Yes (81)
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81
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Finite element modelling of elastic wave propagation in heterogeneous media
Kolman, Radek; Cho, S.S.; González, J. A.; Park, K.C.
2019 - English
In this contribution, we present an explicit scheme based on local time stepping respecting local wave speed and local stability limit for each finite element. The work aim is to suppress the spurious oscillations in wave propagation tasks in heterogeneous bars.
Keywords:
finite element modelling; elastic wave; heterogeneous media
Fulltext is available at external website.
Finite element modelling of elastic wave propagation in heterogeneous media
In this contribution, we present an explicit scheme based on local time stepping respecting local wave speed and local stability limit for each finite element. The work aim is to suppress the spurious ...
The measurement of the heterogeneous particles in the steam
Bartoš, Ondřej; Hrubý, Jan; Ždímal, Vladimír; Kolovratník, Michal; Jiříček, I.; Moravec, Pavel; Zíková, Naděžda
2019 - English
The aim of this extended abstract is to reveal the work done as cooperation between several institutions which was presented and published in recent years (Kolovratník, 2014). The formation of droplets in low-pressure steam turbines has a significant impact on the efficiency of energy conversion due to the strongly nonequilibrium nature of this process . The condensed water also erodes the turbine blades. A very important question is to what extent heterogeneous nucleation contributes to the phase transition process . In the case of heterogeneous nucleation , the number of droplets depends only on the number of h eterogeneous particles in the system, whereas in the case of homogeneous nucleation, the number of created droplets is determined rather by the expansion rate - in a faster expansion, greater supersaturation and more droplets are formed until the released condensation enthalpy quenches the nucleation.\nThe specific number of droplets (number of droplets per unit mass of steam) formed in the turbine can be determined by optical probes, developed first by Walters and later in the Czech Republic improved by Petr and Kolovratník. Until recently, no information was available on the relative importance of heterogeneous nucleation in forming these droplets.
Keywords:
heterogeneous nucleation; steam turbine; ultrafine aerosol particles
Fulltext is available at external website.
The measurement of the heterogeneous particles in the steam
The aim of this extended abstract is to reveal the work done as cooperation between several institutions which was presented and published in recent years (Kolovratník, 2014). The formation of ...
FEM simulation of the nanoindentation test with rigid non-rigid indenter
Kovář, J.; Fuis, Vladimír
2019 - English
This paper focuses on the comparing of the results of the FEM simulations of fused silica nanoindentation tests. Fused silica is modelled like bilinear elasto-plastic material with the parameters estimated from the experiment. FEM simulations are made with the 2D axisymmetric conical indenter which is equivalent to the Berkovich indenter and the indentation curves are evaluated. The FEM simulations were made with the rigid and the non-rigid indenter and the difference between the indentation curves obtained with these models is assessed. The evaluated indentation curves are compared with the indentation curves obtained from the experiment.
Keywords:
nanoindentation; conical indenter; silica; FEM
Fulltext is available at external website.
FEM simulation of the nanoindentation test with rigid non-rigid indenter
This paper focuses on the comparing of the results of the FEM simulations of fused silica nanoindentation tests. Fused silica is modelled like bilinear elasto-plastic material with the parameters ...
Anisotropy of Turbulent Flow around an Airfoil
Uruba, Václav; Procházka, Pavel P.; Skála, Vladislav
2019 - English
The flow around an airfoil is analyzed from the point of view turbulence anisotropy assessment. The turbulent flow-field in the vicinity of an airfoil is populated by vortices, in some locations they tend to regularity in orientation, i.e. to anisotropy. However in the wake behind the plate as well as in the core of the boundary layer on the plate suction side the turbulence is close to isotropic state.
Keywords:
airfoil; flow dynamics; turbulence; anisotropy
Fulltext is available at external website.
Anisotropy of Turbulent Flow around an Airfoil
The flow around an airfoil is analyzed from the point of view turbulence anisotropy assessment. The turbulent flow-field in the vicinity of an airfoil is populated by vortices, in some locations they ...
Numerical simulation of flow in superpak family packings
Smutek, J.; Isoz, Martin
2018 - English
The distillation is currently the most energy-intensive technology of the chemical industry. Commonly, the distillation is performed in the columns lled with a structured packing. Structured packings are complex structures used to increase the size of the interface available for the mass transfer. Because of the high complexity of both the packings and the physical phenomena occurring during the distillation, the design of the distillation columns is still based mostly on empirical data. In this work, we concentrate on modeling the gas ow in the SuperPak family of structured packings. First, we propose an algorithm for automatic generation\nof the packing geometry. Next, we construct and validate a three-dimensional computational uid dynamics (CFD) model of gas ow through SuperPak 250.Y and SuperPak 350.Y packings. The model validation is done by comparing experimental data of dry pressure losses to the values computed by our model. The obtained di erence between the CFD estimates and experiments is bellow 10 %. Finally, we present a parametric study of the SuperPak 250.Y packing geometry. The devised modeling approach may be easily automated and used for optimization of the SuperPak type packing geometry with respect to the gas ow. Furthermore,\nthe proposed CFD model may be extended to account for the multiphase ow.
Keywords:
CFD; OpenFOAM; structured packing; distillation; absorption
Fulltext is available at external website.
