2025-01-19
00:08 |
Parallelization of DEM solver for non-spherical solids: A pathway to scalable CFD-DEM simulations
Studeník, Ondřej ; Kotouč Šourek, M. ; Isoz, Martin ; Kočí, P.
Granular matter formed from non-spherical solids appears in both natural and industrial settings. These include, among others, landslides, mixing, and fluidization. The commonly used predictive method for granular matter is the discrete element method (DEM). However, DEM was initially designed for spherical particles and faces many challenges in modeling the non-spherical ones , which are prevalent. Therefore, various approaches, including multi-sphere clusters, super-quadrics and polyhedral models, were developed to approximate the irregular shapes. The polyhedral approach offers the highest level of fidelity, but comes with the biggest computational costs, particularly for non-convex particles. Hence, optimization and parallelization of codes with polyhedron-based DEM solvers are of great interest. In this work, we present recent advances in the development of our custom polyhedron-based DEM solver, focusing on parallel computing. With improvements in the solver architecture and boosted computational efficiency, the DEM code scales well at least up to 32 cores and allows for efficient coupling with computational fluid dynamics (CFD) to simulate complex\nparticle-laden flows.
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2025-01-19
00:08 |
Reynolds-averaged simulation of turbulent flows with immersed boundaries
Kubíčková, Lucie ; Isoz, Martin
Simulating turbulent flows in complex real-life geometries faces two major problems. First, direct simulation of turbulent flow is extremely costly. Second, a complex geometry-conforming mesh is required, and such mesh presumably suffers from several mesh-quality related problems lowering the solution accuracy and prolonging the simulation time. To solve the first problem, phenomenological turbulence models based on, e.g. Reynolds-averaging, are commonly utilized. To address the second one, a variant of an immersed boundary (IB) method can be used where the complex geometry is projected onto a simple mesh by an indi-cator field and adjustment of governing equations. Consequently, a connection of Reynolds-averaging and an immersed boundary method shall resolve both the problems and provide a simulation approach favorable for e.g. optimizations. However, such a connection is not common. In this contribution, we utilize our custom IB variant, the hybrid fictitious domain-immersed boundary method (HFDIB) and aim on extending the HFDIB by tools of the Reynolds-averaged simulation (RAS). In comparison with standard simulation approaches, the new HFDIB-RAS approach shows acceptable results in wide range of flow Reynolds numbers and in several testing geometries.
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2025-01-19
00:08 |
Data-driven approach to estimating soot distribution inside catalytic filters in utomotive exhaust gas aftertreatment
Khýr, Matyáš ; Plachá, M. ; Hlavatý, Tomáš ; Isoz, Martin
The performance and the necessary regeneration frequency of catalytic filters (CFs) used in the treatment of automotive exhaust gases depend strongly on the solid matter accumulated within their porous walls. Reliable predictions of solid matter (soot) accumulation are crucial in the development and optimisation of CFs. In this contribution, we exploit the tools of artificial intelligence (AI) to estimate the distribution of soot directly in the porous microstructure of CFs. Specifically, our AI model uses deep neural networks (DNNs) and convolutional autoencoders (CAEs) to predict the soot distribution from information about the microstructure and the initial velocity field. To provide the model with training and validation data, we used our previously developed transient numerical model of particle deposition in the CF walls to calculate soot distribution in a dataset of artificial 2D geometries. The results of the developed AI model are in good agreement with simulation regarding the total amount of accumulated soot. However, the accuracy in the spatial distribution of the soot is not optimal, and consequently, using estimated particle deposits to simulate the pressure drop in\nthe artificial microstructure results in 35 % accuracy.
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2025-01-19
00:08 |
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2025-01-19
00:08 |
Using finite volume method to simulate laser shock peening of 7050 Al alloy
Isoz, Martin ; Gruber, Pavel ; Ježek, Ondřej ; Kubíčková, Lucie ; Gabriel, Dušan ; Kaufman, Jan ; Brajer, Jan
Laser shock peening (LSP) is a modern alternative to standard peening processes such as shot peening. In general, peening is used to improve the strength and fatigue resistance of components by hardening their surface. In LSP, a laser-induced shockwave is used to harden the material to a depth of the order of 1 mm, that is, roughly twice as deep as can be achieved with shot peening. Frameworks for LSP simulation have been developed since the end of the 1990s and are exclusively based on the finite element method (FEM). The critical component of the framework is the dynamic simulation of the elastoplastic shockwave that subjects the component material to a strain rate of the order 10−7 s−1. In this contribution, we present a simulation framework for LSP based on the finite volume method (FVM) that allows for modeling the strain-rate hardening of the material. The framework is used to simulate the LSP of the 7050 aluminum alloy. Using a comparison\nof our FVM results with the FEM data available in the literature, we found that FVM can be applied to LSP simulation with the same success as the more traditional FEM.
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2025-01-19
00:08 |
On diffusion, reaction, and flow of high-concentration multicomponent gas mixtures
Hlavatý, Tomáš ; Isoz, Martin
Heterogeneous catalysis contributes to producing more than 80% of all chemical products in the world. Industrial heterogeneous catalysis is a complex process that combines fully three-dimensional mass,momentum, and energy transport on several scales. In the present work, we leverage our previously developed CFD solver for non-isothermal heterogeneously catalyzed reactive flow based on the finite-volume method and extend it with multicomponent Stefan-Maxwell diffusion description to handle high-concetration multicomponent mixtures. The resulting framework is verified and validated on the simple Stefan tube experiment, for which an analytical solution is available.
