In the following report the authors experimentally and numerically study one-and two-dimensional transient flows where the hysteresis of the relationship of suction-water content clearly appears. In the numerical simulation of these flows, by using a finite element method, the hysteresis effect is taken into account by corlsidering both its primary and secondary scanning curves; when the seepage surface occurs, it too is taken into account. The comparison with experimental results shows that in the concerned problems a numerical simulation in which this hysteresis effect is ignored may involve important errors.

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In conjunction with the general subject of the conference, general notions concerning rheology are first of ail put forward. They reveal the relationships which may exist amongst stresses, deformations and deformation speeds of the matter, as weil as a chronological account of the stresses applied.The various traditional models of rheological properties of fluids are then listed, together with the rheometrical measurement methods used for characterizing these properties. This results in a classification offluids, a classification which enables their contribution to the transfers, of which they are the recipient, to be assessed.Finally, a distinction is made between the large-scale flows and the microrheological aspects relating to fine channels occuring in the separation processes, in microfiltration and dialysis.