I will present a seamless multiscale method for the study of fluid systems with unknown constitutive relations
and/or unknown boundary conditions. The multiscale method aims at capturing the macroscale behavior
of the fluid system; this is done by combining the conservation laws for the mass and momentum (the macro model)
and the molecular dynamics (the micro model). The macro model provides the necessary constraint for the micro
model and the micro model supplies the missing data (the stress or the boundary conditions) needed in the macro model.