Aerodynamic Measurements on Transonic Compressor Blade Cascades KR-D-9 and KR-D-10
Šimurda, David; Hála, Jindřich; Luxa, Martin
2023 - anglický This report contains results and evaluation of aerodynamic measurements conducted on two variant transonic compressor blade cascades with MCA profile (KR-D-10) and DCA profile (KR-D-9) at transonic flow regimes. Klíčová slova: compressor blade cascade; experiment; transonic flow; MCA profile; DCA profile Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR. Aerodynamic Measurements on Transonic Compressor Blade Cascades KR-D-9 and KR-D-10

This report contains results and evaluation of aerodynamic measurements conducted on two variant transonic compressor blade cascades with MCA profile (KR-D-10) and DCA profile (KR-D-9) at transonic ...

Šimurda, David; Hála, Jindřich; Luxa, Martin
Ústav termomechaniky, 2023

Interpolation with restrictions -- role of the boundary conditions and individual restrictions
Valášek, Jan; Sváček, P.
2023 - anglický The contribution deals with the remeshing procedure between two computational finite element meshes. The remeshing represented by the interpolation of an approximate solution onto a new mesh is needed in many applications like e.g. in aeroacoustics, here we are particularly interested in the numerical flow simulation of a gradual channel collapse connected with a~severe deterioration of the computational mesh quality. Since the classical Lagrangian projection from one mesh to another is a dissipative method not respecting conservation laws, a conservative interpolation method introducing constraints is described. The constraints have form of Lagrange multipliers enforcing conservation of desired flow quantities, like e.g. total fluid mass, flow kinetic energy or flow potential energy. Then the interpolation problem turns into an error minimization problem, such that the resulting quantities of proposed interpolation satisfy these physical properties while staying as close as possible to the results of Lagrangian interpolation in the L2 norm. The proposed interpolation scheme does not impose any restrictions on mesh generation process and it has a relatively low computational cost. The implementation details are discussed and test cases are shown. Klíčová slova: interpolation; Lagrange multiplier; Lagrange projection Plné texty jsou dostupné v digitálním repozitáři Akademie Věd. Interpolation with restrictions -- role of the boundary conditions and individual restrictions

The contribution deals with the remeshing procedure between two computational finite element meshes. The remeshing represented by the interpolation of an approximate solution onto a new mesh is needed ...

Valášek, Jan; Sváček, P.
Matematický ústav, 2023

Dynamics of dissolved organic carbon in surface water during extreme rainfall-runoff events
Matoušková, M.; Fraindová, K.; Bejčková, M.; Kliment, Z.; Vlach, V.; Vlček, Lukáš
2023 - anglický The release of a greater amount of natural organic matter (NOM) within climate change is registered in many catchments with peatbog areas. The aim of our research is to study the dynamics of releasing dissolved organic carbon (DOC) into surface water in headwater areas with peatbogs. DOC concentrations are analysed in relation to extreme rainfall-runoff (R-R) events and according to the hydrological preconditions of the basin. These preconditions are described using selected hydroclimatic variables (14 days before the R-R event). The source data comes from stations of the Faculty of Science, Charles University, and the Czech Hydrometeorological Institute. For the evaluation of relations and processes, the Principal component analysis (PCA), hysteresis loops or Pearson correlation coefficient was used. The lag time of DOCmax for Qmax, the dependence of DOCmax and groundwater levels were studied. The influence of flow rate on the decline and ascent phases of DOC\nconcentrations by hysteresis loops and the influence of the number of partial flow maximums on the amount of transported DOC during the R-R event was analysed. Our first results show that great influence on the dynamic of DOC concentration in surface water has the change in groundwater-levels in the peatbog and the outflow amount during the R-R event. The hydroclimatic preconditions of the basin have also a significant influence on the DOC release. Changes in concentrations during R-R events also occurred for other compounds that were studied additionally. Particularly significant was the increase in metals (mainly Fe, Al, Mn) and base cation (K) and decrease in nitrate nitrogen. Klíčová slova: natural organic matter; dissolved organic carbon; peatbog; surface water Dokument je dostupný na externích webových stránkách. Dynamics of dissolved organic carbon in surface water during extreme rainfall-runoff events

The release of a greater amount of natural organic matter (NOM) within climate change is registered in many catchments with peatbog areas. The aim of our research is to study the dynamics of releasing ...

Matoušková, M.; Fraindová, K.; Bejčková, M.; Kliment, Z.; Vlach, V.; Vlček, Lukáš
Ústav pro hydrodynamiku, 2023

Some Robust Approaches to Reducing the Complexity of Economic Data
Kalina, Jan
2023 - anglický The recent advent of complex (and potentially big) data in economics requires modern and effective tools for their analysis including tools for reducing the dimensionality (complexity) of the given data. This paper starts with recalling the importance of Big Data in economics and with characterizing the main categories of dimension reduction techniques. While there have already been numerous techniques for dimensionality reduction available, this work is interested in methods that are robust to the presence of outlying measurements (outliers) in the economic data. Particularly, methods based on implicit weighting assigned to individual observations are developed in this paper. As the main contribution, this paper proposes three novel robust methods of dimension reduction. One method is a dimension reduction within a robust regularized linear regression, namely a sparse version of the least weighted squares estimator. The other two methods are robust versions of feature extraction methods popular in econometrics: robust principal component analysis and robust factor analysis. Klíčová slova: dimensionality reduction; Big Data; variable selection; robustness; sparsity Dokument je dostupný na externích webových stránkách. Some Robust Approaches to Reducing the Complexity of Economic Data

The recent advent of complex (and potentially big) data in economics requires modern and effective tools for their analysis including tools for reducing the dimensionality (complexity) of the given ...

