1. 3D multidomain BEM for a Poisson equationMatjaž Ramšak, Leopold Škerget, 2009, izvirni znanstveni članek Opis: This paper deals with the efficient 3D multidomain boundary element method (BEM) for solving a Poisson equation. The integral boundary equation is discretized using linear mixed boundary elements. Sparse system matrices similar to the finite element method are obtained, using a multidomain approach, also known as the ćsubdomain techniqueć. Interface boundary conditions between subdomains lead to an overdetermined system matrix, which is solved using a fast iterative linear least square solver. The accuracy, efficiency and robustness of the developed numerical algorithm are presented using cube and sphere geometry, where the comparison with the competitive BEM is performed. The efficiency is demonstrated using a mesh with over 200,000 hexahedral volume elements on a personal computer with 1 GB memory. Ključne besede: fluid mechanics, Poisson equation, multidomain boundary element method, boundary element method, mixed boundary elements, multidomain method Objavljeno: 31.05.2012; Ogledov: 1615; Prenosov: 64 Povezava na celotno besedilo |
2. Thermal post-impact behaviour of closed-cell cellular structures with fillersMatej Vesenjak, Andreas Öchsner, Zoran Ren, 2007, izvirni znanstveni članek Opis: The study describes the behavior of regular closed-cell cellular structure with gaseous fillers under impact conditions and consequent post-impact thermal conduction due to the compression of filler gas. Two dependent but different analyses types have been carried out for this purpose: (i) a strongly coupled fluid-structure interaction and (ii) a weakly coupled thermal- structural analysis. This paper describes the structural analyses of the closed-cell cellular structure under impact loading. The explicit code LS-DYNA was used to computationally determine the behavior of cellular structure under compressive dynamic loading, where one unit volume element of the cellular structure has been discretised with finite elements considering a simultaneous strongly coupled interaction with the gaseous pore filler. Closed-cell cellular structures with different relative densities and initial pore pressures have been considered. Computational simulations have shown that the gaseous filler influences the mechanical behavior of cellular structure regarding the loading type, relative density and type of the base material. It was determined that the filler's temperature significantly increases due to the compressive impact loading, which might influence the macroscopic behavior of the cellular structure. Ključne besede: mechanics, cellular structures, closed cells, gas fillers, impact loading, fluid-structure interaction, dynamic loads, LS-DYNA, ANSYS CFX 10.0, computational simulations Objavljeno: 31.05.2012; Ogledov: 936; Prenosov: 18 Povezava na celotno besedilo |
3. Application aspects of the meshless SPH methodMatej Vesenjak, Zoran Ren, 2007, izvirni znanstveni članek Opis: Computational simulations have become an indispensable tool for solving complex problems in engineering and science. One of the new computational techniques are the meshless methods, covering several application fields in engineering. In this paper the Smoothed Particle Hydrodynamics (SPH) method and its implementation in the explicit finite element code LS-DYNA is discussed. Its application and efficiency is shown with two practical engineering application examples. The first example describes the modeling of fuel sloshing in a reservoir, where different formulations, using mesh-based and meshless methods, are compared and evaluated according to experimental measurements. The second example describes the impact analysis of a cellular structure, where the influence of viscous fluid pore filler flow has been studied. The SPH method proved to become a reliable and efficient tool, especially for solving large scale and advanced engineering problems. Ključne besede: computational mechanics, smoothed particel hydrodynamics, fluid sloshing, cellular structure Objavljeno: 31.05.2012; Ogledov: 935; Prenosov: 18 Povezava na celotno besedilo |
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5. 3D multidomain BEM for solving the Laplace equationMatjaž Ramšak, Leopold Škerget, 2007, izvirni znanstveni članek Opis: An efficient 3D multidomain BEM for solving problems governed by the Laplace equation is presented. Integral boundary equations are discretized using mixed boundary elements. The field function is interpolated using a continuous linear function while its derivative in a normal direction is interpolated using a discontiuous constant function over surface boundaey elements. Using amultidomain approach, also known as the subdomain technique, sparse system matrices similar to FEM are obtained. Interface boundary conditions between subdomains leads to an over-determined system matrix which is solved using a fast iterative linear least square solver. The accuracy and the robustness of the developed algorithm is presented on a scalar diffusion problem using simple cube geometry and various types of meshes. The efficiency is demonstrated with potential flow around a complex geometry of a fighter airplane using a tetrahedral mesh with over 100.000 subdomains on a personal computer. Ključne besede: fluid mechanics, aerodynamics, multidomain boundary element method, Laplace equation, mixed boundary elements, potential flow Objavljeno: 31.05.2012; Ogledov: 1425; Prenosov: 64 Povezava na celotno besedilo |
