Extended isogeometric boundary element method (XIBEM) for two-dimensional Helmholtz problems.

Isogeometric analysis is a topic of considerable interest in the field of numerical analysis. The boundary element method (BEM) requires only the bounding surface of geometries to be described; this makes non-uniform rational B-splines (NURBS), which commonly describe the bounding curve or surface of geometries in CAD software, appear to be a natural tool for the approach. This isogeometric analysis BEM (IGABEM) provides accuracy benefits over conventional BEM schemes due to the analytical geometry provided by NURBS. When applied to wave problems, it has been shown that enriching BEM approximations with a partition-of-unity basis, in what has become known as the PU-BEM, allows highly accurate solutions to be obtained with a much reduced number of degrees of freedom. This paper combines these approaches and presents an extended isogeometric BEM (XIBEM) which uses partition-of-unity enriched NURBS functions; this new approach provides benefits which surpass those of both the IGABEM and the PU-BEM. Two numerical examples are given: a single scattering cylinder and a multiple-scatterer made up of two capsules and a cylinder

Interactive boundary element analysis for engineering design.

Structural design of mechanical components is an iterative process that involves multiple stress analysis runs; this can be time consuming and expensive. Significant improvements in the eciency of this process can be made by increasing the level of interactivity. One approach is through real-time re-analysis of models with continuously updating geometry. Three primary areas need to be considered to accelerate the re-solution of boundary element problems. These are re-meshing the model, updating the boundary element system of equations and re-solution of the system. Once the initial model has been constructed and solved, the user may apply geometric perturbations to parts of the model. The re-meshing algorithm must accommodate these changes in geometry whilst retaining as much of the existing mesh as possible. This allows the majority of the previous boundary element system of equations to be re-used for the new analysis. For this problem, a GMRES solver has been shown to provide the fastest convergence rate. Further time savings can be made by preconditioning the updated system with the LU decomposition of the original system. Using these techniques, near real-time analysis can be achieved for 3D simulations; for 2D models such real-time performance has already been demonstrated

An isogeometric boundary element formulation for stress concentration problems in couple stress elasticity

An isogeometric boundary element method (IGABEM) is developed for the analysis of two-dimensional linear and isotropic elastic bodies governed by the couple stress theory. This theory is the simplest generalised continuum theory that can eectively model size eects in solids. The couple stress fundamental solutions are explicitly derived and used to construct the boundary integral equations. A new boundary integral equation arises to obtain the moments and rotations introduced by the couple stress formulation. A new analytical solution is also derived in the present work for an elliptical opening in an innite sheet under uniaxial far-eld stress. Several stress concentration problems are examined to illustrate and validate the application of the IGABEM in couple stress elasticity. It is shown that the IGABEM scheme exhibits advantageous convergence properties in comparison with the conventional BEM for boundary value problems within the framework of couple stress elasticity

Comparison of CHIEF and Burton-Miller approaches in collocation Partition of Unity BEM for Helmholtz problems

Use of plane wave basis for the numerical solutions of acoustic wave problems using element based methods has become an attractive approach for extending the allowable frequency range for simulations beyond that available using piecewise polynomial elements. The non-uniqueness of the solution at characteristic frequencies resulting from the use of the conventional boundary integral equation is well known. The standard methods of overcoming this problem are the so-called CHIEF method and that of Burton and Miller. The latter method introduces a hypersingular integral which can be treated in several ways. In this paper we present results for Partition of Unity BEM (PUBEM) for Helmholtz problem and compare the performance of CHIEF against a Burton-Miller formulation regularised using the approach of Chen et al

The equal spacing of N points on a sphere with application to partition-of-unity wave diffraction problems

This paper addresses applications involving the selection of a set of points on a sphere, in which the uniformity of spacing can be of importance in enhancing the computational performance and/or the accuracy of some simulation. For the authors, the motivation for this work arises from the need to specify wave directions in a partition-of-unity approach for numerical analysis of wave diffraction problems. A new spacing method is presented, based on a physical analogy in which an arbitrary number of charged particles are held in static equilibrium on a spherical surface. The new method, referred to in this paper as the Coulomb force method, offers an improvement over simpler methods, e.g., latitude/longitude and discretised cube methods, in terms of both the uniformity of spacing and the arbitrary nature of the number of points N that can be considered. A simple extension to the algorithm allows points to be biased towards a direction of choice. Numerical results of a wave scattering problem solved with a partition-of-unity boundary element method demonstrate the benefits of the algorithm