Computational and numerical analysis of differential equations using spectral based collocation method.

Doctoral Degree. University of KwaZulu-Natal, Pietermaritzburg.In this thesis, we develop accurate and computationally efficient spectral collocation-based methods, both modified and new, and apply them to solve differential equations. Spectral collocation-based methods are the most commonly used methods for approximating smooth solutions of differential equations defined over simple geometries. Procedurally, these methods entail transforming the gov erning differential equation(s) into a system of linear algebraic equations that can be solved directly. Owing to the complexity of expanding the numerical algorithms to higher dimensions, as reported in the literature, researchers often transform their models to reduce the number of variables or narrow them down to problems with fewer dimensions. Such a process is accomplished by making a series of assumptions that limit the scope of the study. To address this deficiency, the present study explores the development of numerical algorithms for solving ordinary and partial differential equations defined over simple geometries. The solutions of the differential equations considered are approximated using interpolating polynomials that satisfy the given differential equation at se lected distinct collocation points preferably the Chebyshev-Gauss-Lobatto points. The size of the computational domain is particularly emphasized as it plays a key role in determining the number of grid points that are used; a feature that dictates the accuracy and the computational expense of the spectral method. To solve differential equations defined on large computational domains much effort is devoted to the development and application of new multidomain approaches, based on decomposing large spatial domain(s) into a sequence of overlapping subintervals and a large time interval into equal non-overlapping subintervals. The rigorous analysis of the numerical results con firms the superiority of these multiple domain techniques in terms of accuracy and computational efficiency over the single domain approach when applied to problems defined over large domains. The structure of the thesis indicates a smooth sequence of constructing spectral collocation method algorithms for problems across different dimensions. The process of switching between dimensions is explained by presenting the work in chronological order from a simple one-dimensional problem to more complex higher-dimensional problems. The preliminary chapter explores solutions of or dinary differential equations. Subsequent chapters then build on solutions to partial differential i equations in order of increasing computational complexity. The transition between intermediate dimensions is demonstrated and reinforced while highlighting the computational complexities in volved. Discussions of the numerical methods terminate with development and application of a new method namely; the trivariate spectral collocation method for solving two-dimensional initial boundary value problems. Finally, the new error bound theorems on polynomial interpolation are presented with rigorous proofs in each chapter to benchmark the adoption of the different numerical algorithms. The numerical results of the study confirm that incorporating domain decomposition techniques in spectral collocation methods work effectively for all dimensions, as we report highly accurate results obtained in a computationally efficient manner for problems defined on large do mains. The findings of this study thus lay a solid foundation to overcome major challenges that numerical analysts might encounter

A numerical study of entropy generation in nanofluid flow in different flow geometries.

This thesis is concerned with the mathematical modelling and numerical solution of equations for boundary layer flows in different geometries with convective and slip boundary conditions. We investigate entropy generation, heat and mass transport mechanisms in non-Newtonian fluids by determining the influence of important physical and chemical parameters on nanofluid flows in various flow geometries, namely, an Oldroyd-B nanofluid flow past a Riga plate; the combined thermal radiation and magnetic field effects on entropy generation in unsteady fluid flow in an inclined cylinder; the impact of irreversibility ratio and entropy generation on a three-dimensional Oldroyd-B fluid flow along a bidirectional stretching surface; entropy generation in a double-diffusive convective nanofluid flow in the stagnation region of a spinning sphere with viscous dissipation and a study of the fluid velocity, heat and mass transfer in an unsteady nanofluid flow past parallel porous plates. We assumed that the nanofluids are electrically conducting and that the velocity slip and shear stress at the boundary have a linear relationship. We also consider different boundary conditions for all the flow models. The study further analyzes and quantifies the influence of each source of irreversibility on the overall entropy generation. The transport equations are solved using two recent numerical methods, the overlapping grid spectral collocation method and the bivariate spectral quasilinearization method, first to determine which of these methods is the most accurate, and secondly to authenticate the numerical accuracy of the results. Further, we determine the skin friction coefficient and the changes in the heat and mass transfer coefficients with various system parameters. The results show, inter alia that reducing the heat transfer coefficient, the particle Brownian motion parameter, chemical reaction parameter, Brinkman number, thermophoresis parameter and the Hartman number all lead individually to a reduction in entropy generation. The overlapping grid spectral collocation method gives better computational accuracy and converge faster than the bivariate spectral quasilinearization method. The fluid flow problems have engineering and industrial applications, particularly in the design of cooling systems and in aerodynamics

Chebyshev spectral pertutrbation based method for solving nonlinear fluid flow problems.

