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Modification of cooling system for laboratory measurement of rotor blade vibration
Maturkanič, Dušan; Procházka, Pavel; Hodboď, Robert; Voronova, Evgeniya; Mekhalfia, Mohammed Lamine
2024 - English
Last year, the replacement of the turbine wheel model was completed in the Laboratory of Rotational Laser Vibrometry of the Institute of Thermomechanics AS CR, v.v.i. Based on previous experience and the expected higher operating load planned for the new wheel, the cooling system was modified at the same time. The paper describes the main effort in this direction and the results that clarify the previous damage of the measuring device.
Keywords:
blade; vibration; cooling system; measurement; laboratory
Available at various institutes of the ASCR
Modification of cooling system for laboratory measurement of rotor blade vibration
Last year, the replacement of the turbine wheel model was completed in the Laboratory of Rotational Laser Vibrometry of the Institute of Thermomechanics AS CR, v.v.i. Based on previous experience and ...
PROPERTIES OF NANOCRYSTALLINE FE-NI PARTICLES PREPARED BY THERMAL REDUCTION OF OXALATE PRECURSORS
Švábenská, Eva; Roupcová, Pavla; Havlíček, Lubomír; Schneeweiss, Oldřich
2024 - English
Recent technological advancements require development of cost-effective and high-performance magnets \nwhich ideally do not contain rare earth metals or noble metals. The promising candidates are Fe-Ni-based \nalloys, in particular, the Fe50Ni50 L10 phase (tetrataenite), which has a great perspective for producing hard \nmagnetic materials. Our study explores a promising method for preparing nanoparticles of Fe-Ni alloy from an \niron-nickel oxalate precursor. The coprecipitation method was employed to prepare oxalate precursors, \nfollowed by controlled thermal decomposition in a reducing hydrogen atmosphere. The morphology and \nproperties of the resulting particles were analysed using scanning electron microscopy (SEM) coupled with \nenergy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), Mössbauer spectroscopy (MS), and \nmagnetic measurements.\nThe SEM analysis revealed that the particles have approximately cube-shaped unit cell morphology with a\nsize in a range of 1 - 2 μm. Upon annealing, the samples contain multiple phases with varying Fe-Ni content.\nMagnetic measurements confirmed the formation of magnetically suitable Fe-Ni phases in the samples after \nannealing. Mössbauer spectroscopy emerged as a highly effective method for characterizing individual phases \nof the Fe-Ni system.
Keywords:
Magnetic materials; thermal decomposition; Mössbauer spectroscopy
Available at various institutes of the ASCR
PROPERTIES OF NANOCRYSTALLINE FE-NI PARTICLES PREPARED BY THERMAL REDUCTION OF OXALATE PRECURSORS
Recent technological advancements require development of cost-effective and high-performance magnets \nwhich ideally do not contain rare earth metals or noble metals. The promising candidates are ...
Epidemiologické modely s agenty
Neruda, Roman
2023 - Czech
Tento příspěvek je jemným úvodem do problematiky agentních modelů a jejich aplikací v epidemiologickém modelování. Představíme agentní modely jednak z hlediska informatiky, jednak jako nástroj modelování v jiných vědních disciplínách. V příkladové studii ukážeme model s agenty a sociální sítí jejich kontaktů, který slouží pro simulaci vývoje epidemie a vlivu protiepidemických opatření.
Available at various institutes of the ASCR
Epidemiologické modely s agenty
Tento příspěvek je jemným úvodem do problematiky agentních modelů a jejich aplikací v epidemiologickém modelování. Představíme agentní modely jednak z hlediska informatiky, jednak jako nástroj ...
Plošné návrhové srážky v českých povodích
Müller, Miloslav; Kašpar, Marek; Hulec, Filip
2023 - Czech
Data o srážkové intenzitě na území Česka s horizontálním rozlišením 1 km2 a časovým krokem 10 minut, získaná adjustací radarových odhadů daty ze srážkoměrných stanic, posloužila k odvození návrhových plošných srážek v českých povodích I. až IV. řádu a v povodích útvarů povrchových vod. Při zdvojnásobení doby akumulace srážky vzroste návrhový úhrn v jednotlivých pixelech v průměru o cca 20 %. S rostoucí plochou povodí velikost návrhových úhrnů klesá, a to především v případě kratších dob akumulace. Data on rainfall intensity on the territory of the Czech Republic with a horizontal resolution of 1 km2 and a time step of 10 minutes, obtained by adjusting radar estimates with data from rain gauge stations, were used to derive design areal precipitation in the Czech river basins of 1st to 4th order and in the basins of surface water bodies. When the rainfall accumulation time is doubled, the design precipitation total in individual pixels increases by about 20% on average. The magnitude of the design totals decreases with increasing catchment area, especially for shorter accumulation periods.
