1,578 research outputs found

    Periodic minimal surfaces of cubic symmetry

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    A survey of cubic minimal surfaces is presented, based on the concept of fundamental surface patches and their relation to the asymmetric units of the space groups. The software Surface Evolver has been used to test for stability and to produce graphic displays. Particular emphasis is given to those surfaces that can be generated by a finite piece bounded by straight lines. Some new varieties have been found and a systematic nomenclature is introduced, which provides a symbol (a ‘gene’) for each triply-periodic minimal surface that specifies the surface unambiguously

    On moduli of rings and quadrilaterals: algorithms and experiments

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    Moduli of rings and quadrilaterals are frequently applied in geometric function theory, see e.g. the Handbook by K\"uhnau. Yet their exact values are known only in a few special cases. Previously, the class of planar domains with polygonal boundary has been studied by many authors from the point of view of numerical computation. We present here a new hphp-FEM algorithm for the computation of moduli of rings and quadrilaterals and compare its accuracy and performance with previously known methods such as the Schwarz-Christoffel Toolbox of Driscoll and Trefethen. We also demonstrate that the hphp-FEM algorithm applies to the case of non-polygonal boundary and report results with concrete error bounds

    Algorithms for recognizing knots and 3-manifolds

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    This is a survey paper on algorithms for solving problems in 3-dimensional topology. In particular, it discusses Haken's approach to the recognition of the unknot, and recent variations.Comment: 17 Pages, 7 figures, to appear in Chaos, Fractals and Soliton

    Finite element methods for integrated aerodynamic heating analysis

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    This report gives a description of the work which has been undertaken during the second year of a three year research program. The objectives of the program are to produce finite element based procedures for the solution of the large scale practical problems which are of interest to the Aerothermal Loads Branch (ALB) at NASA Langley Research Establishment. The problems of interest range from Euler simulations of full three dimensional vehicle configurations to local analyses of three dimensional viscous laminar flow. Adaptive meshes produced for both steady state and transient problems are to be considered. An important feature of the work is the provision of specialized techniques which can be used at ALB for the development of an integrated fluid/thermal/structural modeling capability

    A New Approach to Automatic Generation of all Quadrilateral Finite Element Mesh for Planar Multiply Connected Regions

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    A new approach for the automatic generation and refinement of finite element meshes over multiply connected planar regions has been developed. This paper represents continuation of authors research activities in that area. An algorithm for producing a triangular mesh in a convex polygon is presented in authors recent work. It is used for the finite element triangulation of a complex polygonal region of the plane decomposed into convex polygons. We decompose the convex polygonal regions into simple sub regions in the shape of triangles. These simple regions are then triangulated to generate a fine mesh of triangular elements. We then propose an automatic triangular to quadrilateral conversion scheme.In this scheme, each isolated triangle is split into three quadrilaterals according to the usual scheme, adding three vertices in the middle of the edges and a vertex a the barycentre of the element. To preserve the mesh conformity, a similar procedure is also applied to every triangle of the domain to fully discretize the given complex polygonal domain into all quadrilaterals, thus propagating uniform refinement. This simple method generates a mesh whose elements confirm well to the requested shape by refining the problem domain. We have modified these algorithms and demonstrated their use by generating high quality meshes for some typical multiply connected regions: square domains with regular polygonal holes inside and vice versa. We have also made improvements and modifications to to the above triangulation algorithm of the triangle which can now triangulate a trapezium cut out of a triangle. This new algorithm on the triangulation of a trapezium cut out of a triangle is applied to quadrangulate the planar regions in the shape of a circular annulus and square domain with a square hole inside. We have appended MATLAB programs which incorporate the mesh generation schemes developed in this paper. These programs provide valuable output on the nodal coordinates, element connectivity and graphic display of the all quadrilateral mesh for application to finite element analysi

    Numerical conformal mapping onto a rectangle with applications to the solution of Laplacian problems

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    Let F be the function which maps conformally a simple-connected domain onto a rectangle R, so that four specified points on are mapped Ω∂respectively onto the four vertices of R. In this paper we consider the problem of approximating the conformal map F, and present a survey of the available numerical methods. We also illustrate the practical significance of the conformal map, by presenting a number of applications involving the solution of Laplacian boundary value problems

    A 2D combined advancing front-Delaunay mesh generation scheme

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    A new unstructured triangular mesh generator, DBMesh, is described, incorporating both the Delaunay and advancing front methods. The domain boundary comprising the initial front is discretised by adding nodes based on pre-specified element densities. Internal optimal nodes are then computed from the front such that the latter are each located inside the circumscribed Delaunay circle, and an optimum equiangular triangle is created. The mesh is finally optimised. Advantages of the new method are also outlined. Examples of generated meshes are described, with element quality factors used to generate quadrilaterals if a hybrid, or purely quadrilateral element mesh is required

    Subset Warping: Rubber Sheeting with Cuts

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    Image warping, often referred to as "rubber sheeting" represents the deformation of a domain image space into a range image space. In this paper, a technique is described which extends the definition of a rubber-sheet transformation to allow a polygonal region to be warped into one or more subsets of itself, where the subsets may be multiply connected. To do this, it constructs a set of "slits" in the domain image, which correspond to discontinuities in the range image, using a technique based on generalized Voronoi diagrams. The concept of medial axis is extended to describe inner and outer medial contours of a polygon. Polygonal regions are decomposed into annular subregions, and path homotopies are introduced to describe the annular subregions. These constructions motivate the definition of a ladder, which guides the construction of grid point pairs necessary to effect the warp itself
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