  Black hole-neutron star binary mergers display a much richer phenomenology
than black hole-black hole mergers, even in the relatively simple case -
considered in this paper - in which both the black hole and the neutron star
are nonspinning. When the neutron star is tidally disrupted, the gravitational
wave emission is radically different from the black hole-black hole case and it
can be broadly classified in two groups, depending on the spatial extent of the
disrupted material. We present a phenomenological model for the gravitational
waveform amplitude in the frequency domain that encompasses the three possible
outcomes of the merger: no tidal disruption, "mild", and "strong" tidal
disruption. The model is calibrated to general relativistic numerical
simulations using piecewise polytropic neutron star equations of state. It
should prove useful to extract information on the nuclear equation of state
from future gravitational-wave observations, and also to obtain more accurate
estimates of black hole-neutron star merger event rates in second- and
third-generation interferometric gravitational-wave detectors. We plan to
extend and improve the model as longer and more accurate gravitational
waveforms become available, and we will make it publicly available online as a
Mathematica package. We also present in appendix analytical fits of the
projected KAGRA noise spectral density, that should be useful in data analysis
applications.
