National Repository of Grey Literature 57 records found  1 - 10nextend  jump to record: Search took 0.00 seconds. 
Calibrated finite volume method-based simulation framework for laser shock peening
Isoz, Martin ; Gruber, Pavel ; Schmidt, Jaroslav ; Kubíčková, Lucie ; Štefan, Jan ; Kaufman, Jan ; Brajer, Jan ; Gabriel, Dušan
Modern and highly competitive industry seeks components with high strength and fatigue resistance. Both of these properties may be improved by peening of the component surface and the standard peening processes, such as the shot peening, are widely used in both automotive and aerospace industries. The laser shock\npeening (LSP), i.e. hardening of the material surface by a laser-induced shock wave, is a modern alternative to the standard peening. Concurrently, the industrial applications of LSP are promoted by recently emerged affordable high power-density lasers. However, the nascent LSP applications are still mostly a trial-and-error\nprocesses based on an extensive experimental testing. Consequently, we focused on a highly application-driven development of a framework for LSP modeling, and the internal workings and results of which are the focus of the present contribution.
Simulating particle-laden flows: from immersed boundaries towards model order reduction
Isoz, Martin ; Kubíčková, Lucie ; Kotouč Šourek, M. ; Studeník, Ondřej ; Kovárnová, A.
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.
Modelling of blood flow in a carotid artery with stenoses
Štefek, Martin ; Hájek, Petr (referee) ; Švancara, Pavel (advisor)
This bachelor's thesis deals with the analysis of blood flow in a carotid artery with stenoses in the area of the bifurcation. The current state of knowledge is presented in the theoretical part. As part of the practical part of the work, several 2D models of the artery with stenoses of dif-ferent sizes and distances were created. An ideal mesh of finite volumes was created and select-ed. Using the ANSYS Fluent program, basic hemodynamic parameters such as flow velocity, wall shear stress, pressure and fractional flow reserve (FFR) were evaluated for stationary flow. A time step was determined for the transient flow, and then the flow speed and shear stress on the walls at points were evaluated as a function of time.
Computational modelling of the influence of stenoses on blood flow in the carotid artery
Lukáš, Petr ; Hájek, Petr (referee) ; Švancara, Pavel (advisor)
This diploma thesis deals with blood flow in carotid artery with tandem double stenosis. In the first part there is described cardiovascular system with emphasis on blood and arteries. In the practical part, geometric models of the carotid artery with 30% and 70% stenosis, as well as a model without stenosis, are created. The second stenosis is not included in the model of geometry but modeled using Windkessel effect. Blood is modeled as a non-Newtonian fluid using the Carreau model. After the calculations, the blood flow and arterial wall stress are evaluated, and the results are compared among the different geometry models. Critical values of shear stress, TAWSS, OSI, and FFR, as well as the mass flow rate in the internal carotid artery, are assessed.
Development of Algorithm for Computational Modelling of Pivoted-Pad Journal Bearings
Pokorný, Jan ; Křupka, Ivan (referee) ; Šimek,, Jiří (referee) ; Návrat, Tomáš (advisor)
The presented work deals with the calculation of stiffness and damping coefficients of hydrodynamic tilting-pad journal bearings. For this reason, a computational model of static and dynamic characteristics of these bearings is developed. The calculation is based on the solution of the generalized Reynolds equation simultaneously with the 2D energy equation for both the lubricant film and the pads. As a result, the changes in viscosity and density of the lubricant across the film thickness can be considered. The effect of turbulence is reflected by correction factors. Other influences, such as lubricant mixing, deformation and tilting of the pads, are also included in the calculation. The numerical solution using the finite volume method is programmed in Python. The static equilibrium position of the bearing is found by the efficient bounded Anderson method, which was chosen after comparison with other selected methods. Based on the equilibrium position of the bearing, the stiffness and damping are calculated using the central difference method with the inclusion of flexibility of the pivots. The results of static and dynamic characteristics of the bearing of the selected parameters are presented. Furthermore, the obtained results of the calculations are verified with experimental data taken from the literature and also with in-house measurements. A good agreement between calculations and experiments has been achieved.
