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Determination of aerodynamic coefficients for air flow around U-profiles with different flange porosities
Ledvinková, Blanka; Hračov, Stanislav; Macháček, Michael
2022 - English
Our contribution presents the comparison of the experimental investigations and of the numerical 2D simulations of the air flow around U –profiles having different flange porosities. The U-shaped beams were exposed to the air flow having a given velocity at different angles of the wind attack for obtaining the curves of the aerodynamic coefficients depending on the impact angle. The numerical simulations of the wind tunnel testing were performed using the Unsteady Reynolds Averaged Navier-Stokes (RANS) method, k-ω SST turbulence model was assumed.
Keywords:
U-shaped beams; porosity; wind tunnel; RANS simulation; k-ω SST model
Available in digital repository of the ASCR
Determination of aerodynamic coefficients for air flow around U-profiles with different flange porosities
Our contribution presents the comparison of the experimental investigations and of the numerical 2D simulations of the air flow around U –profiles having different flange porosities. The U-shaped ...
Theoretical analysis of selected trajectories inscribed by a ball freely rolling in a spherical cavity
Náprstek, Jiří; Fischer, Cyril
2022 - English
Indirect monitoring of structures is significantly complicated when an artificial vibration absorber has to be taken into account. Knowledge of the absorber’s behaviour is necessary in order to correctly distinguish the response types obtained during an drive-by measurement. In this work, the mathematical model of the ball-type vibration absorber is used, which is based on the Lagrangian formalism. Three first integrals are identified when no external excitation nor damping is assumed. The paper illustrates the power of this approach, which enables a detailed analysis of free movement of the ball in the spherical cavity. Properties of several particular trajectories depending on initial conditions are presented.
Keywords:
slender structure; vibration absorber; first integral; rolling sphere; structural health monitoring
Available in digital repository of the ASCR
Theoretical analysis of selected trajectories inscribed by a ball freely rolling in a spherical cavity
Indirect monitoring of structures is significantly complicated when an artificial vibration absorber has to be taken into account. Knowledge of the absorber’s behaviour is necessary in order to ...
Effect of oscillating blade on tonal noise of blade cascade with five NACA 0010 profiles
Šnábl, Pavel; Pešek, Luděk; Radolf, Vojtěch; Antoš, Pavel; Procházka, Pavel P.; Prasad, Chandra Shekhar
2022 - English
The airfoil tonal noise is a well known phenomenon which appears on single airfoils in moderate Reynolds numbers at low angles of attack. It can appear on small aircrafts, fans, wind turbines etc. In thispaper, it was observed on a blade cascade consisting of five NACA 0010 profiles placed in a closed rectangular channel with hard walls when for given conditions, i.e. flow velocity and angle of attack, the cascade tunes to one single frequency. During the middle blade oscillation, the single tone splits up to several tones with lower intensity modulated by the excitation frequency. Thus, the oscillation of one blade suppresses the tonal noise generation in the cascade.
Keywords:
aeroacoustics; blade cascade; trailing edge noise; tonal noise; NACA 0010
Fulltext is available at external website.
Effect of oscillating blade on tonal noise of blade cascade with five NACA 0010 profiles
The airfoil tonal noise is a well known phenomenon which appears on single airfoils in moderate Reynolds numbers at low angles of attack. It can appear on small aircrafts, fans, wind turbines etc. In ...
