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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 ...
Simulating particle-laden flows: from immersed boundaries towards model order reduction
Isoz, Martin; Kubíčková, Lucie; Kotouč Šourek, M.; Studeník, Ondřej; Kovárnová, A.
2023 - English
Particle-laden flow is prevalent both in nature and in industry. Its appearance ranges from the trans-port of riverbed sediments towards the magma flow, from the deposition of catalytic material inside particulate matter filters in automotive exhaust gas aftertreatment towards the slurry transport in dredging operations. In this contribution, we focus on the particle-resolved direct numerical simulation (PR-DNS) of the particle-laden flow. Such a simulation combines the standard Eulerian approach to computational fluid dynamics (CFD) with inclusion of particles via a variant of the immersed boundary method (IBM) and tracking of the particles movement using a discrete element method (DEM). Provided the used DEM allows for collisions of arbitrarily shaped particles, PR-DNS is based (almost) entirely on first principles, and as such it is a truly high-fidelity model. The downside of PR-DNS is its immense computational cost. In this work, we focus on three possibilities of alleviating the computational cost of PR-DNS: (i) replacing PR-DNS by PR-LES or PR-RANS, while the latter requires combining IBM with wall functions, (ii) improving efficiency of DEM contact solution via adaptively refined virtual mesh, and (iii) developing a method of model order reduction specifically tailored to PR-DNS of particle-laden flows.
Keywords:
particle-laden flow; CFD-DEM; arbitrarily-shaped particles; finite volume method
Fulltext is available at external website.
Simulating particle-laden flows: from immersed boundaries towards model order reduction
Particle-laden flow is prevalent both in nature and in industry. Its appearance ranges from the trans-port of riverbed sediments towards the magma flow, from the deposition of catalytic material ...
On Reynolds-averaged turbulence modeling with immersed boundary method
Kubíčková, Lucie; Isoz, Martin
2023 - English
The immersed boundary (IB) method is an approach in the computational fluid dynamics in which complex geometry conforming meshes are replaced by simple ones and the true simulated geometry is projected onto the simple mesh by a scalar field and adjustment of governing equations. Such an approach is particularly advantageous in topology optimizations (TO) where it allows for substantial speed-up since a single mesh can be used for all the tested topologies. In our previous work, we linked our custom IB variant, the hybrid fictitious domain-immersed boundary method (HFDIB), with a TO framework and successfully carried out an optimization under laminar flow conditions. However, to allow for optimizations of reallife components, the IB approach needs to be coupled with an affordable turbulence modeling. In this contribution, we focus on extending the HFDIB approach by the possibility to perform Reynolds-averaged simulations (RAS). In particular, we implemented the k − ω turbulence model and wall functions for closure variables and velocity.
Keywords:
immersed boundary; RAS; wall functions; CFD; OpenFOAM
Fulltext is available at external website.
On Reynolds-averaged turbulence modeling with immersed boundary method
The immersed boundary (IB) method is an approach in the computational fluid dynamics in which complex geometry conforming meshes are replaced by simple ones and the true simulated geometry is ...
Finite element modal analysis of a silicone vocal fold filled with fluid
Hájek, P.; Radolf, Vojtěch; Horáček, Jaromír; Švec, J. G.
2023 - English
A three dimensional (3D) finite element (FE) model of a silicone vocal fold (VF) filled with fluid is presented here. The silicone part of the model is based on partial differential equations of the continuum mechanics and consider large deformations. The fluid domain encapsulated in the silicone VF is defined semianalytically as a lumped-element model describing the fluid in hydrostatic conditions. The elongated and pressurized silicone VF was subjected to perturbed modal analysis. Results showed that the choice of the fluid inside the VF substantially influences the natural frequencies. Namely, the water-filling lowers the natural frequencies approximately by half over the air-filling. Besides, the procedure of reverse engineering for obtaining the geometry of the VF from already 3D-printed mold is introduced.
Keywords:
perturbed modal analysis; finite element method; vocal folds; reverse engineering; biomechanics of voice
Fulltext is available at external website.
Finite element modal analysis of a silicone vocal fold filled with fluid
A three dimensional (3D) finite element (FE) model of a silicone vocal fold (VF) filled with fluid is presented here. The silicone part of the model is based on partial differential equations of the ...
From John Graunt to Adolphe Quetelet: on the Origins Of Demography
Kalina, Jan
2023 - English
John Graunt (1620-1674) and Adolphe Quetelet (1796-1874) were two important personalities, who contributed to the origins of demography. As they both developed statistical techniques for the analysis of demographic data, they are important also from the point of view of history of statistics. The contributions of both Graunt and Quetelet especially to the development of mortality tables and models are recalled in this paper. Already from the 17th century, the available mortality tables were exploited for computing life annuities. Also the contribution of selected personalities inspired by Graunt are recalled here, the work of Christian Huygens, Jacob Bernoulli, or Abraham de Moivre is discussed to document that the historical development of statistics and probability theory was connected with the development of demography.
Keywords:
history of demography; history of statistics; probability theory; moral statistics; mortality tables
Fulltext is available at external website.
From John Graunt to Adolphe Quetelet: on the Origins Of Demography
John Graunt (1620-1674) and Adolphe Quetelet (1796-1874) were two important personalities, who contributed to the origins of demography. As they both developed statistical techniques for the analysis ...