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.
Computer simulation and numerical analysis of compressible flow problems
Kubera, Petr ; Felcman, Jiří (advisor) ; Knobloch, Petr (referee) ; Fürst, Jiří (referee)
The thesis deals with the construction of an adaptive 1D and 2D mesh in the framework of the cell- centered finite volume scheme. The adaptive strategy is applied to the numerical solution of problems governed by the Euler equations, which is a hyperbolic system of PDE's. The used algorithm is applicable to nonstationary problems and consists of three independent parts, which are cyclically repeated. These steps are PDE evolution, then mesh adaptation and recovery of numerical solution from the old mesh to the newly adapted mesh. Owing to this the algorithm can be used also for other hyperbolic systems. The thesis is focused on the development of our mesh adaptation strategy, based on the anisotropic mesh adaptation, which preserves the geometric mass conservation law in each computational step. The proposed method is suitable to solve problems with moving discontinuities. Several test problems with moving discontinuity are computed to compare our algorithm with Moving Mesh algorithms.
Numerical Solution of the Three-dimensional Compressible Flow
Kyncl, Martin ; Felcman, Jiří (advisor) ; Dolejší, Vít (referee) ; Brandner, Marek (referee)
Title: Numerical Solution of the Three-dimensional Compressible Flow Author: Martin Kyncl Department: Department of Numerical Mathematics Supervisor: Doc. RNDr. Jiří Felcman, CSc. Abstract: This thesis deals with a fluid flow in 3D in general. The system of the equations, describing the compressible gas flow, is solved numerically, with the aid of the finite volume method. The main purpose is to describe particular boundary conditions, based on the analysis of the incomplete Riemann problem. The analysis of the original initial-value problem shows, that the right hand-side initial condition, forming the Riemann problem, can be partially replaced by the suitable complementary condition. Several modifications of the Riemann problem are introduced and analyzed, as an original result of this work. Algorithms to solve such problems were implemented and used in code for the solution of the compressible gas flow. Numerical experiments documenting the suggested methods are performed. Keywords: compressible fluid flow, the Navier-Stokes equations, the Euler equations, boundary conditions, finite volume method, the Riemann problem, numerical flux, tur- bulent flow
Simulation of temperature-rise in MV switchgear assemblies
Kapalla, Alexej ; Bušov, Bohuslav (referee) ; Valenta, Jiří (advisor)
This thesis focuses on the issue of heating of medium-voltage switchgears. The paper contains descriptions of the individual devices which the switchgear consists of. Furthermore, the paper examine the theoretical relations which describe the heating of the conductor. It also present the normative regulations regarding the heading of MV switchgears as well as specific impacts which influence the final temperature-rise. This is followed by chapters that describe the refining of a 3D model of specific switchgear for purposes of simulating temperature-rise, further followed by chapters that look at the actual simulation environment. The thesis further focuses on the actual simulation of MV switchgear temperature-rise and it will compare the results of the simulation with measurements taken under real conditions. The thesis also includes results of simulated temperature-rise while taking into consideration the forced cooling of the switchgear. In the last part, it focuses on the creation of an excel file, which enables the prediction of final results for the temperature-rise of disconnector based on its contact resistance.
Computational modelling of blood flow in the carotid artery with serial stenosis
Lukáš, Petr ; Hájek, Petr (referee) ; Švancara, Pavel (advisor)
The aim of this bachelor's thesis is to analyse the effect of double stenosis on flow and stress characteristics in the carotid artery. First, based on the stated literature, a literature search is conducted regarding blood flow in the arterial system. Then, the procedure of creating idealized models of an artery with double stenosis and the procedure of mesh creation and numerical solution are described. The models have different size of the stenosis and different distance between stenosis. In the final stage, the results are analysed first for stationary flow, then one model is selected on which is performed the analysis for pulsating flow. Analytical calculation of pressure drop and comparison with numerical calculation is also part of this work.

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