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1.
Two-dimensional velocity-vorticity based LES for the solution of natural convection in a differentially heated enclosure by wavelet transform based BEM and FEM
Jure Ravnik, Leopold Škerget, Matjaž Hriberšek, 2006, izvirni znanstveni članek

Opis: A wavelet transform based boundary element method (BEM) numerical scheme is proposed for the solution of the kinematics equation of the velocity-vorticityformulation of Navier-Stokes equations. FEM is used to solve the kinetics equations. The proposed numerical approach is used to perform two-dimensional vorticity transfer based large eddy simulation on grids with 105 nodes. Turbulent natural convection in a differentially heated enclosure of aspect ratio 4 for Rayleigh number values Ra=107-109 is simulated. Unstable boundary layer leads to the formation of eddies in the downstream parts of both vertical walls. At the lowest Rayleigh number value an oscillatory flow regime is observed, while the flow becomes increasingly irregular, non-repeating, unsymmetric and chaotic at higher Rayleigh number values. The transition to turbulence is studied with time series plots, temperature-vorticity phase diagrams and with power spectra. The enclosure is found to be only partially turbulent, what is qualitatively shown with second order statistics-Reynolds stresses, turbulent kinetic energy, turbulent heat fluxes and temperature variance. Heat transfer is studied via the average Nusselt number value, its time series and its relationship to the Rayleigh number value.
Ključne besede: numerical modelling, boundary element method, discrete wavelet transform, large eddy simulation, velocity-vertocity formulation, natural convection
Objavljeno: 31.05.2012; Ogledov: 1462; Prenosov: 41
URL Povezava na celotno besedilo

2.
Computational approach to contact fatigue damage initiation analysis of gear teeth flanks
Matjaž Šraml, Jože Flašker, 2006, izvirni znanstveni članek

Opis: The paper describes a general computational model for the simulation of contact fatigue-damage initiation in the contact area of meshing gears. The model considers the continuum mechanics approach, where the use of homogenous and elastic material is assumed. The stress field in the contact area and the relationship between the cyclic contact loading conditions and observed contact points on the tooth flank are simulated with moving Hertzian contact pressure in the framework of the finite element method analysis. An equivalentmodel of Hertzian contact between two cylinders is used for evaluating contact conditions at the major point of contact of meshing gears. For the purpose of fatigue-damage analysis, the model, which is used for prediction of the number of loading cycles required for initial fatigue damageto appear, is based on the Coffin-Manson relationship between deformations and loading cycles. On the basis of computational results, and with consideration of some particular geometrical and material parameters, theinitiation life of contacting spur gears in regard to contact fatigue damage can be estimated.
Ključne besede: machine elements, fracture mechanics, gears, contact fatigue, crack initiation, numerical modelling, teeth flanks
Objavljeno: 30.05.2012; Ogledov: 1528; Prenosov: 47
URL Povezava na celotno besedilo

3.
Laminar flow of a shear-thickening fluid in a 90° pipe bend
Jure Marn, Primož Ternik, 2006, izvirni znanstveni članek

Opis: The non-Newtonian fluid flow in a sharp 90 curved pipe is studied numerically to obtain the pressure loss coefficient prompted by disagreement between the existing empirical correlations and results obtained by computer codes. This disagreement results from presumption of fully developed flow throughout the curvature (correlations) while the actual flow is partially developed for the Newtonian and sharp 90 curved bend non-Newtonian flows, and fully developed for slightly bent 90 curvature non-Newtonian flow. The Quadratic model is employed to accommodate the shear-thickening behavior of an electrostatic ash and water mixture. Numerical results are obtained for different values of Reynolds number. Finally, results for local pressure loss coefficient are compared with values obtained for the Power law rheological model.
Ključne besede: shear-thickening fluid, fluid dynamics, rheological model, pipe bend flow, numerical modelling, pressure losses
Objavljeno: 30.05.2012; Ogledov: 1108; Prenosov: 44
URL Povezava na celotno besedilo