M. Sc. University of KwaZulu-Natal, Pietermaritzburg 2014.In this dissertation, a modi cation of the classical perturbation techniques for solving nonlinear ordinary di erential equation (ODEs) and nonlinear partial di erential equations (PDEs) is presented. The method, called the Spectral perturbation method (SPM) is a series expansion based technique which extends the use of the standard perturbation scheme when combined with the Chebyshev spectral method. The SPM solves a sequence of equations generated by the perturbation series approximation using the Chebyshev spectral methods. This dissertation aims to demonstrate that, in contrast to the conclusions earlier drawn by researchers about perturbation techniques, a perturbation approach can be e ectively used to generate accurate solutions which are de ned under the Williams and Rhyne (1980) transformation. A quasi-linearisation technique, called the spectral quasilinearisation method (SQLM) is used for validation purpose. The SQLM employs the quasilinearisation approach to linearise nonlinear di erential equations and the resulting equations are solved using the spectral methods. Furthermore, a spectral relaxation method (SRM) which is a Chebyshev spectral collocation based method that decouples and rearrange a system of equations in a Gauss - Seidel manner is also presented. In the SRM, the di erential equations are decoupled, rearranged and the resulting sequence of equations are numerically integrated using the Chebyshev spectral collocation method. The techniques were used to solve mathematical models in uid dynamics. This study consists of an introductory chapter which gives the description of the methods and a brief overview of the techniques used in developing the SPM, SQLM and the SRM. In Chapter 2, the SPM is used to solve the equations that model magnetohydrodynamics (MHD) stagnation point ow and heat transfer problem from a stretching sheet in the presence of heat source/sink and suction/injection in porous media. Using similarity transformations, the governing partial differential equations are transformed into ordinary di erential equations. Series solutions for small velocity ratio and asymptotic solutions for large velocity ratio were generated and the results were also validated against those obtained using the SQLM. In Chapter 3, the SPM was used to solve the momentum, heat and mass transfer equations describing the unsteady MHD mixed convection ow over an impulsively stretched vertical surface in the presence of chemical reaction e ect. The governing partial di erential equations are reduced into a set of coupled non similar equations and then solved numerically using the SPM. In order to demonstrate the accuracy and e ciency of the SPM, the SPM numerical results are compared with numerical results generated using the SRM and a good agreement between the two methods was observed up to eight decimal digits which is a reasonable level of accuracy. Several simulation are conducted to ascertain the accuracy of the SPM and the SRM. The computational speed of the SPM is demonstrated by comparing the SPM computational time with the SRM computational time. A residual error analysis is also conducted for the SPM and the SRM, in order to further assess the accuracy of the SPM. In Chapter 4, the SPM was used to solve the equations modelling the unsteady three-dimensional MHD ow and mass transfer in a porous space previously reported in literature. E ciency and accuracy of the SPM is shown by validating the SPM results against the results obtained using the SRM and the results were found to be in good agreement. The computational speed of the SPM is demonstrated by comparing the SPM and the SRM computational time. In order to further assess the accuracy of the SPM, a residual error analysis is conducted for the SPM and the SRM. In Chapter 2, we show that the SPM can be used as an alternative to the standard perturbation methods to get numerical solutions for strongly nonlinear boundary value problems. Also, it is demonstrated in Chapter 2 that the SPM is e cient even in the case where the perturbation parameter is large, as the convergence rate is seen to improve with increase in the large parameter value. In Chapters 3 and 4, the study shows that SPM is more e cient in terms of computational speed when compared with the SRM. The study also highlighted that the SPM can be used as an e cient and reliable tool for solving strongly nonlinear partial di erential equations de ned under the Williams and Rhyne (1980) transformation. In addition, the study shows that accurate results can be obtained using the perturbation method and thus, the conclusions earlier drawn by researchers regarding the accuracy of the perturbation method is corrected

On paired decoupled quasi-linearization methods for solving nonlinear systems of differential equations that model boundary layer fluid flow problems.

