81. Natural convection flows in complex cavities by BEMLeopold Škerget, Matjaž Hriberšek, Zoran Žunič, 2003, original scientific article Abstract: 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. Keywords: fluid dynamics, natural convection, boundary element method, differential equations, closed cavity Published in DKUM: 01.06.2012; Views: 2120; Downloads: 91
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82. Weakly coupled analysis of a blade in multiphase mixing vesselMatej Vesenjak, Zoran Ren, Matjaž Hriberšek, 2004, other scientific articles Abstract: Two or more physical systems frequently interact with each other, where the independent solution of one system is impossible without a simultaneous solution of the others. An obvious coupled system is that of a dynamic fluid-structure interaction. š8đ In this paper a computational analysis of thefluid-structure interaction in a mixing vessel is presented. In mixing vessels the fluid can have a significant influence on the deformation of blades during mixing, depending on speed of mixing blades and fluid viscosity.For this purpose a computational weakly coupled analysis has been performed to determine the multiphase fluid influences on the mixing vessel structure. The multiphase fluid field in the mixing vessel was first analyzed with the computational fluid dynamics (CFD) code CFX. The results in the form of pressure were then applied to the blade model, which was the analysed with the structural code MSC.visualNastran forWindows, which is based on the finiteelement method (FEM). Keywords: fluid mechanics, solid mechanics, coupled problems, computational analysis, two-phase fluid, mixing blade, pressure distribution, finite volume method, finite element method Published in DKUM: 01.06.2012; Views: 1877; Downloads: 97
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83. The wavelet transform for BEM computational fluid dynamicsJure Ravnik, Leopold Škerget, Matjaž Hriberšek, 2004, original scientific article Abstract: 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. Keywords: fluid mechanics, computational fluid dynamics, boundary element method, wavelet transform, linear systems of equations, velocity vorticity formulation, driven cavity, natural convection, system matrix compression Published in DKUM: 01.06.2012; Views: 2277; Downloads: 98
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84. Numerical simulation of dilute particle laden flows by wavelet BEM-FEMJure 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: 2231; Downloads: 101
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85. A multidomain boundary element method for unsteady laminar flow using stream function-vorticity equationsMatjaž 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: 2295; Downloads: 108
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86. Heat conduction in closed-cell cellular metalsMatej 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: 2314; Downloads: 104
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87. Boundary domain integral method for high Reynolds viscous fluid flows in complex planar geometriesMatjaž 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: 2229; Downloads: 91
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