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109 lines
5.1 KiB
109 lines
5.1 KiB
\chapter{Introduction} \label{chap:intro}
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\caps{\PROGRAM} translates the output of the \caps{ABAQUS} finite element
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program \cite{bib:abaqus} into the \caps{EXODUS} database format
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\cite{bib:exodus}. \caps{ABAEXO} translates the output of ABAQUS versions
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4-5 and 4-6.
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The \caps{EXODUS} format is used by the
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Engineering Analysis Department plot programs such as \caps{BLOT}
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\cite{bib:blot}.
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\caps{ABAQUS} allows 8-node 2D elements and 20-node 3D elements, but the
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plot programs expect 4-node 2D elements and 8-node 3D elements.
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\caps{\PROGRAM} transforms any 8-node 2D element into four 4-node
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elements and any 20-node 3D element into eight 8-node elements. Any
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multi-node 1D element is transformed into 2-node elements. There is also
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an option to transform 4-node 2D elements into four 4-node elements.
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\section{The Element Transformations} \label{intro:trans}
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The 2D and 3D transformations are shown in Figures 1a and 1b. The solid
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lines show the original elements. The dashed lines show the elements
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that are generated. The circled nodes are nodes which are generated for
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the transformation.
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An 8-node 2D element is broken into four 4-node elements by adding a
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center node. To transform a 4-node 2D element into four 4-node elements,
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a node is added at the center of each side of the element, and then the
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8-node transformation is performed. A side node generated by the 4-node
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transformation may be shared by an adjacent element.
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A 20-node 3D element is broken into eight 8-node elements by adding
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seven nodes: one at the center of each side and one at the center of the
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element. A generated center side node may be shared by an adjacent
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element.
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\newpage \addtocounter{page}{1}
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\notetome{Insert figure produced by ABAFIG.EXE}
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\newcommand{\nodenum}[1] {\em #1}
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\section{Translation of Nodal Quantities} \label{intro:nodal}
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Two types of information for each node are needed: the
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coordinates and the value of the nodal variables.
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The \caps{ABAQUS} output file contains the coordinates of the
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original nodes.
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The coordinates of the generated nodes
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are the average of the coordinates of the original nodes that define the
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new nodes. The center node of the 8-node 2D transformation (\nodenum{9}
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in Figure 1a) is defined by the eight original nodes
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(\nodenum{1}..\nodenum{8}). The side nodes added for the 4-node 2D
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transformation (\nodenum{4}..\nodenum{8}) are defined by the two nodes
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on the side. For example, the coordinates of node \nodenum{5} are the
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average of the coordinates of nodes \nodenum{1} and \nodenum{2}. The
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side nodes of a 20-node 3D element (\nodenum{21}..\nodenum{26} in Figure
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1b) are defined by the eight nodes on the side. For example, the
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coordinates of node \nodenum{21} are the average of the coordinates of
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nodes \nodenum{1}, \nodenum{12}, \nodenum{4}, \nodenum{20}, \nodenum{8},
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\nodenum{16}, \nodenum{5}, and \nodenum{17}. The center node
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(\nodenum{27}) is defined by the original twenty nodes
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(\nodenum{1}..\nodenum{20}).
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The \caps{ABAQUS} output file contains the nodal variables for
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the original nodes.
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The variables at the
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generated nodes are the average of the variables at the original nodes
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that define the new nodes as described for the coordinates.
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\section{Translation of Element Quantities} \label{intro:element}
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Each element must be assigned to an ``element block''. An element block
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distinguishes a material or an element type (such as a truss or
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quadrilateral). The \caps{ABAQUS} output file does not supply the
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element block information, but it does contain an element type name for
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each element with the element connectivity. The element block is either
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determined by the element type name or supplied by the user (with the
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\cmd{MATERIAL} command). If the element type is used, each type forms a
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single block. The number of nodes per element must be the same for all
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elements in an element block.
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In addition to the element block, the following information is needed
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for each element: the dimension of the element, the element
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connectivity, and the values of the element variables.
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The \caps{ABAQUS} output file does not supply the dimension of an
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element, but it does contain the number of nodes and an element type
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name for each element with the element connectivity. Elements with less
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than 4 nodes are assumed to be \caps{1D}, elements with 4 to 7 nodes are
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\caps{2D}, and elements with more than 8 nodes are \caps{3D}. The
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program distinguishes between 8-node \caps{2D} and \caps{3D} element
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types by examining the element type name: it is \caps{3D} if and only if
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the name contains the characters ``\cmd{3D}''.
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The \caps{ABAQUS} output file contains the connectivity for
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the original elements.
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Any element transformations are performed as explained in
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Section~\ref{intro:trans}.
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The new elements replace the original
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elements.
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The \caps{ABAQUS} output file contains the element variables
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for the original elements at appropriate integration points.
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The variables for the
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generated elements are read from the input variables at the appropriate
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integration points. The \caps{ABAQUS} Manual has a diagram of the
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positions of the integration points for each element type. If a
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non-transformed element has more than one integration point, the
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variables for the element are averaged over all the points.
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