  Neutrino-dominated accretion flow (NDAF) around a rotating stellar-mass black
hole (BH) is one of the plausible candidates for the central engines of
gamma-ray bursts (GRBs). Because the time-variant and anisotropic emission of
neutrinos from NDAFs leads to GRB variability, NDAFs can be regarded as the
sources of the strong gravitational waves (GWs). We calculate the dependences
of the GW strains on both the BH spin and the accretion rate. We demonstrate
that for typical GRBs with either single pulse or multiple pulses, the GWs from
NDAFs might be detected at a distance of $\sim 100$ kpc/$\sim 1$ Mpc by
advanced LIGO/Einstein Telescope with a typical frequency of $\sim 10-100$ Hz.
Besides NDAFs, the other two competitive candidates for GRB central engine are
Blandford-Znajek (BZ) mechanism and millisecond magnetars. We explore the GW
signals from these two as well, and compare the corresponding results with
NDAFs'. We find that for a certain GRB, the possible detected distance from
NDAFs is about two orders of magnitude higher than that from BZ mechanism, but
at least two orders of magnitude lower than that from magnetars. The typical GW
frequency for BZ mechanism is the same with that of NDAFs, $\sim 10-100$ Hz,
while the typical frequency for magnetars is $\sim 2000$ Hz. Therefore, the GWs
released by the central engines of adjacent GRBs might be used to determine
whether there is an NDAF, a BZ jet or a magnetar in GRB center.
