1. Fractal geometry as an effective heat sinkMatjaž Ramšak, 2022, izvirni znanstveni članek Opis: "How long is the coast of Britain?" was the question stated by Mandelbrot. Using smaller and smaller rulers the coast length limits to infinity. If this logic is applied to the fractal heat sink geometry, infinite cooling capacity should be obtained using fractals with mathematically infinite surface area. The aim of this article is to check this idea using Richardson extrapolation of numerical simulation results varying the fractal element length from one to zero. As expected, the extrapolated heat flux has a noninfinite limit. The presented fractal heat sink geometry is non-competitive to the straight fins. Ključne besede: fractal heat sink, LED cooling, CPU cooling, conjugate heat transfer, laminar flow, boundary element method, Koch snowflake Objavljeno v DKUM: 14.07.2023; Ogledov: 515; Prenosov: 11 Celotno besedilo (3,00 MB) Gradivo ima več datotek! Več... |
2. Validation of boundary element method for assessment of weld joints accounting for notch stress : magistrsko deloRok Skerbiš, 2022, magistrsko delo Opis: Robust, automated mesh generation on arbitrary weld joint geometries, using finite element method (FEM) is a problematic task. It was previously discovered, that an arbitrary weld joint geometry can be parameterized inside a CAD environment [1], however when it comes to domain discretization and boundary conditions assignment, the parameterized approach becomes too demanding inside FEM. This results in long FEM model preparation times and sometimes in problems with the parametric model itself, which leads to a need for an additional numerical method - boundary element method (BEM), which overcomes this issue and is beneficial in this case. BEM is a numerical method, that in addition to other applications finds a use in the elasto-mechanic problems, where the only concern is the boundary of the considered geometric domain. Since notch stress calculations of weld joints fall into this category, their calculation can be carried out with it. Since there is not much available information on whether or not such calculations are a suitable alternative for the currently used FEM, this thesis had to be confirmed through a structured and step by step procedure. First, a notch mesh quality study has been made, then other entities followed. It was discovered that BEM is applicable to the problem and capable of calculating results with sufficient quality. Furthermore, the parameter driven approach and automated calculation provide for additional advantageous potentials. Ključne besede: weld joint, boundary element method, finite element method, spatial discretization, notch stress Objavljeno v DKUM: 02.11.2022; Ogledov: 403; Prenosov: 0 Celotno besedilo (4,62 MB) |
3. Lagrangian particle tracking in velocity-vorticity resolved viscous flows by subdomain BEMJure Ravnik, Matjaž Hriberšek, Janez Lupše, 2016, izvirni znanstveni članek Opis: A numerical study of particle motion in a cubic lid driven cavity is presented. As a computational tool, a boundary element based flow solver with a Lagrangian particle tracking algorithm is derived. Flow simulations were performed using an in-house boundary element based 3D viscous flow solver. The Lagrangian particle tracking algorithm is capable of simulation of dilute suspensions of particles in viscous flows taking into account gravity, buoyancy, drag, pressure gradient and added mass. The derived algorithm is used to simulate particle behaviour in a cellular flow field and in a lid driven cavity flow. Simulations of particle movement in a cellular flow field were used to validate the algorithm. The main goal of the paper was to numerically simulate the flow behaviour of spheres of different densities and different diameters, as experimentally observed in work of Tsorng et al.The study of slightly buoyant and non-buoyant particles in a lid driven cavity was aimed at discovering cases when particles leave the primary vortex and enter into secondary vortices, a phenomenon described in the work of Tsorng et al. A parametric study of this phenomenon was preformed. The presented computational results show excellent agreement with experiments, confirming the accuracy of the developed computational method. Ključne besede: dispersed two phase flow, Lagrangian particle tracking, cellular flow, lid driven cavity, boundary element method Objavljeno v DKUM: 04.08.2017; Ogledov: 1105; Prenosov: 392 Celotno besedilo (13,57 MB) Gradivo ima več datotek! Več... |
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5. Mixed boundary elements for laminar flowsMatjaž Ramšak, Leopold Škerget, 1999, izvirni znanstveni članek Opis: This paper presents a mixed boundary element formulation of the boundary domain integral method (BDIM) for solving diffusion-convective transport problems. The basic idea of mixed elements is the use of a continuos interpolation polynomial for conservative field function approximation and a discontinuous interpolation polynomial for its normal derivative along the boundary element. In this way, the advantages of continuous field function approximation are retained and its conservation is preserved while the normal flux values are approximated by interpolation nodal points with a uniquely defined normal direction. Due to the use of mixed boundary elements, the final discretized matrix system is overdetermined and a special solver based on the least squares method is applied. Driven cavity, natural and forced convection in a closed cavity are studied. Driven caviaty results at Re=100, 400 and 1000 agree better with the benchmark solution than Finite Element Method of Finite Volume Method results for the same grid density with 21 x 21 degrees of freedom. The average Nusselt number values for natural convection ▫$10^3$▫▫$le$▫Ra▫$le$▫▫$10^6$▫ agree better than 0.1% with benchmark solutions for maximal calculated grid desities 61 x 61 degrees for freedom. Ključne besede: fluid mechanics, incompressible fluid, laminar flow, velocity vorticity formulation, boundary element method, mixed boundary elements Objavljeno v DKUM: 01.06.2012; Ogledov: 2110; Prenosov: 94 Povezava na celotno besedilo |
