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  GridEx incorporates post-processing facilities within the Visualization Tab which permit detailed inspection of volume meshes. Through the use of "crinkle cuts", isolated portions of the volume mesh may be examined to ensure such satisfies all modeling requirements. A crinkle cut is a faceted surface composed of those uncut faces of all tetrahedral elements intersected by a prescribed cutting plane, and it provides insight as to the nature of the mesh local to the cutting plane. A description of the controls provided for the generation of crinkle cuts is provided below.

Cutting Plane Specification

  Crinkle cuts are generated from the volume mesh based upon the placement of a cutting plane, and controls for this specification are provided in the Cutting Plane panel shown below. The controls pictured here permit the specification of an arbitrarily oriented cutting plane. The facilities included permit the user to orient the cutting plane in a variety of ways. The series of radio buttons permits rapid specification of cutting planes which are perpendicular to the coordinate axes, or for more general positioning, the Other radio button may be activated. This option will require user input of vector components in the text fields immediately below in order to define the normal vector for the desired cutting plane. The absolute direction of the vector is unimportant, and components need not define a unit vector; such are accepted and transparently normalized once the Set button is pressed. In this way, cutting planes (and hence crinkle cuts) may be precisely oriented to illuminate specific features of the volume mesh.

 Once the desired orientation has been defined, the New button should be pressed to instruct GridEx to generate the corresponding crinkle cut. This new crinkle cut then becomes the active crinkle cut which is rendered in red while all others are rendered in yellow. A crinkle cut is a selectable object just as is any other surface, and the rendering properties may be changed as desired.

 The Delete button removes only the active crinkle cut from the display.

The Crinkle Cut

  Once a crinkle cut has been introduced, it may be readily repositioned within the domain via translation along its prescribed normal direction. This is performed using the slider bar in the Cut Position panel shown below. The controls pictured here permit the specification of an arbitrarily oriented cutting plane. An upward movement of the central slider control translates the cut plane along the direction of the prescribed normal while a downward movement causes a translation counter to the normal direction. The upper- and lower-most sliders set the respective bounds of the central slider and may be adjusted to limit the traversal of such.

 For cutting planes oriented perpendicular to either of the coordinate axes, the center text field displays the physical position of the cutting plane along the respective axis while the upper and lower fields display the respective bounds within which the plane must be positioned to remain visible. For arbitrarily oriented cutting planes, the upper and lower fields display the extrema of the permitted displacements within a bounding box which encloses the entire domain.

 When the cutting plane is translated, it is by default rendered as a semi-transparent plane to facilitate visual positioning. Once the slider is released, the corresponding crinkle cut is generated and displayed. The Dynamic toggle button causes the generation of the crinkle cut to be performed dynamically as the slider is adjusted, thus the transparent cut plane is then no longer displayed.

 By default, the crinkle cut is composed of the uncut tetrahedral faces which fall on the side of the cut plane counter to the direction of the prescribed normal. The Toggle button simply reverses this convention; the same tetrahedrons are cut though an alternate set of faces (which now lie on the opposite side of the cutting plane corresponding to the positive direction of the normal) are displayed.

 Lastly, the reset button simple "centers" the cutting plane given the upper and lower bounds.

Crinkle Cut Statistics

  As each crinkle cut is a result of an ordered search within the volume mesh, there are certain informational details available from this process. The controls pictured here permit the specification of an arbitrarily oriented cutting plane. The Cut Statistics panel displays the number of unique nodes, the number of tetrahedral elements which have been cut, and a unique identifier for the active crinkle cut. Any number of crinkle cuts may be generated and displayed though it is the statistics for the active crinkle cut which are displayed within this panel. Selection of another crinkle cut makes it the active crinkle cut and also updates the fields in this panel.

Responsible NASA Official: William T. Jones
Site Curator: William T. Jones
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Last Updated: Dec 11, 2001