We develop a new dynamical model for high energy heavy-ion collisions in the
beam energy region of the highest net-baryon densities on the basis of
non-equilibrium microscopic transport model JAM and macroscopic 3+1D
hydrodynamics by utilizing a dynamical initialization method. In this
model,dynamical fluidization of a system is controlled by the source terms of
the hydrodynamic fields. In addition, time dependent core-corona separation of
hot regions is implemented. We show that our new model describes multiplicities
and mean transverse mass in heavy-ion collisions within a beam energy region of
$3<\sqrt{s_{NN } }<30$ GeV. Good agreement of the beam energy dependence of the
$K^+/\pi^+$ ratio is obtained, which is explained by the fact that a part of
the system is not thermalized in our core-corona approach.