Změny poměru nového sněhu a sezónních srážek v horských a podhorských oblastech Česka
Procházka, J.; Lipina, P.; Šustková, V.; Tesař, Miroslav
2022 - Czech
Sněžení a tvorba sněhové pokrývky je důležitým aspektem chladnější části roku v Česku i střední Evropě. Sněhová pokrývka má význam z hlediska klimatologického, hydrologického, ekologického i rekreačního, potažmo ekonomického. Množství nového sněhu závisí kromě srážek především na teplotě vzduchu. S postupným oteplováním se dá předpokládat, že při podobném celkovém úhrnu srážek se bude snižovat podíl srážek ve formě sněhu a schopnost tvorby sněhové pokrývky. Za účelem vyjádření příslušného stavu a změn byl v tomto příspěvku použit poměr sezónního množství nového sněhu v cm a celkových srážek v mm, Sn/P. V této souvislosti byla zpracována data z databáze ČHMÚ pro 112 vybraných horských a podhorských meteorologických stanic Česka pro dvě normálová období 1961–1990, resp. 1991–2020. Hodnocena byla data z chladné části roku a ze stanic s nadmořskou výškou nad 500 m, a to souhrnně nebo dle jednotlivých výškových pásem. Jako chladná část roku zde bylo považováno období listopad až duben, kdy je větší pravděpodobnost tvorby nové sněhové pokrývky. Výsledky studie ukázaly, že poměr Sn/P zaznamenal v období 1991–2020 znatelný pokles v porovnání s obdobím 1961–1990, v průměru tomu bylo z hodnoty 0,54 na hodnotu 0,44, tedy o 18 %. Dokumentovaná změna se projevila především v souvislosti s poklesem sezónního úhrnu nového sněhu, a to z průměrných 168 na 144 cm, zatímco sezónní úhrn srážek v průměru jen mírně vzrostl z 312 na 326 mm. Stav a změny v hodnocených parametrech\nbyly současně prezentovány i prostorově v podobě klimatologických map Česka pro příslušná normálová období. Výhodou hodnocení pomocí poměru Sn/P, v porovnání s hodnocením poměru tuhých a kapalných srážek S/P, je možnost využití dat z většího souboru klimatologických i srážkoměrných stanic. Poměr Sn/P navíc zahrnuje důležitý fenomén chladnější části roku, a to vytváření sněhové pokrývky. Snowfall and snow cover formation is an important aspect of the colder part of the year in the Czech Republic and Central Europe. Snow cover is important from the point of view of climatology, hydrology, ecology and recreation, and therefore economic. In addition to precipitation, the amount of new snow depends mainly on the air temperature. With gradual warming, it can be assumed that with a similar total precipitation, the proportion of precipitation in the form of snow and the ability to form snow cover will decrease. In order to evaluate the mentioned changes, the ratio of the seasonal amount of new snow in cm and total precipitation in mm, Sn/P (cm/mm) was used in this paper. For the analysis, data from the CHMI database for two normal periods 1961–1990 and 1991–2020 were processed for selected mountain and foothill meteorological stations in the Czech Republic. The period from November to April was assessed as a cold part of the year for this purpose, when a new snow cover is more likely to form. The results of the study showed that the Sn/P ratio decreased in the period 1991–2020 compared to the period 1961–1990.
Keywords:
snow cover; meteorological station; raingauge; database CLIDATA; climatological normal
Fulltext is available at external website.
Změny poměru nového sněhu a sezónních srážek v horských a podhorských oblastech Česka
Sněžení a tvorba sněhové pokrývky je důležitým aspektem chladnější části roku v Česku i střední Evropě. Sněhová pokrývka má význam z hlediska klimatologického, hydrologického, ekologického i ...
Determination of current floor during mobile robot elevator ride
Krejsa, Jiří; Věchet, Stanislav; Chen, K. S.
2022 - English
In order for the mobile robot to use the elevator, it must be capable to call the elevator in, detect the control panel, select desired floor and to determine what floor is the elevator located. The paper deals with determination of correct floor the mobile robot is currently at using the processing of onboard accelerometer data. Up to 5 relative floor difference the method exhibits over 95% accuracy.
Keywords:
mobile robot; elevator floor determination; signal processing
Fulltext is available at external website.
Determination of current floor during mobile robot elevator ride
In order for the mobile robot to use the elevator, it must be capable to call the elevator in, detect the control panel, select desired floor and to determine what floor is the elevator located. The ...
Control system architecture for novel experimental microalgae photobioreactor Simbios
Věchet, Stanislav; Krejsa, Jiří; Chen, K. S.
