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      <title>Strand length determination options</title>
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      <div class="title_topic3" id="xps10_pagetitle">Strand length determination options</div>
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      <p class="para_topic">Once the node locations have been established on the surface, the application calculates the accumulated distance to the boundaries along each strand. The <b class="uiTerm">Flat Pattern</b> function approximates the distance along the surface between the points for this computation. The surface distance method provides more accurate results than using chord lengths between node points.
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      <div class="title_division">Minimum angles constraint</div>
      <p class="para_division">The figures shown in  <a class="links" href="javascript:void(0)" onclick="top.openFile('sheetmetaldes/wvn_compo.html');return(false);">Composite Woven Materials</a> shows the distorted pattern of the weave as it works to the surface of the part to be flattened. The degree is indicated by the included angle shown in the figures.
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      <p class="para_division">Theoretically, the skewed angle between the strands could approach 0&deg;. This would allow the material to be smoothly worked to any surface, no matter how rapidly or severe the change in its contour.</p>
      <p class="para_division">Practically, however, there is a limit to this angle. The quasi&ndash;orthogonal strands can only be skewed to the point at which their thickness' start to interfere with each other. When this happens, the material starts to wrinkle or bunch and the layout can no longer be kept smooth. Darts and folds in the material sometimes cannot be avoided.</p>
      <p class="para_division">The algorithms embodied in the woven materials function allow you to specify a minimum skew angle and thereby avoid the bunching condition, if possible. During the iteration procedure to determine the node points on the surface being fitted, the application calculates the included angle of the next quadrilateral to be extended. If the predicted angle is less than the user&ndash;specified minimum angle, the system uses the specified minimum.</p>
      <p class="para_division">This constraint avoids the crowding of the strands. Therefore, if certain areas of the fit cause the constraint to be imposed, flat patterns produced by the application are affected.</p>
      <div class="title_division">Start point and multi&ndash;solutions</div>
      <p class="para_division">There are an infinite number of flat patterns capable of covering a selected surface with a woven material. If the actual properties and forming processes are ignored, there also can be an infinite number of pattern solutions for sheet metal parts.</p>
      <p class="para_division">The input conditions and constraints you specify define the flat pattern that results from the woven materials process. The starting point for working the material to the surface can affect the shape of the resulting flat pattern.</p>
      <p class="para_division">Therefore, you should select the start point in a region of the surface where it is easy to position an undistorted patch of the material. This allows the assumption that the strands in the starting area are originally arranged at right angles to each other.</p>
      <p class="para_division">The <b class="uiTerm">Flat Pattern</b> function allows you to specify the starting point two ways. The first method is to identify the location on the surface as a generic point. The second method defines the location at the center of the surface in the U&ndash;V parametric plane used by NX. Refer to the Creating Free Form Features section of <a class="links" href="javascript:void(0)" onclick="top.popUpPage('modeling/index.html?goto=modeling/title_page.html&vars=-aux,-home','linkInter','menubar=yes,status=yes,resizable=yes,toolbar=yes,scrollbars=yes,location=no,directories=no');return(false);">Modeling Help</a> for a discussion of the U&ndash;V plane.
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      <p class="para_division">Although the U&ndash;V start point method is very convenient and sufficient for demonstration and testing procedures, you should consider the benefits of the extra effort required to select an optimum start point for each surface being processed.</p>
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