  The results of 3D hydrodynamic simulation of mass transfer in semidetached
binaries of different types (cataclysmic variables and low-mass X-ray binaries)
are presented.
  We find that taking into account of a circumbinary envelope leads to
significant changes in the stream-disc morphology. In particular, the obtained
steady-state self-consistent solutions show an absence of impact between gas
stream from the inner Lagrangian point L1 and forming accretion disc. The
stream deviates under the action of gas of circumbinary envelope, and does not
cause the shock perturbation of the disc boundary (traditional `hotspot'). At
the same time, the gas of circumbinary envelope interacts with the stream and
causes the formation of an extended shock wave, located on the stream edge. We
discuss the implication of this model without `hotspot' (but with a shock wave
located outside the disc) for interpretation of observations. The comparison of
synthetic light curves with observations proves the validity of the discussed
hydrodynamic model without `hotspot'.
  We also consider the influence of a circumbinary envelope on the mass
transfer rate in semidetached binaries. The obtained features of flow structure
in the vicinity of L1 show that the gas of circumbinary envelope plays an
important role in the flow dynamics, and that it leads to significant (in order
of magnitude) increasing of the mass transfer rate.
  The comparison of gaseous flows structure obtained in 2D and 3D approaches is
presented. We discuss the common features of the flow structures and the
possible reasons of revealed differences.
