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Consistency of mathematical and experimental model of the autoparametric system
Fischer, Cyril; Náprstek, Jiří
2023 - English
This paper presents a long-overdue comparison of data obtained from experimental investigation of a spherical vibration absorber with the results of two mathematical models of the motion of a heavy sphere in a spherical surface. It shows that the danger posed by the potentially unstable self-parametric nature of the mathematical system is not too great in the case of realistic configurations, and that the values of the parameters describing the realistic structures remain within intervals corresponding to the stable behaviour of the absorber.
Keywords:
vibration absorber; rolling sphere; spherical surface; autoparametric system; structural health monitoring
Available at various institutes of the ASCR
Consistency of mathematical and experimental model of the autoparametric system
This paper presents a long-overdue comparison of data obtained from experimental investigation of a spherical vibration absorber with the results of two mathematical models of the motion of a heavy ...
Comparison of finite element simulation of tungsten nanoindentation with Berkovich and conical indenter
Fiala, L.; Ballo, I.; Kovář, J.; Fuis, Vladimír
2023 - English
Finite Element Method (FEM) was used to study the difference between using Berkovich and conical indenters in nanoindentation test of tungsten specimen. The study was aimed to determine the\nmodulus of elasticity of a tested specimen and how it changes with different indenter. The FEM analysis also revealed that the modulus of elasticity was sensitive to the dimensions of both specimen and the indenter for which were made several numerical calculations with different dimensions.
Keywords:
nanoindentation; FEM; Berkovich indenter; conical indenter; tungsten
Available at various institutes of the ASCR
Comparison of finite element simulation of tungsten nanoindentation with Berkovich and conical indenter
Finite Element Method (FEM) was used to study the difference between using Berkovich and conical indenters in nanoindentation test of tungsten specimen. The study was aimed to determine the\nmodulus ...
Mechanical properties of basalt: a study on compressive loading at different strain rates using SHPB
Falta, J.; Krčmářová, N.; Fíla, T.; Vavro, Martin; Vavro, Leona
2023 - English
This article focuses on the mechanical properties of basalt in compressive loading at different strain-rates. The study employs advanced instrumentation for the evaluation of the results in dynamic conditions, while standard uni-axial loading device is used for evaluation in quasi-static conditions. Basalt specimens were subjected to four different loading-rates from 200–600 s−1 on which the stress-strain dependence was evaluated together with DIC analysis of crack initiation and disintegration process. Understanding the mechanical properties of basalt can provide insights for engineers and designers in creating structures that are durable and able to withstand different loading conditions. The findings of this study can have implications for a wide range of industries, including aerospace, automotive, and construction, among others.
Keywords:
SHPB; basalt; compressive loading; dynamic loading
Available at various institutes of the ASCR
Mechanical properties of basalt: a study on compressive loading at different strain rates using SHPB
This article focuses on the mechanical properties of basalt in compressive loading at different strain-rates. The study employs advanced instrumentation for the evaluation of the results in dynamic ...
Asynchronous time integration while achieving zero interface energy
Dvořák, Radim; Kolman, Radek; Falta, J.; Neühauserová, M.
2023 - English
This contribution deals with an asynchronous direct time integration of the finite-element model. The proposed method is applied to the phenomenon of wave propagation through an elastic linear continuum. The numerical model is partitioned into individual subdomains using the domain decomposition method by means of localized Lagrange multipliers. For each subdomain, different time discretizations are used. No restrictions for relation between subdomain’s time steps are imposed. The coupling of the subdomains is forced by an acceleration continuity condition. Additionally, we use the a posteriori technique to also provide the displacement and velocity continuity at the interfaces, and hence we obtain exact continuity of all three kinematic fields. The proposed method is experimentally validated using the modified SHPB (split Hopkinson pressure bar) setup.
Keywords:
finite element method; direct time integration; asynchronous integration; domain decomposition; localized lagrange multipliers
Available at various institutes of the ASCR
Asynchronous time integration while achieving zero interface energy
This contribution deals with an asynchronous direct time integration of the finite-element model. The proposed method is applied to the phenomenon of wave propagation through an elastic linear ...
Optical and Pneumatic Measurements on TR-U-11 Cascade
Luxa, Martin; Hála, Jindřich; Šimurda, David
2023 - English
The report contains results and evaluation of conducted optical (interferometry and schlieren technique) and pneumatic measurements on the first variant of the new tip section, intended for turbine rotor blade.
Keywords:
transonic flow; rotor turbine blade; tip section
Available at various institutes of the ASCR
Optical and Pneumatic Measurements on TR-U-11 Cascade
The report contains results and evaluation of conducted optical (interferometry and schlieren technique) and pneumatic measurements on the first variant of the new tip section, intended for turbine ...
Ambiguity in Stochastic Optimization Problems with Nonlinear Dependence on a Probability Measure via Wasserstein Metric
Kaňková, Vlasta
2023 - English
Many economic and financial applications lead to deterministic optimization problems depending on a probability measure. It happens very often (in applications) that these problems have to be solved on the data base. Point estimates of an optimal value and estimates of an optimal solutionset can be obtained by this approach. A consistency, a rate of convergence and normal properties, of these estimates, have been discussed (many times) not only under assumptions of independent data corresponding to the distributions with light tails, but also for weak dependent data and the distributions with heavy tails. However, it is also possible to estimate (on the data base) a confidence intervals and bounds for the optimal value and the optimal solutions. To analyze this approach we focus on a special case of static problems depending nonlineary on the probability measure. Stability results based on the Wasserstein metric and the Valander approach will be employed for the above mentioned analysis.
