21. Computational fluid dynamics by boundary-domain integral methodLeopold Škerget, Matjaž Hriberšek, G. Kuhn, 1999, izvirni znanstveni članek Opis: A boundary-domain integral method for the solution of general transport phenomena incompressible fluid motion given by the Navier-Stokes equation set is presented. Velocity-vorticity formulation of the conservations is employed. Different integral representations for conservation field functions based on different fundamental solutions are developed. Special attention is given to the use of subdomain technique and Krylov subspace iterative solvers. The computed solutions of several benchmark problems agree well with available experimental and other computational results.
Ključne besede: fluid mechanics, fluid dynamics, numerical methods, boundary domain integral method, viscous fluid, heat transfer, diffusion-convective solution
Objavljeno v DKUM: 01.06.2012; Ogledov: 2443; Prenosov: 79
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23. Boundary element method for natural convection in non-Newtonian fluid saturated square porous cavityRenata Jecl, Leopold Škerget, 2003, izvirni znanstveni članek Opis: The main purpose of this work is to present the use of the Boundary Element Method (BEM) in the analysis of the natural convection in the square porous cavity saturated by the non-Newtonian fluid. The results of hydrodynamic and heat transfer evaluations are reported for the configuration in which the enclosure is heated from a side wall while the horizontal walls are insulated.The flow in the porous medium is modelled using the modified Brinkman extended Darcy model taking into account the non-Darcy viscous effects. The governing equations are transformed by the velocity-vorticity variables formulation enabling the computation scheme to be partitioned into kinematic and kinetic parts. To analyse the effects of the available non-Newtonian viscosity and to evaluate the presented approach, the power law model for shear thinning fluids (n<1), for shear thickening fluids (n>1) and in the limit for the Newtonian fluids (n=1) is considered. Numerical model is tested also for the Carreau model adequate for many non-Newtonian fluids. Solutions for the flow and temperature fields and Nusselt numbers are obtainedin terms of a modified Rayleigh number Ra*, Darcy number Da, and the non-Newtonian model parameters. The agreement between the results obtained with finite difference method is very good indicating that BEM can be efficiently used for solving transport phenomena in saturated porous medium.
Ključne besede: natural convection, non-Newtonian fluid, porous medium, cavity flow, boundary element method, boundary domain integral method
Objavljeno v DKUM: 01.06.2012; Ogledov: 1928; Prenosov: 96
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24. Experimental models of medium break loss of coolant accidents with and without steam generator tube ruptureJure Marn, Marjan Delić, Leopold Škerget, 2003, izvirni znanstveni članek Opis: This paper reports model experiments simulating medium break loss of coolant accidents, with and without steam generator tube rupture (SGTR), in pressurized water reactors. Apart from a significant influence on the pressure in the reactor coolant system in the early parts of the accident, SGTR generally has only a small effect on the pressures and temperatures during the accident. The initial reactor conditions are found to be more significant. Some results of preliminary numerical models are briefly presented and these are broadly in agreement with the experimental measurements.
Ključne besede: nuclear engineering, nuclear accidents, steam generator tube rupture, loss of coolant, medium break loss of coolant accident, computer program, Melcor, MELCOR computer code, integral test facility
Objavljeno v DKUM: 01.06.2012; Ogledov: 1864; Prenosov: 114
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25. On fracture behaviour of inhomogeneous materials - a case study for elastically inhomogeneous bimaterialsOtmar Kolednik, Jožef Predan, G.X. Shan, N.K. Simha, Franz Dieter Fischer, 2005, izvirni znanstveni članek Opis: This paper presents a case study, examining the influence of a sharp bimaterial interface on the effective crack driving force in a fracture mechanics specimen. The inhomogeneity of the elastic modulus in linear elasticand non-hardening and hardening elastic-plastic bimaterials is considered. The interface is perpendicular to the crack plane. The material properties and the distance between the crack tip and the interface are systematically varied. The effect of the material inhomogeneity is captured in form of a quantity called "material inhomogeneity term",▫$C_inh$▫. This term can be evaluated either by a simple post-processing procedure, following a conventional finite element stress analysis, or by computing the J-integral along a contour around the interface, ▫$J_int$▫. The effective crack driving force,▫$J_tip$▫, can be determined as the sum of ▫$C_inh$▫ and the nominally applied far-field crack driving force, ▫$J_far$▫. The results show that ▫$C_inh$▫ can be accurately determined by both methods even in cases where ▫$J_tip$▫-values are inaccurate. When a crack approaches a stiff/compliant interface,▫$C_inh$▫ is positive and ▫$J_tip$▫ becomes larger than ▫$J-far$▫. A compliant/stiff transition leads to a negative ▫$C_inh$▫, and ▫J_tip$▫ becomes smaller than ▫$J_far$▫. The material inhomogeneity term, ▫$C_inh$▫, can have the same order of magnitude as ▫$J_far$▫. Based on the numerical results, the dependencies of ▫$C_inh$▫ on the material parameters and the geometry are derived. Simple expressions are obtained to estimate ▫$C_inh$▫.
