DMV KEMA, the energy arm of DNV, developed the standard to help accelerate the development of floating offshore wind turbines by establishing design requirements for the floating structure and related systems.
The standard covers a range of issues, including safety philosophy and design principles; site conditions, loads and response; materials and corrosion protection; structural design; design of anchor foundations; floating stability; station keeping; control and mechanical systems; transport and installation; in-service inspection and cable design.
Many densely populated coastal areas around the world are not suitable for traditional bottom-fixed offshore wind turbines. In other areas, the shallow water coast is already developed or challenging seabed conditions makes bottom-fixed offshore wind energy unsuitable. Also, local communities have been known to oppose projects due to negative visual impacts.
Countries like Japan and the U.S. have also made offshore wind energy one focus of their energy policy. A tricky point in the development of offshore wind around the coastal belts of these countries, like the majority of coastal belts around the world, is that water depths can range from dozens to hundreds of meters. This situation demands new technology so in both Japan and the U.S., ideas are turning to floating structures for wind turbines.
In September 2011, DNV initiated a Joint Industry Project (JIP) for the development of the DNV standard for design of floating wind turbine structures. Eleven of the world’s leading players in the wind industry (from Europe, US and Asia) participated in this JIP. The new standard is a supplement to the existing DNV-OS-J101
The JIP focuses on floater specific design issues: suitable safety levels, reliability-based calibration of safety factors, global performance stability, station keeping, site conditions in relation to low frequency floater motions, necessary simulation periods, higher order responses and design of floater-specific structural components.
The JIP secured quality assurance through a technical reference group where each JIP participant had a representative. The standard has recently been issued after internal and external hearings. The technical standard embodies collective industry experience and represents a fully-fledged reference code which supplements existing offshore wind turbine structure codes that do not cover floating units.
The 10 participants in the JIP study are Statoil, Nippon Steel & Sumitomo Metal Corporation, Sasebo Heavy Industries, STX Offshore & Shipbuilding, Navantia, Gamesa, Iberdrola, Alstom Wind, Glosten Associates and Principle Power.