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2025-01-19
00:08 |
Experimental study of homogeneous nucleation of water in carbon dioxide carrier gas
Lukianova, Tetiana ; Lukianov, Mykola ; Hrubý, Jan
The question of the impact of carbon dioxide on a life of our planet is becoming increasingly urgent. One of the impotent contributions of this influence is the dropwise condensation of water in the presence of carbon dioxide. To understand the condensation process, we need to know the thermodynamic parameters of nucleation and growth of water droplets. This process can be studied by adiabatic expansion of gas mixtures of carbon dioxide and water. In this case, the temperature of the mixture decreases and the supersaturation increases. This creates the conditions under which homogeneous nucleation is possible.\nIn this study, we present experimental results on the homogeneous nucleation of water with the carrier gases CO2 and argon. In addition, the real gas correction was applied to the temperature and supersaturation calculations. As it can be seen from experimental results there is significant difference in the nucleation rate behavior of mixtures with argon and CO2 carrier gases. CO2 appears to enhance the nucleation rate. The isotherms showed in our presentation have smaller slope for CO2 carrier gas. By application of the nucleation theorem this allows to conclude that the presence of CO2 decreases the number of water molecules forming the critical cluster.
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2025-01-19
00:08 |
Experimental measuring of homogeneous nucleation rate of water in the presence of various gases in pulse expansion chamber
Lukianova, Tetiana ; Lukianov, Mykola ; Hrubý, Jan
To understand the condensation process, we need to know the thermodynamic parameters of nucleation and growth of water droplets. This process can be studied by adiabatic expansion of gas mixtures with water. In this case, the temperature of the mixture decreases and the supersaturation increases. This creates the conditions under which homogeneous nucleation is possible. The influence of carrier gases on homogeneous nucleation has been studied several times. The first publication was by Viisanen et al. (1993) and the last publication was by Campagna et al. (2021).\nWe performed experiments using the expansion pulse chamber developed by Wagner and Strey in 1984. The study was conducted in the presence of various in a range of nucleation temperatures of 220-260 K and nucleation pressures of 35-75 kPa at various concentrations of water vapor. experimental results shows nucleation rate J (number of droplets formed per unit of time and unit of volume) as function of supersaturation S (ratio of vapor pressure to the saturation pressure of water at given temperature) and temperature for the carrier gases.
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2025-01-19
00:08 |
Měření na ventilové soustavě s traverzovou regulací
Šimurda, David ; Hála, Jindřich ; Mamula, Milan ; Sláma, V.
Zpráva pojednává o užití poloprovozu Aerodynamické tratě pro testování ventilových soustav [1] k měření na modelu vysokotlaké ventilové soustavy tří ventilů s traverzovou regulací. Takovéto ventilové soustavy se v praxi využívají pro regulaci vysokotlaké páry na vstupu do turbín se skupinovou (dýzovou) regulací. Zde zkoumaná soustava byla primárně navržena pro turbíny nižších výkonů (výkony nižší než cca 50 MW). Výhodou traverzové regulace je potřeba jediného servopohonu pro ovládání všech ventilů v soustavě. Cílem měření bylo ověřit funkčnost poloprovozu a dále zjistit tlakové poměry při provozu měřené ventilové soustavy v různých konfiguracích a získat tak tzv. beta křivky, a dále zhodnotit míru tlakových fluktuací v hrdlech ventilů, ke kterým při provozu ventilu dochází. Měření byla provedena v Laboratoři vnitřních proudění Ústavu termomechaniky Akademie věd České republiky v Novém Kníně. Projekt byl řešen ve spolupráci s firmou Doosan Škoda Power s.r.o.. Řešením projektu byla ověřena funkčnost poloprovozu a byly získány kvalitní podklady (pro vytvoření obecné charakteristiky ventilu, validovaného ztrátového modelu a mapy bezpečných a nebezpečných provozů z pohledu vibrací ventilu) pro návrh a praktické využívání ventilu pro vysokotlaké díly parních turbín se skupinovou regulací.
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2025-01-19
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Model ventilové soustavy s traverzovou regulací
Šimurda, David ; Fiala, Petr ; Kroner, A. ; Sláma, V.
Zpráva popisuje konstrukci funkčního vzorku - modelu ventilové soustavy se třemi ventily s traverzovou regulací. Ventilové soustavy s traverzovou regulací se v praxi využívají proregulaci vysokotlaké páry na vstupu do turbín se skupinovou (dýzovou) regulací. Výhodou traverzové regulace je potřeba jediného servopohonu pro ovládání všech ventilů v soustavě. Model byl navržen a vyroben pro aerodynamická měření s cílem zjistit tlakové poměry při provozu této ventilové soustavy v různých konfiguracích a získat tak tzv. beta křivky, a dále zhodnotit míru tlakových fluktuací v hrdlech ventilů, ke kterým při provozu ventilu dochází. Návrh a výroba modelu byly řešeny ve spolupráci s firmou Doosan Škoda Power s.r.o.
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