Number of found documents: 75
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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 ...

Isoz, Martin; Kubíčková, Lucie; Kotouč Šourek, M.; Studeník, Ondřej; Kovárnová, A.
Ústav termomechaniky, 2023

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 ...

Kubíčková, Lucie; Isoz, Martin
Ústav termomechaniky, 2023

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 ...

Hájek, P.; Radolf, Vojtěch; Horáček, Jaromír; Švec, J. G.
Ústav termomechaniky, 2023

Souvislost mezi principem nejmenší akce a termodynamickou podmínkou stability
Maršík, František; Trávníček, Zdeněk; Antošová, Zuzana
2023 - English
The extended principle is formulated for a material point (M.P.) X, which has nonzero mass, temperature, and trajectory x(X,t). The Lagrangian of this variation principle is equal to the kinetic energy from which, the internal energy of the material point (which depends on the entropy) and the additional energy caused by the frictional force are subtracted. The relation between the inertial force and the entropy gradient is found and the gravitational force is completely replaced by the entropy gradient. Thanks to the mentioned properties of the total enthalpy, the Thermodynamic criterion of stability of the state of M.P., is formulated. Keywords: principle of the least action; thermodynamic stability condition; annular swirl flow Fulltext is available at external website.
Souvislost mezi principem nejmenší akce a termodynamickou podmínkou stability

The extended principle is formulated for a material point (M.P.) X, which has nonzero mass, temperature, and trajectory x(X,t). The Lagrangian of this variation principle is equal to the kinetic ...

Maršík, František; Trávníček, Zdeněk; Antošová, Zuzana
Ústav termomechaniky, 2023

Numerical implementation of incremental minimization principle for materials with multiple rate-independent dissipative mechanisms
Frost, Miroslav; Moskovka, Alexej; Sedlák, Petr; Valdman, Jan
2023 - English
The incremental energy minimization approach is a compact variational formulation of the evolutionary boundary value problem for constitutive models of materials with a rate-independent response. Although it can be easily applied to many conventional models, its main advantages arise when applied to models with multiple strongly coupled dissipation mechanisms, where the direct construction of the coupled yield conditions and flow rules may be challenging. However, this usually requires a more complex numerical treatment of the resulting sequence of time-incremental boundary value problems resolved via the finite element method. This contribution presents, compares and discusses two genuine minimization approaches - the staggered solution procedure relying on alternating minimization and the monolithic approach employing global minimization - for an advanced constitutive model of shape memory alloys. Keywords: variational approach; constitutive modeling; numerical implementation Fulltext is available at external website.
Numerical implementation of incremental minimization principle for materials with multiple rate-independent dissipative mechanisms

The incremental energy minimization approach is a compact variational formulation of the evolutionary boundary value problem for constitutive models of materials with a rate-independent response. ...

Frost, Miroslav; Moskovka, Alexej; Sedlák, Petr; Valdman, Jan
Ústav termomechaniky, 2023

Thermal and creep analysis of VVER-1000 reactor pressure vessel at high temperatures caused by fuel melting during severe accident
Gabriel, Dušan; Gál, P.; Kotouč, M.; Dymáček, Petr; Masák, Jan; Kopačka, Ján
2023 - English
Thermal and creep analysis of the VVER-1000 reactor pressure vessel (RPV) was performed at high temperatures caused by fuel melting during severe accident. First, the integral code ASTEC was applied simulating severe accident evolution since an initiating event up to a hypothetical radioactive release into the environment. The ASTEC outputs including the remaining RPV wall thickness, the heat flux achieved and the temperature profile in the ablated vessel wall served as boundary conditions for the consequent assessment of RPV integrity carried out with the aid of finite element method (FEM). The FEM analysis was performed including the creep behaviour of RPV material using a complex creep probabilistic exponential model with damage. The objective of the analysis was to computationally assess emergency condition and, on this basis, to propose a general methodology for evaluating the integrity of RPV at high temperatures due to fuel melting during severe accident. Keywords: integrity of reactor pressure vessel; severe accident; ASTEC; creep; FEM Fulltext is available at external website.
Thermal and creep analysis of VVER-1000 reactor pressure vessel at high temperatures caused by fuel melting during severe accident

Thermal and creep analysis of the VVER-1000 reactor pressure vessel (RPV) was performed at high temperatures caused by fuel melting during severe accident. First, the integral code ASTEC was applied ...

