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71.
Numerical simulation of dilute particle laden flows by wavelet BEM-FEM
Jure Ravnik, Leopold Škerget, Matjaž Hriberšek, Zoran Žunič, 2008, original scientific article

Abstract: A wavelet transform based BEM and FEM numerical scheme was used to simulate laminar viscous flow. The velocity-vorticity formulation of the Navier-Stokes equations was used. The flow simulation algorithm was coupled with a Lagrangian particle tracking scheme for dilute suspensions of massless particles and particles without inertia. The proposed numerical approach was used to simulate flow and particle paths for two test cases: flow over a backward-facing step and flow past a circular cylinder. We present methods of calculating the pressure and stream function field at the end of each time step. The pressure field was used to calculate drag and lift coefficients, which enable qualitative comparison of our results with the benchmark. The stream function enabled the comparison of streamlines and massless particle paths in steady state low Reynolds number value flow fields, and thus provided an estimate on the accuracy of the particle tracking algorithm. Unsteady higher Reynolds number value flows were investigated in terms of particle distributions in vortex streets in the wake of the cylinder and behind the step. Sedimentation of particles without inertia was studied in the flow field behind a backward-facing step at Reynolds number value 5000.
Keywords: boundary element method, velocity-vertocity formulation, discrete wavelet transform, Lagrangian particle tracking, backward-facing step, bluff body flow, dilute particle suspension
Published in DKUM: 01.06.2012; Views: 1957; Downloads: 96
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72.
A multidomain boundary element method for unsteady laminar flow using stream function-vorticity equations
Matjaž Ramšak, Leopold Škerget, Matjaž Hriberšek, Zoran Žunič, 2005, original scientific article

Abstract: The paper deals with the Boundary Element Method (BEM) for modelling 2D unsteady laminar flow using stream function-vorticity formulation of the Navier-Stokes equations. The numerical algorithm for solving a general parabolic diffusion-convection equation is based on linear mixed elements and a multidomain model also known as subdomain technique. Robustness, accuracy and economy of the developed numerical algorithm is shown on a standard case of steady backward facing step flow and a periodic flow past a circular cylinder test case.
Keywords: fluid mechanics, viscous fluid, unsteady laminar flow, boundary element method, multidomain model, stream function, vorticity formulation, backward facing step flow, flow past a cylinder
Published in DKUM: 01.06.2012; Views: 2104; Downloads: 103
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73.
Heat conduction in closed-cell cellular metals
Matej Vesenjak, Zoran Žunič, Andreas Öchsner, Matjaž Hriberšek, Zoran Ren, 2005, original scientific article

Abstract: The purpose of this research was to describe the thermal transport properties in closed-cell cellular metals. Influence of cell size variations with different pore gases has been investigated with transient computational simulations. Heat conduction through the base material and gas in pores (cavities) was considered, while the convection and radiation were neglected in the initial stage of this research. First, parametric analysis for definingthe proper mesh density and time step were carried out. Then, two-dimensional computational models of the cellular structure, consisting of the base material and the pore gas, have been solved using ANSYS CFX software within the framework of finite volume elements. The results have confirmed theexpectations that the majority of heat is being transferred through the metallic base material with almost negligible heat conduction through the gas in pores. The heat conduction in closed-cell cellular metals is therefore extremely depended on the relative density but almost insensitive regarding tothe gas inside the pore, unless the relative density is very low.
Keywords: heat transfer, cellular metal materials, porous materials, closed cells, gas fillers, computational simulations
Published in DKUM: 01.06.2012; Views: 2136; Downloads: 99
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74.
Boundary domain integral method for high Reynolds viscous fluid flows in complex planar geometries
Matjaž Hriberšek, Leopold Škerget, 2005, original scientific article

Abstract: The article presents new developments in boundary domain integral method (BDIM) for computation of viscous fluid flows, governed by the Navier-Stokes equations. The BDIM algorithm uses velocity-vorticity formulation and is basedon Poisson velocity equation for flow kinematics. This results in accurate determination of boundary vorticity values, a crucial step in constructing an accurate numerical algorithm for computation of flows in complex geometries, i.e. geometries with sharp corners. The domain velocity computations are done by the segmentation technique using large segments. After solving the kinematics equation the vorticity transport equation is solved using macro-element approach. This enables the use of macro-element based diffusion-convection fundamental solution, a key factor in assuring accuracy of computations for high Reynolds value laminar flows. The versatility and accuracy of the proposed numerical algorithm is shown for several test problems, including the standard driven cavity together with the driven cavity flow in an L shaped cavity and flow in a Z shaped channel. The values of Reynolds number reach 10,000 for driven cavity and 7500 for L shapeddriven cavity, whereas the Z shaped channel flow is computed up to Re = 400. The comparison of computational results shows that the developed algorithm is capable of accurate resolution of flow fields in complex geometries.
Keywords: fluid mechanics, numerical methods, boundary domain integral method, algorithms, incompressible fluid flow, Navier-Stokes equations, velocity vorticity formulation, segmentation technique, driven cavity flow
Published in DKUM: 01.06.2012; Views: 2003; Downloads: 86
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75.
76.
Numerična analiza zgorevanja KOEL v mali kurilni napravi
Boštjan Rajh, Matej Zadravec, Niko Samec, Matjaž Hriberšek, 2011, published scientific conference contribution

