Numerical modelling of deep penetrating anchors for floating wind installations

Research projects

Project Description:

This Research Project is part of the Aura CDT’s Offshore wind energy geotechnics Cluster.

Floating wind offers the possibility of opening up energy resource in deeper water than feasible with fixed solutions (e.g. monopiles or jackets) which become impractical in water depths over 45m for monopiles and 80m for jackets. While the UK may have sufficient potential capacity in water depths suitable for fixed wind there are large parts of the world where floating wind will be significant due to minimal continental shelves, such as Norway and Japan. There is an opportunity, therefore, for technology and expertise linked to floating wind to be developed in the UK and exported overseas, much as has been done with the current wind technology developed in Europe.

At present, future floating wind support structures are expected to be one of three concepts: spars, tension-leg platforms or semi-submersibles. For each concept there are a number of exciting technical challenges to be addressed if floating wind is to become effective and economic, but one challenge that links them all is anchoring. Anchoring solutions for floating structures of the nature and number anticipated cannot be simply adapted from oil and gas solutions for technical and economic reasons. For example, traditional drag anchor design is based on empirical approaches which are neither linked to seabed deposit mechanical parameters nor adaptable outside of a given anchor geometry. In addition, final installation position is difficult to control, which conflicts with the need for turbines in floating arrays to be precisely located, for moorings to be shared, for adequate space for cabling and for much smaller seabed footprints for closely-spaced array components. Dynamically installed anchors, such as Deep Penetrating Anchors (DPAs), offer a potential solution by allowing precisely located moorings which can be directly below a floating structure. They are installed by allowing a heavy anchor body to drop through a given depth of water above the seabed, and to then penetrate to an embedment level in the seabed, dissipating their own kinetic energy. They avoid the need for long pulls to embed as with a traditional drag anchor, or the use of catenaries (near horizontal pull being a limitation of many anchor types), neither of which are suitable for small seabed footprints.

The aim in this project is to develop a computational model of the installation and life of a DPA to both (a) predict embedment depth in a given soil and (b) arrive at an accurate picture of the state of the disturbed soil above an installed anchor. The tool developed within (a) will allow quick assessment of the effectiveness of new DPA geometries within different soil conditions. Results from (b) could be ported to a standard commercial code for analysis of the longer-term behaviour of the installed anchor.

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