Floating　offshore　wind　turbines　(FOWTs)　have　complex　dynamics　problems　and　strong　coupling　effects　within　their　entire　systems,　and　they　are　sensitive　to　winds　and　sea　waves　that　may　cause　structural　fatigue　damages　and　power　production　fluctuations.　Structural　vibration　control　is　a　promising　way　to　reduce　FOWT　responses,　but　most　previous　studies　focused　on　linear　control　strategies　with　the　limitations　of　requiring　large　strokes　and　having　narrow　effective　frequency　bandwidth.　Nonlinear　energy　sinks　(NESs)　have　emerged　as　an　alternative　to　overcome　the　above　limitations　of　linear　control　methods.　In　the　present　study,　an　OC3-Hywind　spar-buoy　FOWT　is　selected　as　a　prototype　structure　for　developing　an　in-house　model　to　investigate　its　associated　aerodynamics,　hydrodynamics,　and　structural　dynamics.　The　wind　turbine　blades　and　tower　are　modelled　by　three-dimensional　Euler-Bernoulli　beam　elements　and　the　floater　is　assumed　as　a　rigid　body.　The　blades＇　pre-twist,　pitch,　and　rotating　angles　are　also　considered　to　develop　the　system＇s　time-varying　mass,　stiffness,　and　damping　matrices.　The　nonlinear　quasi-static　model　is　adopted　to　calculate　the　forces　generated　by　the　mooring　cables.　The　straightforward　and　efficient　in-house　model　is　validated　against　FAST.　Subsequently,　a　bistable　track　NES　with　a　profile　combining　both　negative　second-order　and　positive　fourth-order　terms　is　proposed,　designed,　and　incorporated　into　the　model　to　mitigate　FOWT　responses　under　two　investigated　environmental　conditions.　Results　show　that　the　in-house　model　is　of　high　accuracy　in　estimating　dynamic　characteristics　and　responses　of　FOWTs,　paving　the　way　for　preliminary　design　and　analysis　of　FOWTs　with　different　platform　types.　Moreover,　the　bistable　track　NES　can　effectively　control　the　fore-aft　displacements　at　the　tower　top　with　practical　strokes.