Keywords:
design precipitation; catchment; return period
Available at various institutes of the ASCR
Plošné návrhové srážky v českých povodích
Data o srážkové intenzitě na území Česka s horizontálním rozlišením 1 km2 a časovým krokem 10 minut, získaná adjustací radarových odhadů daty ze srážkoměrných stanic, posloužila k odvození návrhových ...
Kam a kolik vody odvádí stromy? Modelování vlivu smrkových a bukových porostů na toky vody v půdě během extrémních klimatických podmínek
Zelíková, Nikol; Šípek, Václav
2023 - Czech
Půdní vlhkost propojuje takové procesy, které ovlivňují celý hydrologický cyklus, a tím i dostupnost vodních zdrojů. Jedním z významných faktorů ovlivňující tyto procesy je přítomnost vegetace. Výzkum interakcí mezi vegetací, jejím managementem a procesy ovlivňující toky půdní vody nabývá na významu zejména v době probíhajících klimatických změn i změn krajinného pokryvu. Avšak komplexnost těchto interakcí, ovlivněná navíc jejich rozdílností mezi jednotlivými rostlinnými druhy tento výzkum ztěžuje. Proměna krajinného pokryvu probíhá také v českém lesnictví, konkrétně v podobě obměny smrkových monokultur buky. V této studii je proto zkoumán vliv dvou typů lesních porostů, smrku ztepilého (Picea abies) a buku lesního (Fagus sylvatica), na vodní režim půdy v experimentálním povodí Liz na Šumavě. A to (1) zjištěním rozdílů v množství půdní vláhy na základě dvaceti let naměřených dat a (2) získáním složek vodní bilance (transpirace a perkolace) na těchto dvou kontrastních plochách pomocí modelu bilance půdní vody. Z analýzy dlouhodobých dat půdních vlhkostí vyplývají nepatrně nižší hodnoty půdních vlhkostí pod porosty buku, které zanikají při srovnání průměrných ročních hodnot. Odlišnosti jsou patrné při hodnocení průměrných vlhkostí s hloubkou, kde v nejsvrchnější vrstvě půdního profilu smrk disponuje v průměru o 6 % vyššími zásobami půdní vody než buk. Z pohledu vývoje půdních vlhkostí během vegetační sezóny je půda z počátku sušší pod smrkem, který započíná svou transpiraci dříve. Tento rozdíl je v průběhu sezóny zredukován intenzivní transpirací buku. Výstupy bilančního modelu poukázaly na vyšší míru aktuální evapotranspirace buku a vyšší míru perkolace smrku během každého roku. Tento jev byl zvýrazněn během suchých let, kdežto v letech s dostatkem srážek byly rozdíly minimální. Zvýšení četnosti buku v krajině, tak může ovlivnit míru dotace podzemních vod. Soil moisture links processes that influence the entire hydrological cycle and thus the availability of water resources. One important factor influencing these processes is the presence of vegetation. Research on the interactions between vegetation, its management and the processes affecting soil water fluxes is of particular importance in times of ongoing climate change and land cover changes. However, the complexity of these interactions, further influenced by differences between plant species, makes this research more difficult. Land cover change is also taking place in Czechia, specifically in the replacement of spruce monocultures by beech. Therefore, this study investigates the influence of two types of forest stands, spruce (Picea abies) and beech (Fagus sylvatica), on the soil water regime in the experimental Liz catchment in Bohemian Forest, Czechia. This was performed by (1) evaluating differences in soil moisture based on twenty years of measured data and (2) obtaining the two components of the soil water balance (transpiration and percolation) at two plots (beech and spruce) using a soil water balance model. Analysis of the long-term soil moisture data show slightly lower soil moisture values under the beech stands, which disappear when comparing the annual mean values. Differences are evident when evaluating average soil moisture data with depth, where the topmost layer of the soil profile at the spruce site has on average 6% higher soil water content than beech. At the start of the growing season the soil moisture was initially drier under spruce, due to its earlier start of transpiration. This difference was reduced over the season by the intensive transpiration of beech. The outputs of the balance model indicated a higher rate of actual evapotranspiration of beech and a higher rate of percolation of spruce every year. This effect was more pronounced over the dry years, whereas in years with sufficient rainfall the differences were minimal. Thus, the replacement of spruce trees by beech trees may affect the rate of groundwater recharge.
Keywords:
soil water balance; transpiration; percolation; land cover change; drought
Fulltext is available at external website.
