Posouzení stavu a měření mechanických vlastností dřevěné konstrukce krovu a stropu 1. patra státního zámku Hrádek u Nechanic, rejstř. číslo kult. památky: 18278/6‐619
Kloiber, Michal; Drdácký, Miloš
2024 - český Průzkum popisovaný v této zprávě obsahuje vyhodnocení fyzikálních a mechanických vlastností vybraných nosných trámů dřevěné konstrukce krovu a stropu 1. patra státního zámku Hrádek u Nechanic (obr. 1.1). Podnětem k sepsání zprávy byla objednávka od Projekčního ateliéru pro dokumentaci, průzkum a obnovu historických staveb, spol. s.r.o., se sídlem Nerudova 1139, 544 01 Dvůr Králové nad Labem. Objednávka obsahovala požadavek na posouzení stavu vybraných dřevěných prvků pomocí přístroje Resistograph a především měření mechanických vlastností, které mohou přispět ke statickému posouzení a návrhu šetrné obnovy unikátní konstrukce krovu a stropu. The survey described in this report contains the assessment of physical and mechanical properties of selected beams within timber structures of the truss and 1st floor ceiling in the state-owned castle called Hrádek u Nechanic (Fig. 1.1). The report has been elaborated based on an order placed by Projekční ateliér pro dokumentaci, průzkum a obnovu historických staveb, spol. s.r.o., headquartered Nerudova 1139, 544 01 Dvůr Králové nad Labem. The order included the demand to assess the condition of selected timber elements by Resistograph, and mainly to measure the mechanical properties that can contribute to static assessment and a design of non-intrusive renewal of the unique structures of both the truss and the ceiling. Klíčová slova: timber structures; truss; ceiling; state-owned castle; timber mechanical properties Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR. Posouzení stavu a měření mechanických vlastností dřevěné konstrukce krovu a stropu 1. patra státního zámku Hrádek u Nechanic, rejstř. číslo kult. památky: 18278/6‐619

Průzkum popisovaný v této zprávě obsahuje vyhodnocení fyzikálních a mechanických vlastností vybraných nosných trámů dřevěné konstrukce krovu a stropu 1. patra státního zámku Hrádek u Nechanic (obr. ...

Kloiber, Michal; Drdácký, Miloš
Ústav teoretické a aplikované mechaniky, 2024

Flow simulations approach for flocculation tanks
Idžakovičová, Kristýna; Bílek, V.; Haidl, J.; Isoz, Martin; Pivokonský, M.
2024 - anglický Flocculation in water treatment facilities plays a key role in the separation of colloidal inorganic and organic substances. Its optimization leads to a significant increase in its efficiency and savings of operational costs. However, it is currently based on trial-and-error experimental approaches. In this contribution, we focus on flow modeling in stirred flocculation tanks that would, after coupling with a calibrated model of particle aggregation, enable simulationbased flocculation optimization. Despite the abundance of literature on stirred tank modeling, there is no universal agreement on the methodology used to describe turbulence nor on the approach to the computational mesh creation. Consequently, there is no unified methodology for simulations and their validation. To address this, we present a best-practice methodology for economical, yet reliable flow simulations in the said device. This methodology includes the choice of the turbulence model, the approach to the design of a high quality mesh suitable for arbitrary geometries, and results evaluation. It is developed based on an extensive literature review, a multitude of flow simulations using several meshes of progressively higher quality and resolution, and various strategies to converge to steady-state flow conditions. The simulation quality indicators used here involve comparison with the experimental data on fluid velocity, stirrer power output, and flow rate through the impeller zone. Additionally, the resulting flow simulation models are compared using tracer transport simulations, hinting at their potential for coupling with particle aggregation models. Klíčová slova: flocculation tank; stirring; MRF; CFD; OpenFOAM Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR. Flow simulations approach for flocculation tanks

Flocculation in water treatment facilities plays a key role in the separation of colloidal inorganic and organic substances. Its optimization leads to a significant increase in its efficiency and ...

Idžakovičová, Kristýna; Bílek, V.; Haidl, J.; Isoz, Martin; Pivokonský, M.
Ústav termomechaniky, 2024

Improvement of an unbaffled stirred tank mixing characteristics using variable speed impeller
Gebouský, Ondřej; Haidl, Jan; Bodnár, J.; Pivokonský, Martin
2024 - anglický Unbaffled mixing tanks with magnetically driven impellers are increasingly used in biotechnological and pharmaceutical industries, combining the benefits of a closed, sterile environment with easy equipment cleanability. On the other hand, missing internals, such as baffles or cooling coils, have an adverse effect on the equipment mixing characteristics, namely the batch\nhomogenization time. In our previous research, we uncovered that the eccentricity and inclination of the impeller – both employed routinely to enhance the mixing characteristics of unbaffled vessels – are not fully effective in the suppression of central vortex formation resulting in the increase in the homogenization time. In this work, we propose a simple solution to counteract the central vortex formation – a periodical variation of impeller rotational speed. This approach destabilizes the central vortex, significantly reducing homogenization time while maintaining the benefits of the original unbaffled setup. This innovation can seamlessly integrate into existing industrial setups, promising efficiency gains for biotech and pharmaceutical production. Klíčová slova: unbaffled mixing tanks; variable rotational speed; vortex destabilization; mixing time improvement Plné texty jsou dostupné v digitálním repozitáři Akademie Věd. Improvement of an unbaffled stirred tank mixing characteristics using variable speed impeller

Unbaffled mixing tanks with magnetically driven impellers are increasingly used in biotechnological and pharmaceutical industries, combining the benefits of a closed, sterile environment with easy ...

