  We study gravitational waves emitted in the late inspiral stage of binary
neutron stars by analyzing the waveform obtained in numerical-relativity
simulations. For deriving the physical gravitational waveforms from the
numerical results, the resolution extrapolation plays an essential role for our
simulations. The extrapolated gravitational-wave phases are compared with those
calculated in the post-Newtonian (PN) and effective-one-body (EOB) formalisms
including corrections of tidal effects. We show that the extrapolated
gravitational-wave phases in numerical relativity agree well with those by the
PN and EOB calculations for most of the inspiral stage except for a
tidally-dominated, final inspiral stage, in which the PN and EOB results
underestimate the tidal effects. Nevertheless, the accumulated phase difference
between our extrapolated results and the results by the PN/EOB calculations is
at most 1--3 radian in the last 15 cycles.
