OO-Star WF floating wind concept advances with tank tests

Offshore engineering outfit Dr Techn Olav Olsen's OO-Star WF floating wind concept has taken a leap toward commercialisation, with milestone tank trials now being completed at a research centre in Trondheim, Norway.

The programme at Sintef Ocean, which included a battery of tests on a 1:36-scale model in a range of simulated environments from “benign” Mediterranean to "very harsh Atlantic Sea", is a key step for the innovative semisubmersible design being advanced under the EU's Lifes50+ technology development project as a 10MW nameplate unit.

"It is all progressing well. The model test verifies the excellent motion characteristics as well as the loads in the structure and mooring system," Trond Landbø, renewable-energy business unit manager at Olav Olsen, tells Recharge. "The floater is now tested in a simulation of a very harsh Atlantic Sea environment, for both extreme conditions and operational conditions."

The unit – an aluminium version of the three-armed concrete structure envisioned by Olav Olsen – was put through its paces in wind and waves modelled on conditions in offshore sites in the Mediterranean Sea, Gulf of Maine and West of Scotland. In the last it faced gusts of 50 metres per second and whitecaps.

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"The model testing and the Lifes50+ project will bring the OO-Star up to a TRL5 level on technology – making it ready for full-scale demonstration," he adds, noting that the company is "currently pursuing various opportunities for demonstration projects, and proper model testing is a requirement before funding can be arranged".

"All going to plan", says Landbø, "[a flagship OO-Star could be] "in the water within two years. We believe [the] floating [wind power market] is going to really get going starting in 2020 and we want to be ready for this."

Among the possible pilot sites for the unit is one off Norway, where the government is feeling increasing political heat to open up offshore for use by the wind power industry.

A "floating wind demonstration project" is included in a energy ministry strategy document published last month, alongside a commitment to select by year-end which of 15 already-identified offshore wind farm sites would be tendered for bottom-fixed and floating projects.

Though the country’s expansive hydropower network means the cost of developing offshore wind has been prohibitively high to-date, the potential for export of technology and expertise from Norway’s offshore oil and gas industry into emerging markets, including in the US and several countries in Southeast Asia, has pushed offshore wind back on to the government’s agenda.

“There is huge pressure on the politicians [to develop Norway's offshore wind industry for this reason]," states Landbø. "And floating wind will be an important part of this."

The Lifes50+ project, with an eye on industrialistion of floating wind power, is also running side projects looking at experimental and numerical methods and tools for the wider floating wind sector.

The testing method being used at Sintef Ocean, so-called Real-time Hybrid Model Testing (ReaTHM), is a new approach based on the science of combining advanced simulations, state-of-the-art experimental methods and active control systems.

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"In hybrid testing, one part of the system is studied physically, while another part is represented by a numerical model," explains Landbø. "The parts interact in real-time through actuators and sensors."

The wave tank tests are being combined with wind loads applied from a numerical model, with further wind tunnel test using a turbine mounted on a movable rig, with motions taken from the wave tank test factored in.

"The interaction between two separate models solves the experimental issues related to Reynolds and Froude scaling incompatibility for wave and wind respectively when validating offshore wind turbine concepts in an ocean basin," says Landbø. "The main objective is to improve accuracy of the test results."

The floating wind power sector has catapulted forward in recent weeks with the switch-on of the world's first floating array, Statoil's UK North Sea 30MW Hywind Scotland, and launch of the FloatGen prototype in France. Global market forecasts for 2030 are angling as high as 12GW, when only a year ago most suggested 3.5GW of floating wind might be built by this date.

Germany's Gicon last week reported succcessful tank tests of its tension leg platform design, the SOF, at France's Ecole Central de Nantes. And most recently, Pilot Offshore Resources revealed its stalled Kincardine project off Scotland was back on track with plans to install a 2MW lead-off unit next summer.

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