MAD UFOs: Magnetically Arrested Discs with persistent Ultra-Fast Outflows
Suková, Petra; Zajaček, M.; Karas, Vladimír
2023 - English
We study an outflow that develops in the MAD state in 3D GRMHD simulations. We show that the outflow can be accelerated to\nrelativistic velocities and persist over the course of our simulation. We compare the properties of the outflow from MAD discs with those launched by orbiting secondary at close orbit. The main difference is that the orbiting body launches a more coherent, quasiperiodic ultrafast outflow at lower velocities (v < 0.5c) while the outflow launched in the MAD state (without the body) has a stochastic behaviour and has anapproximately flat velocity distribution between lower anf higher outflow velocities, 0.2c < v < 0.3c and v > 0.5c.
Keywords:
accretion discs; black holes; active galactic nuclei
Fulltext is available at external website.
MAD UFOs: Magnetically Arrested Discs with persistent Ultra-Fast Outflows
We study an outflow that develops in the MAD state in 3D GRMHD simulations. We show that the outflow can be accelerated to\nrelativistic velocities and persist over the course of our simulation. We ...
TESTING THE METHOD OF MULTIPLE SCALES AND THE AVERAGING PRINCIPLE FOR MODEL PARAMETER ESTIMATION OF QUASIPERIODIC TWO TIME-SCALE MODELS
Papáček, Štěpán; Matonoha, Ctirad
2023 - English
Some dynamical systems are characterized by more than one timescale, e.g. two well separated time-scales are typical for quasiperiodic systems. The aim of this paper is to show how singular perturbation methods based on the slow-fast decomposition can serve for an enhanced parameter estimation when the slowly changing features are rigorously treated. Although the ultimate goal is to reduce the standard error for the estimated parameters, here we test two methods for numerical approximations of the solution of associated forward problem: (i) the multiple time-scales method, and (ii) the method of averaging. On a case study, being an under-damped harmonic oscillator containing two state variables and two parameters, the method of averaging gives well (theoretically predicted) results, while the use of multiple time-scales method is not suitable for our purposes.
Keywords:
Dynamical system; Singular perturbation; Averaging; Parameter estimation; Slow-fast decomposition; Damped oscillations
Fulltext is available at external website.
TESTING THE METHOD OF MULTIPLE SCALES AND THE AVERAGING PRINCIPLE FOR MODEL PARAMETER ESTIMATION OF QUASIPERIODIC TWO TIME-SCALE MODELS
Some dynamical systems are characterized by more than one timescale, e.g. two well separated time-scales are typical for quasiperiodic systems. The aim of this paper is to show how singular ...
Different Boundary Conditions For LES Solver PALM 6.0 Used for ABL in Tunnel Experiment
Řezníček, Hynek; Geletič, Jan; Bureš, Martin; Krč, Pavel; Resler, Jaroslav; Vrbová, Kateřina; Trush, Arsenii; Michálek, Petr; Beneš, L.; Sühring, M.
2023 - English
We tried to reproduce results measured in the wind tunnel experiment with a CFD simulation provided by numerical model PALM. A realistic buildings layout from the Prague-Dejvice quarter has been chosen as a testing domain because solid validation campaign for PALM simulation of Atmospheric Boundary Layer (ABL) over this quarter was documented in the past. The question of input data needed for such simulation and capability of the model to capture correctly the inlet profile and its turbulence structure provided by the wind-tunnel is discussed in the study The PALM dynamical core contains a solver for the Navier-Stokes equations. By default, the model uses the Large Eddy Simulation (LES) approach in which the bulk of the turbulent motions is explicitly resolved. It is well validated tool for simulations of the complex air-flow within the real urban canopy and also within its reduced scale provided by wind tunnel experiments. However the computed flow field between the testing buildings did not correspond well to the measured wind velocity in some points. Different setting of the inlet boundary condition was tested but none of them gave completely developed turbulent flow generated by vortex generators and castellated barrier wall place at the entrance of the aerodynamic section of the wind tunnel.
Keywords:
large eddy simulation; wind tunnel; atmospheric boundary layer; PALM model; turbulence
Fulltext is available at external website.
Different Boundary Conditions For LES Solver PALM 6.0 Used for ABL in Tunnel Experiment
We tried to reproduce results measured in the wind tunnel experiment with a CFD simulation provided by numerical model PALM. A realistic buildings layout from the Prague-Dejvice quarter has been ...
Room temperature ethanol detection using carbon materials
Kočí, Michal
2023 - English
Allotropic forms of carbon, in particular graphene oxide (GO) or nanocrystalline diamond (NCD), attracted the attention of many research groups due to their unique electronic structures and extraordinary physical and chemical properties, preferable for many different applications, including sensor devices. This work focuses on responses of various sensing layers (NCD with hydrogen termination (H-NCD), graphene oxide (GO), reduced graphene oxide (rGO), thiol-functionalized graphene oxide (GO-SH) and their hybrid structures to ethanol vapor with concentrations up to 100 ppm in synthetic air at room temperature. The measured parameters of the tested sensors, especially stability, reproducibility and regeneration, are compared and critically evaluated. The high sensitivity of tested sensors achieved at room temperature makes them very promising for monitoring ethanol vapor as well as other volatile substances (e.g., isopropyl-alcohol or acetone).
Keywords:
gas sensor; nanocrystalline diamond (NCD); graphene oxide (GO); reduced graphene oxide (rGO); thiol-functionalized graphene oxide (GO-SH)
Available at various institutes of the ASCR
Room temperature ethanol detection using carbon materials
Allotropic forms of carbon, in particular graphene oxide (GO) or nanocrystalline diamond (NCD), attracted the attention of many research groups due to their unique electronic structures and ...
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