A numerical study of steady viscous flow past a circular cylinder

Numerical solutions have been obtained for steady viscous flow past a circular cylinder at Reynolds numbers up to 300. A new technique is proposed for the boundary condition at large distances and an iteration scheme has been developed, based on Newton's method, which circumvents the numerical difficulties previously encountered around and beyond a Reynolds number of 100. Some new trends are observed in the solution shortly before a Reynolds number of 300. As vorticity starts to recirculate back from the end of the wake region, this region becomes wider and shorter. Other flow quantities like position of separation point, drag, pressure and vorticity distributions on the body surface appear to be quite unaffected by this reversal of trends

A Numerical Method for Conformal Mappings

A numerical technique is presented for calculating the Taylor coefficients of the analytic function which maps the unit circle onto a region bounded by any smooth simply connected curve. The method involves a quadratically convergent outer iteration and a super-linearly convergent inner iteration. If N complex points are distributed equidistantly around the periphery of the unit circle, their images on the edge of the mapped region, together with approximations for the N/2 first Taylor coefficients, are obtained in O(Nlog N) operations. A calculation of time-dependent waves on deep water is discussed as an example of the potential applications of the method

Stable Computations with Flat Radial Basis Functions Using Vector-Valued Rational Approximations

One commonly finds in applications of smooth radial basis functions (RBFs) that scaling the kernels so they are \u27flat\u27 leads to smaller discretization errors. However, the direct numerical approach for computing with flat RBFs (RBF-Direct) is severely ill-conditioned. We present an algorithm for bypassing this ill-conditioning that is based on a new method for rational approximation (RA) of vector-valued analytic functions with the property that all components of the vector share the same singularities. This new algorithm (RBF-RA) is more accurate, robust, and easier to implement than the Contour-Padé method, which is similarly based on vector-valued rational approximation. In contrast to the stable RBF-QR and RBF-GA algorithms, which are based on finding a better conditioned base in the same RBF-space, the new algorithm can be used with any type of smooth radial kernel, and it is also applicable to a wider range of tasks (including calculating Hermite type implicit RBF-FD stencils). We present a series of numerical experiments demonstrating the effectiveness of this new method for computing RBF interpolants in the flat regime. We also demonstrate the flexibility of the method by using it to compute implicit RBF-FD formulas in the flat regime and then using these for solving Poisson\u27s equation in a 3-D spherical shell

A high-order and mesh-free computational model for non-linear water waves

In this paper, we present the ongoing developments of a novel computational model for non-linear water waves that aims to provide a suitable framework for wave-structure inter- action. The proposed model is based on radial basis function-generated finite differences, which allow for arbitrary and moving boundaries without the use of ghost nodes. In order to take advantage of the mesh-free setting, we propose a node generation strategy, suitable for moving boundaries. Numerical properties of the proposed model are investigated and finally the model is benchmarked. The proposed model is expected to provide a suitable computational framework for wave-structure interaction problems, due to its geometric flexibility and high-order nature

Explicit Time Stepping of PDEs with Local Refinement in Space-Time

Traditional numerical time stepping allows variable node densities in space, but not also in time. Having the ability to utilize nodes that are placed irregularly in the space-time domain leads to many advantages when solving time dependent problems. In this paper we introduce a new method utilizing the radial basis function generated �nite di�erence (RBF-FD) approach in order to accomplish this goal. Bene�ts include improved stability conditions and the option to use small time steps only in select spatial regions.</p

Using radial basis function-generated finite differences (RBF-FD) to solve heat transfer equilibrium problems in domains with interfaces

When thermal diffusivity does not vary smoothly within a computational domain, standard numerical methods for solving heat equilibrium problems often converge to an inaccurate solution. In the present paper, we discuss a mesh-free, radial basis function-generated finite difference (RBF-FD)-based method for designing stencil weights that can be applied directly to data that crosses an interface. The approach produces a very accurate solution when thermal diffusivity varies smoothly on either side of an interface. It continues to produce high-quality results when a region between two interfaces is much smaller that the distance between adjacent discrete data nodes in the domain (as becomes the case for thin, nearly insulating layers). We give several test cases that demonstrate the method solving heat equilibrium problems to 4th-order accuracy in the presence of smoothly-curved interfaces

An improved Gregory-like method for 1-D quadrature

The quadrature formulas described by James Gregory (1638--1675) improve the accuracy of the trapezoidal rule by adjusting the weights near the ends of the integration interval. In contrast to the Newton--Cotes formulas, their weights are constant across the main part of the interval. However, for both of these approaches, the polynomial Runge phenomenon limits the orders of accuracy that are practical. For the algorithm presented here, this limitation is greatly reduced. In particular, quadrature formulas on equispaced 1-D node sets can be of high order (tested here up through order 20) without featuring any negative weights