Dynamics of dissipative ordered fluids.

A variational principle is proposed that allows to derive the equations of motion for a fluid with a general microstructure described by a tensorial order parameter. The only constitutive ingredients are the densities of the free energy and the dissipation, both subject to appropriate invariance requirements. As an illustration, it is shown how the hydrodynamic theory for uniaxial nematic liquid crystals can be derived within this setting.