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Thesis (M. Sc. (Applied Mathematics)) -- University of Limpopo, 2021 / Modelling with differential equations is of paramount importance as it provides pertinent insight into the dynamics of many engineering and technological devices and/or processes. Many such models, however, involve differential equations that are inherently nonlinear and difficult to solve. Many numerical methods have been developed to solve a variety of differential equations that cannot be solved analytically. Most numerical methods, however, require discretisation, linearisation of the nonlinear terms and other simplifying approximations that may inhibit the accuracy of the solution. Further, in some methods high computational complexity is involved. Due to the importance of differential equations in modelling real life phenomena and these stated shortfalls, continuous pursuit of more efficient solution techniques by the scientific community is ongoing. Industrial and technological advancement are to a larger extent dependent upon efficient and accurate solution techniques. In this work, we investigate the use of Adomian decomposition method in solving nonlinear ordinary and partial differential equations. One advantage of Adomian decomposition method that has been demonstrated in literature is that it achieves a rapidly convergent infinite series solution. The method is also advantageous in that it does not require one to linearise and discretise the equations as is done with other numerical methods. In our investigation, among other important examples, we will apply the Adomian decomposition method to solve selected fluid flow and heat transfer problems. Fluid flow and heat transfer models have pertinent applications in engineering and technology. The Adomian decomposition method will be compared with other series solution methods, namely the differential transform method and the homotopy analysis method. The desirable attributes of the Adomian decomposition method that are stated in literature have been ascertained in this work and it has also been demonstrated that the Adomian decomposition method compares favourably with the other series solution methods. It has also been demonstrated that in some cases nonlinear complexity results in slow convergence rate of the Adomian decomposition method.

The solutions of nonlinear ordinary or partial differential equations are important in the study of fluid flow and heat transfer. In this thesis we apply the Homotopy Analysis Method (HAM) and obtain solutions for several fluid flow and heat transfer problems. In chapter 1, a brief introduction to the history of homotopies and embeddings, along with some examples, are given. The application of homotopies and an introduction to the solutions procedure of differential equations (used in the thesis) are provided. In the chapters that follow, we apply HAM to a variety of problems to highlight its use and versatility in solving a range of nonlinear problems arising in fluid flow. In chapter 2, a viscous fluid flow problem is considered to illustrate the application of HAM. In chapter 3, we explore the solution of a non-Newtonian fluid flow and provide a proof for the existence of solutions. In addition, chapter 3 sheds light on the versatility and the ease of the application of the Homotopy Analysis Method, and its capability in handling non-linearity (of rational powers). In chapter 4, we apply HAM to the case in which the fluid is flowing along stretching surfaces by taking into the effects of "slip" and suction or injection at the surface. In chapter 5 we apply HAM to a Magneto-hydrodynamic fluid (MHD) flow in two dimensions. Here we allow for the fluid to flow between two plates which are allowed to move together or apart. Also, by considering the effects of suction or injection at the surface, we investigate the effects of changes in the fluid density on the velocity field. Furthermore, the effect of the magnetic field is considered. Chapter 6 deals with MHD fluid flow over a sphere. This problem gave us the first opportunity to apply HAM to a coupled system of nonlinear differential equations. In chapter 7, we study the fluid flow between two infinite stretching disks. Here we solve a fourth order nonlinear ordinary differential equation. In chapter 8, we apply HAM to a nonlinear system of coupled partial differential equations known as the Drinfeld Sokolov equations and bring out the effects of the physical parameters on the traveling wave solutions. Finally, in chapter 9, we present prospects for future work.

<p> The sulphur dioxide converter of the contact sulphuric acid plant ~f the Hamilton Works of Canadian Industries Ltd., is optimized using the so2 conversion as the objective function to be maximized. The simulation model used is fitted to the plant data. The number of beds, the inlet temperatures, the catalyst bed depths and the air addition are the variables considered in this work. The effect due to the imposition of a constraint on the system is also examined. </p> <p> Four integration techniques are studied to solve the set of nonlinear ordinary differential equations that simulates the transformation in a bed. The Runge-Kutta third-order is found to be the most efficient. </p> <p> Four optimization techniques, namely, dynamic programming, gradient search, direct search of Hooke and Jeeves and discrete maximum principle, are used. Their applicability and efficiency are compared. </p> <p> A very flat response (conversion) surface is found in the neighbourhood of the optimum. </p> <p> The optimal operating conditions are compared with the simulation of the C.I.L. operation. The reachability of these optimal conditions in the plant is also considered. </p> / Thesis / Master of Engineering (ME)

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Made available in DSpace on 2014-06-11T19:25:34Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-02-18Bitstream added on 2014-06-13T19:53:27Z : No. of bitstreams: 1 ruy_dv_me_ift.pdf: 500107 bytes, checksum: fef6f049175c290422f569aa7ad7e26e (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Esta dissertação trata da construção de hierarquias compatíveis com a equação PIV a partir dos modelos: AKNS, dois bósons e dois bósons quadráticos. Também são construidos os problema linear de Jimbo-Miwa dos três modelos e discutimos a hamiltoniana correspondente a equação PIV a partir do formalismo lagrangiano / This dissertation contains the construction of compatible hierarchies with the PIV equation from the models: AKNS, two-boson and quadratic two-boson. Also it is build the Jimbo-Miwa linear problem for the three models and we discuss the hamiltonian corresponding to fouth Painlevé equation from the Lagrangian formalism

