821. A numerical study of gas focused non-Newtonian micro-jetsRizwan Zahoor, Saša Bajt, Božidar Šarler, 2024, izvirni znanstveni članek Ključne besede: serial crystallography, micro jets, multiphase flow, fluid rheology, non-Newtonian fluid, flow focusing
Objavljeno v DiRROS: 28.02.2024; Ogledov: 230; Prenosov: 110
 Celotno besedilo (11,78 MB)
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822. A hybrid radial basis function-finite difference method for modelling two-dimensional thermo-elasto-plasticity : Application to cooling of hot-rolled steel bars on a cooling bedGašper Vuga, Boštjan Mavrič, Umut Hanoglu, Božidar Šarler, 2024, izvirni znanstveni članek Povzetek: This paper represents Part 2 of the parallel paper Part 1, where the strong form hybrid RBF-FD method was developed for solving thermo-elasto-plastic problems. It addresses the industrial application of this novel meshless method to steel bars cooling on a cooling bed (CB) where the formation of residual stress is of primary interest. The study investigates the impact of the distance between the bars and the distance to the heat shield above the CB on radiative heat fluxes and, consequently, on thermo-mechanical response. The thermal model is solved on bars cross-section with a RBF-FD method where augmented polyharmonic splines are used for the local approximation. View factors, computed with a Monte-Carlo method, are included in radiative heat fluxes. The thermal solution is incrementally applied on a mechanical model that assumes a generalised plane strain state and captures bars bending. The study employs a hybrid RBF-FD method to resolve a nonlinear discontinuous mechanical problem successfully. The simulation of the process shows how different process parameters influence the thermo-mechanical response of the bars.
Ključne besede: steel bars, cooling bed, thermo-mechanical modelling, hybrid radial basis function, generated finite differences, residual stresses
Objavljeno v DiRROS: 28.02.2024; Ogledov: 189; Prenosov: 118
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823. A hybrid radial basis function-finite difference method for modelling two-dimensional thermo-elasto-plasticity, Part 1 : method formulation and testingGašper Vuga, Boštjan Mavrič, Božidar Šarler, 2024, izvirni znanstveni članek Povzetek: A hybrid version of the strong form meshless Radial Basis Function-Finite Difference (RBF-FD) method is introduced for solving thermo-mechanics. The thermal model is spatially discretised with RBF-FD, where trial functions are polyharmonic splines augmented with polynomials. For time discretisation, the explicit Euler method is employed. An extension of RBF-FD, the hybrid RBF-FD, is introduced for solving mechanical problems. The model is one-way coupled, where temperature affects displacements. The thermo-elastoplastic material response is considered where the stress field is generally non-smooth. The hybrid RBF-FD, where the finite difference method is used to discretise the divergence operator from the balance equation, is shown to be successful when dealing with such problems. The mechanical model is introduced in a plane strain and in a generalised plane strain (GPS) assumption. For the first time, this work presents a strong form RBF-FD for GPS problems subjected to integral form constraints. The proposed method is assessed regarding h-convergence and accuracy on the benchmark with heating an elastoplastic square. It is proven to be successful at solving one-way coupled thermo-elastoplastic problems. The proposed novel meshless approach is efficient, accurate, and robust. Its use in an industrial situation is provided in Part 2 of this paper.
