<s>
In	O
scientific	B-Application
visualization	I-Application
skin	B-Application
friction	I-Application
lines	I-Application
are	O
used	O
to	O
visualize	O
flows	O
on	O
3D-surfaces	O
.	O
</s>
<s>
They	O
are	O
obtained	O
by	O
calculating	O
the	O
streamlines	B-Application
of	O
a	O
derived	O
vector	O
field	O
on	O
the	O
surface	O
,	O
the	O
wall	O
shear	O
stress	O
.	O
</s>
<s>
A	O
skin	B-Application
friction	I-Application
line	I-Application
is	O
a	O
curve	O
on	O
the	O
surface	O
tangent	O
to	O
skin	O
friction	O
vectors	O
.	O
</s>
<s>
A	O
limit	O
streamline	B-Application
is	O
a	O
streamline	B-Application
where	O
the	O
distance	O
normal	O
to	O
the	O
surface	O
tends	O
to	O
zero	O
.	O
</s>
<s>
Limit	O
streamlines	B-Application
and	O
skin	B-Application
friction	I-Application
lines	I-Application
coincide	O
.	O
</s>
<s>
The	O
skin	B-Application
friction	I-Application
lines	I-Application
may	O
exhibit	O
a	O
number	O
of	O
different	O
types	O
of	O
singularities	O
:	O
attachment	O
nodes	O
,	O
detachment	O
nodes	O
,	O
isotropic	O
nodes	O
,	O
saddle	O
points	O
,	O
and	O
foci	O
.	O
</s>
