Concept Description

Criteria

Back in 1995 the Norwegian Research Council started a program called ¡°Dyptvann¡± or Deep Water where one of the main focus of attention was mooring and anchoring. This was a reaction to the offshore industry¡¯s need for more cost-effective solutions as costs for the then present technology was increasing exponentially as oil and gas exploration moved into deeper waters. The council¡¯s criteria for new anchor solutions was that:

• Anchor installation must be simple.
• The anchor must not be complicated or too expensive to fabricate.
• It must have a holding capacity of at least 400-500tons for short-term loads and 300tons for long-term static tension loads.
• The anchoring solution should also allow for taut leg mooring and vertical pullout loading. 

Principles of Concept

The DPA™ is released freely from a predetermined height over the seabed in which gravity is used as the installation force. A 75ton DPA™ for example, dropped from a height of say 50 to 75meters, will acquire a velocity of ca. 25-30m/sec when it reaches the seafloor. At such velocities, deep penetrations are obtainable into stiffer lower lying seabed sediments depending on their strength and deformation characteristics.

The DPA™ concept is built on the following principles: 

• Very large kinetic energy made available through freefall, which ¡°shoots¡± the anchor into the seabed. No external energy source is therefore required e.g. no proof loading necessary.
• Optimum fluid dynamic design to achieve a high freefall velocity and non-rotational stability.
• The anchor design takes advantage of the fact that most deep-water soil sediments have significantly reduced undrained shear strength in a remolded state (during penetration) than after consolidation is complete i.e. when excess pore water pressure has dissipated.

Due to the anchor¡¯s low cross-section area, hydrodynamic forces are limited when lowering through the splash zone and water column and therefore installation is not as weather sensitive as other anchor types may be.