Applying multiquadric quasi-interpolation to solve Fokker-Planck equation

The Fokker-Planck equation (FPE) arises in various fields in physics, chemistry, natural science. It is difficult to obtain analytical solutions, accordingly we resort to numerical methods. In this study, we present a meshfree method to solve FPE. It is based on the multiquadric quasi-interpolation (MQQI) operator LW2 and collocation technique. Here, θ-weighted finite difference scheme is used to discretize the temporal derivative. Then, the unknown function and its spatial derivatives are approximated by the multiquadric quasi-interpolation (MQQI) operator LW2. Furthermore, the stability of the technique is investigated. This method is applied to some examples and the numerical results have been compared with the exact solutions and results of another method.Publisher's Versio

Boundary knot method: A meshless, exponential convergence, integration-free, and boundary-only RBF technique

Based on the radial basis function (RBF), non-singular general solution and dual reciprocity principle (DRM), this paper presents an inheretnly meshless, exponential convergence, integration-free, boundary-only collocation techniques for numerical solution of general partial differential equation systems. The basic ideas behind this methodology are very mathematically simple and generally effective. The RBFs are used in this study to approximate the inhomogeneous terms of system equations in terms of the DRM, while non-singular general solution leads to a boundary-only RBF formulation. The present method is named as the boundary knot method (BKM) to differentiate it from the other numerical techniques. In particular, due to the use of non-singular general solutions rather than singular fundamental solutions, the BKM is different from the method of fundamental solution in that the former does no need to introduce the artificial boundary and results in the symmetric system equations under certain conditions. It is also found that the BKM can solve nonlinear partial differential equations one-step without iteration if only boundary knots are used. The efficiency and utility of this new technique are validated through some typical numerical examples. Some promising developments of the BKM are also discussed.Comment: 36 pages, 2 figures, Welcome to contact me on this paper: Email: [email protected] or [email protected]

Numerical simulation of reaction fronts in dissipative media

Fronts of reaction in certain systems (such as so-called solid flames and detonation fronts) can be simulated by a single-equation phenomenological model of Strunin (1999, 2009). This is a high-order nonlinear partial differential equation describing the shape of the front as a function of spatial coordinates and time. The equation is of active-dissipative type, with 6th-order spatial derivative. For one-dimensional case, the equation was previously solved using the Galerkin method, but only one numerical experiment with limited information on the dynamics was obtained. For two-dimensional case only two numerical ex- periments were reported so far, in which a low-accuracy infinite difference scheme was used. In this thesis, we use a more recent and sophisticated method, namely the one-dimensional integrated radial basis function networks (1D-IRBFN). The method had been developed by Tran-Cong and May-Duy (2001, 2003) and successfully applied to several problems such as structural analysis, viscoelastic flows and fluid-structure interaction. In contrast to commonly used approaches, where a function of interest is differentiated to give approximate derivatives, leading to a reduction in convergence rate for derivatives (and this reduction increases with derivative order, which magnifes errors), the 1D-IRBFN method uses the integral formulation. It utilizes spectral approximants to represent highest-order derivatives under consideration. They are then integrated analytically to yield approximate expressions for lower-order derivatives and the function itself. In this thesis the following main results are obtained. A numerical program implementing the 1D-IRBFN method is developed in Matlab to solve the equation of interest. The program is tested by (a) constructing a forced version of the equation, which allows analytical solution, and verifying the numerical solution against the analytical solution; (b) reproducing one-dimensional spinning waves obtained from the model previously. A modified version of the program is successfully applied to similar high-order equations modelling auto-pulses in fluid flows with elastic walls. We obtained numerically and analyzed a far richer variety of one-dimensional dynamics of the reaction fronts. Two kinds of boundary conditions were used: homogeneous conditions on the edges of the domain, and periodic conditions corresponding to periodicity of the front on a cylinder. The dependence of the dynamics on the size of the domain is explored showing how larger space accommodates multiple spinning waves. We determined the critical domain size (bifurcation point) at which non-trivial settled regimes become possible. We found a regime where the front is shaped as a pair of kinks separated by a relatively short distance. Interestingly, the pair moves in a stable joint formation far from the boundaries. A similar regime for three connected kinks is obtained. We demonstrated that the initial condition determines the direction of motion of the kinks, but not their size and velocity. This is typical for active-dissipative systems. The settled character of these regimes is demonstrated. We also applied the 1D-IRBFN method to two-dimensional topology corresponding to a solid cylinder. Stable spinning wave solutions are obtained for this case

