Attractors for weak and strong solutions of the three-dimensional Navier-Stokes equations with damping

In this paper we obtain the existence of global attractors for the dynamical systems generated by weak solution of the three-dimensional Navier-Stokes equations with damping. We consider two cases, depending on the values of the parameters \b{eta},{\alpha} controlling the damping term and the viscosity {\mu}. First, for \b{eta} we define a multivalued dynamical systems and prove the existence of the global attractor as well. Second, for either \b{eta}>3 or \b{eta}=3, 4{\alpha}{\mu}>1 the weak solutions are unique and we prove that the global attractor for the corresponding semigroup is more regular. Also, we prove in this case that it is the global attractor for the semigroup generated by the strong solutions. Finally, some numerical simulations are performed.