Ilmenau, Techn. University, Diss., 2005.

Η εν λόγω διπλωματική εργασία έχει ως αντικείμενο μελέτης το ρόλο των διαφόρων συντελεστών μεταφοράς σε συνθήκες ψυχρού πλάσματος, για τη δημιουργία και διάδοση των κυμάτων ιονισμού (streamers), και τον υπολογισμό αυτών των συντελεστών μέσω του λογισμικού επίλυσης της εξισώσεως Boltzmann, καθώς και τη σύγκλιση που παρουσιάζει πειραματικά και θεωρητικά ο υπολογισμός αυτών με τη χρήση του συγκεκριμένου προγράμματος. Εν αρχή παρουσιάζονται κάποιες βασικές έννοιες και στοιχεία σχετικά με τις ηλεκτρικές εκκενώσεις, το πλάσμα και τις αρχές που το διέπουν. Το πλάσμα παράγεται μέσω ηλεκτρικών εκκενώσεων σε αέρια, τα οποία μετατρέπονται σε αγώγιμα μέσα. Με κριτήρια την ηλεκτρονική του θερμοκρασία, πυκνότητα και το βαθμό ιονισμού του το κατατάσσουμε σε ψυχρό, θερμικό και θερμό. Η δημιουργία πλάσματος εξαρτάται από μια πληθώρα παραγόντων, όπως η γεωμετρία του αντιδραστήρα και του διακένου, τα χαρακτηριστικά του αερίου και φυσικά το σύστημα τροφοδοσίας. Οι εφαρμογές του ποικίλλουν, και κυμαίνονται από την παραγωγή Laser, ηλεκτρικής ισχύος μέσω της θερμοπυρηνικής σύντηξης, όζοντος αλλά και την επεξεργασία υλικών και επιφανειών. Ακολουθεί έπειτα μια σύντομη ανάλυση των εξισώσεων Μεταφοράς Boltmann και κατανομής Maxwell-Boltzmann. Παρακάτω ακολουθεί η ανάπτυξη στοιχείων της θεωρίας των ηλεκτρικών εκκενώσεων, όπως αυτών της διάσπασης δια του μηχανισμού Streamer. Εν συνεχεία, αναλύεται ο ρόλος των προγραμμάτων επιλύσεως της εξισώσεως Boltzmann στον υπολογισμό των συντελεστών μεταφοράς και στην αξιόπιστη εξομοίωση των φαινομένων των ηλεκτρικών εκκενώσεων, παρουσιάζεται το λογισμικό επιλύσεως της εξίσωσης Boltzmann, Bolsig+, οι παράμετροι λειτουργίας καθώς και οι δυνατότητες αυτού. Κατόπιν, ακολουθούν σε αντιπαραβολή πειραματικές μετρήσεις με τις αντίστοιχες προβλέψεις του Bolsig+ για ταυτόσημες συνθήκες. Εν κατακλείδι, συνοψίζεται η χρησιμότητα αξιόπιστων προγραμμάτων επίλυσης, όπως το προαναφερθέν καθώς και η βαρύτητα των συντελεστών μεταφοράς στα υπό μελέτη φαινόμενα ηλεκτρικών εκκενώσεων. / The main subject of this thesis is the investigation of the importance and role of the macroscopic coefficients, in cold plasma conditions, in the creation and propagation of streamers and also the calculation of these coefficients through the sollution of the Boltzmann equation, via a Boltzmann equation solver, and their convergence with experimental data. First some fundamental principles ,concerning electric discharges, are presented. Plasma is produced through gas discharges, which become conductive as a result. Depending on their electronic temperature, density and ionization degree the plasmas are categorized as cold, thermal and thermonuclear. The creation of plasma depends on a number of factors, such as the reactor's and the gap's geometry, the nature of the gas and the power system. Its applications vary, ranging from Lasers, production of electric power through nuclear fusion, ozone production to the processing of materials and surfaces. A brief analysis of Boltzmann's Distribution Law and Boltzmann's Transport equation follows, while the fundamental principles of gas discharges, such as the streamer mechanism, are also presented. In addition to the above, the specific method for the numerical solution of the Boltzmann equation used by the Boltzmann solvers, such as BOLSIG+, is thoroughly analyzed. The importance of the equation's solution is further explained, as are the natural processes and mechanisms that lead to the creation and propagation of the streamer phenomenon. Moreover, several calculations of the macroscopic coefficients, through experimental data and their respective models are presented in comparison to calculations of the same coefficients through the solution of Boltzmann's Transport equation. Finally, the necessity for reliable and fast Boltzmann equation solvers is summarized, as well as the gravity of the transport coefficients in the investigation and analysis of gas discharges, such as streamers.