Doctoral Degree. University of KwaZulu-Natal, Pietermaritzburg.Two numerical methods, namely the spectral quasilinearization method (SQLM) and the spectral local linearization method (SLLM), have been found to be highly efficient methods for solving boundary layer flow problems that are modeled using systems of differential equations. Conclusions have been drawn that the SLLM gives highly accurate results but requires more iterations than the SQLM to converge to a consistent solution. This leads to the problem of figuring out how to improve on the rate of convergence of the SLLM while maintaining its high accuracy. The objective of this thesis is to introduce a method that makes use of quasilinearization in pairs of equations to decouple large systems of differential equations. This numerical method, hereinafter called the paired quasilinearization method (PQLM) seeks to break down a large coupled nonlinear system of differential equations into smaller linearized pairs of equations. We describe the numerical algorithm for general systems of both ordinary and partial differential equations. We also describe the implementation of spectral methods to our respective numerical algorithms. We use MATHEMATICA to carry out the numerical analysis of the PQLM throughout the thesis and MATLAB for investigating the influence of various parameters on the flow profiles in Chapters 4, 5 and 6. We begin the thesis by defining the various terminologies, processes and methods that are applied throughout the course of the study. We apply the proposed paired methods to systems of ordinary and partial differential equations that model boundary layer flow problems. A comparative study is carried out on the different possible combinations made for each example in order to determine the most suitable pairing needed to generate the most accurate solutions. We test convergence speed using the infinity norm of solution error. We also test their accuracies by using the infinity norm of the residual errors. We also compare our method to the SLLM to investigate if we have successfully improved the convergence of the SLLM while maintaining its accuracy level. Influence of various parameters on fluid flow is also investigated and the results obtained show that the paired quasilinearization method (PQLM) is an efficient and accurate method for solving boundary layer flow problems. It is also observed that a small number of grid-points are needed to produce convergent numerical solutions using the PQLM when compared to methods like the finite difference method, finite element method and finite volume method, among others. The key finding is that the PQLM improves on the rate of convergence of the SLLM in general. It is also discovered that the pairings with the most nonlinearities give the best rate of convergence and accuracy

Numerical Simulation

Nowadays mathematical modeling and numerical simulations play an important role in life and natural science. Numerous researchers are working in developing different methods and techniques to help understand the behavior of very complex systems, from the brain activity with real importance in medicine to the turbulent flows with important applications in physics and engineering. This book presents an overview of some models, methods, and numerical computations that are useful for the applied research scientists and mathematicians, fluid tech engineers, and postgraduate students

Research in progress and other activities of the Institute for Computer Applications in Science and Engineering

This report summarizes research conducted at the Institute for Computer Applications in Science and Engineering in applied mathematics and computer science during the period April 1, 1993 through September 30, 1993. The major categories of the current ICASE research program are: (1) applied and numerical mathematics, including numerical analysis and algorithm development; (2) theoretical and computational research in fluid mechanics in selected areas of interest to LaRC, including acoustic and combustion; (3) experimental research in transition and turbulence and aerodynamics involving LaRC facilities and scientists; and (4) computer science

A mathematical study of boundary layer nanofluid flow using spectral quasilinearization methods.

Doctoral Degree. University of KwaZulu-Natal, Pietermaritzburg.Heat and mass transfer enhancement in industrial processes is critical in improving the efficiency of these systems. Several studies have been conducted in the past to investigate different strategies for improving heat and mass transfer enhancement. There are however some aspects that warrant further investigations. These emanate from different constitutive relationships for different non-Newtonian fluids and numerical instability of some numerical schemes. To investigate the convective transport phenomena in nanofluid flows, we formulate models for flows with convective boundary conditions and solve them numerically using the spectral quasilinearisation methods. The numerical methods are shown to be stable, accurate and have fast convergence rates. The convective transport phenomena are studied via parameters such as the Biot number and buoyancy parameter. These are shown to enhance convective transport. Nanoparticles and microorganisms’ effects are studied via parameters such as the Brownian motion, thermophoresis, bioconvective Peclet number, bioconvective Schmidt number and bioconvective Rayleigh number. These are also shown to aid convective transport

International Conference on Mathematical Analysis and Applications in Science and Engineering – Book of Extended Abstracts

The present volume on Mathematical Analysis and Applications in Science and Engineering - Book of Extended Abstracts of the ICMASC’2022 collects the extended abstracts of the talks presented at the International Conference on Mathematical Analysis and Applications in Science and Engineering – ICMA2SC'22 that took place at the beautiful city of Porto, Portugal, in June 27th-June 29th 2022 (3 days). Its aim was to bring together researchers in every discipline of applied mathematics, science, engineering, industry, and technology, to discuss the development of new mathematical models, theories, and applications that contribute to the advancement of scientific knowledge and practice. Authors proposed research in topics including partial and ordinary differential equations, integer and fractional order equations, linear algebra, numerical analysis, operations research, discrete mathematics, optimization, control, probability, computational mathematics, amongst others. The conference was designed to maximize the involvement of all participants and will present the state-of- the-art research and the latest achievements.info:eu-repo/semantics/publishedVersio

Applied Mathematics and Computational Physics

As faster and more efficient numerical algorithms become available, the understanding of the physics and the mathematical foundation behind these new methods will play an increasingly important role. This Special Issue provides a platform for researchers from both academia and industry to present their novel computational methods that have engineering and physics applications