2022 - English
Photo-bioreactors for growing biomass based on various microalgae cultures gains interests nowadays due to have possible positive impact to society because of the potential to serve as an atmospheric carbon dioxide removal (CDR) device, produce food or fuel. We present an overall architecture of a control system designed with focus to keep the photo-bioreactor alive for long term continuous operation without any human supervision needed. To test overall control system stability we design a custom build spiral photo-bioreactor (PBR) with novel hyperbolic shaped illuminated part. The shape of the illuminated part was design with the goal to increase the ratio of spiral part to volume due to the fact that the light is crucial for microalgae to grow. The control system was created from scratch while adopting reliable IoT sensors combined with highly reliable custom build embedded control system including a cloud data processing and storage. As a result we have scalable and reliable solution which is suitable for photo-bioreactors of various shapes and sizes to operate in fully autonomous mode without any human supervision needed.
Keywords:
photobioreactor; IoT sensors; control system,
Fulltext is available at external website.
Control system architecture for novel experimental microalgae photobioreactor Simbios
Photo-bioreactors for growing biomass based on various microalgae cultures gains interests nowadays due to have possible positive impact to society because of the potential to serve as an atmospheric ...
Correction of gradient pulse shape distortions in radial MRI
Vitouš, Jiří
2022 - English
This paper focuses on the optimization of gradient-pulse shapes in MRI measurement. The main topic investigated in this paper is optimization of slice-selective gradient, where imperfections may produce phase distortion in the resulting image and also signal loss in the acquired signal. A method for correction is proposed based on the Nelder-Mead algorithm followed by coordinate ascent search in the neighborhood of the found solution. The adjustment is evaluated using a simple Fast low angle shot (FLASH) sequence with radial readout. The results show a significant improvement in the Free induction decay (FID) signal magnitude, echo stability, and an improvement in the homogeneity of image phase.
Keywords:
MRI; gradient; Nelder–Mead; slice; adjustment
Fulltext is available at external website.
Correction of gradient pulse shape distortions in radial MRI
This paper focuses on the optimization of gradient-pulse shapes in MRI measurement. The main topic investigated in this paper is optimization of slice-selective gradient, where imperfections may ...
Two Composition Operators for Belief Functions Revisited
Jiroušek, Radim; Kratochvíl, Václav; Shenoy, P. P.
2022 - English
In probability theory, compositional models are as powerful as Bayesian networks. However, the relation between belief-function graphical models and the corresponding compositional models is much more complicated due to several reasons. One of them is that there are two composition operators for belief functions. This paper deals with their main properties and presents sufficient conditions under which they yield the same results.
Keywords:
probability theory; Bayesian networks; belief functions
Fulltext is available at external website.
Two Composition Operators for Belief Functions Revisited
In probability theory, compositional models are as powerful as Bayesian networks. However, the relation between belief-function graphical models and the corresponding compositional models is much more ...
Modeling COVID Pandemics: Strengths and Weaknesses of Epidemic Models
Šmíd, Martin
2022 - English
We generally discuss modeling the present COVID pandemics. We argue that useful models have to be simple in the first case, yet their uncertainty has to be handled properly. In order to study circumstances of the upcoming wave of infection,\nwe construct a simple stochastic model and present predictions it gives. We conclude that the autumn wave is most likely unavoidable and suggest concentrating to mitigation.
Keywords:
COVID; Epidemic Models; stochastic model
Fulltext is available at external website.
Modeling COVID Pandemics: Strengths and Weaknesses of Epidemic Models
We generally discuss modeling the present COVID pandemics. We argue that useful models have to be simple in the first case, yet their uncertainty has to be handled properly. In order to study ...
Analysis of Impact of Covariates Entering Stochastic Optimization Problem
Volf, Petr
2022 - English
In the contribution we study consequences of imperfect information to precision of stochastic optimization solution. In particular, it is assumed that the characteristics of optimization problem are influenced by a set of covariates. This dependence is described via a regression model. Hence, the uncertainty is then caused by statistical estimation of regression parameters. The contribution will analyze several regression model cases, together with their application. Precision of results will be explored, both theoretically as well as with the aid of simulations.
Keywords:
stochastic optimization; regression model; statistical estimation
Fulltext is available at external website.
Analysis of Impact of Covariates Entering Stochastic Optimization Problem
In the contribution we study consequences of imperfect information to precision of stochastic optimization solution. In particular, it is assumed that the characteristics of optimization problem are ...
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