New ways for deploying piles for an offshore windfarm

New ways for deploying piles for an offshore windfarm
Marginal Column

November 2017


When Large Diameter Drilling (LDD) wanted to deploy piles for a new offshore wind farm, absolute precision was key. That’s why the company choose a new way of working that had not been used before.

Wind farms are becoming increasingly popular as they can generate vast amounts of energy in an environmentally friendly way. Their use offshore has many advantages, one being that wind speeds are typically higher compared with on land, so the contribution in terms of electricity supplied is also higher. LDD specializes in subsea foundation installation services and was keen to improve its current methods of subsea piling – placing piles (the bases on which wind turbines are located) individually – with a faster and more integrated, truly intelligent system. In this specific case, LDD sought to optimize both the performance and efficiency of their template used for deploying piles at a new offshore wind farm, located 65 kilometers off the Baltic coast.

The project itself involved the deployment of 70 wind turbines in the sea, which had a maximum sea depth of 100 meters. These would be positioned on four subsea piles which needed to be a specific distance apart with minimal margin of error. With each pile weighting up to 175 tons, being 62 meters long and 2.7 meters wide, the template used to accurately align the piles was of significant importance. This type of project would be challenging on land, let alone when considering the other factors faced at sea, such as current, pitch, yaw, and gusty winds.

Exploring new horizons

Traditional piling methods position and align each pile sequentially with each subsequent pile location measured from its predecessor. However there are many factors that the process must compensate for. Therefore the idea of an ‘intelligent template’ – one that can continuously react to changes in challenging conditions, with a degree of control and automatically correcting the positioning and angle of the pile during installation – was a concept initially thought out by LDD. With the help of Bosch Rexroth’s innovative thinking, a bespoke hybrid solution was designed and developed which continually monitors and ensures the accurate positioning of the piles through the creation of a reactive template.

Rexroth’s role was to draw on its extensive experience to design the hydraulic and control system, verify its effectiveness and suitability, then select the most appropriate materials capable of withstanding the uniquely challenging operating environment. Such a system was unprecedented and required extensive virtual testing to mitigate both technical and commercial risk, before it could be implemented in a real application.

Unprecedented precision

The resulting precision heavy-duty electro-hydraulic control system delivered unprecedented accuracies beyond the scope of traditional methods. Unlike traditional techniques, the new active template presented the ability to simultaneously hold the four piles together as a ‘set’, as it optimized the positioning of each pile with a ‘group’ reference including: the seabed, the template and the adjacent pile. This saved a considerable amount of time, and ultimately money, which could typically reach a six-figure sum each day. The final system included fault level detection, with algorithms allowing the generation of error signals which, combined with predictive technology enabled the control system to deliver sequential correction.

The system proved ideal in this application, but perhaps more importantly its capabilities are now being explored for other challenging applications where the accurate positioning of machinery and components is vital for safety and operational reasons.

Bosch Rexroth’s precision subsea Electro Hydraulic Equipment. Magnifier

Bosch Rexroth’s precision subsea Electro Hydraulic Equipment.