Keywords: kapljevita goriva, male kurilne naprave, numerična analiza
Published in DKUM: 01.06.2012; Views: 1877; Downloads: 46
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77.
78.
Primerjava simulacije delovanja Darrieusove vodne turbine po postopku z modelom gibanja togega telesa in postopkom MFR
Matjaž Fleisinger, Matej Zadravec, Matej Vesenjak, Matjaž Hriberšek, Karli Udovičič, 2011, published scientific conference contribution

Abstract: Med tehnologijami za izkoriščanje vodne energije se vse pogosteje uporabljajo tudi prilagojene tehnologije za izkoriščanje energije vetra. K njihovemu razvoju pripomorejo sodobne računalniške simulacije. Predstavljena je primerjava dveh metod numerične simulacije Darrieusove turbine s poudarkom na ustreznosti delovanja nove metode z uporabo modela gibanja togega telesa (modul 6DOF). Ta omogoča simulacijo turbine, pri kateri je le-ta gnana s tokom tekočine, se pravi, da bolje opiše realne obratovalne razmere kot uveljavljen postopek MFR.
Keywords: energija vetra, Darrieusova turbina, hitrostna polja
Published in DKUM: 01.06.2012; Views: 2270; Downloads: 67
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79.
Magnetic particle separation in viscous flows by BEM
Matjaž Hriberšek, Jure Ravnik, Primož Kocutar, 2011, published scientific conference contribution

Abstract: A boundary element method based solver for particle motion simulation in dilute suspensions under the influence of hydrodynamic and magnetic forces was applied. The Euler-Lagrangian formulation for simulation of dilute two-phase flow was applied. The algorithm solves the incompressible Navier-Stokes equations written in velocity-vorticity formulation. The non uniform magnetic field was defined analytically for the case of a set of long thin wires. The particle trajectories were computed by applying the 4th order Runge-Kutta method. The computed test case consisted of a narrow channel under the influence of a nonuniform magnetic field, where magnetite and aluminium particles were suspended in water. The results of computations show the distributions of particles along the channel and confirms the suitability of the proposed configuration as a separation device under ideal conditions.
Keywords: boundary element method, laminar flow, magnetic particles, viscous fluids
Published in DKUM: 01.06.2012; Views: 2479; Downloads: 55
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80.
Primerjava valčne transformacije in metode mnogokratnih polov za reševanje integralskih enačb Poissonovega tipa
Jure Ravnik, Leopold Škerget, Matjaž Hriberšek, 2009, published scientific conference contribution

Abstract: Če metodo robnih elementov uporabimo za rešitev nehomogene parcialne diferencialne enačbe, moramo po diskretizaciji izračunati polno matriko območnih integralov. V prispevku primerjamo dve metodi: metodo mnogokratnih polov in valčno transformacijo, ki omogočata izdelavo razpršene aproksimacije območnih matrik. Pri metodi mnogokratnih polov uporabljamo razvoj integralskega jedra po sferičnih harmonikih. Uporabljena valčna transformacija temelji na diskretni Haarovi transformaciji za vektorje poljubnih dolžin. Metodi smo testirali na skalarni Poissonovi enačbi in vektorski hitrostno vrtinčni enačbi kinematike. Rezultati kažejo, da metoda večkratnih polov daje natančnejše rezultate pri enaki stopnji razpršenosti območne matrike. Po drugi strani pa valčno transformacijo lahko uporabljamo nespremenjeno za katerokoli matriko, medtem ko je metoda večkratnih polov odvisna od razvoja integralskega jedra v vrsto.
Keywords: metoda robnih elementov, nehomogene parcialne diferencialne enačbe, diskretizacija, metoda mnogokratnih polov, valčna transformacija
Published in DKUM: 31.05.2012; Views: 1679; Downloads: 29
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