<s>
Grid	O
or	O
mesh	B-Algorithm
is	O
defined	O
as	O
smaller	O
shapes	O
formed	O
after	O
discretisation	O
of	O
geometric	O
domain	O
.	O
</s>
<s>
Mesh	B-Algorithm
or	O
grid	O
can	O
be	O
in	O
3	O
-	O
dimension	O
and	O
2-dimension	O
.	O
</s>
<s>
The	O
two-dimensional	O
meshing	O
includes	O
simple	O
polygon	B-General_Concept
,	O
polygon	B-General_Concept
with	O
holes	O
,	O
multiple	O
domain	O
and	O
curved	O
domain	O
.	O
</s>
<s>
Before	O
defining	O
the	O
mesh	B-Algorithm
type	O
it	O
is	O
necessary	O
to	O
understand	O
elements	O
(	O
their	O
shape	O
and	O
size	O
)	O
.	O
</s>
<s>
They	O
are	O
typically	O
based	O
on	O
aspect	B-Device
ratio	I-Device
i.e.	O
</s>
<s>
the	O
aspect	B-Device
ratio	I-Device
of	O
element	O
decide	O
whether	O
a	O
particular	O
element	O
would	O
be	O
good	O
to	O
use	O
or	O
we	O
should	O
go	O
for	O
another	O
element	O
with	O
different	O
aspect	B-Device
ratio	I-Device
.	O
</s>
<s>
For	O
example	O
,	O
if	O
the	O
aspect	B-Device
ratio	I-Device
is	O
large	O
the	O
speed	O
of	O
solver	O
reduces	O
while	O
if	O
this	O
ratio	O
is	O
small	O
the	O
solver	O
speed	O
increases	O
.	O
</s>
<s>
Large	O
aspect	B-Device
ratio	I-Device
has	O
another	O
limitation	O
of	O
leading	O
to	O
interpolation	B-Algorithm
errors	O
.	O
</s>
<s>
But	O
if	O
the	O
results	O
vary	O
with	O
direction	O
then	O
we	O
use	O
large	O
aspect	B-Device
ratio	I-Device
.	O
</s>
<s>
In	O
this	O
system	O
the	O
implementation	O
of	O
finite	B-Algorithm
volume	I-Algorithm
method	I-Algorithm
is	O
simpler	O
and	O
easier	O
to	O
understand	O
.	O
</s>
<s>
Stepwise	O
approximation	O
is	O
not	O
smooth	O
and	O
thus	O
leads	O
to	O
significant	O
error	O
,	O
though	O
the	O
grid	O
can	O
be	O
refined	O
by	O
using	O
a	O
fine	O
mesh	B-Algorithm
to	O
cover	O
the	O
wall	O
region	O
but	O
this	O
leads	O
to	O
waste	O
of	O
computer	O
memory	O
resources	O
.	O
</s>
<s>
Two-dimensional	O
structured	O
mesh	B-Algorithm
use	O
quadrilaterals	O
elements	O
while	O
three	O
dimension	O
meshes	B-Algorithm
use	O
hexahedra	O
.	O
</s>
<s>
In	O
orthogonal	O
mesh	B-Algorithm
the	O
grid	O
lines	O
are	O
perpendicular	O
to	O
intersection	O
.	O
</s>
<s>
To	O
generate	O
meshes	B-Algorithm
so	O
that	O
it	O
includes	O
all	O
the	O
geometrical	O
features	O
mapping	O
is	O
very	O
important	O
.	O
</s>
<s>
There	O
are	O
regions	O
where	O
dense	O
mesh	B-Algorithm
is	O
done	O
deliberately	O
to	O
accommodate	O
complex	O
features	O
.	O
</s>
<s>
Each	O
region	O
has	O
different	O
type	O
of	O
mesh	B-Algorithm
structure	O
.	O
</s>
<s>
Different	O
blocks	O
can	O
be	O
handled	O
with	O
required	O
degree	O
of	O
fineness	O
in	O
mesh	B-Algorithm
.	O
</s>
<s>
In	O
this	O
case	O
two-dimensional	O
unstructured	O
mesh	B-Algorithm
uses	O
triangle	O
elements	O
while	O
three-dimensional	O
uses	O
tetrahedral	O
elements	O
.	O
</s>
<s>
These	O
are	O
combination	O
of	O
small	O
structured	O
mesh	B-Algorithm
arranged	O
in	O
unstructured	O
pattern	O
.	O
</s>
<s>
The	O
advantage	O
of	O
this	O
type	O
of	O
grids	O
is	O
that	O
mesh	B-Algorithm
can	O
be	O
refined	O
wherever	O
needed	O
.	O
</s>
<s>
Various	O
automatic	O
techniques	O
especially	O
those	O
associated	O
with	O
Finite	B-Application
Element	I-Application
Method	I-Application
also	O
utilize	O
unstructured	O
grids	O
.	O
</s>
<s>
Mesh	B-Algorithm
refinement	O
and	O
adaption	O
is	O
easy	O
in	O
unstructured	O
grids	O
.	O
</s>
<s>
In	O
mesh	B-Algorithm
smoothing	O
the	O
location	O
of	O
mesh	B-Algorithm
vertices	O
are	O
adjusted	O
.	O
</s>
