Seminar Mechanics of Machines and Mechanisms - Models and Mathematical Methods
PROGRAM
Plan rada Seminara Mehanika mašina i mehanizama - modeli i matematičke metode za NOVEMBAR 2024.
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Utorak, 05.11.2024. u 17:00, Live stream
Nikolaos Rogkas, School of Mechanical Engineering, National Technical University of Athens, Greece
MODELING AND CAPTURING AERATION CHARACTERISTICS IN ROTATING THIN-FILM FLOW SYSTEMS
Rotating thin-film flow systems, such as those in wet clutch assemblies experience power losses due to drag torque, which results from the lubricant’s viscosity. In low-speed regimes, these losses increase with rising rotational speed, as shear stress within the lubricant is proportional to speed. However, once a critical rotational speed is reached, the pressure of the lubricant near the outer radius begins to drop, allowing air to enter the flow from the housing’s opening and creating a complex two-phase mixture of air and lubricant. This shift results in a sharp decrease in drag torque due to the much lower viscosity of air, which reduces flow resistance. Accurately predicting the distribution of this two-phase flow is essential across industries like automotive and helicopter transmissions, as it significantly impacts energy efficiency. However, achieving accurate predictions is challenging, especially when textured or grooved disc surfaces are involved. These surface features, often designed to improve lubrication and minimize wear, introduce additional complexity to the distribution of air and lubricant due to the distinct flow patterns created by the grooves. This lecture will present recent advancements in modeling and characterizing air-lubricant flow within these systems. The latest analytical, computational, and experimental techniques developed to capture the characteristics of the two-phase flow behavior will be explored and discussed. As surface texturing and functionalization become integral to the design of new tribosystems, developing refined models for predicting air-lubricant flow, particularly considering textured surfaces, will be invaluable. These advancements are expected to play an important role in improving energy efficiency and optimizing performance across diverse mechanical applications.
Utorak, 12.11.2024. u 17:00, sala 301f, Kneza Mihaila 36 i Live stream
Milan Raković, Faculty of Mechanical Engineering, Belgrade University
MATHEMATICAL MODELING AND EXPERIMENTAL DETERMINATION OF BUBBLE DRAG COEFFICIENT IN TWO-PHASE BUBBLY FLOW
For the successful execution of the numerical simulations of the two-phase bubble flow, it is necessary to correctly mathematically model the forces that describe the interaction of the two phases flowing in the common domain. These forces are called interfacial forces, and a special place among them belongs to the drag force that effects the bubble. In this presentation, the existing mathematical models of the drag coefficient of bubbles will be presented, with a special emphasis on the shear flow influence on the value of the drag coefficient. This influence is clearly seen through the results of numerical simulations of this type of two-phase flow. New experimental results are of great importance for the improvement of existing mathematical models of the drag coefficient. The procedure and results of an experimental investigation of two-phase bubbly flow in a vertical channel will be presented. Experimental results allow us to better understand physical phenomena, as well as improve existing mathematical models. It will be shown how new experimental results serve to determine the influence of shear flow on the value of the bubble drag coefficient.
Utorak, 19.11.2024. u 17:00, Live stream
Aurea Iñurritegui Marroquin, Faculty of Engineering, Mondragon University, Spain
SPHERICAL GEAR COUPLINGS WORKING IN MISALIGNED APPLICATIONS
Spherical gear couplings are commonly used mechanical components to transmit power between highly misaligned rotating shafts. Their main geometry characteristic is the appearance of undercut sections on the hub when machining a high amount of longitudinal crowning. This possibility is even more significant when gear couplings with a low number of teeth are manufactured directly on the shaft.
Moreover, gear couplings working at high misalignment angles cause a drastic decrease in the number of teeth in contact. In consequence, higher tooth-root stresses in those in contact are suffered and result in the failure of the component by tooth root breakage. However, the scientific literature has focused on gear couplings working in applications where the misalignment angles are below 1
o, thus mainly centered on failures other than bending fatigue, such as fretting or surface wear.
In this lecture we will be able to learn about, how the geometry of highly crowned gear couplings is generated, how they work and which is their load distribution, numerically with a finite element model and, and finally, how to choose the preliminary geometrical parameters for their design and manufacturing.