4.
Symmetry breaking phenomena of purely viscous shear-thinning fluid flow in a locally constricted channel
Primož Ternik, 2008, izvirni znanstveni članek

Opis: The goal of a present study is to investigate the effects of generalized Newtonian fluids on the threshold of the transition from flow symmetry to its asymmetry for the flow through a locally constricted channel. We consider purely viscous shear-thinning fluid and compare it with the Newtonian fluid. Fluid flow is studied numerically by solving the two dimensional momentum equations along with the continuity equation and the Carreau-Yasuda rheological model. We report systematic results in a range of generalized Reynolds number 250▫$leq$▫Re▫$leq$▫150 with a focus on its critical value. Results indicate that the shear-thinning viscous behaviour decreases the onset of bifurcation phenomena and the critical value of Reynolds number. Last but not least, a systematic grid refinement analysis and numerical accuracy study is performed and present numerical results may be treated as the benchmark.
Ključne besede: bifurcation, inelastic shear-thinning fluid, Carreau-Yasuda model, numerical modelling
Objavljeno: 31.05.2012; Ogledov: 904; Prenosov: 48
URL Povezava na celotno besedilo

5.
Computational model for the analysis of bending fatigue in gears
Janez Kramberger, Matjaž Šraml, Srečko Glodež, Jože Flašker, Iztok Potrč, 2004, izvirni znanstveni članek

Opis: A computational model for the determination of service life of gears with regard to bending fatigue in a gear tooth root is presented. The fatigue process leading to tooth breakage is divided into crack initiation (Ni) and crack propagation (Np) periods, where the complete service life is defined as N = Ni + Np. The strain-life method in the framework of the FEM method has been used to determine the number of stress cycles Ni required for fatigue crack initiation. Gear tooth crack propagation was simulated using a FEM method based computer program which uses principles of linear elastic fracture mechanics. The Paris equation is then used for the further simulation of the fatigue crack growth. The presented model is used to determine the service life of a real spur gear made from through-hardened steel 42CrMo4.
Ključne besede: machine elements, gears, bending fatigue, service life, fatigue crack initiation, fatigue crack propagation, computational simulations, numerical modelling, fracture mechanics
Objavljeno: 01.06.2012; Ogledov: 2126; Prenosov: 50
URL Povezava na celotno besedilo

6.
Numerical procedure for predicting the rolling contact fatigue crack initiation
Matjaž Šraml, Jože Flašker, Iztok Potrč, 2003, izvirni znanstveni članek

Opis: A computational numerical model for contact fatigue damage analysis of mechanical elements is presented in this paper. The computational approach is based on continuum mechanics, where a homogenous and elastic material model isassumed in the framework of the finite element method analysis. Cyclic contact loading conditions are simulated with moving Hertzian contact pressure. The time-depending loading cycles are defined for each observed material point on and under the contact area. Furthermore, the influence of friction upon rolling-sliding contact loading cycles is analysed in detail, using Coulombćs friction law. The model for prediction of the number of loading cycles, required for initial fatigue damages to appear, is based on Coffin-Manson relations between deformations and loading cycles, and includes characteristic material fatigue parameters. As a general example, the model isused to analyse a fundamental contact problem of a cylinder and flat surface, which is usually a substitutional model for analysing real mechanicalproblems. However, the results concerning the identification of critical material points and the number of loading cycles, required for initial fatigue damages to appear at those points, are the main purpose of thepresented study.
Ključne besede: machine elements, gears, contact problems, contact fatigue, crack initiation, numerical modelling
Objavljeno: 01.06.2012; Ogledov: 1024; Prenosov: 33
URL Povezava na celotno besedilo

7.
Simplified modeling of detailed chemistry description in premixed turbulent combustion by BEM
Niko Samec, Leopold Škerget, 2002, izvirni znanstveni članek

