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Finite element approximation of fluid structure interaction using Taylor-Hood and Scott-Vogelius elements
Vacek, Karel; Sváček, P.
2024 - anglický
This paper addresses the problem of fluid flow interacting a vibrating solid cylinder described by one degree of freedom system and with fixed airfoil. The problem is described by the incompressible Navier-Stokes equations written in the arbitrary Eulerian-Lagrangian (ALE) formulation. The ALE mapping is constructed with the use of a pseudo-elastic approach. The flow problem is numerically approximated by the finite element method (FEM). For discretization of the fluid flow, the results obtained by both the Taylor-Hood (TH) element and the Scott-Vogelius (SV) finite element are compared. The TH element satisfies the Babuška-Brezzi inf-sup condition, which guarantees the stability of the scheme. In the case of the SV element the mesh, that is created as a barycentric refinement of regular triangulation, is used to satisfy the Babuška-Brezzi condition. The numerical results for two benchmark problems are shown. Klíčová slova: finite element method; arbitrary Lagrangian-Eulerian method; Scott-Vogelius element; Taylor-Hood element Plné texty jsou dostupné v digitálním repozitáři Akademie Věd.
Finite element approximation of fluid structure interaction using Taylor-Hood and Scott-Vogelius elements

This paper addresses the problem of fluid flow interacting a vibrating solid cylinder described by one degree of freedom system and with fixed airfoil. The problem is described by the incompressible ...

Vacek, Karel; Sváček, P.
Matematický ústav, 2024

Microstructure modifications of Al-Si-coated press-hardened steel 22MnB5 by laser welding
Šebestová, Hana; Horník, Petr; Mika, Filip; Mikmeková, Šárka; Ambrož, Ondřej; Mrňa, Libor
2024 - anglický
Weld microstructure depends on the characteristics of welded materials and parameters of welding technology, especially on the heat input that determines the peak temperature and the cooling rate. When the coated sheets are welded, the effect of the chemical composition of the coating must be also considered even though its thickness is only a few tens of microns. During 22MnB5+AlSi laser welding experiments, the ferrite-stabilizing elements of coating modified the weld metal microstructure. Ferrite appeared in a quenched weld metal. The rapid cooling rate accompanying welding with a focused beam limited the homogenization of the weld metal which resulted in the formation of ferritic bands in the regions rich in Si and especially in Al. On the other hand, a high level of homogenization was reached when welding with the defocused beam. The ferritic islands uniformly distributed in the weld metal were formed at 0.4 wt% and 1.6 wt% of Si and Al, respectively. The doubled heat input reduced the Al content to 0.7 wt% insufficient for the ferrite formation at still relatively high cooling rates. Predicting the distribution of ferrite in the weld metal is challenging due to its dependence on various factors, such as cooling rate and the volume of dissolved coating, which may vary with any modifications made to the welding parameters. Klíčová slova: laser welding; high-strength steel; microstructure; heat input; ferrite stabilization Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Microstructure modifications of Al-Si-coated press-hardened steel 22MnB5 by laser welding

Weld microstructure depends on the characteristics of welded materials and parameters of welding technology, especially on the heat input that determines the peak temperature and the cooling rate. ...

Šebestová, Hana; Horník, Petr; Mika, Filip; Mikmeková, Šárka; Ambrož, Ondřej; Mrňa, Libor
Ústav přístrojové techniky, 2024

Influence of ball material on the resulting fatigue life of thermal sprayed HVOF coatings in dynamic impact testing
Duliškovič, J.; Daniel, Josef; Houdková, Š.
2024 - anglický
Dynamic impact wear, i.e. contact between two components in the presence of high cyclic local loads, is a challenging failure mode that occurs in many mechanical applications. Many previous studies have confirmed that dynamic impact testing is suitable for evaluating the contact fatigue of thermal sprayed coatings. However, the effect of the test parameters on the resulting lifetime is unclear. The aim of this study describes the effect of the ball material used in the dynamic impact test on the resulting fatigue life of the HVOF thermal sprayed coating. Three test balls made of WC/Co alloy, Si3N4 silicon nitride and 440 C steel were chosen for this study. Dynamic impaction testing was carried out on the Cr3C2-NiCr coating, which was sprayed by HVOF on a 1.2376 high-speed steel substrate. The impact lifetime was described by the number of critical impacts, i.e. the number of impacts before coating fatigue occurs. Furthermore, the depth and volume of impact craters were measured. Using scanning electron microscopy (SEM), the surface of the impacts as well as the microstructure of the coating on the cross-section in the region of the impacts were observed. Furthermore, the mechanism of crack propagation in the coating and the microstructure of the indentor were investigated. Klíčová slova: dynamic impact test; HVOF; Cr3C2-NiCr; fatigue Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Influence of ball material on the resulting fatigue life of thermal sprayed HVOF coatings in dynamic impact testing

