曲面上葉狀結(jié)構(gòu)的研究與多元Birkhoff插值
[Abstract]:Computational conformal geometry is an interdisciplinary subject between computer science and pure mathematics. Its purpose is to transform the concepts and theorems of modern geometry and classical geometry into computer algorithms to serve engineering practice. Quadratic differentiation is an important concept in conformal geometry. It is of great significance in the study of Teichmuller space. It is directly related to the leaf structure on a surface. Horizontal and vertical trajectories of holomorphic quadratic differentiation form the leaf structure on a surface. However, due to the obscurity of holomorphic quadratic differentiation, few people can master it. In this paper, a generalized harmonic mapping algorithm for high genus Riemannian surfaces to graphs is implemented for the first time. The leaf structure on the surface is obtained and visualized. Meanwhile, the Hopf differential induced by the generalized harmonic mapping from Riemannian surfaces to graphs is holomorphic. Quadratic Differentiation (Strebel Differentiation) allows the algorithm to further compute holomorphic quadratic differentials. By inputting loop and height parameters on different surfaces, the algorithm can control topological homotopy classes and geometric properties of leaf structures, and thus the obtained holomorphic quadratic differentials are controllable. Holomorphic quadratic differentials have been visualized extensively, which enables us to understand these concepts more intuitively and then apply them to engineering fields. In the generation of hexahedron meshes, the equivalence relations among the three concepts of dyeable quadrangular meshes, finite measurable leaf structures and Strebel differentials are expounded for the first time in this paper. Lattice generation algorithm provides a solid theoretical foundation; and based on the leaf structure on the surface and Strebel differentiation, a fully automatic hexahedron mesh generation algorithm is proposed and implemented, which makes a significant breakthrough in the so-called "holy grail" problem of hexahedron mesh generation. In addition, this paper also introduces a class of problems in Birkhoff interpolation which have the same minimal monomial basis under any monomial order, and puts forward the criteria for this kind of problems, so that we can use the minimal monomial basis under dictionary order to calculate quickly. The so-called foliation is to decompose a n n-dimensional manifold into (n-1) dimensional submanifolds. The decomposition method has a direct product structure locally. As shown in Figure 1 (a), we decompose a surface with genus 2 into a family of curves. Each curve is called a piece. Leaves. Points where three leaves intersect on a surface are called singular points. The leaf structure and Strebel differentiation on a surface with genus 2 in Fig. 1. To obtain the leaf structure on a surface, we consider a generalized harmonic mapping from a surface to a graph. As shown in the three orange curves in Fig. 1 (a), we specify a set of loops (closed curves) {gamma} on the surface. 1, gamma 2, gamma 3} and the corresponding set of loops with height parameters divide the curved surface into two pairs of pants (a surface with three edges of genus zero). This decomposition can be defined as a graph, as shown in Figure 1 (b), each pair of pants corresponds to a node, each loop corresponds to an edge, and the length of the edge corresponds to a height parameter; if the loops have three edges, each pair corresponds to a node. Gromov and Schoen [20] define the hyperbolic properties of a graph and prove the existence and uniqueness of generalized harmonic mappings from a surface to a graph. Our algorithm uses the nonlinear heat flux method to solve the generalized harmonic mappings from a surface to a graph. As shown in Figure 1, (b) the original image of the node in the middle graph is a red curve; (b) the original image of the point on the edge of the middle graph is a leaf on the surface in (a). The leaf on the surface of the leaf structure can be a loop (closed curve) or an infinite extension of the helix, all the leaves are equal. The foliate structure of a loop is called a finite measurable foliate structure. The foliate structure computed by our algorithm through generalized harmonic mapping is a finite measurable foliate structure. A holomorphic quadratic derivative is shown in Fig. 1 (c). The foliate structure induced by the horizontal orbit is exactly the given foliate structure. The holomorphic quadratic differential with finite measurable foliate structure is called Strebel differential. The equivalence relations of the following three concepts are first expounded and proved: {dyeable quadrilateral mesh} (?) {finite measurable foliate structure} (?) {Strebel differential} theorem 0.0.1 (trinity) Let S be a closed Riemannian surface with genus greater than 1. Given a dyeable quadrilateral mesh Q on a surface, there exists a Q-induced finite measurable foliate structure (FQ, muQ), the same as There exists a unique Strebel differential_. So that_-induced horizontal finite measurable foliate structures (F, mu_) are exactly equal to (FQ, mu Q). Conversely, given Strebel differential_, finite measurable foliate structures (F, mu_) can be constructed. Induced dyeable quadrilateral grid Q. This Trinity theoretical framework allows us to construct dyeable foliate structures using Strebel differential. Color quadrilateral meshes are then extended to generate hexahedral meshes of the interior entities of the surface. The algorithm flow is as follows: the input genus is g 1 closed surface, the interior space of the surface constitutes a high genus entity. (1) The user sets a set of disjoint simple loops on the input surface, and assigns a height parameter to each loop; (2) calculates the unique one. Strebel Differential; (3) Strebel Differential divides the input surface into a cylindrical surface and generates a dyeable quadrilateral mesh; (4) According to the cylindrical division of the surface, extending to the inner space of the surface, the cylindrical division of the generated body; (5) Calculate the differential homeomorphism mapping of each separated topological cylinder to the standard cylinder; (6) On the standard cylinder. The hexahedron mesh is pulled back to the original topological cylinder, that is, the hexahedron mesh is generated on each partitioned cylinder. Finally, the hexahedron mesh is obtained by splicing the hexahedron mesh. High genus surface registration. Based on the leaf structure on the surface, a new surface registration method is proposed. For two homeomorphic surfaces with the same topology, we first register their graphs and then register the corresponding leaves. Fig. 2 shows the flow of our surface registration algorithm. Given two surfaces with genus g = 4, we give a graph. The curved surface can be decomposed into 3g-3 loops of 2g-2 trousers automatically, and then the trousers decomposition graph can be induced. The same trousers decomposition graph can be induced by decomposition of the same topology on two curved surfaces. Points correspond to a leaf on the source surface and a leaf on the target surface. This gives the correspondence between the leaves and ensures the correspondence between the cylindrical surface and the singular trajectory. As shown in Figure 2, the corresponding cylindrical surface is rendered with the same color on the two surfaces. Finally, the mapping between the corresponding leaves is adjusted. The problem of minimal monomial basis of Birkhoff interpolation is also studied in this paper. In addition, a class of multivariate Birkhoff interpolation problems with the same minimal monomial basis under any monomial order are studied. The following conclusions are obtained: If all elimination orders are given, a certain-Birkhoff interpolation problem is solved. If there exists a unique minimal interpolation monomial basis B, then the minimal interpolation monomial basis of the interpolation problem under any monomial order is B. We prove the correctness of the theorem by induction, combining the conclusion that the vector corresponding to a single term in any non-interpolation basis is linearly related to the vector corresponding to a single term strictly smaller than the single term. We can use the fast algorithm of minimal monomial basis under dictionary order to solve other problems under monomial order.
【學(xué)位授予單位】:吉林大學(xué)
【學(xué)位級別】:博士
【學(xué)位授予年份】:2017
【分類號】:O18
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