Longitude Engineering, a specialist marine engineering subsidiary of the LOC Group, has developed an innovative analysis and modelling process to understand why large windfarm monopiles oscillate in smaller wave heights.
The research was conducted to widen the safe operating window to give more flexibility to the windfarm installation process in light of the ever increasing of monopiles and turbines as windfarms move farther offshore.
Peter Kingsland, principal consultant/naval architect at Longitude, said: “The piles used for the Rampion site weigh up to 850 tonnes which is close the working limit of the crane. Dynamic effects can lead to much larger forces than purely static loads and so it was important to understand the conditions which caused the piles to oscillate. We developed a numerical model of the pile and the rigging which we ran under a variety of conditions."
Longitude also oversaw a series of tank tests and advised on and post processed data from instrumentation on the jack-up vessels to measure the motion of the piles as they were being lowered.
Mr Kingsland added: “This allowed us to develop a robust set of operating guidelines which gave confidence to Rampion and its marine warranty surveyors that pile installation would remain safe.”
At the Rampion Offshore Wind Farm, which is currently under construction off the south coast of the UK, the developer was concerned that these large structures were beginning to oscillate in relatively small wave height.This was affecting the operational window for lowering them into position.
As installation limits are generally set by operator experience, Rampion recognised that the oscillation had the potential to cause difficulties and invited Longitude to work with them to assist with developing solutions and more rigorous guidelines.
In addition to this and following an initiative from Rampion, Longitude also collaborated with the manufacturers of the crane tugger winch control system to numerically model its functionality and to develop an enhanced control system that would sense and damp down the motion of the piles.
This innovative work was coordinated and implemented by Rampion Offshore Wind and is the first of its kind to be developed and applied to the offshore windfarm sector and has the potential to be used in a variety of other offshore applications.
Longitude has a proven track record of working on a variety of renewable projects including cable installations, vessel conversions metocean studies, wave and tidal energy devices, windfarm component transportation and subsea deployment.
The 400MW Rampion Offshore Wind Farm is being built 13km off the Sussex coast by E.ON, the UK Green Investment Bank plc and Canadian energy company Enbridge. It’s scheduled to be completed in 2018.
By Anne-Marie Causer
