  Graphene grain boundaries are known to affect phonon transport and thermal
conductivity, suggesting that they may be used to engineer the phononic
properties of graphene. Here, the effect of two buckled grain boundaries on
long-wavelength flexural acoustic phonons has been investigated as a function
of angle of incidence using molecular dynamics. The flexural acoustic mode has
been chosen due to its importance to thermal transport. It is found that the
transmission through the boundaries is strongly suppressed for incidence angles
close to 35$^\circ$. Also, the grain boundaries are found to act as diffraction
gratings for the phonons.
