  We present a study by computer simulations of a class of complex-valued
solutions of the three-dimensional Navier-Stokes equations in the whole space,
which, according to Li and Sinai, present a blow-up (singularity) at a finite
time. The computer results allow a detailed study of the blow-up mechanism, and
show interesting features of the behavior of the solutions near the blow-up
time, such as the concentration of energy and enstrophy in a small region
around a few points of physical space, while outside this region the "fluid"
remains "quiet".
