Jiang L., LeBlond P.H. (1991, 1992 - 1994)

• model of a Bingham plastic fluid
       (visco-plastic fluid)
• two distinct zones in the flow: in the shear flow, the shear stress exceeds the yield stress, and the velocity varies in z; in the plug flow, the stress is smaller than the yield stress, and the horizontal velocity must be uniform in z