North Sea climate at the touch of a button

Test chamber simulates how marine climate and mechanical stress can damage offshore wind turbines

In the climate chamber, parts of offshore structures can be extensively tested. © Fraunhofer-Gesellschaft / IWES
Read out

Fraunhofer researchers have developed a new climate chamber. With their help, it is now possible for the first time to simulate in the laboratory how the harsh marine climate and the mechanical loads caused by wind and waves damage the offshore wind turbines. Since March 2011, manufacturers in the chamber have been able to thoroughly test materials.

The oceans are a harsh environment for wind turbines. Waves beating against the tower, salt mist settles on nacelle and rotor blade. Especially in summer, intensive UV radiation is added. So far no one knows how well the wind turbines will survive the planned 20 years of service - because such stresses as in the sea wind turbines had to resist in any other place in the world. Of particular interest is the question of how destructive all these environmental conditions interact.

New climate chamber developed

The Fraunhofer Institute for Wind Energy and Energy System Technology IWES in Bremerhaven has therefore developed its own climate chamber in which parts of offshore structures can be comprehensively tested. "We combine the ambient climate with mechanical loads, " says project manager Leena Kruse. "Such a combination is so far unique."

Researchers can test sheets, fiber composites and other materials in the chamber. The system mimics everything that happens to the wind turbine at sea. It sprays salt mist. It irradiates the samples with aggressive UV light. During the "swirl test", the sheets and the plastics are quenched with a cold water jet, which simulates the wave impact. In addition, the chamber can be tempered from minus 30 to plus 100 degrees Celsius at a relative humidity of 10 to 95 percent.

Combined check

The material samples, according to the researchers, are clamped between two steel jaws to simulate mechanical stress, bending the samples back and forth. An advantage of this combination test is that for the first time it is possible to determine very precisely which forces or environmental conditions cause damage. "We can combine various factors and limit the causes very precisely, " says Kruse. display

The chamber is made of tough offshore steel that can withstand harsh test conditions. It took almost two years from the initial idea to full implementation in the factory. The result is a robust and powerful test instrument - with hydraulic drives, valves, water hoses and nozzles. Among other things, the tests are monitored by sensors that are applied to the components - strain gauges, for example, which feel when the material cracks.

The measured values ​​of the sensors are routed to a man-sized control cabinet, where the technicians select exactly the test conditions and at the same time evaluate the sensor data. In this way, it is possible to determine under which conditions and in what seconds a component fails, and also when a sensor acknowledges its service.

Sensors monitor test run

According to the researchers, the sensors fulfill a dual purpose. On the one hand, they monitor the test run. On the other hand, they are tested in the climate chamber itself. In the future, offshore wind turbines will increasingly be equipped with sensors so that the state of the wind turbines can be monitored from the mainland. For this, robust sensors are particularly important. The chamber complies with DIN and ISO standards. Ultimately, however, it does a great deal more, because up to now there are no standards or regulations for systems that simultaneously simulate climate tests and mechanical loads.

Plant already in operation

The plant has been in operation since the beginning of March, according to the scientists. In the future, IWES will in particular carry out tests on behalf of offshore manufacturers. At the Hanover Fair from 4 to 8 April 2011, the Fraunhofer researchers will be presenting the new system to the public for the first time.

(Fraunhofer-Gesellschaft, 15.03.2011 - DLO)