OCEN 201 Introduction to Ocean & Coastal EngineeringPowerPoint PresentationSlide 3Slide 4Slide 5Slide 6Slide 7Slide 8OFFSHORE STRUCTURESOFFSHORE PRODUCTION & DRILLINGOFFSHORE PLATFORMDRILLING RIG & SPARSlide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28OCEN 201Introduction to Ocean & Coastal Engineering Offshore StructuresJun [email protected] Structures •Drilling rigs: Exploration of oil and gas Stay in a place for a few months (Mobil or movable) - Jack-up drilling rig- MODU (Mobil Offshore Drilling Unit) • Production platforms: Production of oil and gas Stay in a place for at least a few years (usually 20 -30 years)- Ground-base structure ( <500~800 m)- Floating Structures (> 800 m)Fig. 3-2Example of jack-up drilling rigLegs are retractableFig. 3-3A semi-submersibleDrilling Rig•Mooring system•or Dynamic positioningDP -Dynamic PositioningFig. 3-5Steel Jacket Platform in 20 – 200 m waters< 500 mCannot be movedOFFSHORE PLATFORMOFFSHORE PLATFORMFig. 3-6Concrete Gravity StructureOFFSHORE STRUCTURESOFFSHORE PRODUCTION & DRILLING•AUGER TLP•OCEAN CLIPPEROFFSHORE PLATFORM•SPAR•FIXED JACKETEDDRILLING RIG & SPARFig. 3-10 pp56New version Fig. 12 pp61Articulated TowerFig. 3-11 pp56New Version Fig.13 pp62Single Anchor Leg MooringSystemWave Forces on Offshore Structures•Morrison Equations•Diffraction/Radiation Theory* (Potential theory, neglect water viscosity)•CFD (Computational Fluid Dynamics)*(Navier-Stokes Equations, considering water viscosity)Keulegan-Carpenter Number (Non-dimensional)describing the relation between an oscillatory flow and a cylinder /Peak (amplitude of) vlocity of the flow Period DiametermmK U T DUTDK=- - - -- - - -- - - ->25 Particle movement is much greater than 5 255 Particle movement is smaller than / 0.2 Wavelength is much greater than / 0.2 Wavelength is not much greater or smaller DKK DD L DD L< <<<> than DMorrison Equations & Modified ME12----- Drag Coefficient, ------ Volume ---- Added Mass Coefficient----- Projected area (normal to current)Additional term due to votex induce (lateral) force12in d A m Vd VmAl Ldd C d C ddtC dCdd Cr rr= +=nn nuF u uF20 0cos(2 ),, ------- Strouhal Number----------- Lifting CoefficientALd f tfDS SCp �=nnuuWave Forces on A Vertical CylinderVelocity & acceleration are a function of z & t Force (function of t)20 00212, , 4 212 +4(3 4)in d A m VA z V zin in d zh hm zhdd C d C ddtDd Dd d D d Rd C D ddD C ddtr rprpr- --= += = == =� -� ��nn nn nnuF u uF F u uuWave Forces on A Vertical CylinderWave Forces on a Horizontal CylinderVelocity & acceleration are a function of t only20212, , 4 212 4------ Length of the cylinderin d A m VA z V zin inhd mdd C d C ddtDd Dd d D d RddL C D D CdtLr rppr-= += = == =� �+� �� ��nn nnn nuF u uF Fuu uWave Forces on a Horizontal CylinderExample of Problem 3-1 pp73 (old v. pp64)Computing the horizontal load on a vertical cylinderDrag coefficient of a cylinder pp 72 & 75 (old v. pp63 & 64)Added-Mass coefficient of a cylinder pp 72 (old v. pp64)Wind & Current ForcesSteady & oscillatory portionsSteady current forces21 Inline force21cos(2 ), Transverse force2in dl LC A U UC A U f trr p== �FFWind Forces��0.113 0.12510101, 2 Steady wind velocity Fluctuated velocity (wind gustiness)Applied at the center of pressure ( )10- wind velocity at 10 m above the sea in a dPpPC A U U U U UUUZZU Z UUr= = +��=����F:Forces on Pipeline Due to Wave & Currentssin 0 (3.33) horizontalcos 0 (3.34) vertical (3.35) Coeff. of friction Minimum submerged weight (remain at sea bed) (3.36)cos sind i fn lf nd i lbbm mmm b b+ - + =+ - == - -+ +=-F F F wF F wF FF F FwDrag force; inertia forceNormal force; lifting forceFriction force; Submerged weightd in lf- - - -- - - -- - -F FF FF wblFnFfFdFiFWFree Body diagram of A Pipe under the impact of Wave &