Accurate accessibility prediction for SOV thanks to HIL simulator
Senior Project Manager
Research and Development
Damen Shipyards Gorinchem
Damen turned to Maritime Research Institute Netherlands (MARIN) to test its pioneering Service Operations Vessel (SOV), together with the vessel’s Dynamic Positioning system and its walk-to-work telescopic gangway. The Damen SOV is purposebuilt for the transfer and accommodation of offshore personnel and the groundbreaking design guarantees fast, safe and comfortable access to wind turbines. The first vessel of this type, the Bibby WaveMaster 1, is expected to be available from end-August 2017.
Representing more than 4 years of Research and Development, the new SOV design underwent its initial seakeeping tests at MARIN’s Offshore Basin in Wageningen in the Netherlands to examine its DP capabilities during the turbine approach. Damen also asked MARIN to assess the power management system and the gangway through numerical simulations. The project resulted in an integrated HIL simulator, which has now been installed at Damen’s headquarters.
Jorinus Kalis, Manager Development, R&D at Damen explains: “Given that this was a completely new design, we wanted to test the vessel itself, but also the process behind it. We didn’t have any vessel type that came close to this new SOV so needed to know the functional requirements and look at the possibilities, considering the specific mission of the end user.
“We had to think of a way of testing it to make sure the SOV has the right performance levels. Normally we would test separate systems before the trials – the engine and propeller, etc. – but we have never carried out combined tests on all of the control systems before.”
MARIN performed the basin tests in September 2015 to examine the SOV’s ability to approach and keep position alongside the turbines and to test the extension and touchdown of the walk-to-work arm.
Auke Ditzel, MARIN Senior Project Manager, comments: “This enabled us to get the full picture about how the vessel responds when performing maintenance activities, the planned route between the turbine locations and the best way of getting the technicians safely on and off the turbines before moving on to the next turbine. We could see if the maintenance sequence could be done in a certain time, and how many turbines could be maintained in a certain number of hours.”
The measurements from the basin were then input into the HIL simulation software. Mr Ditzel emphasises: “We integrated the full DP system as it is used on board the Bibby Wavemaster 1 and the walk-to-work arm. This integrated setup is combined with the route planner.
This project is unique in that Damen wanted MARIN to look at the whole, integrated system, he says. “And crucially the DP system and gangway are what will be used in reality on the vessel. Therefore, Damen knows what it can guarantee in terms of uptime, giving Damen and its client – Bibby Marine Services in this case – confidence.
“MARIN always aims to bridge the gap between engineering and operations. With these desktop numerical studies and simulations, Damen and Bibby could test the possibilities and immediately see the operational impact.”
The HIL simulator could later be fine-tuned. “The end result was that actually the SOV could remain at the turbines for longer than originally thought – gaining more uptime. The tuning of the DP system resulted in the DP system becoming ‘stiffer’, reducing the maximum movement, thereby increasing the operational envelope.
“That is the beauty of the simulator, all the systems can be put under test and the conclusions are much closer to the true end result. It is much easier to predict workability and uptime capabilities.”
Mr Kalis adds: “You learn so much and it facilitates performance contracting. The HIL simulator enables us to compare operational performance; it gives answers about how many maintenance operations can be carried out in a year given the specific wind farm. We know what we can expect in real life rather than in ‘ideal’ test conditions.”
For example, the ‘base case’ was that the SOV should have access to the turbines in 2.5 metre significant wave heights in good conditions, but what would happen in unfavourable conditions? The HIL simulator enables Damen to prove that the SOV can manage 2.5 metre significant wave heights in any conditions, even challenging environmental conditions,” he says.
As the wind farms go farther offshore, workability is even more important, they stress. Mr Ditzel comments: “It is very useful to test a maintenance plan and see if it can still work in a certain sea state. Can the shipbuilder or operator guarantee this plan up to a certain sea state? By investigating the possibilities in a numerical model it is much easier. And if you can stretch the operational envelope by only 10% this is tremendously significant.”
Mr Kalis stresses: “Damen is always pushing performance for higher workability. If the SOV can operate 20 more days a year over 20 years… The offshore wind industry is pressing on every margin to get energy costs down, so 20 more days – the implications are huge.
“This new HIL simulator is a definite enabling technology for performance contracting. We are not just looking to sell vessels, but, in the future, also their availability.”