Gabriel, Dušan; Gál, P.; Kotouč, M.; Dymáček, Petr; Masák, Jan; Kopačka, Ján
Ústav termomechaniky, 2023

Simulation of heterogeneously-catalyzed non-isothermal reactive flow in industrial packed beds
Hlavatý, Tomáš; Isoz, Martin; Khýr, M.
2023 - English
Packed bed reactors are the most frequently used devices to perform heterogeneously catalyzed reactions on industrial scales. An industrial real-life heterogeneous catalysis is 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 couple it with our\nin-house DEM-based method for preparation of random packed beds. The resulting framework is verified in the simplified cases against available analytical solutions and correlations and is used to study an industrially-relevant case of ethylene oxychlorination performed in a tubular packed bed comprising CuCl2-coated catalyst carrying particles. In particular, we compare properties of three different industrially used catalyst carrying particles: Raschig rings, Reformax, and Wagon wheels Keywords: CFD; OpenFOAM; non-isothermal flow Available in a digital repository NRGL
Simulation of heterogeneously-catalyzed non-isothermal reactive flow in industrial packed beds

Packed bed reactors are the most frequently used devices to perform heterogeneously catalyzed reactions on industrial scales. An industrial real-life heterogeneous catalysis is complex process that ...

Hlavatý, Tomáš; Isoz, Martin; Khýr, M.
Ústav termomechaniky, 2023

Implementation of wall functions into a hybrid fictitious domain-immersed boundary method
Kubíčková, Lucie; Isoz, Martin
2023 - English
Hybrid fictitious domain-immersed boundary method (HFDIB) is a simulation approach used in computational fluid dynamics. The approach avoids usage of complex geometry-conforming computational domains. Instead, a simple domain is used and the geometry is projected onto it by a scalar field and adjustment of governing equations. Hence, the time spent on mesh generation is substantially reduced. It is advantageous to use the HFDIB in geometry optimizations where it allows for a massive optimization speed-up. Nevertheless, there is a problem with simulation of the fluid behavior in the boundary layer in the vicinity of the immersed walls. Especially, in simulation of highly turbulent flows, where the boundary layer is very thin and the usage of finer mesh is unaffordable. In this work, we aim to solve this problem by implementation of Reynolds averaged turbulence models in our custom HFDIB variant. In particular, we implemented the k-ω turbulence model and blended wall functions for closure variables and velocity. Keywords: wall functions; immersed boundary method; CFD; RAS Fulltext is available at external website.
Implementation of wall functions into a hybrid fictitious domain-immersed boundary method

Hybrid fictitious domain-immersed boundary method (HFDIB) is a simulation approach used in computational fluid dynamics. The approach avoids usage of complex geometry-conforming computational domains. ...

Kubíčková, Lucie; Isoz, Martin
Ústav termomechaniky, 2023

Model order reduction of transport-dominated systems with rotations using shifted proper orthogonal decomposition and artificial neural networks
Kovárnová, A.; Isoz, Martin
2023 - English
In the present work, we concentrate on particle-laden flows as an example of industry-relevant transport-dominated systems. Our previously-developed framework for data-driven model order reduction (MOR) of such systems, the shifted proper orthogonal decomposition with interpolation via artificial neural networks, is further extended by improving the handling of general transport operators. First, even with intrusive MOR approaches, the underlying numerical solvers can provide only discrete realizations of transports linked to the movement of individual particles in the system. On the other hand, our MOR methodology requires continuous transport operators. Thus, the original framework was extended by the possibility to reconstruct continuous approximations of known discrete transports via another artificial neural network. Second, the treatment of rotation-comprising transports was significantly improved. Keywords: model order reduction; CFD; shifted POD Fulltext is available at external website.
Model order reduction of transport-dominated systems with rotations using shifted proper orthogonal decomposition and artificial neural networks

In the present work, we concentrate on particle-laden flows as an example of industry-relevant transport-dominated systems. Our previously-developed framework for data-driven model order reduction ...

Kovárnová, A.; Isoz, Martin
Ústav termomechaniky, 2023

Development, validation, and application of a solver for non-isothermal non-adiabatic packed bed reactors
Hlavatý, Tomáš; Isoz, Martin; Khýr, M.
2023 - English
Packed bed reactors are the most frequently used devices to perform heterogeneously catalyzed reactions on industrial scales. The main contribution of our work is the development of a numerical model applicable to simulations of such reactors. The developed model is based on the finite volume method, couples the momentum, mass and energy balances, and is free of any empirical closures. As such, the solver falls into the domain of the direct numerical simulation. In the talk, we will (i) present the new solver fundamental working principles, (ii) report on the verication of each of the solver components against existing literature data and (iii) demonstrate an application of the solver on an industrially relevant case of ethylene oxichlorination performed in a tubular reactor packed with Raschig rings coated by CuCl2 catalyst. Keywords: CFD; oxichlorination; heterogenous catalysis Fulltext is available at external website.
Development, validation, and application of a solver for non-isothermal non-adiabatic packed bed reactors

Packed bed reactors are the most frequently used devices to perform heterogeneously catalyzed reactions on industrial scales. The main contribution of our work is the development of a numerical model ...

Hlavatý, Tomáš; Isoz, Martin; Khýr, M.
Ústav termomechaniky, 2023

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