Ključne besede: thermo-mechanical modelling, von Mises small strain plasticity, hybrid radial basis function generated finite differences, polyharmonic splines
Objavljeno v DiRROS: 28.02.2024; Ogledov: 218; Prenosov: 110
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824. Formulation of the method of fundamental solutions for two-phase Stokes flowZlatko Rek, Božidar Šarler, 2024, izvirni znanstveni članek Povzetek: The method of fundamental solutions with a subdomain technique is used for the solution of the free boundary problem associated with a two-phase Stokes flow in a 2D geometry. The solution procedure is based on the collocation of the boundary conditions with the Stokeslets. It is formulated for the flow of unmixing fluids in contact, where the velocity, pressure field, and position of the free boundary between the fluids must be determined. The standard formulation of the method of fundamental solutions is, for the first time, upgraded for the case with mixed velocity and pressure boundary conditions and verified on a T-splitter single-phase flow with unsymmetric pressure boundary conditions. The standard control volume method is used for the reference solution. The accurate evaluation of the velocity derivatives, which are required to calculate the balance of forces at the free boundary between the fluids, is achieved in a closed form in contrast to previous numerical attempts. An algorithm for iteratively calculating the position of the free boundary that involves displacement, smoothing and repositioning of the nodes is elaborated. The procedure is verified for a concurrent flow of two fluids in a channel. The velocity and velocity derivatives show fast convergence to the analytical solution. The developed boundary meshless method is easy to code, accurate and computationally efficient since only collocation at the fixed and free boundaries is needed.
Ključne besede: Stokes equations, two-phase flow, free boundary problems, method of fundamental solutions, subdomain technique
Objavljeno v DiRROS: 28.02.2024; Ogledov: 212; Prenosov: 124
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825. General position polynomialsVesna Iršič, Sandi Klavžar, Gregor Rus, James Tuite, 2024, izvirni znanstveni članek Povzetek: A subset of vertices of a graph $G$ is a general position set if no triple of vertices from the set lie on a common shortest path in $G$. In this paper we introduce the general position polynomial as $\sum_{i \geq 0} a_i x^i$, where $a_i$ is the number of distinct general position sets of $G$ with cardinality $i$. The polynomial is considered for several well-known classes of graphs and graph operations. It is shown that the polynomial is not unimodal in general, not even on trees. On the other hand, several classes of graphs, including Kneser graphs $K(n,2)$, with unimodal general position polynomials are presented.
Ključne besede: general position set, general position number, general position polynomial, unimodality, trees, Cartesian product of graphs, Kneser graphs
Objavljeno v DiRROS: 28.02.2024; Ogledov: 229; Prenosov: 132
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826. An improved local radial basis function method for solving small-strain elasto-plasticityGašper Vuga, Boštjan Mavrič, Božidar Šarler, 2024, izvirni znanstveni članek Povzetek: Strong-form meshless methods received much attention in recent years and are being extensively researched and applied to a wide range of problems in science and engineering. However, the solution of elasto-plastic problems has proven to be elusive because of often non-smooth constitutive relations between stress and strain. The novelty in tackling them is the introduction of virtual finite difference stencils to formulate a hybrid radial basis function generated finite difference (RBF-FD) method, which is used to solve small-strain von Mises elasto-plasticity for the first time by this original approach. The paper further contrasts the new method to two alternative legacy RBF-FD approaches, which fail when applied to this class of problems. The three approaches differ in the discretization of the divergence operator found in the balance equation that acts on the non-smooth stress field. Additionally, an innovative stabilization technique is employed to stabilize boundary conditions and is shown to be essential for any of the approaches to converge successfully. Approaches are assessed on elastic and elasto-plastic benchmarks where admissible ranges of newly introduced free parameters are studied regarding stability, accuracy, and convergence rate.
Ključne besede: Von Mises elasto-plasticity, radial basis function, finite differences, polyharmonic splines, two dimensions, hybrid discretization
Objavljeno v DiRROS: 28.02.2024; Ogledov: 199; Prenosov: 115
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827. Raziskava vpliva procesnih parametrov na dolgoročno dimenzijsko stabilnost velikih komponent iz trde poliuretanske pene, izdelanih z ROM tehnologijo : magistrsko deloMatjaž Sekavčnik, 2023, magistrsko delo Ključne besede: trda poliuretanska pena, dimenzijska stabilnost, ROM tehnologija, tlak dolivanja izocianata, mešalno razmerje, čas vzdrževanja izdelka v orodju, magistrsko delo
Objavljeno v DiRROS: 28.02.2024; Ogledov: 258; Prenosov: 0
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