Kalina, Jan
Ústav teorie informace a automatizace, 2023

Statistical Method Selection Matters: Vanilla Methods in Regression May Yield Misleading Results
Kalina, Jan
2023 - anglický 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 and 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 illustrations reveal that choosing suitable methods represent an important (and often difficult) part of the analysis of economic data. Klíčová slova: linear regression; assumptions; non-standard situations; robustness; diagnostics Dokument je dostupný na externích webových stránkách. 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 ...

Kalina, Jan
Ústav informatiky, 2023

Fractionally Isomorphic Graphs and Graphons
Hladký, Jan; Hng, Eng Keat
2023 - anglický Fractional isomorphism is a well-studied relaxation of graph isomorphism with a very rich theory. Grebík and Rocha [Combinatorica 42, pp 365–404 (2022)] developed a concept of fractional isomorphism for graphons and proved that it enjoys an analogous theory. In particular, they proved that if two sequences of graphs that are fractionally isomorphic converge to two graphons, then these graphons are fractionally isomorphism. Answering the main question from ibid, we prove the converse of the statement above: If we have two fractionally isomorphic graphons, then there exist sequences of graphs that are fractionally isomorphic converge and converge to these respective graphons. As an easy but convenient corollary of our methods, we get that every regular graphon can be approximated by regular graphs. Klíčová slova: graph; graphon; graph fractional isomorphism Plné texty jsou dostupné v digitálním repozitáři Akademie Věd. Fractionally Isomorphic Graphs and Graphons

Fractional isomorphism is a well-studied relaxation of graph isomorphism with a very rich theory. Grebík and Rocha [Combinatorica 42, pp 365–404 (2022)] developed a concept of fractional isomorphism ...

Hladký, Jan; Hng, Eng Keat
Ústav informatiky, 2023

Summary of the Liquid-Gas Ejector Hydraulic Behavior - Theory and Practice
Gebouský, Ondřej; Haidl, Jan
2023 - anglický Liquid-gas ejectors (LGEs) are fascinating devices that use the kinetic energy of the liquid jet to entrain and eventually compress the gas. LGEs find applications in both industry and everyday life, e.g., as sprayers. However, a complex and reliable method for LGE design was not available in the open literature until recently. This contribution follows up on our recent works about the hydraulic behavior of LGE with undisturbed and destabilized liquid jets. This paper aims to summarize the device’s complicated hydraulics and characterize its optimal design for three industrially relevant applications - (a) LGE as the vacuum pump, (b) LGE as the gas purification equipment, and (c) LGE as the gas distributor for bioreactors. Klíčová slova: liquid-gas ejector; jet pump; design method Plné texty jsou dostupné v digitálním repozitáři Akademie Věd. Summary of the Liquid-Gas Ejector Hydraulic Behavior - Theory and Practice

Liquid-gas ejectors (LGEs) are fascinating devices that use the kinetic energy of the liquid jet to entrain and eventually compress the gas. LGEs find applications in both industry and everyday life, ...

Gebouský, Ondřej; Haidl, Jan
Ústav pro hydrodynamiku, 2023

Jánovce. Paleomagnetic research. Report
Elbra, Tiiu; Kdýr, Šimon; Uçar, Hakan; Pruner, Petr; Schnabl, Petr
2023 - anglický Klíčová slova: Jánovce archeological site; Paleomagnetism; Rock magnetism Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR. Jánovce. Paleomagnetic research. Report

Elbra, Tiiu; Kdýr, Šimon; Uçar, Hakan; Pruner, Petr; Schnabl, Petr
Geologický ústav, 2023

Dynamics of a cantilever beam with piezoelectric sensor: Parameter identification
Cimrman, Robert; Kolman, Radek; Musil, Ladislav; Kotek, Vojtěch; Kylar, Jaromír
2023 - anglický 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. Klíčová slova: finite element method; piezo-electricity; floating potential; dynamic simulation; parameter identification Dokument je dostupný na externích webových stránkách. 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 ...

Cimrman, Robert; Kolman, Radek; Musil, Ladislav; Kotek, Vojtěch; Kylar, Jaromír
Ústav termomechaniky, 2023

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 - anglický 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. Klíčová slova: yield surface distortion; strain hardening; multiaxial ratcheting; flow rule Dokument je dostupný na externích webových stránkách. 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 ...

Svárovský, Jiří; Parma, Slavomír; Štefan, Jan; Ciocanel, C.; Feigenbaum, H. P.; Marek, René; Klepač, Vilém; Plešek, Jiří
Ústav termomechaniky, 2023