1. Yield strength modelling of formed material using evolutionary computational methodLeo Gusel, Rebeka Rudolf, 2009, izvirni znanstveni članek Opis: In this paper we propose an evolutionary computation approach for the modelling of yield strength in formed material. One of the most general evolutionary computation methods is genetic programming, which was used in our research. Genetic programming is an automated method for creating a working computer program from a problemćs high-level statement. Genetic programming does this by genetically breeding a population of computer programs using the principles of Darwinianćs natural selection and biologically inspired operations. During our research, material was cold formed by drawing using different process parameters and then determining yield strengths (dependent variable) of the specimens. On the basis of a training data set, various different genetic models for yield strength distribution were developed during simulated evolution. The accuracies of the best models were proved by a testing data set and comparing between the genetic and regression models. The research showed that very accurate genetic models can be developed by the proposed approach.
Ključne besede: metal forming, yield strength, genetic programming, modelling
Objavljeno: 31.05.2012; Ogledov: 1531; Prenosov: 27
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2. Two-dimensional velocity-vorticity based LES for the solution of natural convection in a differentially heated enclosure by wavelet transform based BEM and FEMJure 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: 1746; Prenosov: 62
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3. Slip modeling in timber-framed walls with wood-based or fibre-plaster sheathing boardsMiroslav Premrov, Peter Dobrila, Branko Bedenik, Igor Špacapan, 2007, izvirni znanstveni članek Opis: The paper provides mathematical modelling for prefabricated timber-framed walls composed of a timber frame and two different types of sheathing boards. Since by wood-based boards (WBB) the tensile strength is similar to the compressive one, there are practically no cracks appearing in the boards. On the other hand, in case of fibre-plaster sheathing boards (FPB) the tensile strength is approximately 10-times lower than the compressive one and therefore cracks in the tensile diagonal boardćs direction usually appear. Based on analysis of experimental research results [1] special approximate mathematical models have been developed. The models enable simultaneously to consider the flexibility of mechanical fasteners in the connecting areas, as well as possible cracks appearing in the tensile area of the sheathing boards.
Ključne besede: civil engineering, timber structures, walls, CFRP strips, carbon fibre-reinforced polymer, mathematical modelling
Objavljeno: 31.05.2012; Ogledov: 1401; Prenosov: 29
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4. Modeling of impact toughness of cold formed material by genetic programmingLeo Gusel, Miran Brezočnik, 2006, izvirni znanstveni članek Opis: In the paper, an approach completely different from the conventional methods for determination of accurate models for the change of properties of cold formed material, is presented. This approach is genetic programming (GP) method which is based on imitation of natural evolution of living organisms. The main characteristic of GP is its non-deterministic way of computing. No assumptions about the form and size of expressions were made in advance, but they were left to the self organization and intelligence of evolutionary process. First, copper alloy rods were cold drawn under different conditions and then impact toughness of cold drawn specimens was determined by Charpy tests. The values of independent variables (effective strain, coefficient of friction) influence the value of the dependent variable, impact toughness. On the basis of training data, different prediction models for impact toughness were developed by GP. Only the best models, gained by genetic programming were presented in the paper. Accuracy of the best models was proved with the testing data set. The comparison between deviation of genetic model results and regression model results concerning the experimental results has showed that genetic models are more precise and more varied then regression models.
Ključne besede: metal forming, genetic programming, evolutionary computing, impact toughness, copper alloy, modelling
Objavljeno: 30.05.2012; Ogledov: 1581; Prenosov: 84
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5. Computational approach to contact fatigue damage initiation analysis of gear teeth flanksMatjaž 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: 1816; Prenosov: 69
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6. Laminar flow of a shear-thickening fluid in a 90° pipe bendJure 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: 1354; Prenosov: 68
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7. Influence of blending functions on volumetric cloud imagesBogdan Lipuš, Nikola Guid, 2008, izvirni znanstveni članek Opis: Various blending functions can be applied in the volumetric modelling of clouds. This paper analyzes the impact of five different blending functions (linear, cubic, Wyvill-1, Wyvill-2, and cosine) on cloud shape, structure, and area. We have found that there are only negligible differences among them. Therefore, we can conclude that the simple linear blending function satisfies all the desired properties for generating cloud images by volumetric modelling.
Ključne besede: computer graphics, volumetric modelling, cloud modelling, natural phenomena
Objavljeno: 31.05.2012; Ogledov: 1121; Prenosov: 97
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8. Symmetry breaking phenomena of purely viscous shear-thinning fluid flow in a locally constricted channelPrimož 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: 1149; Prenosov: 87
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9. Advanced modelling and simulation methods for communication networksJože Mohorko, Matjaž Fras, Saša Klampfer, 2008, izvirni znanstveni članek Opis: This paper contains a brief overview of suitable simulation tools available for education and research on network technologies and protocols. Among the mentioned tools we present advanced methods for network simulations using the OPNET modeler simulation tool. This is one of the most widespread simulation tools for network simulations, appropriate for both for teaching and also for the researching procedures of new internet devices and protocols. The basic package is intended for simulating communication networks and for protocols and devices development. There are also additional specific modules, such as a module assigned to the simulation of wireless networks, an ACE module for application analyzing, 3DNV module for visualizing networks on virtual terrain and the "System in the loop" module for simulating networks with real communication equipment in the loop, in real-time.
Ključne besede: network simulation, simulation tools, modelling, communication networks, OPNET
Objavljeno: 31.05.2012; Ogledov: 1329; Prenosov: 32
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