific and Artistic Research Work of Researchers [01-3394/1]; [451-03-65/2024-03/200156
Doping Mn Induced Modification on the Crystal Structure, Morphology and Optical Properties of Mechanically Activated SrTiO3 Powders
No full textMechanically activated strontium titanate (SrTiO3) powders with various manganese dioxide (MnO2) doping levels (1.5, 3 and 6 wt%) were prepared by solid state method. Due to the possibility of manganese ion incorporation in SrTiO3 at Ti4+ and/or Sr2+ sites a detailed analysis of the influence of dopants on the microstructure, morphology and optical properties of perovskite oxide was conducted. The investigation showed that manganese was incorporated into the lattice and surface layers of SrTiO3 particles with the presence of manganese segregation and inhomogeneities. Optical measurements indicated a shift of the absorption edge to higher values of wavelengths where the lowest value of the band gap (3.10 eV) was for the longest activation time (120 min) and the highest weight percentage of dopant (6 wt%). In the case of lower concentration (1.5 wt%), there was a significant relative contribution of the substitution of Sr2+ ions by Mn2+ ions, while the substitution of Ti4+ ions by Mn4+ ions dominated samples with an increased concentration
Modeling of shaped charge jet penetration depth: Analytical and numerical approach
No full textShaped charge is the most effective armor-piercing mechanism, harnessing explosive charge detonation energy to form and accelerate a hypervelocity metal penetrator known as a jet. The process entails intricate dynamics including detonation wave propagation, its interaction with the metal liner, and subsequent liner collapse leading to jet formation. While both analytical and numerical models offer insight into this complex process, each approach presents distinct challenges. Analytical models, while conceptually straightforward, often rely on simplifications that compromise accuracy. Conversely, uncertainty or even unavailability of relevant material properties and high computational cost are the most important drawbacks of numerical models. Notably, the jet penetration phase imposes significantly greater computational demands compared to preceding processes of jet formation. This research aims at providing a deeper understanding of the jet interaction with target, as well as on determining its influence on penetration depth. We revisit an analytical model based on the virtual origin concept and complement it with numerical simulations using Abaqus/Explicit in a pure Eulerian domain. Through comprehensive analysis, we explore various jet parameters – such as kinetic energy, diameter, length, velocity gradient, and effective standoff distance – and their impact on penetration depth. The insights derived from this study hold practical significance for the preliminary evaluation of the shaped charge’s effectiveness and consequent refinement of the design of shaped charge projectiles or warheads
Wave propagation in tailored metastructures consisting of elastic beams and rigid bodies
No full textThis paper presents a study of wave propagation through an infinite periodic structure that consists of elastic Timoshenko beams interconnected with rigid bodies. This is a generalized approach in which the beams are not coaxial and the centre of mass of each rigid body is placed away from the intersection of their neutral axes. An analytical approach is used by applying the transfer matrix method (TMM), along with the Floquet–Bloch theorem for elastic wave propagation. Subsequent parametric analysis is performed with visualization of resulting band diagrams of a representative structure. These results are verified through comparison with solutions obtained using the finite-element method (FEM). In this manner, a comprehensive dynamical analysis of tailored metastructures is provided. This article is part of the theme issue ‘Current developments in elastic and acoustic metamaterials science (Part 2)’
Wet cooling of air on plate finned tube heat exchangers
No full textThe objective of this paper is to provide the reliable calculation procedure for determining heat and mass flow rates for plate finned tube heat exchangers in dehumidification regimes that can be used easily in engineering practice. For this purpose, the experiments are conducted on two heat exchangers, and datasets for six more heat exchangers are used from literature. Comprehensive database is established with total of 637 sets of data, and it gathers 365 new measurement sets and 272 sets from open literature. The new calculation procedure predicts heat transfer rate and condensate flow rate where new methodology approach (based on the porous velocity, the ratio of characteristic surfaces and hydraulic diameter) is used. Predicted results show 5–10 % deviation for heat duty and up to 20 % for mass flow rate from experimental results, which is of importance to industrial practice
NUMERICAL SIMULATION OF POOL BOILING WITH TWO-FLUID MODEL AND GRID-RESOLVED HEAT TRANSFER MECHANISMS
No full textMost nucleate boiling simulations are based on the Eulerian modelling of bulk liquid-vapour two-phase flow and subgrid presence of all mechanistically partitioned heat transfer modes in fluid control volumes in contact with the heated wall. Such mechanistic partitioning heat transfer approach predicts the total heat flux from the heated wall towards the boiling two-phase mixture as the sum of (i) the single-phase convection heat transfer from the heated wetted wall not covered with the rising bubbles, (ii) the transient conduction caused by the rewetting of the heated wall hot spot after the bubble detachment, known as quenching heat flux and (iii) the evaporation heat flux. Here presented research introduces a new approach to the numerical modelling of pool boiling based on the grid resolved mechanisms of boiling heat transfer. The spots of bubble growth and the wetted areas are distinguished and two grid resolved modes of heat transfer are considered: the conjugate heat transfer from the heated wall to the rising bubble at the bubble footprint until the bubble departure and the conjugate heat transfer from the heated wall to the wetting liquid. The constituents of the heat transfer model at the footprint of the bubble growth are the bubble residence time and the bubble departure diameter. The presented model is validated by experimental data from the literature. It was shown that the model can predict the wall temperature transient at bubble footprint location as well as the mean wall superheating. Appropriate modelling of vapour generation at the discrete locations of the bubble growth enables good prediction of two-phase mixture pattern in the boiling pool, the void fraction distribution along pool height and swell level position. Further analysis includes the application of both subgrid and grid resolved modelling approaches to the simulation of pool boiling under high heat fluxes. It is shown that the subgrid wall boiling model does not predict adequately the wall temperature transient behaviour and the void fraction distribution in the boiling pool under high heat fluxes, while the grid resolved model provides plausible results. Presented simulations are obtained with the in-house computer code based on the modified Semi-Implicit Method for Pressure Linked Equations (SIMPLE) for the solving of mass, momentum and energy balance equation for each phase and appropriate closure laws for the prediction of vapour-liquid interface transport phenomena