Počet nalezených dokumentů: 2724
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Improving computational efficiency of contact solution in fully resolved CFD-DEM simulations with arbitrarily-shaped solids
Studeník, Ondřej; Kotouč Šourek, M.; Isoz, Martin
2023 - anglický
The abundance of industrial processes containing both solid and liquid phases generate demand for fully resolved models allowing for detailed analysis and optimization of these processes. An established approach providing such models is based using a variant of an immersed boundary method to couple the computational fluid dynamics (CFD) and discrete element method (DEM). In the talk, we will present our custom and monolithic implementation of a fully-resolved CFDDEM solver and concentrate on the intricacies of solving contact between two arbitrarily-shaped solids. We shall propose an efficient contact treatment based on the concept of a virtual mesh, which provides the mesh resolution required by DEM through dividing the space around the contact point in a finite volume fashion without any changes to the CFD mesh itself. A substantial part of the talk will devoted to the parallelization of the contact solution, especially in the context of the domain decomposition method imposed by the CFD solver. Klíčová slova: CFD; DEM; virtual mesh Dokument je dostupný na externích webových stránkách.
Improving computational efficiency of contact solution in fully resolved CFD-DEM simulations with arbitrarily-shaped solids

The abundance of industrial processes containing both solid and liquid phases generate demand for fully resolved models allowing for detailed analysis and optimization of these processes. An ...

Studeník, Ondřej; Kotouč Šourek, M.; Isoz, Martin
Ústav termomechaniky, 2023

Simulating particle-laden flows: from immersed boundaries towards model order reduction
Isoz, Martin; Kubíčková, Lucie; Kotouč Šourek, M.; Studeník, Ondřej; Kovárnová, A.
2023 - anglický
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. Klíčová slova: particle-laden flow; CFD-DEM; arbitrarily-shaped particles; finite volume method Dokument je dostupný na externích webových stránkách.
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 - anglický
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. Klíčová slova: immersed boundary; RAS; wall functions; CFD; OpenFOAM Dokument je dostupný na externích webových stránkách.
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 - anglický
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. Klíčová slova: perturbed modal analysis; finite element method; vocal folds; reverse engineering; biomechanics of voice Dokument je dostupný na externích webových stránkách.
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

Comparison of finite element simulation of tungsten nanoindentation with Berkovich and conical indenter
Fiala, L.; Ballo, I.; Kovář, J.; Fuis, Vladimír
2023 - anglický
Finite Element Method (FEM) was used to study the difference between using Berkovich and conical indenters in nanoindentation test of tungsten specimen. The study was aimed to determine the\nmodulus of elasticity of a tested specimen and how it changes with different indenter. The FEM analysis also revealed that the modulus of elasticity was sensitive to the dimensions of both specimen and the indenter for which were made several numerical calculations with different dimensions. Klíčová slova: nanoindentation; FEM; Berkovich indenter; conical indenter; tungsten Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Comparison of finite element simulation of tungsten nanoindentation with Berkovich and conical indenter

Finite Element Method (FEM) was used to study the difference between using Berkovich and conical indenters in nanoindentation test of tungsten specimen. The study was aimed to determine the\nmodulus ...

Fiala, L.; Ballo, I.; Kovář, J.; Fuis, Vladimír
Ústav termomechaniky, 2023

Souvislost mezi principem nejmenší akce a termodynamickou podmínkou stability
Maršík, František; Trávníček, Zdeněk; Antošová, Zuzana
2023 - anglický
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. Klíčová slova: principle of the least action; thermodynamic stability condition; annular swirl flow Dokument je dostupný na externích webových stránkách.
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

Annular Impinging Jets and an Active Control of Hysteretic Effects
Devani, Yogendrasasidhar; Antošová, Zuzana; Trávníček, Zdeněk
2023 - anglický
An annular impinging air jet with and without flow control was studied experimentally using measurements of the wall pressure and flow velocity by the Pitot probe. To investigate flow control swirling effects, eight synthetic jets were generated from the nozzle center body. The experiments cover Reynolds numbers 4000–10,000 (evaluated from the outer exit diameter of the annular nozzle). For Re<9000, the bistability and hysteresis were identified and two different flow field patterns (A, B) were found under the same boundary conditions. For higher Re>9000, the hysteresis were not found. Klíčová slova: annular jet; impinging jet; hysteresis Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Annular Impinging Jets and an Active Control of Hysteretic Effects

An annular impinging air jet with and without flow control was studied experimentally using measurements of the wall pressure and flow velocity by the Pitot probe. To investigate flow control swirling ...

Devani, Yogendrasasidhar; Antošová, Zuzana; Trávníček, Zdeněk
Ústav termomechaniky, 2023

A new blade cascade for flutter studies
Šnábl, Pavel; Pešek, Luděk; Procházka, Pavel P.; Skála, V.
2023 - anglický
In this paper, a new blade cascade, developed in the Institute of Thermomechanics, is presented. The geometry of the cascade was modified so now the stall flutter can occur. It has some major construction improvements over the original cascade which now allow more precise and reliable measurements. The stability of the new blade cascade with five NACA 0010 profiles with rotational degree of freedom is assessed by Travelling Wave Mode approach and Aerodynamic Influence Coefficient approach. Klíčová slova: blade cascade; stability; travelling wave mode; aerodynamic influence coefficient Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
A new blade cascade for flutter studies

In this paper, a new blade cascade, developed in the Institute of Thermomechanics, is presented. The geometry of the cascade was modified so now the stall flutter can occur. It has some major ...

Šnábl, Pavel; Pešek, Luděk; Procházka, Pavel P.; Skála, V.
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 - anglický
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. Klíčová slova: variational approach; constitutive modeling; numerical implementation Dokument je dostupný na externích webových stránkách.
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 - anglický
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. Klíčová slova: integrity of reactor pressure vessel; severe accident; ASTEC; creep; FEM Dokument je dostupný na externích webových stránkách.
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

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