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Design, selection of anchoring systems and mooring blocks

Types of mooring systems include:

Floating Production, Storage and Offloading vessels (FPSO):

Typically oil tanker conversions that require multi-anchor catenary moorings to accommodate motions and absorb loads, so flexible risers are required. Grouped anchors provide less riser interference and result in lower mooring loads, redundancy, and better resistance to progressive failure.

Tension Leg Platforms (TLP):

Used for oil and gas systems, and for offshore wind and hydrokinetic systems, TLP’s are buoyant platforms held to the seabed by tendons - usually steel pipe. Surge stiffness is a function of excess buoyancy and the angle of the tension, not tendon stiffness.

Anchor systems:

Anchors are best categorized by the loading they are designed to withstand: horizontal, vertical, or somewhere in between. The choices have significant seabed footprint implications. Drag embedment anchors require horizontal pull for setting and low mooring angle in service.

Piling-based Systems:

Driven piles are used for both downward and uplifting vertical loads and for side loads. Suction piles are the predominant mooring and foundation system in the deepwater O&G sector, and they have the advantages of easy installation and removal, low noise, and leveling to within one degree.

Deadweight anchors:

Good, general purpose anchor that works in most soil. Rough underside is useful. Material options - concrete, granite, scrap steel.

Offshore wind systems have special requirements for mooring systems:

  • Wind turbines: 
    • Pitch and roll stability in varying winds, currents, and waves.
    • Surge stability in waves.
  • Marine current turbines: 
    • Resistance to drag forces and moments.
    • Stability in waves and current fluctuations.
  • Wave energy converters 
    • Resistance to drag forces and moments.
    • Stability in waves.