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yếu tố của hình học trong khi vẫn kiểm soát số lượng tự do của phân khúc cụ thể. Trong các yếu tố cao hơn, các nút này cũng nằm trên các khía cạnh của phần này và trong nội thất của nó. Có hai loại cơ bản rời rạc được sử dụng trong hầu hết các phân tích phần tử hữu hạn phần mềm ngày nay. | THE THEORY OF SHEET METAL BEHAVIOR 71 THE THEORY OF SHEET METAL BEHAVIOR FIGURE 2-7 Methods of representation in finite element analysis. element s geometry while controlling the amount of freedom of that particular segment. In higher-order elements these nodes are also located on the facets of the part and in its interior. There are two basic types of discretization used in most finite element analysis software nowadays. There is a method utilizing H-elements where H represents the size of a particle with P-elements utilized elsewhere. The main difference is the order of calculations which are of lowest order for H-elements with higher order calculations for P-elements. Convergence Method Using H-Elements. Finite element analyses performing convergence with H-elements consider the stress evenly distributed throughout each finite element which in itself can be the cause of many discrepancies. The coarseness of the mesh can be of additional hindrance here. The more crude the mesh the more error-prone the convergence analysis will be see Fig. 2-8a b . Since we will not be able to restrict further refinements to the areas of interest only but rather the whole mesh will be refined uniformly all over we may not achieve a decrease of error due to approximation and yet we will suffer the increase in calculating time. Convergence Method using P-Elements. P-elements in this convergence method are interpolating polynomials of higher order see Fig. 2-8c . Some software packages use an impressive order of nine as the highest. The mesh can consist of tetrahedrals 4-node particles or 8-node bricks and often it can be quite crude with refinement applicable to the areas of interest only. The accuracy of calculations is greatly improved by the higher order Downloaded from Digital Engineering Library @ McGraw-Hill www.digitalengineeringlibrary.com Copyright 2004 The McGraw-Hill Companies. All rights reserved. Any Use is subject to the Terms of Use as given at the website. THE THEORY
