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3. DOLOČANJE VSEBNOSTI BETULINA IN BETULINSKE KISLINE V LUBJU BREZERobi Staniša, 2010, diplomsko delo Opis: Eni največjih virov prostih radikalov oz. največjih oksidantov so kisik, kajenje, UV-sevanje in onesnaženost, ki prihaja iz okolja. O antioksidantih je bilo narejenih ogromno raziskav in študij, saj so bistvenega pomena za naše zdravje in vitalnost, imajo zavirajoč vpliv na rakave celice, staranje in bolezni nasploh.(1) Betulin in betulinska kislina iz brezinega lubja nas varujeta pred škodljivimi prostimi radikali, saj sodita med antioksidante oziroma lovilce prostih radikalov.(2)
V diplomski nalogi smo izolirali betulin in betulinsko kislino iz lubja breze s superkritično ekstrakcijo s CO2. Poskuse smo opravili pri različnih temperaturah, tlakih in času, da smo ugotovili, pri katerih pogojih je izkoristek najboljši. Najboljši izkoristek smo dobili pri ekstrakciji, ki je potekala 2 uri pri 80°C in tlaku 300 bar. K superkritičnemu CO2 smo dodali tudi kotopili metanol in etanol ter primerjali rezultate. Dobljene produkte smo nato analizirali s HPLC, kjer smo predhodno s standardom betulina in betulinske kisline določili vrednosti na kromatogramih pri valovni dolžini 215 nm in z računalniško integracijo ploščin izračunali maso aktivnih komponent na gram ekstrakta pri različnih pogojih in topilih. Določili smo tudi kinetiko poteka ekstrakcije.
Ključne besede: betulin, betulinska kislina, ekstrakcija, breza, superkritični fluid
Objavljeno: 23.12.2010; Ogledov: 1725; Prenosov: 125
 Celotno besedilo (2,64 MB) |
4. Natural convection of micropolar fluid in an enclosure with boundary element methodMatej Zadravec, Matjaž Hriberšek, Leopold Škerget, 2009, izvirni znanstveni članek Opis: The contribution deals with numerical simulation of natural convection in micropolar fluids, describing flow of suspensions with rigid and underformable particles with own rotation. The micropolar fluid flow theory is incorporated into the framework of a velocity-vorticity formulation of Navier-Stokes equations. The governing equations are derived in differential and integral form, resulting from the application of a boundary element method (BEM). In integral transformations, the diffusion-convection fundamental solution for flow kinetics, including vorticity transport, heat transport and microrotation transport, is implemented. The natural convection test case is the benchmark case of natural convection in a square cavity, and computations are performed for Rayleigh number values up to 107. The results show, which microrotation of particles in suspension in general decreases overall heat transfer from the heated wall and should not therefore be neglected when computing heat and fluid flow of micropolar fluids.
Ključne besede: natural convection, micropolar fluid, boundary element method
Objavljeno: 31.05.2012; Ogledov: 1431; Prenosov: 67
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5. BEM simulation of compressible fluid flow in an enclosure induced by thermoacoustic wavesLeopold Škerget, Jure Ravnik, 2009, izvirni znanstveni članek Opis: The problem of unsteady compressible fluid flow in an enclosure induced by thermoacoustic waves is studied numerically. Full compressible set of Navier-Stokes equations are considered and numerically solved by boundary-domain integral equations approach coupled with wavelet compression and domain decomposition to achieve numerical efficiency. The thermal energy equation is written in its most general form including the Rayleigh and reversible expansion rate terms. Both, the classical Fourier heat flux model and wave heat conduction model are investigated. The velocity-vorticity formulation of the governing Navier-Stokes equations is employed, while the pressure field is evaluated from the corresponding pressure Poisson equation. Material properties are taken to be for the perfect gas, and assumed to be pressure and temperature dependent.
Ključne besede: compressible fluid flow, boundary element method, thermoacoustic waves, velocity-vorticity fomulation
Objavljeno: 31.05.2012; Ogledov: 1360; Prenosov: 64
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6. 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: 1564; Prenosov: 64
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7. Fast single domain-subdomain BEM algorithm for 3D incompressible fluid flow and heat transferJure Ravnik, Leopold Škerget, Zoran Žunič, 2009, izvirni znanstveni članek Opis: In this paper acceleration and computer memory reduction of an algorithm for the simulation of laminar viscous flows and heat transfer is presented. The algorithm solves the velocity-vorticity formulation of the incompressible Navier-Stokes equations in 3D. It is based on a combination of a subdomain boundary element method (BEM) and single domain BEM. The CPU time and storage requirements of the single domain BEM are reduced by implementing a fast multipole expansion method. The Laplace fundamental solution, which is used as a special weighting function in BEM, is expanded in terms of spherical harmonics. The computational domain and its boundary are recursively cut up forming a tree of clusters of boundary elements and domain cells. Data sparse representation is used in parts of the matrix, which correspond to boundary-domain clusters pairs that are admissible for expansion. Significant reduction of the complexity is achieved. The paper presents results of testing of the multipole expansion algorithm by exploring its effect on the accuracy of the solution and its influence on the non-linear convergence properties of the solver. Two 3D benchmark numerical examples are used: the lid-driven cavity and the onset of natural convection in a differentially heated enclosure.
Ključne besede: boundary element method, fast multipole method, fluid flow, heat transfer, velocity-vorticity fomulation
Objavljeno: 31.05.2012; Ogledov: 1348; Prenosov: 53
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8. Numerical optimisation of a waste-to-energy plant's operating parameters using CFDMiran Kapitler, Niko Samec, Filip Kokalj, 2011, izvirni znanstveni članek Opis: The combustion process for using municipal solid waste as a fuel within a waste to energy plant calls for a detailed understanding of the following phenomena. Firstly, this process depends on many input parameters such as proximate and ultimate analyses, the season of the year, primary and secondary inlet air velocities and, secondly, on output parameters such as the temperatures or mass-flow rates of the combustible products. The variability and mutual dependence of these parameters can be difficult to manage in practice. Another problem is how these parameters can be tuned to achieving optimal combustible conditions with minimal pollutant emissions, during the plant-design phase. in order to meet these goals, a waste-to-energy plant with bed combustion was investigated by using computational fluid-dynamics approach. The adequate variable input boundary conditions based on the real measurement are used and the whole computational work is updated using real plant geometry and the appropriate turbulence, combustion, or heat transfer models. The operating parameters were optimized on output parameters through a trade-off study. The different operating conditions were varied and the combustible products were predicted and visualized. Finally, the response charts and matrix among the input and output parameters during the optimization process are presented, which monitored the dependence among these parameters.
Ključne besede: municipal solid waste, bed combustion, computational fluid dynamics, numerical optimization, goal driven optimization, trade-off study, parameters correlation
Objavljeno: 01.06.2012; Ogledov: 1056; Prenosov: 58
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9. 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: 915; Prenosov: 18
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10. 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: 912; Prenosov: 18
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