Civil Engineering Reference
In-Depth Information
recovered, and the total CPU time required is 20.83 s. Figure 4.87c shows the magnified
views of the hands. It can be seen that intersection lines have already been incorporated
into the surface by a local mesh modification procedure. After mesh optimisation, elements
of size and shape compatible with those on the surface are generated along the lines of the
intersection.
4.5.8 Intersection of surfaces of quadrilateral elements
Surfaces discretised into quadrilateral and/or triangular elements can also be merged by the
TNOIT algorithm (Lo and Wang 2003, 2004). All steps for intersection remain the same
except that in the neighbour-tracing process, quadrilaterals have to be first divided into two
triangles. Quadrilaterals are divided into triangles according to the following:
1. The surface curvature has to be maintained by dividing quadrilaterals such that the
dihedral angle between adjacent triangles is as close to 180° as possible.
2. In case surface curvature does not indicate any preferential subdivision into triangles,
the quadrilateral is divided into triangles along the shorter diagonal.
An aeroplane and a space shuttle consisting of, respectively, 2891 and 7087 triangular
and quadrilateral elements are intersected, as shown in Figure 4.88; 674 intersection line
segments can be traced out in the neighbour-tracing process.
4.5.8.1 Closure
An algorithm based on TNOIT for the determination of intersection lines between sur-
faces of triangular and quadrilateral elements has been presented in detail. Along with the
(a)
(b)
Figure 4.88
Intersection between aeroplane and space shuttle: (a) view from top; (b) view from bottom.
