ARC Centre of Excellence Geotechnical Science & Engineering

Dutch Company Takes on Board New Anchor Design

Dutch Company Takes on Board New Anchor Design
Pic: Conleth O'Loughlin (COFS), Senol Ӧzmutlu (Vryhof) and Joris Roozen (Vryhof) with the DEPLA anchor.
Pic: Conleth O’Loughlin (COFS), Senol Ӧzmutlu (Vryhof) and Joris Roozen (Vryhof) with the DEPLA anchor.

An innovative offshore anchor designed by CGSE researchers at The University of Western Australia has already been snapped up by Dutch anchor specialists Vryhof Anchors.

The Dynamically Embedded Plate Anchor (DEPLA) was developed by Associate Professor Conleth O’Loughlin, from UWA’s Centre for Offshore Foundation Systems (COFS), and Dr Mark Richardson, a former PhD student at COFS.

The new anchor design, aimed at mobile drilling units and floating production systems in deep and ultra-deep water, would reduce installation time, costs and materials, Associate Professor O’Loughlin said.

Associate Professor O’Loughlin, who has been researching dynamically installed anchors for the past 10 years, said the anchor was a hybrid system able to sustain significant vertical load and required no external energy source or mechanical operation for installation.

“The anchor resembles a dart, and is installed using gravity, similar to other dynamically installed anchors such as the torpedo pile,” he said.

“However the main part of the ‘dart’, which we call the follower, is removed after the anchor is embedded in the seabed and re-used for the next installation.  This leaves the anchor flukes in the seabed, which then become the plate anchor.”

Associate Professor O’Loughlin said global energy company Petrobras had been using a gravity-embedded design since the mid-1990s.

“But the rest of the world has been slow to follow,” he said.  “However, one of the limitations of the Petrobras design is that it is not the most efficient – it doesn’t have a lot of capacity relative to its weight.

“The DEPLA boasts all the installation advantages of the torpedo pile, but is much more efficient at resisting load, meaning that much smaller and cheaper units can be used for mooring offshore facilities.  Being able to re-use the follower is a significant bonus.”

Vryhof project director Senol Ozmutlu said results indicated the DEPLA exhibited similar behaviour to other dynamically installed anchors during installation, but with much higher capacities and predictability than other dynamically installed anchors that resisted load in friction.

The DEPLA has been tested at model scale in the geotechnical centrifuge facilities at COFS.  In these experiments, soil samples are spun at up to 200 times Earth’s gravity, creating stress conditions in the centrifuge sample that are equivalent to tens of metres of the seabed.

The DEPLA was put through its paces in these tests, with the centrifuge data playing a pivotal role in informing the final design concept.  This is now a well-accepted approach for obtaining performance data of geotechnical systems and COFS is a world leader, with both beam and drum centrifuge facilities that are heavily utilised by the offshore industry worldwide.

Vryhof’s Business Development Director Leo Bello said the company was extremely happy with the new anchor.

“It will give us a reliable product for ultra-deep water uses that will help our clients reduce their overall mooring cost,” Mr Bello said.  “The DEPLA combines the advantages of dynamically installed anchors and vertically loaded anchors and is fully patented.”

The DEPLA has been extensively tested at a quarter scale and it will be now Vryhof ‘s task to engineer and test a full-scale prototype.

“Vryhof was the ideal industry partner to continue development of the DEPLA and we look forward to assisting them in making it a real prospect for the offshore industry” Associate Professor O’Loughlin said.