Ključne besede: mechanics of structures, fracture toughness, inhomogeneous materials, J-integral, crack driving force, interface, material force
Objavljeno v DKUM: 01.06.2012; Ogledov: 1720; Prenosov: 34
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26. Boundary domain integral method for high Reynolds viscous fluid flows in complex planar geometriesMatjaž Hriberšek, Leopold Škerget, 2005, izvirni znanstveni članek Opis: 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.
Ključne besede: fluid mechanics, numerical methods, boundary domain integral method, algorithms, incompressible fluid flow, Navier-Stokes equations, velocity vorticity formulation, segmentation technique, driven cavity flow
Objavljeno v DKUM: 01.06.2012; Ogledov: 2229; Prenosov: 89
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27. On the local variation of the crack driving force in a double mismatched weldJožef Predan, Nenad Gubeljak, Otmar Kolednik, 2007, izvirni znanstveni članek Opis: A material inhomogeneity in the direction of crack extension causes a difference between the near-tip crack driving force, Jtip, and the nominally applied far-field crack driving force, Jfar. This difference can be quantified by a material inhomogeneity term, Cinh, which is evaluated by a post-processing procedure to a conventional finite element stress analysis. The magnitude of the material inhomogeneity term is evaluated for cracks in an inhomogeneous welded joint made of a high-strength low-alloy steel. Both a crack proceeding from the under-matched (UM) to the over-matched (OM) and from the OM to the UM weld metal are treated. The effects of the inhomogeneity of the different material parameters (modulus of elasticity, yield strength, and strain hardening exponent) on Cinh and Jtip are systematically studied. The results demonstrate that the material inhomogeneity term is primarily influenced by the inhomogeneity of the yield strength. A crack growing towards an OM/UM interface experiences an accelerated crack growth rate or a pop-in, an UM/OM interface leads to a reduced crack growth rate or a crack arrest. The application of global assessment methods of the mismatch effect which are included in the Engineering Treatment Model (ETM) or in the Structural Integrity Assessment Procedures for European Industry (SINTAP) is discussed.
Ključne besede: crack driving force, material inhomogeneity, mismatched weld, interface, J-integral, finite element modeling
Objavljeno v DKUM: 31.05.2012; Ogledov: 1754; Prenosov: 88
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28. LEIBNIZ-NEWTONOVA FORMULA IN NJENE POSPLOŠITVESara Topler, 2012, diplomsko delo Opis: V diplomskem delu obravnavamo Leibniz-Newtonovo formulo in njene posplošitve. Pojem Riemannovega oz. določenega integrala je vpeljan s pomočjo Darbouxovih in Riemannovih vsot, pri čemer je poudarjena ekvivalentnost omenjenih pristopov. V tretjem poglavju so predstavljeni potrebni pogoji za integrabilnost funkcij, v četrtem pa ena izmed povezav med določenimi integrali in primitivnimi funkcijami. Sledi pomemben matematični rezultat Leibniza in Newtona, t. i. Leibniz-Newtonova formula, poznana tudi kot osnovni izrek analize. V nadaljevanju obravnavamo posplošitve te formule; pri prvi obliki nadomestimo obojestranski odvod z desnim odvodom, v drugi nastopa Schwarzov odvod, tretja posplošitev Leibniz-Newtonove formule pa se nanaša na funkcije, ki izpolnjujejo Lipschitzev pogoj. V zadnjem poglavju je navedenih nekaj primerov, kjer postane računanje določenega integrala s pomočjo Leibniz-Newtonove formule precej lažje kot računanje po definiciji določenega integrala. Ključna sta primera, ki ponazarjata napake, ki nastanejo pri uporabi rešitev iz tablic nedoločenih integralov na neustreznih intervalih. Pokazali smo, kako se tem napakam uspešno izogniti.
