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Offshore Wind Journal

Masters of measurement make offshore work more accurate

Tue 26 Jun 2018 by David Foxwell

Masters of measurement make offshore work more accurate
Pliant Offshore’s IMS can speed up monopile installation and obviates the need for ‘stop and start’ measurement

Measuring things might not sound that exciting but Pliant Offshore specialises in measuring things that can make offshore operations such as pile driving and laying cable run more smoothly and cost-effectively

Pliant Offshore, part of Pliant Group in the Netherlands, has quickly gained a foothold in the offshore wind industry thanks to the adoption of its technology by leading contractors such as Tideway and Van Oord and, in the relatively short time since the offshore offshoot of the group was formed, sensor and software systems it has developed have been used on some well-known projects.

Speaking exclusively to OWJ, Rik Zwinkels, the company’s commercial manager, highlighted two examples of how measuring technology Pliant Offshore has developed are being used offshore, and anticipates there will be more in due course.

The first is an inclination measurement system (IMS) that determines the inclination of objects such as monopile foundations when they are being driven into the seabed.

Van Oord credited the IMS with significant cost savings on a recent project when it was installed on the heavy lift installation vessel Svanen and used while installing the monopile foundations on the Arkona offshore windfarm in Germany. It was also used on the Walney offshore windfarm in the UK.

The system allows for real-time measurement of the inclination of a monopile during installation, providing continuous measurements as piling takes place. This is in contrast to conventional techniques in which a step-by-step process – piling, measuring, correcting – is used to ensure a monopile is perpendicular. Cameras used in the conventional process are not always very well equipped for accurate measurement either, because they are sensitive to changing weather conditions such as fog and rain, so it is common practice to place a levelling device against the monopile. However, a ‘dump’ in the monopile or a skewed weld can make it impossible to accurately determine whether a pile is really perpendicular.

Using 3D ‘point cloud’ technology and laser sensors developed inhouse by Pliant Offshore, the company can measure and ‘reconstruct’ the objects it is measuring enabling the inclination of a pile to be measured with pinpoint accuracy without the need to stop and start on a regular basis. The system also incorporates a motion-compensation system that compensates for the movement of a vessel while an operation is under way.

“Using IMS enables a contractor to install piles more quickly and accurately,” said Mr Zwinkels. “Over the course of a project on a large windfarm, that equates to significant cost savings.” The system measures the position, orientation, inclination and height of a monopile and compares this with design parameters.

Because it continuously measures inclination with a high level of accuracy, any deviation from the targeted inclination can be addressed almost immediately. The system is also able to cope with local deformation in a pile by measuring it for deformations in advance of installation. Because it measures this misalignment, ‘oval’ piles no longer result in angle deviation, saving time and money. “With the IMS there’s no need to suspend piling in order for conventional contact measurements to be made,” Mr Zwinkels said. The IMS is still evolving as Mr Zwinkels explained, as another well-known client has tied it into a vessel’s dynamic positioning system and achieved further efficiencies in so doing.

The other product Mr Zwinkels highlighted, the departure angle measurement system or ‘DAMS’ has also been used by Van Oord, on its cable lay vessel Nexus. It enables accurate, reliable measurement of the departure angle of cables from a vessel.

In DAMS, Pliant Offshore has integrated what it describes as “an advanced 3D engine” with optimised tracking and filtering algorithms. The company believes the performance of the system exceeds others on the market. Mr Zwinkels said it had proved to be extremely reliable in simulated stress-tests and fully automated cable laying operations conducted over hundreds of kilometres in all kinds of weather conditions.

The system allows the cable laying to be automated, thus speeding up the process, reducing downtime and saving money. It provides logging information for events and incidents, making it useful for survey and reporting. It is accurate up to 0.2° over the entire field of view for vertical angles, and 0.5° horizontally.

As highlighted above, pile-driving and cable installation are only some of the potential applications of Pliant’s technology. Mr Zwinkels said the company, which recently formed a strategic partnership with Ashtead Technology, also anticipates a role for the technology in other offshore operations where the ability to make measurements very accurately are also important, such as rock installation by fallpipe vessels. Other leading players in the market are already talking to the company about these and other applications.

 

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