Dynamic impact wear, i.e. contact between two components in the presence of high cyclic local loads, is a challenging failure mode that occurs in many mechanical applications. Many previous studies ...

Duliškovič, J.; Daniel, Josef; Houdková, Š.
Ústav přístrojové techniky, 2024

Functional Tungsten-based thin films and their characterization
Košelová, Zuzana; Horáková, L.; Sobola, Dinara; Burda, Daniel; Knápek, Alexandr; Fohlerová, Z.
2024 - anglický
Anodizing is a technique by which thin oxide layers can be formed on a surface. Thin oxide layers have been found to be useful in a variety of applications, including emitters of electrons. Tungsten is still a common choice for cold field emitters in commercial microscopy applications. Its suitable quality can be further improved by thin film deposition. Not only the emission characteristic can be improved, but also the emitter operating time can be extended. Tungsten oxide is known for its excellent resistance to corrosion and chemical attack due to its stable crystal structure and strong chemical bonds between tungsten and oxygen atoms. Many techniques with different advantages and disadvantages have been used for this purpose. Anodization was chosen for this work because of the controllable uniform coverage of the material and its easy availability without the need for expensive complex equipment. The anodizing process involves applying an electrical potential to tungsten while it is immersed in an electrolyte solution. This creates a thin layer of tungsten oxide on the surface of the metal. The thickness and properties of the resulting oxide layer can be controlled by adjusting the anodization conditions, such as the electrolyte solution, voltage, and the duration of the process. In this work, H3PO4 was used as the electrolyte to test whether these tungsten oxide layers would be useful for electron emitters, for use in electron guns and other devices that require high-quality electron emitters. The properties were evaluated using appropriate techniques. In general, anodization of tungsten to form thin layers of tungsten oxide layers is a promising technique for producing high quality electron emitters. Klíčová slova: cold-field emission; thin layer deposition; tungsten oxide; resonance enhanced tunneling; anodization Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Functional Tungsten-based thin films and their characterization

Anodizing is a technique by which thin oxide layers can be formed on a surface. Thin oxide layers have been found to be useful in a variety of applications, including emitters of electrons. Tungsten ...

Košelová, Zuzana; Horáková, L.; Sobola, Dinara; Burda, Daniel; Knápek, Alexandr; Fohlerová, Z.
Ústav přístrojové techniky, 2024

Numerical study of the steady airflow in the human respiratory system during inhaling and exhaling
Lancmanová, Anna; Bodnár, Tomáš
2024 - anglický
This paper presents some of the initial results of the numerical simulations of a steady turbulent flow in human upper airways during inhalation and exhalation. The mathematical model is based on the system of Reynolds-Averaged incompressible Navier-Stokes equations complemented by the SST k − ω turbulence model. The simulations were performed using finite-volume open source solver OpenFOAM on a realistic three-dimensional geometry. The main aim of this particular study is to verify the computational setup with special focus on appropriate choice and implementation of boundary conditions. The prescribed boundary conditions are chosen to mimic the physiological conditions during normal breathing cycle. This study aims to gain an insight into the airflow behavior during the inhalation and exhalation process by comparing the results of two distinct simulations corresponding to two different (opposite) flow rates . The obtained local flow rates and flow fields for both cases are presented and mutually compared. This initial work should serve as a foundation for future more complex simulations that will include the time-dependent and compressible effects. Klíčová slova: human airways; incompressible Navier-Stokes; OpenFOAM Plné texty jsou dostupné v digitálním repozitáři Akademie Věd.
Numerical study of the steady airflow in the human respiratory system during inhaling and exhaling

This paper presents some of the initial results of the numerical simulations of a steady turbulent flow in human upper airways during inhalation and exhalation. The mathematical model is based on the ...

