  By dispersive models of fluid mechanics we are referring to the
Euler-Lagrange equations for the constrained Hamilton action functional where
the internal energy depends on high order derivatives of unknowns. The mass
conservation law is considered as a constraint. The corresponding
Euler-Lagrange equations include, in particular, the van der Waals--Korteweg
model of capillary fluids, the model of fluids containing small gas bubbles and
the model describing long free-surface gravity waves. We obtain new
conservation laws generalizing the helicity conservation for classical
barotropic fluids.
