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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
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.
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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
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.
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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.
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.
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Octree-generated virtual mesh for improved contact resolution in CFD-Dem coupling
Studeník, O. ; Kotouč Šourek, M. ; Isoz, Martin
The present work is focused on improving the efficiency of a computational fluid dynamics (CFD) – discrete element method (DEM) solver allowing for computations with non-spherical solids. In general, the combination of CFD and DEM allows for simulations of freely moving solid particles within a computational domain containing fluid. The standard approach of CFD-DEM solvers is to approximate solid bodies by spheres, the geometry of which can be fully defined via its radius and center position. Consequently, the standard DEM contact models are based on an overlap depth between particles, which can be easily evaluated for a sphere-sphere contact. However, for a contact between two non-spherical particles, the overlap depth cannot be used and has to be replaced by the more general overlap volume. The precision of the overlap volume computation is (i) crucial for the correct evaluation of contact forces, and (ii) directly dependent on the computational mesh resolution. Still, the contact volume evaluation in DEM for arbitrarily shaped bodies is usually by at least one order of magnitude more demanding on the mesh resolution than the CFD. In order to improve the computational efficiency of our CFD-DEM solver, we introduce the concept of an OCTREEbased virtual mesh, in which the DEM spatial discretization is adaptively refined while the CFD mesh remains unchanged.
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Estimating rheological properties of suspensions formed of arbitrarily-shaped particles via CDF-Dem
Kotouč Šourek, M. ; Isoz, Martin
In recent years, new methods combining computational fluid dynamics (CFD) and discrete element method (DEM) have been intensively studied. Usually, these methods are focused on simulations of spherical particles. Nevertheless, this is inadequate for a simulation of a common suspension, the rheology of which is affected by particle shapes. In this work, we leverage the capabilities of an in-house developed CFD-DEM solver to simulate suspensions formed of arbitrarily-shaped particles. Specifically, we simulate a rheological measurement to estimate the suspension viscosity. The CFD-DEM estimates are in very good agreement with available experimental data and correlations proving the new solver capabilities regarding firstprinciples-based simulations of complex non-Newtonian suspension behaviour. The practical potential of suspension simulation is illustrated in a numerical study of the washcoating process in the preparation of a catalytic filter for automotive exhaust gas after-treatment.
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