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Dynamics of a cantilever beam with piezoelectric sensor: Finite element modeling
Cimrman, Robert; Kolman, Radek; Musil, Ladislav; Kotek, Vojtěch; Kylar, Jaromír
2023 - English
An elastodynamical model of a cantilever beam coupled with a piezoelectric sensor is introduced and its discretization using the finite element method is presented. The mathematical model includes additional terms that enforce the floating potential boundary condition for keeping a constant charge on an electrode of the sensor. The behaviour of the model is illustrated using a numerical example corresponding to an experimental setup, where vibrations of the beam and the potential on the sensor are measured.
Keywords:
finite element method; piezo-electricity; floating potential; dynamic simulation
Fulltext is available at external website.
Dynamics of a cantilever beam with piezoelectric sensor: Finite element modeling
An elastodynamical model of a cantilever beam coupled with a piezoelectric sensor is introduced and its discretization using the finite element method is presented. The mathematical model includes ...
Topical Problems of Fluid Mechanics 2023
Šimurda, David; Bodnár, T.
2023 - English
Proceedings contain collection of papers presented during the conference Topical Problems of Fluid Mechanics 2023. Majority of papers is concerned with numerical simulations covering wide range of applications in fluid mechanics.\n
Keywords:
experimental fluid mechanics; mathematical modelling; CFD; turbulence; stratified fluid; multiphase flow; vortex structures; supersonic flow
Available at various institutes of the ASCR
Topical Problems of Fluid Mechanics 2023
Proceedings contain collection of papers presented during the conference Topical Problems of Fluid Mechanics 2023. Majority of papers is concerned with numerical simulations covering wide range of ...
Dynamics of a cantilever beam with piezoelectric sensor: Parameter identification
Cimrman, Robert; Kolman, Radek; Musil, Ladislav; Kotek, Vojtěch; Kylar, Jaromír
2023 - English
The piezoelectric materials are electroactive materials often applied for real-time sensing or structural health monitoring, both important research topics in dynamics. Mathematical models of such structures have to allow also for the external electrical circuits and contain several material parameters that need to be identified from experiments. We present a model of a simple experiment involving dynamics of a cantilever beam with an attached piezoelectric sensor excited by a suddenly removed weight. The external circuit can be taken into account as having either a finite or infinite resistance. We also outline the parameter identification procedure based on automatic differentiation and present the experimental and numerical results.
Keywords:
finite element method; piezo-electricity; floating potential; dynamic simulation; parameter identification
Fulltext is available at external website.
Dynamics of a cantilever beam with piezoelectric sensor: Parameter identification
The piezoelectric materials are electroactive materials often applied for real-time sensing or structural health monitoring, both important research topics in dynamics. Mathematical models of such ...
Modální analýza pryží odpruženého kola Stadler se dvěma variantami listových tlumičů
Šnábl, Pavel; Pešek, Luděk; Bula, Vítězslav
2023 - Czech
Cílem těchto modálních analýz bylo identifikovat vlastní frekvence a tlumení pryžo-odpruženého kola a porovnat jak obě varianty tlumičů mezi sebou sebou, tak s dřívějším měřením gumo-odpruženého kola typu Stadler bez tlumičů. Experimentální modální analýza probíhala v laboratoři ÚT s použitím jednobodového buzení (SIMO) na pryžo-odpruženém kole. Z této dynamické analýzy byly získány vlastní frekvence a tvary kmitání kola v pásmu do 6,4 kHz. Následně byly provedeny i detailnější analýzy v úzkém frekvenčním pásmu zaměřené na chování tlumičů se smykovým elementem v důležitých rezonancích pro vznik valivého a kvílivého hluku. The aim of this work was an experimental modal analysis of the Stadler tram wheel for two shock absorber variants: a) standard leaf shocks, b) leaf shear shocks. In the report the measurement methodology is described and the results of the modal analysis are tabulated. The results of the modal behaviour of each damper variant give an assessment of their effectiveness in suppressing significant resonances and the corresponding mode shapes. Standard leaf dampers designed as an open steel-rubber sandwich contributed most to the damping enhancement for the R3 shape, followed by R2. Newly developed leaf shear dampers provided a significant increase in damping for the R2 shape compared to standard dampers.
