OCEN 201 Introduction to Ocean & Coastal Engineering Offshore Structures Jun Zhang

Offshore 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 years) - Ground-base structure ( <500~800 m) - Floating Structures(> 800 m)

Fig. 3-2 Example of jack-up drilling rig Legs are retractable

Fig. 3-3 A semi- submersible Drilling Rig Mooring system or Dynamic positioning

DP - Dynamic Positioning

Fig. 3-5 Steel Jacket Platform in 20 – 200 m waters < 500 m Cannot be moved

OFFSHORE PLATFORM

Fig. 3-6 Concrete Gravity Structure

OFFSHORE STRUCTURES

OFFSHORE PRODUCTION & DRILLING AUGER TLPOCEAN CLIPPER

OFFSHORE PLATFORM SPARFIXED JACKETED

DRILLING RIG & SPAR

Fig pp56 New version Fig. 12 pp61 Articulated Tower

Fig pp56 New Version Fig.13 pp62 Single Anchor Leg Mooring System

Wave Forces on Offshore Structures Morrison Equations Diffraction/Radiation Theory* (Potential theory, neglect water viscosity) CFD (Computational Fluid Dynamics)* (Navier-Stokes Equations, considering water viscosity)

Morrison Equations & Modified ME

Wave Forces on A Vertical Cylinder Velocity & acceleration are a function of z & t Force (function of t)

Wave Forces on A Vertical Cylinder

Wave Forces on a Horizontal Cylinder Velocity & acceleration are a function of t only

Wave Forces on a Horizontal Cylinder

Example of Problem 3-1 pp73 (old v. pp64) Computing the horizontal load on a vertical cylinder Drag coefficient of a cylinder pp 72 & 75 (old v. pp63 & 64) Added-Mass coefficient of a cylinder pp 72 (old v. pp64)

Wind & Current Forces Steady & oscillatory portions Steady current forces

Wind Forces

Forces on Pipeline Due to Wave & Currents

Free Body diagram of A Pipe under the impact of Wave & Currents