Petak, 22.11.2024. u 12:15, Pariske Komune bb, Niš i Live stream
Milan Cajić, Mathematical Institute SANU, Belgrade
TOPOLOGICALLY PROTECTED STATES IN LATTICES WITH BEYOND-NEAREST NEIGHBOUR COUPLING
Topologically protected states are well known to exist in classical one-dimensional periodic lattices, resulting in topological invariant winding number matching with the number of interface/edge states of the corresponding super-cell lattice system. This rule is no more valid in the case when beyond-nearest neighbour (BNN) coupling is introduced, which requires a different approach to investigate topological nature of such mechanical systems. Here we will focus on the investigation of non-trivial topological behaviour of locally resonant lattices with both springs and inerters as BNN coupling mechanical elements.
Danilo Karličić, Mathematical Institute SANU, Belgrade
CAHN–HILLIARD DIFFUSION AND PHASE SEPARATION OF MAGNETO-ACTIVE HYDROGELS IN THE FINITE DEFORMATION REGIME
Magneto-active hydrogels are composed of a polymeric matrix embedded with magnetic particles, enabling functional actuation under external magnetic stimuli. In this study, we will develop a unified framework based on continuum thermodynamics and the principle of virtual power, which couples the Cahn-Hilliard type diffusion with large elastic deformations of magneto-active hydrogels. The presented multi-physical model will account the swelling, deswelling and phase separation caused by fluid constituent diffusion, giving rise to coexisting regions with different degrees of swelling. The proposed theoretical model can serve as a foundation for modelling more complex phenomena across a broad spectrum of soft materials, with applications in tissue engineering, drug delivery, and energy storage.
Zajednički sastanak sa seminarom Differential Geometry, Continuum Mechanics and Mathematical Physics.
Utorak, 26.11.2024. u 17:00, sala 301f, Kneza Mihaila 36 i Live stream
Mehmet Bozca, Yildiz Technical University, Mechanical Engineering Faculty, Turkey
INVESTIGATION OF THE CORRELATION BETWEEN THE RATTLE NOISE AND DESIGN PARAMETERS OF GEARBOX IN AUTOMOTIVE TRANSMISSIONS
Investigation of correlation between the rattle noise and design parameters of gearbox in automotive transmissions is studied. Rattle noise is calculated and simulated based on design parameters of 5-speed gearbox. All pinion gears and wheel gears are helical gear. All gears are made of 16MnCr5. Rattle noise profiles are obtained depend on design parameters. It is concluded in simulation that while increasing of geometrical parameters of gearbox such as module, teeth number and axial clearance result in increasing of rattle noise, increasing of backlash result in decreasing of rattle noise. Changing of face width result in constant level of rattle noise. Operational parameters of gearbox such as angular acceleration and excitation frequency result in increasing of rattle noise of gearbox.
In optimization, two different objective functions are considered. Firstly, average rattle noise level is considered as objective function and design parameters are optimized under constraints of bending stress, contact stress and constant center distance of gears. Secondly, a four-degree-of-freedom torsional vibration model of the pinion gear-wheel gear system is obtained and minimum singular value of transfer matrix is considered as objective functions and design parameters are optimized under constraints of bending stress, contact stress and constant center distance of gears.
In optimization, it is concluded that while decreasing of geometrical parameters of gearbox such as module, teeth number and axial clearance result in decreasing of rattle noise, decreasing of backlash result in increasing of rattle noise. Although, there is no relation between face width and rattle noise, face width is necessary to satisfy desired contact safety. Therefore, by optimizing geometrical parameters of gearbox such as, module, teeth number, axial clearance, and backlash, it is possible to obtain light-weight-structure of gearbox and to minimize the rattling noise.
It is concluded in optimization that optimized geometrical design parameters cause average 10 percentage lower rattle noise than calculated rattle noise for sample gearbox. All optimized geometrical design parameters satisfy all constraints as well.
Seminar Mehanika mašina i mehanizama - modeli i matematičke metode započeo je sa radom u junu 2018.god. Seminar se održava do dva puta mesečno, utorkom u periodu od 17.00 - 19.00 u Matematičkom institutu SANU.
dr Ivana Atanasovska
Rukovodilac seminara
Stepa Paunović
Sekretar seminara