Keywords:
rail-way wheel; vibration dampers; modal analysis
Available at various institutes of the ASCR
Modální analýza pryží odpruženého kola Stadler se dvěma variantami listových tlumičů
Cílem těchto modálních analýz bylo identifikovat vlastní frekvence a tlumení pryžo-odpruženého kola a porovnat jak obě varianty tlumičů mezi sebou sebou, tak s dřívějším měřením gumo-odpruženého kola ...
Development of autonomous experimental system to analyse yield surfaces distortion due to multiaxial ratcheting
Svárovský, Jiří; Parma, Slavomír; Štefan, Jan; Ciocanel, C.; Feigenbaum, H. P.; Marek, René; Klepač, Vilém; Plešek, Jiří
2023 - English
Multiaxial ratcheting is a failure mode of structures characterized by the accumulation of plastic strain due to cyclic loading. Despite several models having been developed to predict multiaxial ratcheting, they often fail when validated with experimental data collected under a wide array of loading conditions. In this study, an experimental setup was developed and an autonomous testing procedure was used to experimentally analyze the evolution of the yield surface shape due to cyclic biaxial loading. Thin-walled tubular test specimens were made of 304L steel with a diameter of 40mm and underwent axial-torsional testing using the Instron 8852 system. The total axial strain was increased from 0 to 1% while the total shear strain underwent 5 cycles with the strain amplitude of 0.5% and the mean strain of 0.5%. Three yield surfaces were measured after the straining sequence was completed. Results showed strong directional distortional hardening and good agreement between the flow vectors and the normals to the yield surface, lending support to the associative flow rule.
Keywords:
yield surface distortion; strain hardening; multiaxial ratcheting; flow rule
Fulltext is available at external website.
Development of autonomous experimental system to analyse yield surfaces distortion due to multiaxial ratcheting
Multiaxial ratcheting is a failure mode of structures characterized by the accumulation of plastic strain due to cyclic loading. Despite several models having been developed to predict multiaxial ...
Vyjádření ke zprávě ÚJV DITI 2301/1308 – Analýzy dopadu zvýšení výkonu na hodnocení radiačního bobtnání, radiačního tečení a IASCC VČR
Štefan, Jan; Gabriel, Dušan
2023 - Czech
Tato technická zpráva byla vypracována pro Státní úřad pro jadernou bezpečnost v rámci expertní podpory v oblasti hodnocení pevnosti a životnosti. Zpráva byla zpracována jako posudek k technické zprávě: ÚJV DITI 2301/1308: Analýzy dopadu zvýšení výkonu na hodnocení radiačního bobtnání, radiačního tečení a IASCC VČR, vypracované pracovníky oddělení Hodnocení pevnosti a životnosti ÚJV Řež, a. s. Účelem zprávy T575/23 bylo podat SÚJB nezávislé vyjádření k výrokům autorů zprávy ÚJV. V souladu s požadavkem SÚJB byl při zpracování posudku kladen důraz zejména na materiálové aspekty dané problematiky. Posuzovatel zaujal k předložené zprávě ÚJV souhlasné stanovisko s jedinou významnější námitkou vůči jednomu aspektu problematiky radiačního bobtnání a s několika minoritními připomínkami vesměs formální povahy. This technical report has been elaborated for the State Office for Nuclear Safety (SÚJB) in the framework of expert support in the field of strength and durability assessment. The report was elaborated as a review on the technical report: ÚJV DITI 2301/1308: Analýzy dopadu zvýšení výkonu na hodnocení radiačního bobtnání, radiačního tečení a IASCC VČR elaborated by the staff of the Strength and lifetime evaluation department of ÚJV Řež, a. s. The purpose of the report T575/23 was to provide the SÚJB with an independent review of the statements made by the authors of the ÚJV report. In accordance with the requirement of SÚJB, the emphasis was placed on the material aspects of the issue. The reviewer expressed a favourable attitude towards the submitted UJV report with only one major objection to one aspect of the issue of radiation swelling and a few minor comments of a mostly formal nature.
Keywords:
nuclear energy; material engineering; safety assessment
Available at various institutes of the ASCR
Vyjádření ke zprávě ÚJV DITI 2301/1308 – Analýzy dopadu zvýšení výkonu na hodnocení radiačního bobtnání, radiačního tečení a IASCC VČR
Tato technická zpráva byla vypracována pro Státní úřad pro jadernou bezpečnost v rámci expertní podpory v oblasti hodnocení pevnosti a životnosti. Zpráva byla zpracována jako posudek k technické ...
