Imposing essential boundary conditions in the natural element method by means of density-scaled alpha-shapes

A new method is proposed for the 'exact' imposition of essential boundary c onditions in the context of the natural element method (NEM). This is a new technique in the field of Computational Mechanics and can be considered as a meshless method. Unlike most of these methods, the NE shape functions ar e strictly interpolant and the essential boundary conditions can be imposed by directly substituting the corresponding terms in the system of equation s. However, these shape functions are not strictly linear over non-convex b oundaries and the approach does not make the test functions vanish over the whole essential boundary region, A modification of the initial NEM version is considered based on alpha-shapes and alpha-complexes, which are widely used in the field of scientific visualization. Using alpha-shapes in the co ntext of the NEM allows the construction of models entirely in terms of nod es and also ensures the linear precision of the interpolant over convex and non-convex boundaries. Results on some benchmark problems are presented af ter a theoretical description of the method. Copyright (C) 2000 John Wiley & Sons, Ltd.