Numerical simulation of flow in superpak family packings
The distillation is currently the most energy-intensive technology of the chemical industry. Commonly, the distillation is performed in the columns lled with a structured packing. Structured packings ...
Model order reduction technique for large scale flow computations
Isoz, Martin
2018 - English
Current progress in numerical methods and available computational power combined with industrial needs promote the development of more and more complex models. However, such models are, due to their complexity, expensive from the point of view of the data storage and the time necessary for their evaluation. The model order reduction (MOR) seeks to reduce the computational complexity of large scale models. We present an application of MOR to the problems originating in the finite volume (FV) discretization of incompressible Navier-Stokes equations. Our approach to MOR is based on the proper orthogonal decomposition (POD)\nwith Galerkin projection. Moreover, the problems arising from the nonlinearities present in the original model are adressed within the framework of the discrete empirical interpolation method (DEIM). We provide a link between the POD-DEIM based MOR and OpenFOAM, which is an open-source CFD toolbox capable of solving even industrial scale problems. The availability of a link between OpenFOAM and POD-DEIM based MOR enables a direct order reduction for large scale systems originating in the industrial practice.
Keywords:
proper orthogonal decomposition; discrete empirical interpolation method; computational fluid dynamics; OpenFOAM
Fulltext is available at external website.
Model order reduction technique for large scale flow computations
Current progress in numerical methods and available computational power combined with industrial needs promote the development of more and more complex models. However, such models are, due to their ...
Comparison of Finite Volume and Spectral/HP Methods on Navier - Stokes Equations for Unsteady Incompressible Flow
Pech, Jan; Louda, Petr
2018 - English
We provide a comparison of solutions to the incompressible Navier-Stokes equations obtained using codes based on finite volume and spectral element methods. Convergence properties are compared on test case with analytical solution. The dependence of Strouhal and Reynolds numbers for flow over a cylinder is reconstructed for both methods.\n\n
Keywords:
finite volume method; spectral element method; incompressible Navier-Stokes
Fulltext is available at external website.
Comparison of Finite Volume and Spectral/HP Methods on Navier - Stokes Equations for Unsteady Incompressible Flow
We provide a comparison of solutions to the incompressible Navier-Stokes equations obtained using codes based on finite volume and spectral element methods. Convergence properties are compared on test ...
Flow in Branched Channel
Uruba, Václav; Procházka, Pavel P.; Skála, Vladislav
2018 - English
Flow in a branched channel is investigated experimentally using the PIV method. The branches are issuing from the main cannel perpendicularly, all channels are of rectangular cross-section. The time-mean flow-fields in the main channel and in the branches are studied in details.
Keywords:
channel; branches; PIV
Fulltext is available at external website.
Flow in Branched Channel
Flow in a branched channel is investigated experimentally using the PIV method. The branches are issuing from the main cannel perpendicularly, all channels are of rectangular cross-section. The ...
Low Cost Laser Rangefinder Evaluation
Krejsa, Jiří; Věchet, Stanislav
2018 - English
Laser rangefinders are essential tools in indoor mobile robot navigation. Lately several low-cost models become available, enabling the use of this type of sensor in broader range of applications. This paper evaluates the properties of currently (2018) the cheapest sensor available, particularly RPLidar A1M8, in order to determine whether it is usable in mobile robot development. As the sensor is based on triangulation principle, the increase of errors with the measured distance was expected, the experiments proved these expectations. Furthermore, the increasing, but linear trend in absolute measurement error was observed. The influence of surface material and color was also evaluated. The measurements indicate that RPLidar A1M8 can serve as a useful alternative for more expensive types of laser rangefinders.
Keywords:
laser rangefinder; mobile robot; localization
Fulltext is available at external website.
Low Cost Laser Rangefinder Evaluation
Laser rangefinders are essential tools in indoor mobile robot navigation. Lately several low-cost models become available, enabling the use of this type of sensor in broader range of applications. ...
DEM-CFD study of flow in a random packed bed
Šourek, M.; Isoz, Martin
2018 - English
Most catalytic surface reactions as well as other industrial applications take advantage of fixed packed bed reactors. Designers of these reactors rely mostly on empirical formulas derived for various simplifying assumptions, e.g. uniformly distributed porosity. The made simplifications and especially the assumption of uniformly distributed porosity fail if the tube to particle diameter ratio goes under 10 and the „wall effect“ becomes more significant. In such a case, the complete three-dimensional structure of the packed bed has to be considered. Thanks to ongoing improvements in numerical mathematics and computational power, the methods of computational fluid dynamics (CFD) have become a great tool for comprehensive description of the packed beds with low tube to particle diameter ratio. Three-dimensional simulations of the flow through two fixed beds differing in the type of the used particle are presented and compared with available experimental and empirical results. To generate the random fixed beds, we propose a custom approach based on the discrete element method (DEM) code implemented in open-source software Blender. Thereafter, OpenFOAM tools (snappyHexMesh, simpleFoam) are used for creation of the computational mesh and solution of the governing equations describing a single-phase flow in the packed bed.
Keywords:
CFD; DEM; random fixed bed; pressure drop; OpenFOAM
Fulltext is available at external website.
DEM-CFD study of flow in a random packed bed
Most catalytic surface reactions as well as other industrial applications take advantage of fixed packed bed reactors. Designers of these reactors rely mostly on empirical formulas derived for various ...
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