2026-01-11
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Accelerating parameter identification in bread baking simulations via model order reduction
Kovárnová, Anna ; Isoz, Martin ; Hlavatý, Tomáš ; Sluková, M. ; Moucha, T.
Bread has been one of the cornerstones of people's diets for thousands of years, and its recipes and baking procedures are being improved to this day. However, mathematical modeling of bread\nbaking is still a complicated task, as bread is a multiphase system and models need to cover heat transfer, mass transfer, and deformation. Furthermore, the literature often lacks specific values\nof some of the coefficients used in the models, such as thermal conductivity, providing relatively wide ranges of possible values. In this contribution, we operate on a preliminary model of rigid\ndough baking and compare the temperature values computed by the model with an experiment. We then strive to determine the optimal values of the thermal conductivity of the solid phase and\nthe coefficient of evaporation. The computational costs are reduced by employing model order reduction. We utilize a posteriori methods, i. e. temperature fields for several pairs of parameters\nare used to construct the reduced order model, which then cheaply predicts temperature fields for any pair of parameters in between. In particular, we combine proper orthogonal decomposition\nfor the reduced basis construction with interpolation via artificial neural networks.\n
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2026-01-11
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Dynamic analysis of the Data Processing Unit for the Vigil mission
Gabriel, Dušan ; Masák, Jan ; Pešek, Luděk ; Mračko, Michal ; Zolotarev, Igor ; Bula, Vítězslav ; Šnábl, Pavel ; Souček, Jan ; Snížek, Jan
This paper presents the latest results of the experimental validation of the computational model of the proposed Data Processing Unit (DPU) for the Vigil mission using modal analysis and forced vibration. Several geometric modifications were performed, including changes to both the frame and the shielding baffles, in order to find the optimum design that would result in the desired reduction in deflections during booster launch. The final designed geometry of the DPU unit was subjected to all the prescribed calculations required for its certification.
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2026-01-11
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Tension-compression tests of 3D-printed PETG
Vaňková, Tereza ; Krystek, J.
The present study focuses on the tension-compression tests of 3D-printed PETG. The anti-buckling device is designed and manufactured to perform the test. The printed specimens are exposed to tensile and subsequently compressive loading at five different temperatures. The obtained data are then processed and compared with the results of the monotonic tension and compression tests. The influence of loading and temperature on the mechanical properties of the material is analysed.
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2026-01-11
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Properties of alternative refrigerants and heat transfer liquids – Modeling and experiments
Vinš, Václav ; Hrubý, Jan ; Prokopová, Olga ; Čenský, Miroslav ; Součková, Monika ; Blahut, Aleš ; Celný, David
Applications in the field of refrigeration and cooling face a challenging problem of finding convenient and durable operating fluids. On the one hand, refrigerants and heat transfer liquids need to exhibit technically suitable properties such as low viscosity, high heat of vaporization and specific heat over given temperature ranges, or non-corrosive behavior, and on the other hand, low toxicity, non-flammability and, last but not least, low environmental impact. Most of commonly used refrigerants based on halogenated hydrocarbons (CFCs, HFCs, HFOs) cause undesirable environmental harms such as ozone layer depletion, global warming or represent so-called PFAS (per- and polyfluoroalkyl substances) “forever chemical” that accumulate in nature. New operating fluids based on aqueous mixtures, various blends of hydrocarbons such as propane and isobutane, or carbon dioxide are being studied as possible alternatives in heat transfer applications. \nSome of these issues are briefly discussed in the introductory part. The main part of the presentation introduces two decades of both experimental and theoretical research of our team on the thermophysical properties of refrigerants and heat transfer liquids. The selected systems cover various refrigerants, aqueous systems applicable as heat transfer liquids such as water with ethylene glycol, methanol, ethanol or sodium chloride. Current focus is mostly on hydrofluoroethers (HFEs) that find high application potential, e.g., in electronics cooling and cleaning or as possible admixtures in refrigerant blends. The thermodynamic properties and phase equilibria of various refrigerants were successfully modeled with the state-of-the-art equations of state (EoSs) of SAFT-type (statistical associating fluid theory) supported by common cubic EoSs such as Peng-Robinson. The employment of density gradient theory enabled prediction of vapor-liquid phase interfaces and the surface tension of pure fluids and binary mixtures. The pressure-temperature-density relations are being investigated experimentally by using self-calibrated vibrating tube densimeters and single-sinker buyoancy method. The temperature dependence of surface tension is determined with the Wilhelmy plate method, du Noüy ring and the in-house developed capillary rise technique.