Orientador: Abraham Hirsz Zimerman / Banca: Iberê Luiz Caldas / Banca: Roberto André Kraenkel / Resumo: Esta dissertação trata da construção de hierarquias compatíveis com a equação PIV a partir dos modelos: AKNS, dois bósons e dois bósons quadráticos. Também são construidos os problema linear de Jimbo-Miwa dos três modelos e discutimos a hamiltoniana correspondente a equação PIV a partir do formalismo lagrangiano / Abstract: This dissertation contains the construction of compatible hierarchies with the PIV equation from the models: AKNS, two-boson and quadratic two-boson. Also it is build the Jimbo-Miwa linear problem for the three models and we discuss the hamiltonian corresponding to fouth Painlevé equation from the Lagrangian formalism / Mestre

Orientadores: Djairo Guedes de Figueiredo, Olimpio Hiroshi Miyagaki / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Matematica, Estatistica e Computação Cientifica / Made available in DSpace on 2018-08-13T07:50:56Z (GMT). No. of bitstreams: 1 Junges-Miotto_Taisa_D.pdf: 1407780 bytes, checksum: c2871097b4e97e35198b351dbcfa999b (MD5) Previous issue date: 2009 / Resumo: O objetivo deste trabalho é obter estimativas ABP para operadores completamente não lineares e estudar problemas do tipo Ambrosetti-Prodi para o operador p-Laplaciano nos casos superlinear para a equação e sublinear para sistema, aplicando o método de sub e supersolução e a teoria do grau de Leray Schauder, para obtermos nos casos de Ambrosetti-Prodi, multiplicidade de soluções. Para aplicarmos a teoria do grau de Leray Schauder precisamos obter estimativas a priori das eventuais soluções dos problemas, estimativas essas que serão obtidas aplicando-se técnicas diferentes em cada caso. No Capítulo 1 enunciaremos alguns resultados auxiliares que serão utilizados no decorrer do trabalho. No Capítulo 2 obtemos estimativas do tipo ABP para soluções de viscosidade de uma classe de operadores completamente não lineares, o qual um exemplo é o operador p-Laplaciano. No Capítulo 3 estudamos o problema do tipo Ambrosetti-Prodi para equação com o p-Laplaciano no caso superlinear, fazendo uso da técnica blow up e de teoremas do tipo Liouville. No Capítulo 4 estudamos o problema do tipo Ambrosetti-Prodi para sistema com o p-Laplaciano no caso sublinear, utilizando para isso soluções de viscosidade e a caracterização do autovalor principal. / Abstract: The aim of this work is to obtain ABP estimates for fully nonlinear operators and to study problems of the Ambrosetti-Prodi type for the p-Laplacian operator in two cases: superlinear case for the equation and the sublinear case for the system. For this, we use the sub and supersolution method and the Leray Schauder degree theory, to obtain in the two cases, multiplicity of solutions. To apply the degree theory, we need a priori estimates of the possible solutions, obtained applying di_erent techniques in each problem. In Chapter 1 we will cite some auxiliary results, which will use during this work. In Chapter 2 we will obtain ABP estimates for viscosity solutions to a class of fully nonlinear operators, whose example is the p_Laplacian operator. In Chapter 3 we will study the Ambrosetti-Prodi type problems for the superlinear case, using the blow up technique and Liouville theorems type. In Chapter 4 we will study the Ambrosetti-Prodi type problem for system in the sublinear case, using for this viscosity solutions and the variational characterization of the principal eigenvalue. / Doutorado / Doutor em Matemática

Orientadores: Marcelo da Silva Montenegro, Massimo Grossi / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Matemática, Estatística e Computação Científica / Made available in DSpace on 2018-08-20T13:53:15Z (GMT). No. of bitstreams: 1 Neves_SergioLeandroNascimento_D.pdf: 694748 bytes, checksum: 52d4109b562640e98c9a0a6098d9cb46 (MD5) Previous issue date: 2012 / Resumo: Neste trabalho, consideramos uma classe de problemas de Neumann com perturbação singular e fazemos um estudo do número de soluções do tipo "single peak" que se concentram em um mesmo ponto. Estudamos casos de concentração no interior e na fronteira do domínio. Obtemos um resultado de multiplicidade exata que relaciona o número de tais soluções com o número de zeros estáveis de um campo vetorial associado / Abstract: In this work, we consider a class of Neumann problems with singular perturbation and we study the number of single peak solutions which concentrate at the same point. We study concentration in the interior and at the boundary of the domain. We obtain an exact multiplicity result which relates the number of such solutions with the number of stable zeros of an associated vector field. / Doutorado / Matematica / Doutor em Matemática

The inadequacy of Fick’s law to incorporate causality can be overcome by replacing it with the Green–Naghdi type II (GNII) flux relation. Combining the GNII assumption and conservation of mass leads to [see document for equation] where r (x, t) is the density function, S(p) is a source term and c¥ is a positive constant which carries (SI) units of m/sec. A general source term given by [see document for equation] is proposed. Here, the constants y and ps are the rate coefficient and saturation density respectively. The travelling wave solutions and numerical analysis of four special cases of equation (2), namely: Pearl-Verhulst Growth law, Zel’dovich Law, Newmann Law and Stefan- Boltzmann Law are investigated. For both analysis, results are compared with the available literature and extended for other cases. The numerical analysis is carried out by imposing well-studied Initial Boundary Value Problem and implementing a built-in method in the software package Mathematica 9. For Pearl-Verhulst source type, the results are compared to those found in literature [1]. Confirming the validity of built-in method for Pearl-Verhulst law, the generic built-in method is extended to study the transient signal response for similar initial boundary value problems when the source terms are Zel’dovich law, Newmann law and Stefan-Boltzmann law.