<s>
An	O
unstructured	B-Algorithm
grid	I-Algorithm
or	O
irregular	B-Algorithm
grid	I-Algorithm
is	O
a	O
tessellation	B-Algorithm
of	O
a	O
part	O
of	O
the	O
Euclidean	O
plane	O
or	O
Euclidean	O
space	O
by	O
simple	O
shapes	O
,	O
such	O
as	O
triangles	O
or	O
tetrahedra	O
,	O
in	O
an	O
irregular	O
pattern	O
.	O
</s>
<s>
Grids	O
of	O
this	O
type	B-Algorithm
may	O
be	O
used	O
in	O
finite	B-Application
element	I-Application
analysis	I-Application
when	O
the	O
input	O
to	O
be	O
analyzed	O
has	O
an	O
irregular	O
shape	O
.	O
</s>
<s>
Unlike	O
structured	O
grids	O
,	O
unstructured	B-Algorithm
grids	I-Algorithm
require	O
a	O
list	O
of	O
the	O
connectivity	O
which	O
specifies	O
the	O
way	O
a	O
given	O
set	O
of	O
vertices	O
make	O
up	O
individual	O
elements	O
(	O
see	O
graph	B-Application
(	I-Application
data	I-Application
structure	I-Application
)	O
)	O
.	O
</s>
<s>
Ruppert	O
's	O
algorithm	O
is	O
often	O
used	O
to	O
convert	O
an	O
irregularly	O
shaped	O
polygon	O
into	O
an	O
unstructured	B-Algorithm
grid	I-Algorithm
of	O
triangles	O
.	O
</s>
<s>
In	O
addition	O
to	O
triangles	O
and	O
tetrahedra	O
,	O
other	O
commonly	O
used	O
elements	O
in	O
finite	B-Application
element	I-Application
simulation	O
include	O
quadrilateral	O
(	O
4-noded	O
)	O
and	O
hexahedral	O
(	O
8-noded	O
)	O
elements	O
in	O
2D	O
and	O
3D	O
,	O
respectively	O
.	O
</s>
