Masthead30_June2014 H.pub - page 16

The Masthead
By Bruce Hays, Principal Naval Architect, DRS Technologies, Inc.
Orca3D’s “Corner
Wrap” Function
O
ne of the characteristics of tensor product NURBS surfaces is that they fundamentally have four
corners
and four
edges
. As
they are applied to hull design, the four
edges
usually correspond to the sheer line, the stem, the bottom profile, and the
transom edge. The four
corners
are the intersections of these four
edges
. Generally, the
corners
represent geometric discontinui-
ties in the surface, with the exception of the stem-bottom profile
corner
(forefoot). Here, it's usually the case that a smooth transi-
tion is desired, with at least slope continuity, but preferably with curvature continuity (which requires a surface that is cubic in
both the U and V directions).
Orca3D provides a function to precisely place the corner control point to smoothly wrap one edge to another, with slope and cur-
vature (if the surface is cubic or higher degree) continuity. Note that the Corner Wrap command requires that the surface have
the same degree in both directions in order to guarantee curvature continuity. The next figure shows an Orca control polygon:
A closer look at the forefoot shows the control point that is the corner of the surface:
To demonstrate the function, the corner control point has been moved, deliberately creating a discontinuity in the joint between
the stem and the bottom profile:
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