A roll damping prediction method for a FPSO (Floating Production Storage and Offloading) with steady drift motion is deduced on the bases of the prediction method for a conventional cargo ship developed by one of authors. In the present method, the effects of drift motion on vortex shedding strength from bilge keels and pressure distribution on the hull surface generated by them are taken into account. The predicted results are compared with experimental results to confirm the accuracy of the prediction method. Using the method some effects on the roll damping of a FPSO are investigated.
bbk: breadth of bilge keel B: sectional breadth of a hull Bbk: bilge keel damping coefficient in equivalent linear form B44: total roll damping coefficient in equivalent linear form BN: normal force component of bilge keel component BS: surface pressure component of bilge keel component Cd: drag coefficient of bilge keels d: sectional draft of a hull f: correction factor for increase of flow velocity at bilge keel H0: sectional half breadth to draft ratio (B/2d) ℓ1: distance from center of bilge keel to roll axis OG: distance from water level to center of gravity of a vessel (+ downward OG = d-KG) r: distance from roll axis to tip of bilge keel T: roll period Vd: drift velocity ρ : fluid density σ : sectional area coefficient (= Am/Bd Am: area of cross section) φ•: roll motion velocity φ : roll angle; roll motion is assumed to be φ =φa sinωt ω : circular frequency (rad/sec.)
A FPSO vessel has become a popular offshore production solution in recent years.