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2026-01-11
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Experimental Study of Elastic Wave Propagation in Metallic Multimaterial Specimens Made by Additive Manufacturing
Kylar, Jaromír ; Dvořák, Radim ; Kolman, Radek ; Kober, Jan
Wave propagation in 3D printed metals is an area of research that focuses on the behavior of mechanical waves in metallic materials produced by additive technologies, specifically 3D printing. This process is increasingly being used to produce complex geometric structures that can exhibit different properties compared to traditionally manufactured materials. In this context, the focus is on how the structure of the printing material, the microscopic arrangement of particles, porosity, and anisotropy affect the wave behavior. The aim of the research is to understand how different printing parameters (e.g., layer orientation, material composition) affect wave propagation and how this knowledge can be applied for e.g., defect detection, sound insulation, or structures with optimized mechanical properties. This work focuses on the instrumentation of 3D printed samples with actuators and measurement labels, the creation of an experimental setup and the mea-\nsurement of initial high frequency mechanical wave propagation experiments
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2026-01-11
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Acoustic metamaterials with flexoelectric or piezoelectric microstructures incorporating electric circuits
Rohan, E. ; Cimrman, Robert
We consider periodic elastic microstructures composed of flexoelectric, or piezoelectric materials and involving electrodes which enable for control of the response due to the electromechanical transmission and tunable external electric circuits (EEC). Moreover, large contrast in the stiffness of the microstructure constituents provide the band gap property of such acoustic metamaterials which are derived using the asymptotic homogenization. The wave dispersion analysis based on the Bloch theorem shows the influence of the EEC.
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2026-01-11
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Solving piezoelastic problems on periodic lattices using block preconditioners
Cimrman, Robert
Polymer materials, such as polyvinylidene fluoride (PVDF), can be polarized duri ng or after the 3D printing process, making them suitable for producing electroa ctive metamaterials. A 3D-printed periodic lattice made of such a piezoelectric material can then exhibit electroactivity that differs from that of the original material. One example is flexoelectricity, in which the electric polarization i s coupled with the strain gradient instead of the strain. Designing such periodi c lattices requires the ability to perform numerical simulations efficiently. Th is work presents an approach based on\niterative solvers preconditioned by state- of-the-art preconditioners, such as the cell-by-cell Schur complement preconditi oner. The performance of these solvers, as implemented in the open-source finite element code SfePy, is demonstrated by numerical examples showing the convergen ce of the solvers for various levels of uniform mesh refinement or different arr angements of a\nreference periodic cell.
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2026-01-11
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Synthetic Jet Array for Active Control of Laminar Channel Flow
Antošová, Zuzana ; Trávníček, Zdeněk
The study focuses on an experimental investigation of a synthetic jet (SJ) array. The array is studied with respect to its future use as array of vortex generating jets in a low-speed (laminar) cross-flow in closed channel. Two driving mechanisms for SJ actuators were tested - piezoelectric transducer and solenoid (magnetic shaker). Bothperpendicular and inclined jet exit orifices with diameter D = 2.1 mm were studied. From the preliminary test it can be concluded that perpendicular jets penetrate further to its surroundings than the inclined ones, while the inclined ones interact more with each other, which leads to desired vortex structures necessary for the creation ofquasi-turbulent flow in the channel.
