A　modified　wake　oscillator　model　for　modelling　vortex-induced　vibrations　(VIVs)　of　a　free-hanging　riser　subjected　to　vessel　motion　is　presented.　Different　from　the　conventional　wake　oscillators　which　have　typically　utilized　in　the　prediction　of　steady　flow　VIVs　,　the　new　model　can　be　applied　to　simulate　VIVs　introduced　by　the　vessel　motion　where　the　flows　around　the　riser　are　not　known　in　advance.　This　has　been　achieved　by　introducing　an　equivalent　flow　based　on　the　relative　flow　velocity　and　coupling　the　wake　oscillator　with　the　acceleration　of　the　riser　in　the　lift　direction.　The　modified　wake　oscillator　model　is　tuned　against　the　experiments　of　riser　VIVs　subjected　to　steady　flows　and　a　set　of　empirical　parameters　is　obtained.　The　model　is　then　applied　to　simulate　the　VIVs　of　a　large-scale　free-hanging　water　intake　riser　(WIR)　subjected　to　different　vessel　motions　and　the　simulated　results　are　compared　to　those　of　experiments.　The　comparison　shows　that　the　proposed　model　is　able　to　predict　response　frequency　in　good　agreement　with　the　experiment,　and　generates　satisfactory　prediction　with　respect　to　the　response　amplitude　for　three　test　cases　out　of　five　that　have　been　studied　in　the　present　paper.