Optimizing mooring and dynamic cable design requirements for floating wind

DNV has launched the Floating Wind Reliability Joint Industry Project (JIP) aimed at optimizing design requirements for mooring and dynamic inter-array cable systems applicable for commercial scale floating wind projects. The JIP will provide new and valuable insights on load and capacity of these critical components and the recommendations will form the basis for tomorrow’s design requirements.

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Challenge

According to DNV’s predictions, offshore wind alone will account for 25% of all electricity generation in Europe in 2050. Floating wind at scale will be required to make use of offshore areas in deeper waters to meet the high ambitions. To enable the cost reductions needed to make floating wind commercially viable, it is important that the design requirements are optimized. The mooring and dynamic cable system are critical components in a floating wind farm, both to ensure the integrity of the structures and to ensure production availability.

The dynamic cable system and lack of optimized acceptance criteria is a challenging part of floating wind design. Today’s requirements are mainly based on requirements for similar types of structures (e.g. umbilicals), which are not necessarily representative. Calibrating utilization factors for cables based on combined tension and curvature response and design fatigue factors for the cables will be an important part of the work in the JIP. Furthermore, guidance on a holistic and simplified methodology that can be used in the early cable system design process is lacking in today’s rules and regulations and will be addressed.

For mooring, the design needs to accommodate the high loading (extreme and cyclic/fatigue loading) imposed from both operational and idling conditions and ensure compliance with cable offset requirements. Improved mooring design methodology and optimized safety factors will be recommended based on the findings in the project.

Objective

The Floating Wind Reliability JIP is initiated to establish consistent design philosophy and analysis methodologies for design of mooring and inter-array cable systems optimized for commercial-scale floating wind applications. The ambition is to provide cost-efficient design requirements without compromising on safety.   

Approach

The work will build on a probabilistic approach applying state-of-the-art coupled time-domain analysis to evaluate the reliability level and re-calibrate safety factors for mooring and cable design. It will, for a confined set of cases, address the design for Ultimate Limit State (ULS), Accidental Limit State (ALS) and Fatigue Limit State (FLS) of mooring lines and inter-array cables, with objectives:

• Evaluate cost-optimal reliability/safety level(s) for mooring and inter-array cable systems
• Establish overall design philosophy and corresponding analysis methodology
• Apply structural reliability analysis and calibrate optimized safety factors for target reliability level given the defined analysis methodology. The mooring line tensions, cable tension and curvature responses will be based on coupled time domain simulation across a range of relevant designs and locations (environmental conditions and water depth).  

The work will form the basis for updating standard DNV-ST-0119 Floating wind turbine structures enabling cost-optimized mooring and dynamic cable designs. Furthermore, alignment of requirements and procedures will provide a reliable basis for design and certification of commercial wind farms, improved predictability for developers, designers, component manufacturers. Investors, lenders, insurance companies and authorities will take advantage of up-to-date requirements which will positively impact project safety, availability, cost and schedules. 

Project status

The Joint Industry Project was launched on 20 June 2023 and is still open to participants.

Duration

The JIP will be running until the end of 2025 and be constituted by a range of project developers, designers, suppliers and regulators.

The partners

Acteon/Bruce Anchor, Aker Offshore Wind/Mainstream Renewable Power, Aker Solutions, APL -NOV, Bardex Corporation, BayWa r.e. Offshore Wind, Bluewater, BP, Brunel Floating, Cathie, Corio Generation, COWI, Delmar Systems, Delp, DOF Subsea, EDF Re, EnBW, Equinor, Goldwind, Hafslund, Hengtong, HSE, Iberdrola, Invenergy, Kongsberg Maritime, Ming Yang, Mooreast, Moreld, Nexans, NKT HV Cables, Noble Drilling, Ocean Winds, OMV, Ore Catapult, OSI Renewables, PSA, RWE Offshore Wind, Ryder Geotechnical, Saipem, SBM, Schottel Marine Technologies, Shell, Sofec, SSE Renewable Services, Statkraft, Stiesdal Offshore, Subsea7, Sumitomo Electric, TechnipFMC, Teijin Aramid, TotalEnergies, Vattenfall, Vicinay Marine, Ørsted Wind Power.