Ključne besede: Darbouxove vsote, Riemannove vsote, Riemannov integral, določeni integral, primitivna funkcija, desni odvod, Schwarzov odvod, Lipschitzev pogoj, Leibniz-Newtonova formula, napake pri uporabi Leibniz-Newtonove formule.
Objavljeno v DKUM: 23.04.2012; Ogledov: 2633; Prenosov: 124
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29. Funkcija gamaTamara Prešern, 2011, diplomsko delo Opis: Osrednja tema diplomskega dela je funkcija gama. Definiramo jo z nepravim integralom in dokažemo njene osnovne karakteristike. Dokažemo tudi izrek, ki opisuje pogoje, ki funkcijo gama enolično določajo. Nato še definiramo funkcijo beta in navedemo nekaj osnovnih lastnosti in povezav med funkcijama beta in gama. Na koncu še izpeljemo Stirlingove formule in s pomočjo le-teh dokažemo Wallisovo formulo.
Ključne besede: funkcija gama, funkcija beta, Stirlingova formula, konveksnost, nepravi integral, Wallisova formula
Objavljeno v DKUM: 18.07.2011; Ogledov: 3696; Prenosov: 159
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30. Prilagoditev vojaške infrastrukture poklicni vojski s poudarkom na izvajanju programov celostne skrbi za pripadnike Slovenske vojske : magistrska nalogaZdenka Veselič, 2009, magistrsko delo/naloga Opis: Slovenija je po osamosvojitvi organizirala vojaško obrambo na način, kot je bil v nekdanji skupni državi. Razvijala je številčno veliko vojsko, v katero so bili vključeni z majhnim deležem pripadniki stalne sestave ter pripadniki rezervne sestave, ki so bili v enote SV razporejeni na podlagi zakonsko obveznega služenja v rezervni sestavi. Pripadniki moškega spola so se usposabljanja za obrambo domovine udeleževali na služenju vojaškega roka, ki je bil prav tako zakonsko obvezen za vse zdravstveno sposobne moške državljane, stare med 18 in 27 let. Ob nadaljnjem razvoju Slovenske vojske se je vse bolj kazala potreba po drugačnem organiziranju vojaške obrambe, ki bi tako zagotovila doseganje novih doktrinarnih in strateških obrambnih načel. Vse bolj se je kristalizirala potreba po prehodu na poklicni način popolnjevanja vojske.
Slovenska vojska je s prehodom na poklicni način popolnjevanja, dopolnjenega s pogodbeno rezervo doživela številne spremembe tako v kadrovski kot tudi v organizacijski strukturi. Vse te spremembe pa so zahtevale spremembe tudi na drugih področjih, med njimi vojaški infrastrukturi. Po izvedeni koncentraciji sil in sredstev v perspektivne objekte, ki jih uporablja Slovenska vojska, je sledilo zagotavljanje bivalnih in delovnih zmogljivosti, kjer je nastanjena poklicna vojska. Sledeč cilju razviti majhno in dobro usposobljeno vojsko, so bili posodobljeni ali na novo zgrajeni tudi nekateri objekti, namenjeni izobraževanju, usposabljanju in urjenju.
Pripadnik je najpomembnejši in ključni dejavnik v delovanju Slovenske vojske. Celostna skrb za pripadnike Slovenske vojske je postala s profesionalizacijo vojske pomembna dejavnost, ki pa do danes še ni zaživela v celoti. Prostorska urejenost za izvajanje programov celostne skrbi za pripadnike Slovenske vojske je marsikje še v obliki načrtov.
Ključne besede: vojaška infrastruktura, celostna skrb, vojašnica, Slovenska vojska, military infrastructure, integral care, barrack, Slovenian Army
Objavljeno v DKUM: 18.08.2009; Ogledov: 2994; Prenosov: 268
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