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Robert Mikola, 2009, undergraduate thesis

Abstract: Tema diplomske naloge je proizvodnja brez napak z uporabo Boundary Scan metode testiranja, načrtovanje zanesljivosti, kakovosti in testiranja pri razvoju novega izdelka v elektrotehniki ter njegova uvedba na trg. V današnjem konkurenčnem in hitro spreminjajočem se trgu elektronike, imata hitrost in učinkovitost testiranja izdelka pomemben učinek na razvoj, proizvodno linijo in uvedbo izdelka na trg. Temeljni namen naloge je prikazati razvoj izdelka od same ideje, do njegove uvedbe na trg ter opisati tehnične in ekonomske prednosti uporabe Boundary Scan metode testiranja skozi celoten življenjski cikel omenjenega izdelka, od načrtovanja do servisa. Pri uvajanju izdelka na trg je treba biti pozoren na to, katere marketinške dejavnosti bi bilo treba opraviti, da bo izdelek uresničil pričakovanja. Zelo pomembne so pravilne odločitve o strategiji in taktiki v fazi uvajanja novega izdelka na trg.
Keywords: testiranje, Boundary Scan, zanesljivost, načrtovanje, izdelek, trg
Published: 02.02.2012; Views: 1442; Downloads: 92
.pdf Full text (2,02 MB)

Natural convection of micropolar fluid in an enclosure with boundary element method
Matej Zadravec, Matjaž Hriberšek, Leopold Škerget, 2009, original scientific article

Abstract: 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.
Keywords: natural convection, micropolar fluid, boundary element method
Published: 31.05.2012; Views: 1631; Downloads: 81
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BEM simulation of compressible fluid flow in an enclosure induced by thermoacoustic waves
Leopold Škerget, Jure Ravnik, 2009, original scientific article

Abstract: 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.
Keywords: compressible fluid flow, boundary element method, thermoacoustic waves, velocity-vorticity fomulation
Published: 31.05.2012; Views: 1576; Downloads: 75
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3D multidomain BEM for a Poisson equation
Matjaž Ramšak, Leopold Škerget, 2009, original scientific article

Abstract: 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.
Keywords: fluid mechanics, Poisson equation, multidomain boundary element method, boundary element method, mixed boundary elements, multidomain method
Published: 31.05.2012; Views: 1830; Downloads: 72
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Fast single domain-subdomain BEM algorithm for 3D incompressible fluid flow and heat transfer
Jure Ravnik, Leopold Škerget, Zoran Žunič, 2009, original scientific article

Abstract: 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.
Keywords: boundary element method, fast multipole method, fluid flow, heat transfer, velocity-vorticity fomulation
Published: 31.05.2012; Views: 1508; Downloads: 72
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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, original scientific article

Abstract: 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.
Keywords: numerical modelling, boundary element method, discrete wavelet transform, large eddy simulation, velocity-vertocity formulation, natural convection
Published: 31.05.2012; Views: 1746; Downloads: 62
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3D multidomain BEM for solving the Laplace equation
Matjaž Ramšak, Leopold Škerget, 2007, original scientific article

Abstract: An efficient 3D multidomain BEM for solving problems governed by the Laplace equation is presented. Integral boundary equations are discretized using mixed boundary elements. The field function is interpolated using a continuous linear function while its derivative in a normal direction is interpolated using a discontiuous constant function over surface boundaey elements. Using amultidomain approach, also known as the subdomain technique, sparse system matrices similar to FEM are obtained. Interface boundary conditions between subdomains leads to an over-determined system matrix which is solved using a fast iterative linear least square solver. The accuracy and the robustness of the developed algorithm is presented on a scalar diffusion problem using simple cube geometry and various types of meshes. The efficiency is demonstrated with potential flow around a complex geometry of a fighter airplane using a tetrahedral mesh with over 100.000 subdomains on a personal computer.
Keywords: fluid mechanics, aerodynamics, multidomain boundary element method, Laplace equation, mixed boundary elements, potential flow
Published: 31.05.2012; Views: 1581; Downloads: 74
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Boundary domain integral method for the study of double diffusive natural convection in porous media
Janja Kramer Stajnko, Renata Jecl, Leopold Škerget, 2007, original scientific article

Abstract: The main purpose of this paper is to present a boundary domain integral method(BDIM) for the solution of natural convection in porous media driven by combining thermal and solutal buoyancy forces. The Brinkman extension of the classical Darcy equation is used for the momentum conservation equation. The numerical scheme was tested on a natural convection problem within a square porous cavity, where different temperature and concentration values are applied on the vertical walls, while the horizontal walls are adiabatic and impermeable. The results for different governing parameters (Rayleigh number, Darcy number, buoyancy ratio and Lewis number) are presented and compared withpublished work. There is a good agreement between those results obtained using the presented numerical scheme and reported studies using other numerical methods.
Keywords: double diffusive natural convection, porous medium, velocity-vorticity formulation, Brinkman extended Darcy formulation, boundary domain integrated method
Published: 31.05.2012; Views: 1318; Downloads: 66
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