Národní úložiště šedé literatury Nalezeno 30 záznamů.  1 - 10dalšíkonec  přejít na záznam: Hledání trvalo 0.00 vteřin. 
Numerical study of the steady airflow in the human respiratory system during inhaling and exhaling
Lancmanová, Anna ; Bodnár, Tomáš
This paper presents some of the initial results of the numerical simulations of a steady turbulent flow in human upper airways during inhalation and exhalation. The mathematical model is based on the system of Reynolds-Averaged incompressible Navier-Stokes equations complemented by the SST k − ω turbulence model. The simulations were performed using finite-volume open source solver OpenFOAM on a realistic three-dimensional geometry. The main aim of this particular study is to verify the computational setup with special focus on appropriate choice and implementation of boundary conditions. The prescribed boundary conditions are chosen to mimic the physiological conditions during normal breathing cycle. This study aims to gain an insight into the airflow behavior during the inhalation and exhalation process by comparing the results of two distinct simulations corresponding to two different (opposite) flow rates . The obtained local flow rates and flow fields for both cases are presented and mutually compared. This initial work should serve as a foundation for future more complex simulations that will include the time-dependent and compressible effects.
Numerical evaluation of mass-diffusive compressible fluids flows models
Bodnár, Tomáš ; Fraunié, P.
This contribution presents first numerical tests of some recently published alternative models for solution of viscous compressible and nearly incompressible models. All models are solved by high resolution compact finite difference scheme with strong stability preserving RungeKutta time stepping. The two simple but challenging computational test cases are presented, based on the double-periodic shear layer and the Kelvin-Helmholtz instability. The obtained time-dependent flow fields are showing pronounced shear and vorticity layers being resolved by the standard as well as by the new mass-diffusive modified models. The preliminary results show that the new models are viable alternative to the well established classical models.
On the development of a numerical model for the simulation of air flow in the human airways
Lancmanová, Anna ; Bodnár, Tomáš ; Sequeira, A.
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.
Validation of numerical simulations of a simple immersed boundary solver for fluid flow in branching channels
Keslerová, R. ; Lancmanová, Anna ; Bodnár, Tomáš
This work deals with the flow of incompressible viscous fluids in a two-dimensional branching channel. Using the immersed boundary method, a new finite difference solver was developed to interpret the channel geometry. The numerical results obtained by this new solver are compared with the numerical simulations of the older finite volume method code and with the results obtained with OpenFOAM. The aim of this work is to verify whether the immersed boundary method is suitable for fluid flow in channels with more complex geometries with difficult grid generation.
Numerical assessment of stratification influence in simple algebraic turbulence model
Uhlíř, V. ; Bodnár, Tomáš ; Caggio, Matteo
This paper presents rst few results obtained using a newly developed test code aimed at validation and cross-comparison of turbulence models to be applied in environmental flows. A simple code based on nite di erence discretization is constructed to solve steady flows of incompresible non-homogeneous (variable denstity) fluids. For the rst tests a simple algebraic turbulence model was implemented, containing stability function depending on the stratification via the gradient Richardson number. Numerical tests were performed in order to explore the capabilities of the new code and to get some insight into its behavior under di erent stratification. The two-dimensional simulations were performed using immersed boundary method for the flow over low smooth hill. The resulting flow fields are compared for selected Richarson numbers ranging from stable up to unstable strati cation conditions.
Numerical validation of a simple immersed boundary solver for branched channels simulations
Lancmanová, A. ; Bodnár, Tomáš ; Keslerová, D.
This contribution reports on an ongoing study of incompressible viscous fluid flow in two dimensional branched channels. A new finite difference solver was developed using a simple implementation of an immersed boundary method to represent the channel geometry. Numerical solutions obtained using this new solver are compared with outputs of an older finite volume code working on classical wall tted structured multiblock grid. Besides of the comparative evaluation of obtained solution, the aim is to verify whether the immersed boundary method is suitable (accurate and e cient enough) for simulations of flow in channels with complicated geometry where the the grid generation might be challenging.
Numerical tests of vanishing diffusion stabilization in Oldroyd-B fluid flow simulations
Pires, M. ; Bodnár, Tomáš
This work presents some numerical tests of finite element solution of incompressible Oldroyd-B fluids flows, using different types of numerical stabilization. In this study the diffusive term (Laplacian of extra stress) is added to the tensorial constitutive relation where it is multiplied by a coefficient, that is variable in time. The goal is to make this diffusion coefficient vanish in time, so that the final solution remains unaffected by the added diffusion term. A series of numerical tests was performed for the steady two-dimensional Oldroyd-B fluid flow in corrugated channel (tube) to compare different versions of the vanishing stabilization terms and assess their efficiency in enforcing the solution convergence, without affecting the final steady state.
Second-order model for atmospheric turbulence without critical Richardson number
Caggio, M. ; Schiavon, M. ; Tampieri, F. ; Bodnár, Tomáš
The purpose of this communication is to present a derivation of the non-dimensional vertical gradients of the mean wind speed and mean potential temperature expressed in terms of the so-called similarity functions for very stable conditions of the atmosphere where theoretical approaches provide conflicting results (see e.g. Luhar et al. [19]). The result is based on the analysis of the second-order model equations in the boundary layer approximations in which new heat flux equations are proposed. The model employs a recent closure for the pressure-temperature correlation, avoiding the issue of a critical treshold for the Richardson number.
Fluid-structure interaction between blood and dissipating artery wall
Fara, Jakub ; Tůma, Karel (vedoucí práce) ; Bodnár, Tomáš (oponent)
V této práci představíme nový model pro popis interakce mezi tekutinou a pevnou látou v Eulerovsém popisu. Tento model je navržen pro tok krve mezi viskoelastickou tepennou stěnou. Pro tekutinu je použit nenewtonský Oldroyd-B model, zatímco pevná látka je popsána pomocí Kelvin-Voigt modelu. Přechod mezi těmito materiály je zaručen pomocí konzervativní level-set metody. Num- erické řešení tohoto modelu je zajištěno metodou konečných prvků. Dále pomocí tohoto modelu jsou simulovány dva problémy: dvou dimenzionální kanál s viskoe- lastickými stěnami a pulsujícím přítokem a Turek-Hron FSI benchmark. 1
Kdy může smlouva založit vztah ovlivnění nebo ovládání a jejich případné důsledky?
Bodnar, Tomáš ; Čech, Petr (vedoucí práce) ; Černá, Stanislava (oponent)
Kdy může smlouva založit vztah ovlivnění nebo ovládání a jejich případné důsledky? Cílem mé diplomové práce je popis právní úpravy podnikatelských seskupení (s výjimkou koncernového práva) s akcentem na možnost založit tento vztah smluvním vztahem. Snažím se dokázat, že takové založení vztahu ovlivnění a ovládání je možné. Pokouším se dále dovodit, že takové situace nebudou v praxi obvyklé. Vztah ovládání založený smluvními vztahy bude dokonce velmi výjimečný. Dalším cílem mé práce je popsat právní důsledky podnikatelských seskupení podle zákona o obchodních korporacích, zejména náhradu újmy. Chci se ale zabývat také ostatními důsledky, které zákon o obchodních korporacích s podnikatelskými seskupeními spojuje.

Národní úložiště šedé literatury : Nalezeno 30 záznamů.   1 - 10dalšíkonec  přejít na záznam:
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