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Boštjan Mavrič, Grega Belšak, Marjan Maček, N. Talat, Rizwan Zahoor, Božidar Šarler, 2016, projektna dokumentacija (idejni projekt, izvedbeni projekt)

Najdeno v: osebi
Ključne besede: XFEL, simulation, microjet, gas, method of fundamental solutions
Objavljeno: 20.06.2016; Ogledov: 821; Prenosov: 0
.pdf Polno besedilo (66,05 KB)

Meshless modeling of thermo-mechanics of low-frequency electromagnetic direct chill casting
Boštjan Mavrič, 2017, doktorska disertacija

Opis: The aim of this dissertation is to devise a meshless model describing the thermomechanical phenomena, which occur during DC casting of aluminium alloys under the influence of electromagnetic stirring. The thermoemchanical phenomena are important, because they can cause several type of defects, which can significantly deteriorate the quality of the resulting billet. The two most important of them are the hot tearing, which causes cracks to appear in the mushy zone, and the porosity, which demonstrates itself as micrometer sized voids in the microstructure of the billet. To calculate the stresses and strains, a computational model of the stationary state of the process, stated in axial symmetry, is formulated. It uses Eulerian formulation by fixing the computational domain to the mold of the casting device allowing the material to move through the computational domain. The stresses are calculated from the stress equilibrium equations. The small strain approximation is used to consider the three contributions to strain. The strain consists of the thermal strain, which is caused by the inhomogeneous thermal profile in the billet, the viscoplastic strain, which is caused by the irreversible deformation because of the large stresses occurring in the billet, and the elastic strain. The spatial discretization of the governing equations is performed by local radial basis function collocation method (LRBFCM) and the temporal discretization is achieved by the method of lines with implicit Euler formula. The method used for spatial discretization uses radial basis functions augmented by monomials to approximate the solution values on localized stencils. This approximation is used to construct the discretization coefficients of the differential operators present in the model. A flexible framework for formulation of multiphysics problems is developed to use the obtained discretization coefficients to construct the temporal discretization of the governing equations. The node arrangement, on which the spatial discretization is performed, was generated by a point-repel algorithm. The performance of the method is tested on several benchmark test cases. The accuracy of the discretization is estimated by comparing the analytic and the numerical solution to several stationary problems in thermomechancis. Of special interest is the performance of the method with respect to the choice of the shape parameter, which determines the spatial scale of the radial basis functions. Besides this, the dependence of the condition number of the interpolation matrix on the shape parameter is studied. The condition number is found fit to replace the condition number as the shape-determining free parameter of the method. The implementation of the solver of time dependent problems is tested on problem of thermoelasticity, which couples the thermal transport with the elastic waves. The results of the problem are compared with the finite element method, showing good agreement of the two methods. The results are also compared with the results obtained by meshless local Petrov-Galerkin method and the proposed local collocation method demonstrated significantly better solution quality in the studied case. The performance of the solver used to solve the system of nonlinear equations given by the viscoplastic constitutive equations is estimated on a quasi zero-dimensional problem. The results are found to match perfectly. Solution of a more complicated problem is obtained with the proposed method and the finite-element method, both methods giving practically the same solution, although some serious limitations of the chosen finite element solver are exposed during the selection of the problem parameters. Finally, the devised method is applied to the problem of DC casting of aluminium alloys. The thermomechanical model relies on a model of heat and mass transfer to obtain the input fields needed in the solver. The required fields are: temperature, pressure, liquid
Najdeno v: osebi
Ključne besede: thermomechanics, viscoplasticity, aluminium alloys, direct-chill casting, electromagnetic stirring, hot tearing, porosity, meshless methods, local collocation method, radial basis functions, shape parameter
Objavljeno: 28.06.2017; Ogledov: 333; Prenosov: 9
.pdf Polno besedilo (21,30 MB)

Artem V. Badasyan, Boštjan Mavrič, Matjaž Valant, objavljeni povzetek znanstvenega prispevka na konferenci

Opis: Conformations of polymer molecules in solution crucially depend on the sign of the effective potential energy of interaction between the monomers, also known as the quality of solvent. Therefore in “poor” solvent regime, when effective attraction overwhelms, the experimental measurements of polymer sizes are complicated by the agglomeration of macromolecules, followed by precipitation. This phenomenon, also known as spinodal decomposition, causes serious problems when the goal is to determine properties of individual macromolecules. Interestingly, while in the case of carbon-based polymers the precipitation-related problems can be easily avoided with dilution, this is not the case for polysilanes, i.e. polymeric chains on basis of silicon. Although the linear polysilanes were first synthesized in early 1920’s, the aggregationrelated problems have hampered their studies and applicability until recently. In the Materials Research Laboratory of University of Nova Gorica we have developed a technology to strengthen the scratch-resistance nanocoating for glass on the basis of polysilane dendritic polymers we synthesized. Through the prism of the Flory-Huggins theory, that provides a miscibility phase diagram in temperature-volume fraction variables, the quality of polymer solution can be manipulated by changing the temperature. Using Dynamic Light Scattering (DLS) and Differential Scanning Calorimetry (DSC) we have managed to show, that at temperatures in the range of 40- 50 C the deagglomeration of the dendritic polysilane takes place in tetrahydrofuran (THF) [1], and the system becomes a true molecular dispersion with particles 20 nm in size [2]. Introducing such molecular dispersion into the alumina precursor solution yields an amorphous nanocomposite stabilized by a high level of strain. This resulted in an extraordinary increase of hardness and scratch resistance of the alumina – polymer nanocomposite coating that can be used for glass protection [3].
Najdeno v: osebi
Ključne besede: Polysilane, dendrimer, solubility
Objavljeno: 12.09.2017; Ogledov: 91; Prenosov: 0
.pdf Polno besedilo (53,55 KB)

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