The installation of wind turbines at sea today only takes place in very mild weather conditions due to the risk of severe impact of the legs of wind turbine installation vessels (WTIV) with the seabed, resulting in damage structural to the ship or cargo.
If the weather deteriorates, vessels must wait for conditions to improve before they can resume work. “However, high daily rates make delays very costly and there is increasing pressure to widen the weather window to undertake projects more efficiently as the industry moves progressively further into new territories with more difficult weather conditions. and less tolerant seabed (soil) conditions,” says the JIP director. committee chair Andries Hofman of GustoMSC.
Additionally, seismic hazard regions also require new operating philosophies such as operating the crane with the WTIV in a semi-verified state.
JIP Announces Common Approach to WTIV Security and Performance
The lack of class guidelines or good models to fully understand and estimate bottom impact forces and operations in the semi-verified condition triggered the formation of the JIP in November 2020. “The objective was to investigate the operational limitations of the WTIV and potential new operational philosophies.
Reducing installation costs is key to lowering the levelized cost of offshore wind energy as part of the drive to increase energy security. But in a process-driven industry where time is money, pushing the boundaries based on proper knowledge is crucial. Doing it based on limited data is very risky,” says Hofman.
Work carried out in phase 1
With input from all JIP participants, DNV developed a numerical model to accurately predict bottom impact forces. This allows operators to assess the limit of the sea state in each situation for safe lowering of the riser legs, without the risk of damaging the vessel, cargo or the environment or endangering endanger the crew. It applies to both existing and new WTIVs, ensuring from the design phase that vessels can operate within a reasonable range of conditions.
“The digital model developed incorporates vessel heading, weather and ground conditions, as well as the strength of the WTIV, to potentially expand the weather window where the WTIV can be safely installed,” says Antonio Goncalves, Head of JIP project, Business Lead, Technical Advisory at DNV. “Harder ground generates more impact than soft ground, while stronger winds and higher waves can exaggerate impact events. Deeper water also causes ships to behave differently compared to shallow water Geotechnical, hydrodynamic and environmental conditions must match the structural capabilities of a given WTIV.
Is it possible to operate in a semi-locked state?
The JIP also considered the loads and movements of the WTIV in a semi-jacked state, that is, with the legs resting on the seabed and the hull in a partially submerged state. This applies especially in seismic hazard regions where contractors prefer the hull of the WTIV to be as close to the water surface as possible.
“Currently, a number of challenges exist with respect to (soil) liquefaction and accelerations/displacements when lifting the turbine and installing the bolts. Consideration must be given to the movements of the tower and the turbine as well as the vessel. If we fail to strike a balance between movement and investment in the foundation, semi-jack operation can pose safety issues. The issue requires further technical calculations and we look forward to appropriate advice from DNV in the future,” says Benjamin Haak, marine surveyor at RWE Renewables.
Large-scale instrumentation measurements can validate model output
Predictive simulation, however, is only one dimension of the challenge to reach a final solution. Another dimension is to apply large scale instrumentation (sensor) measurements to validate the model output under real conditions. “Predicted forces have not yet been correlated to actual forces measured during actual operations. This is a key area where significant progress can be made to improve the operability of the WTIV,” Goncalves says.
The third dimension documents the role of safety factors on structural failure probabilities. The JIP concluded that the probabilities of structural failure can be relatively high under certain conditions. “We got great information about the simulations and the effect of different parameters, but we still need more information about the appropriate safety factors needed to ensure safe operations. With more insights from validating theoretical models and appropriate safety factors, we will reap huge benefits from increased operational efficiency, new operating philosophies, new designs, and more. says Goncalves.
Phase 2 in the pipeline will bring even more value
DNV is currently preparing a proposal for a second phase of the JIP. Scope tentatively includes calibration of bottom and partially submerged impact models, calibration of safety factors, ground model improvement, further evaluation of crane boom/hook movements in partially submerged conditions, the use of movement criteria when moving in place and the development of guidelines.
“With such team collaboration, I am confident that the next phase will bring even more value to all parties,” says Goncalves. “Our goal is to define a comprehensive safety factor approach using real data to benchmark the model so that it can be used as recommended best practice on an equal footing,” Hofman says.
Reassurance on data sharing and confidentiality
To ensure the reliability of the numerical models, data is required from multiple assets operating in both good and bad weather, developers/contractors on site ground conditions, and potentially even turbine suppliers. Jan Sand Schanke-Jørgensen from Fred. Olsen Windcarrier says the industry wants to get the full picture, even as new ships come onto the market. “For example, if ships are shown to be oversized, including less steel could reduce construction costs while allowing more equipment on deck. Reducing emissions is also a key factor for make the whole installation ecosystem as efficient as possible.”
While providing data presents a clear business case in terms of improving the operability of the WTIV and preventing harm, there is residual concern about what might happen with proprietary data once shared. Goncalves emphasizes that all data will be treated confidentially by DNV and only the guidelines developed will be shared.
Participants express their enthusiasm for the “creative arena”
The JIP process was unanimously appreciated. Positive comments included the following: “It’s fantastic to sit down and talk about important topics without being driven by internal commerce. Focusing on critical safety issues for our crews, assets and the environment is why this is successful,” said Sand Schanke-Jørgensen.
Kevin van de Leur, Principal Engineer at Van Oord Offshore Wind, said: “We have done this type of site assessment analysis before, but it is difficult to do it properly alone. By working together, we can develop a common industry standard that everyone trusts. »
Eric Romeijn, R&D Manager at Huisman Equipment, added: “We consider bottom impact simulations to be crucial to further optimize Huisman’s next-generation lifting systems for offshore WTIVs. We expect further benefits from a second JIP phase contributing to safe and reliable jackup operations. Fu Qiang, director of CIMC Raffles’ R&D center, as well as director of the marketing center expressed similar sentiments. “We are proud to have participated in this JIP and look forward to continuing the work,” he said.
Eduard Lopkov, Principal Wind Turbine Installation Specialist, EPC and Operations, at Ørsted, adds that as a major player in the value chain, Ørsted is quite selective about which JIPs it joins. “But this one has the potential to significantly improve operations, having shed light on an area not sufficiently explored before. We can use our combined knowledge to create robust standards and a reliable predictive model that can make jack-up installations safer while reducing the downtime factor due to weather.
In terms of a level playing field, having uniform guidelines will make the procurement process easier. This applies to both winter and summer operations and seabed conditions, where we are already seeing projects move from sandbanks to more challenging sites with heavy, rocky clay soils, and deeper water. In terms of data sharing, DNV has an excellent record in managing proprietary data. We look forward to the next step to develop specific directions that will benefit everyone.
Knowledge sharing is the best format
The work of the JIP will be relevant for a long time, because fixed wind farms requiring a jack-up installation will remain the most attractive in terms of costs to diversify our energy mix. “The market is growing faster than the rules and the only way to make significant leaps is to share knowledge,” says Goncalves. “Our goal is to make recommendations that are robust and easily accessible. With a better understanding of the forces at play for a specific site and their consequences, we can increase performance and safety in more difficult sea conditions, enabling more efficient and faster turbine installation, which is a great opportunity for the entire industry.
Door wide open to new partners
Goncalves points out that the JIP is open to more partners, whether energy companies, installation contractors, designers and shipyards, crane manufacturers or wind turbine manufacturers. General benefits include reduced risk of project delays, accidents and damage to installed equipment, reduced transaction costs, consideration of specific concerns and objectives in guidelines, and last but not least the ability to network with leaders in the field.
Source: DNV, www.dnv.com