Gebouský, Ondřej; Haidl, Jan; Bodnár, J.; Pivokonský, Martin
Ústav pro hydrodynamiku, 2024

Monitoring chemismu srážkových vod na území NPČS. Závěrečná zpráva za rok 2023-2024
Navrátil, Tomáš; Dobešová, Irena; Rohovec, Jan
2024 - český Klíčová slova: deposition; bulk precipitation; acidificants; main elements; throughfall Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR. Monitoring chemismu srážkových vod na území NPČS. Závěrečná zpráva za rok 2023-2024

Navrátil, Tomáš; Dobešová, Irena; Rohovec, Jan
Geologický ústav, 2024

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

Vrt DO 599. Paleomagnetický a magnetomineralogický výzkum. Závěrečná zpráva
Kdýr, Šimon; Pruner, Petr; Uçar, Hakan; Elbra, Tiiu
2024 - český Klíčová slova: palaeomagnetism; rock-magnetism; greigite Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR. Vrt DO 599. Paleomagnetický a magnetomineralogický výzkum. Závěrečná zpráva

Kdýr, Šimon; Pruner, Petr; Uçar, Hakan; Elbra, Tiiu
Geologický ústav, 2024

Využití termografie v průzkumech památek
Valach, Jaroslav; Eisler, Marek
2024 - český Termografie rozšiřuje portfolia metod, jimiž lze studovat vlastnosti objektů okolního světa. Ještě před deseti lety byla tato technologie kvůli potenciálním vojenským aplikacím úzkostlivě kontrolována, což omezovalo konkurenci v nabídce výrobků a výrobců a vedlo k vysokým cenám zařízení založených na těchto principech. Teprve díky uvolnění této kontroly došlo k rozmachu výroby a zpřístupnění zjednodušených výrobků masovému využití, takže si dnes může zákazník například pořídit chytrý telefon s doplňkovým termografickým modulem jen s malým navýšením ceny. Spolu s dostupností zařízení pozorujeme nárůst uplatnění termografie v mnoha oblastech, včetně průzkumů staveb a památek. Thermography expands the portfolio of methods that can be used to study the properties of objects in the surrounding world. As recently as a decade ago, the technology was frowned upon for potential military applications controlled, which limited competition in the offer of products and manufacturers and led to high prices of devices based on these principles. It was only thanks to the release of this control that it happened to expand production and make simplified products available to mass use, so get it today for example, a customer can purchase a smartphone with an additional thermographic module for only with a small price increase. Together with the availability of equipment, we observe an increase in the application of thermography in many areas, including surveys of buildings and monuments. Klíčová slova: thermography; survey of historical structures Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR. Využití termografie v průzkumech památek

Termografie rozšiřuje portfolia metod, jimiž lze studovat vlastnosti objektů okolního světa. Ještě před deseti lety byla tato technologie kvůli potenciálním vojenským aplikacím úzkostlivě ...

Valach, Jaroslav; Eisler, Marek
Ústav teoretické a aplikované mechaniky, 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

QUANTUM-MECHANICAL STUDY OF INTERNAL STRUCTURAL TRANSFORMATIONS IN Pb-SUPERSATURATED Pb-Sn ALLOYS
Friák, Martin; Čípek, Petr; Pavlů, J.; Roupcová, Pavla; Miháliková, Ivana; Msallamová, Š.; Michalcová, A.
2024 - anglický Motivated by a decades-long controversy related to the crystal structure of Pb-supersaturated solid solutions of Pb in Sn, we have performed a quantum-mechanical study of these materials. Focusing on both body-centred-tetragonal beta-Sn and simple-hexagonal gamma-Sn structures, we have computed properties of two alloys with the chemical composition Pb5Sn11, i.e. 31.25 at. % Pb, which is close to the composition of the experimentally found alloy (30 at. % Pb). The 16-atom computational supercells were designed as multiples of the elemental beta- and gamma-Sn unit cells, where the Pb atoms were distributed according to the special quasi-random structure (SQS) concept. Full structural relaxations of both beta- and gamma-phase-based alloys resulted in very significant re-arrangements into structures which do not exhibit any apparent structural features typical for the original alloys, and are, therefore, difficult to classify. The formation energies of the beta- and gamma-phase-originating equilibrium phases are 50 meV/atom and 53 meV/atom, respectively. Therefore, they are not stable with respect to the decomposition into the elemental lead and tin. Moreover, our calculations of elastic constants of both phases revealed that they are close to mechanical instability. Our results indicate that the studied Pb-supersaturated Pb-Sn solid solutions may be prone to structural instability, transformations into different phases and decomposition. Our findings may contribute into the identification of the reason why the subsequent experimental studies did not reproduce the initial published data. Klíčová slova: tin; crystal; Pb-Sn alloys; stability; supersaturation; quantum-mechanical calculations Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR. QUANTUM-MECHANICAL STUDY OF INTERNAL STRUCTURAL TRANSFORMATIONS IN Pb-SUPERSATURATED Pb-Sn ALLOYS

Motivated by a decades-long controversy related to the crystal structure of Pb-supersaturated solid solutions of Pb in Sn, we have performed a quantum-mechanical study of these materials. Focusing on ...

Friák, Martin; Čípek, Petr; Pavlů, J.; Roupcová, Pavla; Miháliková, Ivana; Msallamová, Š.; Michalcová, A.
Ústav fyziky materiálů, 2024