41. 
42. Lagrangian particle tracking in velocityvorticity 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 inhouse 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 nonbuoyant 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: 04.08.2017; Ogledov: 260; Prenosov: 153 Celotno besedilo (13,57 MB) Gradivo ima več datotek! Več...

43. The use of the mesh free methods (radial basis functions) in the modeling of radionuclide migration and moving boundery value problemsLeopold Vrankar, Franc Runovc, Goran Turk, 2007, izvirni znanstveni članek Opis: Recently, the mesh free methods (radial basis functionsRBFs) have emerged as a novel computing method in the scientific and engineering computing community. The numerical solution of partial differential equations (PDEs) has been usually obtained by finite difference methods (FDM), finite element methods (FEM) and boundary elements methods (BEM). These conventional numerical methods still have some drawbacks. For example, the construction of the mesh in two or more dimensions is a nontrivial problem. Solving PDEs using radial basis function (RBF) collocations is an attractive alternative to these traditional methods because no tedious mesh generation is required. We compare the mesh free method, which uses radial basis functions, with the traditional finite difference scheme and analytical solutions. We will present some examples of using RBFs in geostatistical analysis of radionuclide migration modeling. The advectiondispersion equation will be used in the Eulerian and Lagrangian forms. Stefan's or moving boundary value problems will also be presented. The position of the moving boundary will be simulated by the moving data centers method and level set method. Ključne besede: mesh free methods, radial basis functions, finite difference methods, finite elemnt methods, boundary elements methods, geostatistics, Eulerian method, Lagrangian method, level set method Objavljeno: 18.05.2018; Ogledov: 254; Prenosov: 19 Celotno besedilo (214,16 KB) Gradivo ima več datotek! Več...

44. Double diffusive natural convection in a horizontal porous layer with the boundary domain integral methodRenata Jecl, Janja Kramer Stajnko, Leopold Škerget, 2009, izvirni znanstveni članek Opis: We present the boundarydomain integral method, one of the numerical methods for solving the transport phenomena in porous media. The results for the case of double diffusive natural convection in a porous horizontal layer, which is fully saturated with an incompressible fluid, are obtained. Modified NavierStokes equations were used to describe the fluid motion in porous media in the form of conservation laws for mass, momentum, energy and species. Several results for different cases of double diffusive natural convection in a porous horizontal layer are presented and compared with some published studies in which calculations with other numerical methods were performed. Ključne besede: porous media, boundary domain integral method, double diffusive natural convection, DarcyBrinkman equation Objavljeno: 06.06.2018; Ogledov: 85; Prenosov: 21 Celotno besedilo (454,56 KB) Gradivo ima več datotek! Več...

45. A new solution for shallow and deep tunnels by considering the gravitational loadsMohammad Reza Zareifard, Ahmad Fahimifar, 2012, izvirni znanstveni članek Opis: A new, elastoplastic, analyticalnumerical solution, considering the axialsymmetry condition, for a circular tunnel excavated in a strainsoftening and Hoek–Brown rock mass is proposed. To examine the effect of initial stress variations, and also the boundary conditions at the ground surface, the formulations are derived for different directions around the tunnel. Furthermore, the effect of the weight of the plastic zone is taken into account in this regard. As the derived differential equations have no explicit analytical solutions for the plastic zone, the finitedifference method (FDM) is used in this study. On the other hand, analytical expressions are derived for the elastic zone. Several illustrative examples are given to demonstrate the performance of the proposed solution, and to examine the effect of various boundary conditions. It is concluded that the classic solutions, based on the hydrostatic farfield stress, and neglecting the effect of the boundary conditions at the ground surface, give applicable results for a wide range of practical problems. However, ignoring the weight of the plastic zone in the analyses can lead to large errors in the calculations. Ključne besede: groundresponse curve, elastoplastic analysis, boundary condition, axial symmetry, gravitational loads Objavljeno: 13.06.2018; Ogledov: 265; Prenosov: 30 Celotno besedilo (406,96 KB) Gradivo ima več datotek! Več...

46. Analytical solutions for onedimensional consolidation in unsaturated soils considering the nonDarcy law of water flowJiwei Li, Huabin Wang, 2014, izvirni znanstveni članek Opis: Analytical solutions were derived for the nonlinear, onedimensional consolidation equations for unsaturated soils. The governing equations with a nonhomogeneous mixedboundary condition were presented, in which the water flow was assumed to be governed by a nonDarcy law, whereas the air flow followed the Darcy law. The nonDarcy law was actually the nonlinear, fluxgradients relationship. The consolidation equations were thus present in a strong, nonlinear way. In order to analytically solve the equation, a homotopy analysis method (HAM) was introduced in the study, which is an analytical technique for nonlinear problems. Firstly, a governing equation in a dimensionless form was derived for a onedimensional consolidation under unsaturated soils. The method was then used for a mapping technique to transfer the original nonlinear differential equations to a number of linear differential equations. These differential equations were independent with respect to any small parameters, and were convenient for controlling the convergence region. After this transferring, a series solution to the equations was then obtained using the HAM by selecting the linear operator and the auxiliary parameters. Meanwhile, comparisons between the analytical solutions and the results of the finitedifference method indicate that the analytical solution is more efficient. Furthermore, our solutions indicate that the dissipation of air pressure is much faster than that of water pressure, and the values for the threshold gradient I have obvious effects on the dissipation values of the excess porewater pressure, but no significant effect on that of the excess poreair pressure. Ključne besede: unsaturated soil, homotopy analysis method, analytical solutions, nonDarcy law, initial and boundary conditions Objavljeno: 14.06.2018; Ogledov: 87; Prenosov: 46 Celotno besedilo (295,39 KB) Gradivo ima več datotek! Več...

47. Numerical analysis of fluid flow in a vialŽiga Časar, 2019, magistrsko delo Opis: Lyophilization or freezedrying is a widely used process in the pharmaceutical and food industry. In the process the solvent will be removed under extreme conditions of low temperature and low system pressures, whereby sublimation happens, the transition from the solid phase to the gas phase, with skipping the liquid phase, which happens bellow the triple point. This study focuses on numerical modeling at the start of the process, the so called primary drying. For this stage the highest mass flow rates of vapor are typical, since the driving force of the process is the pressure difference between the sublimation front and surrounding area. In this stage the nonbonded solvent is removed. Because of the extreme conditions the typical computational fluid dynamics approach is not suitable anymore and has to be corrected. One way to do this is to use additional models for fluid behavior at the solid wall. The study focuses on the influence of different boundary conditions on the solid wall, NoSlip, Free Slip and Maxwell Slip, and their effect on fluid flow inside the vial. A quantitative and qualitative comparison of the results is presented. Ključne besede: Lyophilization, Knudsen number, computational fluid dynamics, fluid flow, numerical modeling, slip boundary condition Objavljeno: 09.07.2019; Ogledov: 195; Prenosov: 48 Celotno besedilo (2,66 MB) 