No description available.

Thesis (M.S.)--University of Wyoming, 2008. / Title from PDF title page (viewed on August 3, 2009). Includes bibliographical references (p. 65-68).

In this study, the applicability of the Lattice Boltzmann Method to neutron transport is investigated. The transport model used, is derived from the Boltzmann equation for neutral particles by inverting the streaming operator and casting the integral transport equation into an operator form. From the operator equation, an iterative solution to the transport problem is presented, with the first collision source as the starting point for the iteration scheme. One of the main features of the method is the simultaneous discretization of the phase space of the problem, whereby particles are restricted to move on a lattice. A full description of the discretization scheme is given along with the iterative procedure and quadrature set used for the angular discretization. To mitigate lattice ray effects, an angular refinement scheme is introduced to increase the angular coverage of the problem phase space. The method is then applied to a model problem to investigate its applicability to neutron transport. Three cases are considered where constant, linear and exponential interpolants are used to account for the accumulation of flux due to the streaming of particles between nodes. The results obtained are compared to a reference solution, that was calculated by using the MCNP code and to the values calculated using a nodal SN method. Finally, areas of improvement are identified and possible extensions to the algorithm are provided. / Thesis (MIng (Engineering Sciences in Nuclear Engineering))--North-West University, Potchefstroom Campus, 2013

In this study, the applicability of the Lattice Boltzmann Method to neutron transport is investigated. The transport model used, is derived from the Boltzmann equation for neutral particles by inverting the streaming operator and casting the integral transport equation into an operator form. From the operator equation, an iterative solution to the transport problem is presented, with the first collision source as the starting point for the iteration scheme. One of the main features of the method is the simultaneous discretization of the phase space of the problem, whereby particles are restricted to move on a lattice. A full description of the discretization scheme is given along with the iterative procedure and quadrature set used for the angular discretization. To mitigate lattice ray effects, an angular refinement scheme is introduced to increase the angular coverage of the problem phase space. The method is then applied to a model problem to investigate its applicability to neutron transport. Three cases are considered where constant, linear and exponential interpolants are used to account for the accumulation of flux due to the streaming of particles between nodes. The results obtained are compared to a reference solution, that was calculated by using the MCNP code and to the values calculated using a nodal SN method. Finally, areas of improvement are identified and possible extensions to the algorithm are provided. / Thesis (MIng (Engineering Sciences in Nuclear Engineering))--North-West University, Potchefstroom Campus, 2013

Thesis (M. S.)--Paper Science Engineering, Georgia Institute of Technology, 2010. / Committee Chair: Aidun, Cyrus; Committee Member: Graham, Samuel; Committee Member: Joshi, Yogendra. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Bielefeld, University, Diss., 2003.

Nürnberg, Universiẗat, Diss., 2004--Erlangen.

Tese (doutorado) - Universidade Federal de Santa Catarina, Centro Tecnológico, Programa de Pós-Graduação em Engenharia Mecânica, Florianópolis, 2010 / Made available in DSpace on 2013-07-16T04:02:02Z (GMT). No. of bitstreams: 1 282342.pdf: 2052768 bytes, checksum: 75c659632cf9c038726ffe0c9b6bd6e1 (MD5) / Para que se possa simular as equações macroscópicas totalmente compressíveis partindo da equação de Boltzmann é necessário muito cuidado no processo de discretização do espaço de velocidades. Deste modo, a conexão física existente entre a equação de Boltzmann em rede (lattice-Boltzmann equation) e a sua similar no contínuo deve ser levada em consideração, e para tal um procedimento é formalmente derivado. A discretização do espaço de velocidades é feita através de um processo de quadratura, onde a norma dos polinômios de Hermite do espaço de Hilbert contínuo é igualada à norma do espaço discreto de velocidades O método, chamado de quadratura com abscissas prescritas, permite que se fixem os pólos de integração, podendo deste modo ter-se o processo de propagação exata, característica importante dos métodos que resolvem a equação de Boltzmann em rede. Utilizando a quadratura com abscissas prescritas, redes tradicionais do método são derivadas, tais como D1Q3, D2Q7, D2Q9, D3Q15, D3Q19 e D3Q27, e também redes de ordens mais altas para uma, duas e três dimensões. Ao invés de usar a técnica de ajuste dos coeficientes polinomiais para a expansão da distribuição de equilíbrio, a distribuição de Maxwell-Boltzmann é aproximada para uma dada ordem. Uma análise de estabilidade linear é então feita e mostra a melhor performance do método proposto frente a outros métodos.