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Iskalni niz: "avtor" (Robert Vertnik) .

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1.
Assessment of local radial basis function collocation method for diffusion problems structured with multiquadrics and polyharmonic splines
Izaz Ali, Umut Hanoglu, Robert Vertnik, Božidar Šarler, 2024, izvirni znanstveni članek

Povzetek: This paper aims to systematically assess the local radial basis function collocation method, structured with multiquadrics (MQs) and polyharmonic splines (PHSs), for solving steady and transient diffusion problems. The boundary value test involves a rectangle with Dirichlet, Neuman, and Robin boundary conditions, and the initial value test is associated with the Dirichlet jump problem on a square. The spectra of the free parameters of the method, i.e., node density, timestep, shape parameter, etc., are analyzed in terms of the average error. It is found that the use of MQs is less stable compared to PHSs for irregular node arrangements. For MQs, the most suitable shape parameter is determined for multiple cases. The relationship of the shape parameter with the total number of nodes, average error, node scattering factor, and the number of nodes in the local subdomain is also provided. For regular node arrangements, MQs produce slightly more accurate results, while for irregular node arrangements, PHSs provide higher accuracy than MQs. PHSs are recommended for use in diffusion problems that require irregular node spacing.
Ključne besede: meshless method, polyharmonic splines, multiquadrics, augmentation, heat diffusion equation
Objavljeno v DiRROS: 04.04.2024; Ogledov: 71; Prenosov: 32
.pdf Celotno besedilo (2,79 MB)
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2.
Numerical modelling of macrosegregation in three-dimensional continuous casting of steel billets
Katarina Mramor, Robert Vertnik, Božidar Šarler, 2023, objavljeni znanstveni prispevek na konferenci

Povzetek: Macrosegregation presents a considerable defect in the continuous casting of billets and can critically affect the final properties of the product. The numerical modelling can help to predict and better understand the segregation and flow patterns inside the mould. The process is modelled with a physical model described by a set of conservation equations describing the t heat transfer, turbulence, fluid flow, solidification and segregation. A two-equation low-Re k-epsilon model and Abe-Kondoh-Nagano closures are used to close governing equations in this incompressible fluid flow example. The Boussinesq approximation is applied to account for the thermo-solutal buoyancy effects, and the Darcy approximation is applied for the description of the flow through the porous mushy zone. On a microscale, a lever rule solidification model is used to couple liquid fraction, temperature and concentration. The three-dimensional model is solved with the method based on local collocation with multiquadric radial basis functions on seven-nodded subdomains. The aim of this contribution is to explore the three-dimensional macrosegregation patterns of 0.51 wt% carbon steel in the solidified shell of the steel in the mould.
Ključne besede: modeling, continuous casting of steel, CFD, turbulence modeling, LES, meshless methods, RANS
Objavljeno v DiRROS: 21.03.2024; Ogledov: 110; Prenosov: 64
.pdf Celotno besedilo (1,48 MB)
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