6. The influence of rotating domain size in a rotating frame of reference approach for simulation of rotating impeller in a mixing vesselMatej Zadravec, Sani Bašič, Matjaž Hriberšek, 2007, izvirni znanstveni članek Opis: This paper presents simulation of rotating impeller in a mixing vessel by means of Computational Fluid Dynamics (CFD). A special emphasis is devoted to the study of influence of the choice of numerical model for simulation of rotation of impeller when mixing a Newtonian fluid in a vessel equipped with Rushton impeller, and operating under turbulent flow conditions. In order to determine the best simulation approach experimental validation of the selected problem is done by means of Particle Image Velocimetry (PIV) system. When using the rotating frame of reference approach, the stirring vessel geometry has to be split into a stationary and rotating part, and the questionarises where to position the interface between both regions in order to avoid numerical errors, originating in numerical approximations at the interface. To answer this question, a comparison between the CFD based numerical results and experimental results, was made. Ključne besede: fluid mechanics, turbulent flow, Computational Fluid Dynamics, Particle Image Velocimetry, rotating frame of reference Objavljeno: 31.05.2012; Ogledov: 1305; Prenosov: 38 Povezava na celotno besedilo |
7. Non-Newtonian fluid flow through a planar symmetric expansion: shear thickenning fluidsPrimož Ternik, Jure Marn, Zoran Žunič, 2006, izvirni znanstveni članek Opis: The incompressible non-Newtonian fluid flow through a symmetric sudden expansion is studied numerically in order to obtain Reynolds number critical value. The Quadratic model is employed to accommodate the shear-thickening behavior of corn-starch and water mixture. Numerical procedure is validated with results for the Newtonian fluid flow in a range of the Reynolds number Re=10,20,.,100. Results for the non-Newtonian fluid show that the shear-thickening behavior lowers the threshold of the transition from flow symmetry to its asymmetry (lowers the onset of the bifurcation and the critical value of the Reynolds number) and increases the reattachment length. In addition, the results for the Quadratic model are compared to the results obtained with the Power law. Ključne besede: fluid mechanics, bifurcation, sudden expansion, shear thickenningfluid, quadratic model, powr law Objavljeno: 31.05.2012; Ogledov: 1058; Prenosov: 24 Povezava na celotno besedilo |
8. Velocity vorticity-based large eddy simulation with the bounadr element methodJure Ravnik, Leopold Škerget, Matjaž Hriberšek, 2006, objavljeni znanstveni prispevek na konferenci (vabljeno predavanje) Opis: A large eddy simulation using the velocity-vorticity formulation of the incompressible Navier-Stokes equations in combination with the turbulent heat transfer equation is proposed for the solution of the turbulent natural convection drive flow in a 1:4 enclosure. The system of equations is closed by an enthropy-based subgrid scale model.The Prandtl turbulent number is used to estimate turbulent diffusion in the heat transfer equation. The boundary element method is used to solve the kinematics equation and estimate the boundary vorticity values. The vorticity transport equation is solved by FEM. The numerical example studied in this paper is the onset of a turbulent flow regime occuring at high Rayleigh number values ▫$(Ra=10^7-10^10)$▫. The formation of vortices in the boundary layer is observed, along with buoyancy driven diffusive convective transport. Quantitative comparison with the laminar flow model and the worh of other authors is also presented in terms of Nusselt number value oscillations. Ključne besede: fluid mechanics, incompressible viscous fluid, turbulent flow, velocity vorticity formulation, finite element method, large eddy simulation Objavljeno: 31.05.2012; Ogledov: 1294; Prenosov: 18 Povezava na celotno besedilo |
9. Behaviour of cellular materials under impact loadingMatej Vesenjak, Zoran Ren, Andreas Öchsner, 2008, izvirni znanstveni članek Opis: The paper describes experimental and computational testing of regular open-cell cellular structures behaviour under impact loading. Open-cell cellular specimens made of aluminium alloy and polymer were experimentally tested under quasi-static and dynamic compressive loading in order to evaluate the failure conditions and the strain rate sensitivity. Additionally, specimens with viscous fillers have been tested to determine the increase of the energy absorption due to filler effects. The tests have shown that brittle behaviour of the cellular structure due to sudden rupture of intercellular walls observed in quasi-static and dynamic tests is reduced by introduction of viscous filler, while at the same time the energy absorption is increased. The influence of fluid filler on open-cell cellular material behaviour under impact loading was further investigated with parametric computational simulations, where fully coupled interaction between the base material and the pore filler was considered. The explicit nonlinear finite element code LS-DYNA was used for this purpose. Different failure criteria were evaluated to simulate the collapsing of intercellular walls and the failure mechanism of cellular structures in general. The new computational models and presented procedures enable determination of the optimal geometric and material parameters of cellular materials with viscous fillers for individual application demands. For example, the cellular structure stiffness and impact energy absorption through controlled deformation can be easily adapted to improve the efficiency of crash absorbers. Ključne besede: mechanics, porous materials, cellular materials, impact loading, mechanical testing, fluid-structure interaction, failure mechanism Objavljeno: 31.05.2012; Ogledov: 1049; Prenosov: 49 Povezava na celotno besedilo |
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