Redistribution of Nodes with Two Constraints in Meshless Method of Line to Time-Dependent Partial Differential Equations

Meshless method of line is a powerful device to solve time-dependent partial differential equations. In integrating step, choosing a suitable set of points, such as adaptive nodes in spatial domain, can be useful, although in some cases this can cause ill-conditioning. In this paper, to produce smooth adaptive points in each step of the method, two constraints are enforced in Equidistribution algorithm. These constraints lead to two different meshes known as quasi-uniform and locally bounded meshes. These avoid the ill-conditioning in applying radial basis functions. Moreover, to generate more smooth adaptive meshes another modification is investigated, such as using modified arc-length monitor function in Equidistribution algorithm. Influence of them in growing the accuracy is investigated by some numerical examples. The results of consideration of two constraints are compared with each other and also with uniform meshes

Compact integrated radial basis function modelling of particulate suspensions

The present Ph.D. thesis is concerned with the development of computational procedures based on Cartesian grids, point collocation, immersed boundary method, and compact integrated radial basis functions (CIRBF), for the simulation of heat transfer and steady/unsteady viscous flows in complex geometries, and their applications for the prediction of macroscopic rheological properties of particulate suspensions. The thesis consists of three main parts. In the first part, integrated radial basis function approximations are developed into compact local form to achieve sparse system matrices and high levels of accuracy together. These stencils are employed for the discretisation of the Navier-Stokes equation in the pressurevelocity formulation. The use of alternating direction implicit (ADI) algorithms to enhance the computational efficiency is also explored. In the second part, compact local IRBF stencils are extended for the simulation of flows in multiply-connected domains, where the direct forcing-immersed boundary (DFIB) method is adopted to handle such complex geometries efficiently. In the third part, the DFIB-CIRBF method is applied for the investigation of suspensions of rigid particles in a Newtonian liquid, and the prediction of their bulk viscosity and stresses. The proposed computational procedures are verified successfully with several test problems in Computational Fluid Dynamics and Computational Rheology. Accurate results are achieved using relatively coarse grids

Solitary Wave Solutions of the Generalized Rosenau-KdV-RLW Equation

This paper investigates the solitary wave solutions of the generalized Rosenau–Korteweg-de Vries-regularized-long wave equation. This model is obtained by coupling the Rosenau–Korteweg-de Vries and Rosenau-regularized-long wave equations. The solution of the equation is approximated by a local meshless technique called radial basis function (RBF) and the finite-difference (FD) method. The association of the two techniques leads to a meshless algorithm that does not requires the linearization of the nonlinear terms. First, the partial differential equation is transformed into a system of ordinary differential equations (ODEs) using radial kernels. Then, the ODE system is solved by means of an ODE solver of higher-order. It is shown that the proposed method is stable. In order to illustrate the validity and the efficiency of the technique, five problems are tested and the results compared with those provided by other schemes.info:eu-repo/semantics/publishedVersio

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

Fast Method of Particular Solutions for Solving Partial Differential Equations

Method of particular solutions (MPS) has been implemented in many science and engineering problems but obtaining the closed-form particular solutions, the selection of the good shape parameter for various radial basis functions (RBFs) and simulation of the large-scale problems are some of the challenges which need to overcome. In this dissertation, we have used several techniques to overcome such challenges. The closed-form particular solutions for the Matérn and Gaussian RBFs were not known yet. With the help of the symbolic computational tools, we have derived the closed-form particular solutions of the Matérn and Gaussian RBFs for the Laplace and biharmonic operators in 2D and 3D. These derived particular solutions play an important role in solving inhomogeneous problems using MPS and boundary methods such as boundary element methods or boundary meshless methods. In this dissertation, to select the good shape parameter, various existing variable shape parameter strategies and some well-known global optimization algorithms have also been applied. These good shape parameters provide high accurate solutions in many RBFs collocation methods. Fast method of particular solutions (FMPS) has been developed for the simulation of the large-scale problems. FMPS is based on the global version of the MPS. In this method, partial differential equations are discretized by the usual MPS and the determination of the unknown coefficients is accelerated using a fast technique. Numerical results confirm the efficiency of the proposed technique for the PDEs with a large number of computational points in both two and three dimensions. We have also solved the time fractional diffusion equations by using MPS and FMPS