  A model of a cloud formed by massive strings is used as a source of Bianchi
type II. We assumed that the expansion $(\theta)$ in the model is proportional
to the shear $(\sigma)$. To get exact solution, we have considered the equation
of state of the fluid to be in the stiff form. It is found that the bulk
viscosity plays a very important rule in the history of the universe. In
presence of bulk viscosity the particles dominate over strings whereas in
absence of it, strings dominate over the particles which is not in consistence
with the recent observations. Also we observe that the viscosity caused the
expansion of the universe to be accelerating. Our models are evolving from an
early decelerating phase to a late time accelerating phase. The physical and
geometrical behavior of these models are discussed.