Kam a kolik vody odvádí stromy? Modelování vlivu smrkových a bukových porostů na toky vody v půdě během extrémních klimatických podmínek
Půdní vlhkost propojuje takové procesy, které ovlivňují celý hydrologický cyklus, a tím i dostupnost vodních zdrojů. Jedním z významných faktorů ovlivňující tyto procesy je přítomnost vegetace. Výzkum ...
On the structure and values of betweenness centrality in dense betweenness-uniform graphs
Ghanbari, B.; Hartman, David; Jelínek, V.; Pokorná, Aneta; Šámal, R.; Valtr, P.
2023 - English
Betweenness centrality is a network centrality measure based on the amount of shortest paths passing through a given vertex. A graph is betweenness-uniform (BUG)if all vertices have an equal value of betweenness centrality. In this contribution, we focus on betweenness-uniform graphs with betweenness centrality below one. We disprove a conjecture about the existence of a BUG with betweenness value α for any rational numberαfrom the interval (3/4,∞) by showing that only very few betweenness centrality values below 6/7 are attained for at least one BUG. Furthermore, among graphs with diameter at least three, there are no betweenness-uniform graphs with a betweenness centrality smaller than one. In graphs of smaller diameter, the same can be shown under a uniformity condition on the components of the complement.
Keywords:
betweenness; graphs
Available in digital repository of the ASCR
On the structure and values of betweenness centrality in dense betweenness-uniform graphs
Betweenness centrality is a network centrality measure based on the amount of shortest paths passing through a given vertex. A graph is betweenness-uniform (BUG)if all vertices have an equal value of ...
Adaptation of methods for cyclo-stationary processes for noisy structural health data
Fischer, Cyril; Bayer, Jan; Náprstek, Jiří; Urushadze, Shota
2023 - English
In structural health analysis, various techniques, including indirect measurement via monitoring vehicles, often yield data with significant randomness and insufficient frequency separation. Conversely, the desired attributes under scrutiny are periodic in nature. Thus, methodologies designed to identify cyclo-stationary properties within noisy data can be adapted for such scenarios, assuming an adequate length of the recorded data.
Keywords:
data analysis; cyclo-stationary processes; structural health monitoring
Available at various institutes of the ASCR
Adaptation of methods for cyclo-stationary processes for noisy structural health data
In structural health analysis, various techniques, including indirect measurement via monitoring vehicles, often yield data with significant randomness and insufficient frequency separation. ...
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 ...
Ceramic protection of anti-corrosion layers of 3-glycidyloxypropyl-triethoxysilane on steel
Pokorný, P.; Prodanović, N.; Janata, Marek; Brožek, Vlastimil
2023 - English
There are various variations on the problem of steel reinforcement bond strength in concrete. Along with geometrical considerations, corrosion performance of steels with varying chemical compositions in interaction with variable chemical compositions of concrete are crucial. One approach is to cover steel surfaces with organosilane compounds, which increases the reinforcement resistance to corrosion in both acidic and alkaline conditions but, on the other hand, may weaken the reinforcement bond strength on concrete. The issue is resolved by intentionally forming a thin-walled, highly adhering corundum layer that is highly porous and impregnated with 3-glycidyloxypropyltriethoxysilane. This procedure also includes testing the adhesion properties between the ceramic and the metal and the cement prior to conducting a corrosion test in a chloride environment.
Keywords:
steel; concrete; ceramics
Available at various institutes of the ASCR
Ceramic protection of anti-corrosion layers of 3-glycidyloxypropyl-triethoxysilane on steel
There are various variations on the problem of steel reinforcement bond strength in concrete. Along with geometrical considerations, corrosion performance of steels with varying chemical compositions ...
On the development of a numerical model for the simulation of air flow in the human airways
Lancmanová, Anna; Bodnár, Tomáš; Sequeira, A.
2023 - English
This contribution reports on an ongoing study focusing on reduced order models for incompressible viscous fluid flow in two dimensional channels. A finite difference solver was developed using a simple implementation of the immersed boundary method to represent the channel geometry. The solver was validated for unsteady flow by comparing the obtained two-dimensional numerical solutions with analytical profiles computed from the Womersley solution. Finally the 2D model was coupled to a simple 1D extension simulating the flow in axisymmetric elastic vessel (tube). Some of the coupling principles and implementation issues are discussed in detail.
Keywords:
reduced order model; incompressible Navier-Stokes equations; finite difference approximation; coupling method
Available in digital repository of the ASCR
On the development of a numerical model for the simulation of air flow in the human airways
This contribution reports on an ongoing study focusing on reduced order models for incompressible viscous fluid flow in two dimensional channels. A finite difference solver was developed using a ...
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