Keywords:
Stochastic optimization problems; static problems; empirical measure; point estimates; interval estimates; nonlinear dependence
Fulltext is available at external website.
Ambiguity in Stochastic Optimization Problems with Nonlinear Dependence on a Probability Measure via Wasserstein Metric
Many economic and financial applications lead to deterministic optimization problems depending on a probability measure. It happens very often (in applications) that these problems have to be solved ...
The design of Bayesian diagnostic expert system Querix and it’s engineering application
Věchet, Stanislav; Krejsa, Jiří; Chen, K.-S.
2023 - English
Expert systems have gained attention over the last two decades as they bring the possibility of using expert knowledge in various control systems. However, it has lost attraction in favor of artificial neural networks in recent years, which is mostly influenced by the availability of data to train neural network models and the availability of various frameworks to achieve fast time-to-market applications for given solutions.
Keywords:
expert system; decision making; advanced diagnostic; autonomous navigation; RPA
Available at various institutes of the ASCR
The design of Bayesian diagnostic expert system Querix and it’s engineering application
Expert systems have gained attention over the last two decades as they bring the possibility of using expert knowledge in various control systems. However, it has lost attraction in favor of ...
Statistical Approach for BTT probes distribution
Mekhalfia, Mohammed Lamine; Procházka, Pavel; Šmíd, R.; Tchawou Tchuisseu, Eder Batista
2023 - English
Blade tip timing (BTT) system is a non-invasive method used for measuring the blade tip timing of rotating machinery. The BTT system typically consists of sensor probes, signal conditioning system, and data acquisition unit. The sensor probes are placed in proximity to the rotating blade tips, Sensors measure the time at which each blade passes by the probe. By measuring the blade tip timing, the BTT system can detect changes in the blade tip vibration, which is an important for the health monitoring and performance optimization of rotating machinery [1]. To ensure accurate measurement of blade tip timing, the probe arrangement is crucial. The placement of the probe relative to the blade tips can affect the measurement accuracy, and thus, several arrangement algorithms have been developed to optimize the placement of the probes. Instead of considering the condition number, a statistical algorithms is followed to optimize the placement of probes for accurate measurement of blade tip timing in turbo-machinery. The statistical approach will be employed to determine the optimal locations for probes, with the aim of reducing errors in the measurement of blade tip timing. \n
Keywords:
blade tip timing principle; RMSE; blade´s dynamics
Available at various institutes of the ASCR
Statistical Approach for BTT probes distribution
Blade tip timing (BTT) system is a non-invasive method used for measuring the blade tip timing of rotating machinery. The BTT system typically consists of sensor probes, signal conditioning system, ...
Programs and Algorithms of Numerical Mathematics 21 : Jablonec nad Nisou, June 19-24, 2022 : Proceedings of Seminar
Chleboun, J.; Kůs, Pavel; Papež, Jan; Rozložník, Miroslav; Segeth, Karel; Šístek, Jakub
2023 - English
These proceedings contain peer-reviewed papers that are based on the invited lectures, short communications, and posters presented at the 21st seminar Programs and Algorithms of Numerical Mathematics (PANM) held in Merkur Hotel, Jablonec nad Nisou, Czech Republic, June 19-24, 2022.\nThe seminar was organized by the Institute of Mathematics of the Czech Academy of Sciences under the auspices of EU-MATHS-IN.CZ, Czech Network for Mathematics in Industry, and with the nancial support provided by the RSJ Foundation. It continued the previous seminars on mathematical software and numerical methods held (biennially, with only one exception) in Alšovice, Bratříkov, Janov nad Nisou, Kořenov, Lázně Libverda, Dolní Maxov, Prague, and Hejnice in the period 1983-2020. The objective of this series of seminars is to provide a forum for presenting and discussing advanced topics in numerical analysis, computer implementation of numerical algorithms, new approaches to mathematical modeling, and single- or multi-processor applications of computational methods.
Keywords:
numerical mathematics
Available in digital repository of the ASCR
Programs and Algorithms of Numerical Mathematics 21 : Jablonec nad Nisou, June 19-24, 2022 : Proceedings of Seminar
These proceedings contain peer-reviewed papers that are based on the invited lectures, short communications, and posters presented at the 21st seminar Programs and Algorithms of Numerical Mathematics ...
Statistical Method Selection Matters: Vanilla Methods in Regression May Yield Misleading Results
Kalina, Jan
2023 - English
The primary aim of this work is to illustrate the importance of the choice of the appropriate methods for the statistical analysis of economic data. Typically, there exist several alternative versions of common statistical methods for every statistical modeling task\nand the most habitually used (“vanilla”) versions may yield rather misleading results in nonstandard situations. Linear regression is considered here as the most fundamental econometric model. First, the analysis of a world tourism dataset is presented, where the number of international arrivals is modeled for 140 countries of the world as a response of 14 pillars (indicators) of the Travel and Tourism Competitiveness Index. Heteroscedasticity is clearly recognized in the dataset. However, the Aitken estimator, which would be the standard remedy in such a situation, is revealed here to be very inappropriate. Regression quantiles represent a much more suitable solution here. The second illustration with artificial data reveals standard regression quantiles to be unsuitable for data contaminated by outlying values. Their recently proposed robust version turns out to be much more appropriate. Both\nillustrations reveal that choosing suitable methods represent an important (and often difficult) part of the analysis of economic data.
Keywords:
linear regression; assumptions; non-standard situations; robustness; diagnostics
Fulltext is available at external website.
Statistical Method Selection Matters: Vanilla Methods in Regression May Yield Misleading Results
The primary aim of this work is to illustrate the importance of the choice of the appropriate methods for the statistical analysis of economic data. Typically, there exist several alternative versions ...
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