RESUMEN

Let ug  represent the velocity of a Bingham fluid in a bounded domain Ω of R², with initial value uº, and plasticity threshold g. In [5] it was shown that if g is large enough (say g ≥ gc) ug  becomes zero after some time. Moreover, [7] computed gc for the specific stationary case of a cylindrical pipe of section Ω, when the exterior forces are constant.

Our purpose is threefold: a) we show that ׀ ug ׀ (the L² (Ω) – energy of the fluid) is a decreasing function of g, proving thus a conjecture stated in [4] and verified numerically in [1]. b) we show that Bingham fluids have backward uniqueness properties before they (eventually) become zero. c) we strengthen some know results, thanks to the ones proven in a), b).