Lancmanová, Anna; Bodnár, Tomáš
Matematický ústav, 2024

Česká putování za Richardem Wagnerem
Fránek, Michal; Kopecký, J.
2024 - český
Studie zkoumá fenomén českých cest za slavným německým skladatelem Richardem Wagnerem a do míst spojených s jeho kultem (Mnichov, Bayreuth, Curych atd.). Zaměřuje se na wagnerovské cesty – uskutečněné i neuskutečněné – českých skladatelů (Bedřich Smetana, Antonín Dvořák, Zdeněk Fibich, Josef Bohuslav Foerster), interpretů (Ema Destinnová, Karel Burian aj.), hudebních kritiků (Otakar Hostinský, V. V. Zelený), malířů (Jaroslav Čermák) a spisovatelů (Julius Zeyer, Jaroslav Maria, Teréza Nováková), přičemž sleduje jejich různé motivace. The study explores the phenomenon of Czech travels to famous German composer Richard Wagner and to the places associated with his cult (Munich, Bayreuth, Zurich, etc.). It focuses on the Wagnerian journeys – accomplished and not – of Czech composers (Bedřich Smetana, Antonín Dvořák, Zdeněk Fibich, Josef Bohuslav Foerster), performers (Ema Destinnová, Karel Burian, etc.), music critics (Otakar Hostinský, V. V. Zelený), painters (Jaroslav Čermák) and writers (Julius Zeyer, Jaroslav Maria, Teréza Nováková), tracing their different motivations. Klíčová slova: Richard Wagner; travelling to artists Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Česká putování za Richardem Wagnerem

Studie zkoumá fenomén českých cest za slavným německým skladatelem Richardem Wagnerem a do míst spojených s jeho kultem (Mnichov, Bayreuth, Curych atd.). Zaměřuje se na wagnerovské cesty – uskutečněné ...

Fránek, Michal; Kopecký, J.
Ústav pro českou literaturu, 2024

Numerical evaluation of mass-diffusive compressible fluids flows models
Bodnár, Tomáš; Fraunié, P.
2024 - anglický
This contribution presents first numerical tests of some recently published alternative models for solution of viscous compressible and nearly incompressible models. All models are solved by high resolution compact finite difference scheme with strong stability preserving RungeKutta time stepping. The two simple but challenging computational test cases are presented, based on the double-periodic shear layer and the Kelvin-Helmholtz instability. The obtained time-dependent flow fields are showing pronounced shear and vorticity layers being resolved by the standard as well as by the new mass-diffusive modified models. The preliminary results show that the new models are viable alternative to the well established classical models. Klíčová slova: compressible Navier-Stokes; nearly incompressible flow; mass diffusion; compact finite-difference Plné texty jsou dostupné v digitálním repozitáři Akademie Věd.
Numerical evaluation of mass-diffusive compressible fluids flows models

This contribution presents first numerical tests of some recently published alternative models for solution of viscous compressible and nearly incompressible models. All models are solved by high ...

Bodnár, Tomáš; Fraunié, P.
Matematický ústav, 2024

Motion of fluids in the moving domain
Nečasová, Šárka
2024 - anglický
It is a survay paper where the problem of the existence of weak solutions of compressible barotropic solutions in a moving bounded domain is studied. Klíčová slova: compressible fluid; moving domain; weak solutions Plné texty jsou dostupné v digitálním repozitáři Akademie Věd.
Motion of fluids in the moving domain

It is a survay paper where the problem of the existence of weak solutions of compressible barotropic solutions in a moving bounded domain is studied.

