Particularly, for two dimensional problems this set will principally look like the one
illustrated in Figure 5.1, where AI and ^2 denote the eigenvalues of the permeability
tensor A. It is interesting to note that in contrast to e.g. the two dimensional
conductivity problem the laminate structure is not necessarily optimal with respect
to Stokes flow. This is most easily seen for low volume fractions by using the following
argument: due to the no-slip condition along the surfaces of the laminate it is obvious
that the values of AI and Aj must be lower than for example those corresponding to
the structure consisting of one circular fiber in each period. Thus, even the points
(0, a) and (a, 0) are nontrivial to determine.