Page 30 - Microtectonics

2.5 · Homogeneous and Inhomogeneous Flow and Deformation 17
the angular velocity curve is just touching the zero by the angle α between one of the ISA and the side of
k
angular velocity axis and only one irrotational line the shear box. The first three of these parameters are de-
exists; this flow type is known as simple shear flow fined as (Fig. 2.6):
(Fig. 2.6 bottom). All non-coaxial flows have a mono-
clinic symmetry.

Since flow can be visualised by two simple curves, it
must be possible to describe flow using parameters of
these curves such as their amplitude, the elevation of each
of the curves with respect to the horizontal axis, and the
orientation of special directions such as ISA in the cho- Ö is a measure of the strain rate (the amplitude
k
sen reference frame. This orientation can be expressed of the stretching rate curves in Fig. 2.5 and 2.6). W is
k

Fig. 2.6. Three types of isochoric flow, represented by: a Graphs of stretching rate (Ö ) and angular velocity of material lines (ω) against
k
line orientation α k . b Spatial distribution of material lines with arrows indicating sense of stretching rate and angular velocity. c Velocity
vectors (flow pattern). W Kinematic vorticity number; ISA instantaneous stretching axes; IL orientation of irrotational material lines;
k
FA fabric attractor, one of the IL (Sect. 2.9)