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2026-01-11
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Validated high-pressure vibrating tube densimeter for accurate fluid density data at pressures up to 600 bar
Prokopová, Olga ; Čenský, Miroslav ; Hénin, Nicolas ; Blahut, Aleš ; Součková, Monika ; Vinš, Václav
Vibrating tube densimeters (VTDs) have been widely used over the past fifty years for accurate density measurements of gases and liquids. These instruments determine fluid density by measuring the natural frequency of a U- or V-shaped tube filled with the sample, when the added mass of the fluid changes the tube's vibration characteristics [J. Chem. Thermodynamics 173 (2022) 106855].\nThis study presents the design and testing of an in-house designed and built support system for the Anton Paar DMA HP densimeter, a commercial high-pressure VTD. The instrument is capable of measuring densities from 0 to 3000 kg/m³ at pressures up to 700 bar and temperatures ranging from -10 to 200 °C. While the device includes internal temperature control via a Peltier thermal block, pressure must be externally generated and controlled. For this purpose, a high-pressure sampling system was developed.\nGiven that density measurements are highly sensitive to temperature, particular attention was paid to accurate temperature monitoring. In addition to the built-in Peltier control, we installed an external resistance Pt100 thermometer connected to a precision thermometry bridge, with the sensor placed in the center of the measuring U-shaped cell. To prevent moisture condensation during experiments, the VTD was enclosed in a dry box of own design.\nWe describe the technical details of the setup, including the calibration procedures for both pressure and temperature sensors. Results for the temperature dependence of fluid density at pressures up to 600 bar are presented for several reference liquids—water, ethanol, and ethylene glycol—and compared with standard reference data. Calibration of the U-tube cell at high pressure was performed using vacuum and an ultrapure water. To relate density to the vibration period, several calibration models were considered such as the Anton Paar model, polynominal model by Oucalt [J. Res. Natl. Inst. Stan. 123 (2018), 123017], or a physically-based model considering material and mechanical properties of a Hastelloy cell by May et al. [Rev. Sci. Instrum. 85 (2014), 095111]. The instrument was found to provide promising results with the uncertainty of around 0.1 % for the selected liquids.
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2026-01-11
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Studie proveditelnosti ekologické změny tepelného zpracování pokročilými technologiemi ve vzájemné korelaci kvalitativních změn vlastností a ekologické zátěže.
Štěpánek, Ivo ; Štěpánová, Lucie ; Pechová, Andrea ; Kesl, M. ; Štěpán, V.
Studie proveditelnosti se zabývá proveditelností ekologické transformace procesů tepelného zpracování se zaměřením na korelace mezi technologickými parametry a mechanicko – strukturními vlastnostmi ve vazbě na vybrané materiálové jakosti a požadavky na funkční vlastnosti výrobků. Výzkum hodnotí možnosti náhrady konvenčních, environmentálně zatěžujících médií (zejména solných lázní s obsahem baria) ekologičtějšími alternativami v celém spektru procesů – od předehřevu, austenitizace, kalení až po popouštění. Pro kompenzaci kvalitativní ztráty i pro dosažení vyšší přidané hodnoty jsou zkoumány kombinace s chemicko-tepelným zpracováním a pokročilými metodami PVD depozice (zejména nízkonapěťovým obloukovým odpařováním ve vakuu). Pro bezpečnější využití solných lázní jsou voleny alternativy solí a metody zvyšování životnosti komponent pecí zejména kelímků optimalizovanou volbou materiálových jakostí v kombinaci s povrchovými úpravami. Studie proveditelnosti se následně zabývá ekonomickými rozvahami a návrhem navazujících projektových cest pro vývoj a produkci inovativních produktů s vysokými přidanými hodnotami do reálných provozních podmínek. Projekt je řešen v rámci výzvy OP TAK – Proof of Concept, aktivita a).
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