We present a seamless multiscale model and an efficient coupling scheme for the
study of complex fluids. The multiscale model consists of macroscale conservation laws for mass
and momentum, molecular dynamics on fiber bundles, as well as the Irving-Kirkwood formula which
links the macroscale stress tensor with the microscopic variables. The macroscale and microscale
models are solved with a macro time step and a micro time step respectively. The two models are
synchronized at each time step by exchanging the velocity gradient (from macro to micro) and the
stress tensor (from micro to macro). The multiscale method is applied to study the dynamics of
polymer fluids in a channel driven by external forces.