Opis: A simplified modeling of premixed turbulent combustion based on detailed chemical kinetics and simplified mixing is presented. The main conservation equations of mass energy and species mass have been solved numerically applying boundary doma integral method for diffusive coonective transport equation with constant and linear source term. The model has been applied to the particular case of the premixed charge in a spark-ignited internal combustion engine. The model predictions are in good agreement with measurements.
Ključne besede: combustion, turbulence, numerical modelling, boundary element method, internal combustion engines
Objavljeno: 01.06.2012; Ogledov: 735; Prenosov: 44
URL Povezava na celotno besedilo

8.
A computational model for determination of service life of gears
Srečko Glodež, Matjaž Šraml, Janez Kramberger, 2002, izvirni znanstveni članek

Opis: A computational model for determination of service life of gears in regard to bending fatigue in a gear tooth root is presented. The fatique process leading to tooth breakage is divided into crack initiation and crack propagation period. The strain-life method in the framework of the FEM-methods has been used to determine the number of stress cycles Ni required for the fatique crack initiation, where it is assumed that the crack is initiated at the point of the largest stresses in a gear tooth root. The simple Paris equations is then used for the further simulation of the fatigue crack growth. The functional relationship between the stress intensity factor and crack length K=f(a), which is needed for determination ofthe required number of loading cycles Np for a crack propagation from the initial to the critical length, is obtained using displacement correlation method in the framework of the FEM-method. The total number of stress cycles N for the final failure to occur is then a sum of Ni and Np. The model is used for determination of service life of real spur gear made from through-hardened steel 42CrMo4, where required material parameters have been determined previously by the appropriate test specimens.
Ključne besede: machine elements, fatigue, fatigue crack growth, numerical modelling, gears, service life
Objavljeno: 01.06.2012; Ogledov: 1334; Prenosov: 63
URL Povezava na celotno besedilo

9.
Numerical and experimental study of water/oil emulsified fuel combustion in a diesel engine
Niko Samec, Breda Kegl, Robert W. Dibble, 2002, izvirni znanstveni članek

Opis: Numerical and experimental studies were made on some of the chemical and physical properties of wateržoil emulsified fuel (W/OEF) combustion characteristics. Numerical investigations of W/OEF combustion's chemical kinetic aspects have been performed by simulation of water/n-heptane mixture combustion, assuming a model of a homogenous reactor's concentric shells. The injection and fuel spray characteristics are analyzed numerically also in order to study indirectly the physical effects of water present in diesel fuel during the combustion process. The experimental results of W/OEF combustion in the DI diesel engine are also presented and discussed. The results of engine testing in a broad field of engine loads and speeds have shown a significant pollutant emission reduction with no worsening of specific fuel consumption.
Ključne besede: internal combustion engines, Diesel engines, combustion, emissions, numerical modelling
Objavljeno: 01.06.2012; Ogledov: 1177; Prenosov: 58
URL Povezava na celotno besedilo

10.
Fatigue behaviour of 42CrMo4 steel under contact loading
Péter Göncz, Rok Potočnik, Srečko Glodež, 2010, izvirni znanstveni članek

Opis: The presented paper describes the experimental determination of fatigue crack growth parameters for high strength low-alloy steel 42CrMo4. The experiments were performed according to the ASTM E647 standard and the parameters of the Paris equation (C and m) were determined. Test specimens were subjected to impulsive cyclic tensile loading on a testing machine. During that the fatigue crack propagation was monitored as a function of elapsed fatigue cycles. Taking these experimental results into account the fatigue crack growth rates at different stress-intensity factor ranges was determined. To consider the variable material properties of the slewing bearing ring trough depth, specimens of different hardnesses were tested. Beside the experimental result a 2D contact fatigue crack propagation model is also presented. This model can be used for the simulation of surface initiated contact fatigue crack propagation on the roller slewing bearing's raceway. As a computational example the results of a finite element method contact fatigue crack propagation simulation are presented.
Ključne besede: crack propagation, slewing bearings, numerical modelling, experiments
Objavljeno: 07.06.2012; Ogledov: 1110; Prenosov: 38
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