Numerical minimization of energy functionals in continuum mechanics using hp-FEM in MATLAB
Moskovka, Alexej; Frost, Miroslav; Valdman, Jan
2023 - English
Many processes in mechanics and thermodynamics can be formulated as a minimization of a particular energy functional. The finite element method can be used for an approximation of such functionals in a finite-dimensional subspace. Consequently, the numerical minimization methods (such as quasi-Newton and trust region) can be used to find a minimum of the functional. Vectorization techniques used for the evaluation of the energy together with the assembly of discrete energy gradient and Hessian sparsity are crucial for evaluation times. A particular model simulating the deformation of a Neo-Hookean solid body is solved in this contribution by minimizing the corresponding energy functional. We implement both P1 and rectangular hp-finite elements and compare their efficiency with respect to degrees of freedom and evaluation times.
Keywords:
hp-FEM; energy functionals; numerical minimization
Fulltext is available at external website.
Numerical minimization of energy functionals in continuum mechanics using hp-FEM in MATLAB
Many processes in mechanics and thermodynamics can be formulated as a minimization of a particular energy functional. The finite element method can be used for an approximation of such functionals in ...
Předběžné výsledky měření na HVAC jednotce pro H2-Bus s chladivy R454C a R513A
Blahut, Aleš; Kordík, Jozef; Šulc, V.; Vinš, Václav
2023 - Czech
Technická zpráva shrnuje předběžné vyhodnocení experimentálních zkoušek chladící jednotky a tepelného čerpadla (HVAC) pro vodíkový autobus s chladivy R454C a R513A. V klimakomoře Elektrotechnického zkušebního ústavu, s. p. v Praze Troji byla v říjnu 2023 podrobně testována zkušební HVAC jednotka v režimech klimatizace a tepelného čerpadla při teplotách okolí od -25 °C do +45 °C. Ve zprávě jsou analyzovány základní výkonové parametry HVAC jednotky zahrnující topný a chladící výkon na kondenzátoru, resp. výparníku, topné a chladící faktory okruhu a izoentropickou účinnost kompresoru.
Available at various institutes of the ASCR
Předběžné výsledky měření na HVAC jednotce pro H2-Bus s chladivy R454C a R513A
Technická zpráva shrnuje předběžné vyhodnocení experimentálních zkoušek chladící jednotky a tepelného čerpadla (HVAC) pro vodíkový autobus s chladivy R454C a R513A. V klimakomoře Elektrotechnického ...
The influence of first CNN layer initialization on training convergence
Krejsa, Jiří; Věchet, Stanislav; Chen, K.S.
2023 - English
During evaluation of convolution neural networks on the task of sign language single hand alphabet classification we have discovered that in small but not negligible number of cases the training of the network does not converge at all. This paper investigates the problem that we believe is independent of the application. While the true cause of training divergence was not discovered, we can offer the reader an easy solution from practical point of view – initialization of the first CNN layer using pretrained networks parameters.
Keywords:
convolution neural networks; training; initialization
Available at various institutes of the ASCR
The influence of first CNN layer initialization on training convergence
During evaluation of convolution neural networks on the task of sign language single hand alphabet classification we have discovered that in small but not negligible number of cases the training of ...
Post-processing the results of the topology optimization with the level set technique
Ježek, Ondřej; Kopačka, Ján; Gabriel, Dušan
2023 - English
Topology optimization (TO) has come to the fore with the development of 3D printing. The most commonly used method is SIMP, a density-based approach, which outputs a per-element constant density field and thus requires post-processing to obtain the shape. Conventional post-processing methods extract optimized topologies in the form of brep models. It yields only C0 continuous geometries, which are usually not suitable for downstream applications such as prototyping, design validation, and design exploration. In this paper, we present a new post-processing method based on the level set principle that overcomes common post-processing issues, such as the lack of smoothness.
Keywords:
topology optimization; post-processing; level-set; signed distance function
Available at various institutes of the ASCR
Post-processing the results of the topology optimization with the level set technique
Topology optimization (TO) has come to the fore with the development of 3D printing. The most commonly used method is SIMP, a density-based approach, which outputs a per-element constant density field ...
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