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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
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 v RUNG: 28.06.2017; Ogledov: 5852; Prenosov: 255
Celotno besedilo (21,30 MB)

Opis: Earthen architecture represents a long building tradition of numerous indigenous communities in Mexico, in particular in the state of Chiapas, where a significant number of examples represent a rich historical tradition of earthen architecture and a valuable source of information, hence a fertile ground for a deeper investigation on its potential significance and, more broadly, for a greater understanding of sustainable building today. Despite the fact that the relevance of earthen architecture is widespread all over the world, traditional earthen architecture in Chiapas is scarcely documented, it lacks systematic research projects aimed at preserving this important tradition of these indigenous groups who often live in precarious conditions. Hence, this research highlights not only the widespread employment of earth as a traditional building material for the indigenous groups of Chiapas, but also its additional function as being an authentic expression of the architectural legacy of indigenous culture and thus a key potential factor for the development of the self construction. The first part of the dissertation introduces a general overview and prevailing knowledge on earthen architecture, mainly through investigating the bibliographic, historical and technical sources as well as the particular studies on earthen architecture in Mexico. The second part discusses the results of the field studies related to the specific conditions of earthen architecture in Chiapas through sampling, testing, photographic reference and interviews. On analysing the results of the field studies it can be established that the local population has shown a particular interest in the continuity of the earthen building tradition, in spite of this period of far-reaching globalisation building trends. For this reason the final part of dissertation propooses the manual. The main objective of the manual is to improve the traditional earthen building system by introducing a number of minor variations to the building technologies and new sustainable suggestions for the management of the living space, without sacrificing the flair and simplicity found within the local building tradition, thus giving new opportunities for the development of local populations through the preservation of the earthen building tradition.
Ključne besede: earthen architecture, indigenous, self-construction, manual, tradition, local communities
Objavljeno v RUNG: 01.12.2015; Ogledov: 4753; Prenosov: 148
Celotno besedilo (34,58 MB)