A search for dark matter pair production in association with a $Z'$ boson is performed using 36.1$\,$fb$^{-1}$ of LHC $pp$ collision data at $\sqrt{s} = 13\,$TeV recorded with the ATLAS detector.
Events are characterised by large missing transverse momentum and a hadronically decaying vector boson reconstructed as either a pair of small-radius jets, or as a single large-radius jet with a two-body decay substructure.
Results are interpreted in terms of simplified models which describe the interaction of dark matter and Standard Model particles.