Nečasová, Šárka
Matematický ústav, 2024

Železniční cestovatel Eduard Bazika aneb Cestování s manželkou
Hlavačka, Milan
2024 - český
Ing. Eduard Bazika (1830–1914) nebyl profesionální poutník, ale poutník z profese. Jako absolvent pražské polytechniky se celý život specializoval na železniční stavitelství a jako inženýr nejdříve státních drah a od roku 1855 až do odchodu na odpočinek v roce 1891 soukromé Společnosti státní dráhy (StEG) celý život procestoval, respektive před výstavbou prochodil svěřené železnice v české a moravské krajině. I po odchodu na penzi pracoval pro Zemský výbor Království českého a jeho Železniční výbor a v této pozici opět pracovně putoval po všech koutech Čech, aby posuzoval rentabilitu budoucích místních drah. Jeho zvláštností bylo, že se vždy snažil skloubit své cestovní povinnosti s rodinným životem, což mělo za následek, že jeho žena a děti putovaly s ním po nejrůznějších štacích a železničních stavbách. Stranou neponechával ani dlouhodobější náročnější soukromé cesty s manželkou na světové výstavy a po historických památkách Itálie (v doprovodu Jiřího Stibrala) či k obhlídce nově dokončených alpských železnicích. Jako představitel sebevědomé české střední třídy, která už disponovala volným časem a finančními prostředky (a samozřejmě režijní jízdenkou) dovedl skloubit cestovatelskou povinnost s cestovatelskou vášní a putování vnímal jako nezbytnou součást aktivního životního stylu moderního člověka. Ing. Eduard Bazika (1830–1914) was not a professional pilgrim, but a pilgrim by profession. As a graduate of the Prague Polytechnic, he specialized in railway construction all his life and as an engineer, first of all for the State railways, and from 1855 until his retirement in 1891, he traveled all his life for the private State Railway Company (StEG), or rather, before construction, he traveled the entrusted railways in the Bohemian and Moravian landscape. Even after retiring, he worked for the Land Committee of the Kingdom of Bohemia and its Railway Committee, and in this position he once again traveled to all corners of Bohemia to assess the profitability of future local railways. A peculiarity of his was that he always tried to combine his traveling duties with his family life, which resulted in his wife and children traveling with him to various estates and railway constructions. He did not leave aside longer, more demanding private trips with his wife to world exhibitions and historical monuments in Italy (accompanied by Jiří Stibral) or to inspect the newly completed Alpine railways. As a representative of the self-confident Czech middle class, who already had free time and financial resources (and, of course, an overhead ticket), he was able to combine the obligation to travel with a passion for travel and perceived traveling as a necessary part of the active lifestyle of a modern person. Klíčová slova: Ing Eduard Bazika; pilgrim by profession; railway Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Železniční cestovatel Eduard Bazika aneb Cestování s manželkou

Ing. Eduard Bazika (1830–1914) nebyl profesionální poutník, ale poutník z profese. Jako absolvent pražské polytechniky se celý život specializoval na železniční stavitelství a jako inženýr nejdříve ...

Hlavačka, Milan
Historický ústav, 2024

TESTING THE METHOD OF MULTIPLE SCALES AND THE AVERAGING PRINCIPLE FOR MODEL PARAMETER ESTIMATION OF QUASIPERIODIC TWO TIME-SCALE MODELS
Papáček, Štěpán; Matonoha, Ctirad
2023 - anglický
Some dynamical systems are characterized by more than one timescale, e.g. two well separated time-scales are typical for quasiperiodic systems. The aim of this paper is to show how singular perturbation methods based on the slow-fast decomposition can serve for an enhanced parameter estimation when the slowly changing features are rigorously treated. Although the ultimate goal is to reduce the standard error for the estimated parameters, here we test two methods for numerical approximations of the solution of associated forward problem: (i) the multiple time-scales method, and (ii) the method of averaging. On a case study, being an under-damped harmonic oscillator containing two state variables and two parameters, the method of averaging gives well (theoretically predicted) results, while the use of multiple time-scales method is not suitable for our purposes. Klíčová slova: Dynamical system; Singular perturbation; Averaging; Parameter estimation; Slow-fast decomposition; Damped oscillations Dokument je dostupný na externích webových stránkách.
TESTING THE METHOD OF MULTIPLE SCALES AND THE AVERAGING PRINCIPLE FOR MODEL PARAMETER ESTIMATION OF QUASIPERIODIC TWO TIME-SCALE MODELS

Some dynamical systems are characterized by more than one timescale, e.g. two well separated time-scales are typical for quasiperiodic systems. The aim of this paper is to show how singular ...

Papáček, Štěpán; Matonoha, Ctirad
Ústav teorie informace a automatizace, 2023

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