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7. Boundary element method for natural convection in non-Newtonian fluid saturated square porous cavityRenata Jecl, Leopold Škerget, 2003, izvirni znanstveni članek Opis: The main purpose of this work is to present the use of the Boundary Element Method (BEM) in the analysis of the natural convection in the square porous cavity saturated by the non-Newtonian fluid. The results of hydrodynamic and heat transfer evaluations are reported for the configuration in which the enclosure is heated from a side wall while the horizontal walls are insulated.The flow in the porous medium is modelled using the modified Brinkman extended Darcy model taking into account the non-Darcy viscous effects. The governing equations are transformed by the velocity-vorticity variables formulation enabling the computation scheme to be partitioned into kinematic and kinetic parts. To analyse the effects of the available non-Newtonian viscosity and to evaluate the presented approach, the power law model for shear thinning fluids (n<1), for shear thickening fluids (n>1) and in the limit for the Newtonian fluids (n=1) is considered. Numerical model is tested also for the Carreau model adequate for many non-Newtonian fluids. Solutions for the flow and temperature fields and Nusselt numbers are obtainedin terms of a modified Rayleigh number Ra*, Darcy number Da, and the non-Newtonian model parameters. The agreement between the results obtained with finite difference method is very good indicating that BEM can be efficiently used for solving transport phenomena in saturated porous medium. Ključne besede: natural convection, non-Newtonian fluid, porous medium, cavity flow, boundary element method, boundary domain integral method Objavljeno v DKUM: 01.06.2012; Ogledov: 1722; Prenosov: 94 Povezava na celotno besedilo |
8. Natural convection flows in complex cavities by BEMLeopold Škerget, Matjaž Hriberšek, Zoran Žunič, 2003, izvirni znanstveni članek Opis: A numerical method for the solution of Navier-Stokes equations is developed using an integral representation of the conservation equations. The velocity- vorticity formulation is employed, where the kinematics is given with the Poisson equation for a velocity vector, while the kinetics is represented with the vorticity transport equation. The corresponding boundary-domain integral equations are presented along with discussions of the kinetics and kinematics of the fluid flow problem. THE BEM formulation is developed and tested for natural convection flows in closed cavities with complex geometries. Ključne besede: fluid dynamics, natural convection, boundary element method, differential equations, closed cavity Objavljeno v DKUM: 01.06.2012; Ogledov: 1918; Prenosov: 85 Povezava na celotno besedilo |
9. The wavelet transform for BEM computational fluid dynamicsJure Ravnik, Leopold Škerget, Matjaž Hriberšek, 2004, izvirni znanstveni članek Opis: A wavelet matrix compression technique was used to solve systems of linear equations resulting from BEM applied to fluid dynamics. The governing equations were written in velocity-vorticity formulation and solutions of the resulting systems of equations were obtained with and without wavelet matrix compression. A modification of the Haar wavelet transform, which can transformvectors of any size, is proposed. The threshold, used for making fully populated matrices sparse, was written as a product of a user defined factor and the average value of absolute matrix elements values. Numerical tests were performed to assert, that the error caused by wavelet compression depends linearly on the factor , while the dependence of the error on the share of thresholded elements in the system matrix is highly non-linear. The results also showed that the increasing non-linearity (higher Ra and Re numbervalues) limits the extent of compression. On the other hand, higher meshdensity enables higher compression ratios. Ključne besede: fluid mechanics, computational fluid dynamics, boundary element method, wavelet transform, linear systems of equations, velocity vorticity formulation, driven cavity, natural convection, system matrix compression Objavljeno v DKUM: 01.06.2012; Ogledov: 2042; Prenosov: 94 Povezava na celotno besedilo |
10. Integral formulation of a diffusive-convective transport equation for reacting flowsNiko Samec, Leopold Škerget, 2004, izvirni znanstveni članek Opis: This peper deals with a numerical solution of a diffusive-convective transport equation for reacting flows based on boundary domain integral formulation for diffusive-convective fundamental solution. A great part of attention has been dedicated to the numerical treatment of the diffusive-convective transport equation for high Pe number and reaction term values as the convective or reaction term becomes dominant compared to the diffusion one. In this case, the hyperbolic character predominates the ellipticity or parabolicity of the governing transport equation, and stability problems arise in the numerical solution. Numerical efficiency of the developed numerical implementation is tested against analytical and numerical results for the typical test cases of diffusive-convective transport problems (i.e. multicomponent reacting flows). Ključne besede: fluid mechanics, boundary element method, diffusion, convection, transport problems, reacting flow Objavljeno v DKUM: 01.06.2012; Ogledov: 1528; Prenosov: 97 Povezava na celotno besedilo |