MARINET test of iowep at AAU Denmark

2012-0927 MARINET-456 540-360

An experimental study of the Intentium offshore wave energy converter (iowec) has been conducted in the Deep Water Wave Basin at Aalborg University (AAU) through the EU-funded MARINET initiative. The iowep concept is characterized by a long float moored to a front buoy and stabilized with its longest side normal to the incoming and dominant wave front. The float is further connected to a double-acting water pump with a buoyancy controlled water anchor, attached at the lower end. The full scale PTO has analogy with hydro power, and consists of accumulator, water turbine and generator. The concept is international patent pending through WO2011065841A1. The objectives of the study has been to investigate, to verify and, to a certain extent to optimize the intentium concept. The model to be tested was set up in 1:30 scale and included all main assemblies. The PTO-assembly were constructed with adjustable spring loaded friction brakes for both heave- and pitch movement.

The wave conditions which were tested, were well known wave conditions from the North Sea with focus on the five standardized wave states describing energy in the Danish seas, commonly used by AAU in test programs. The tests included both regular and irregular waves.

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The test-model showed a good and fairly consistent efficiency through wave state 1 (WS1) to wave state 5 (WS5). The efficiency ranged from 23,8% in WS1 to 8,7% in WS5 in regular waves, with an average full scale power output ranging from 24kW in WS1 to 310kW in WS5. Due to time limitations, only five irregular wave states were run. These irregular test-runs, showed an efficiency higher or similar to what was found in regular waves. In WS2 irregular waves, the test-model showed an efficiency of 16,5% giving an averaged power output of 57kW in full scale. In a previous numerical simulation study by Sintef MARINTEK [3], dynamic motion response and power output of the intentium concept was studied by frequency domain analysis. The numerical simulation study and this experimental test study shows consistently results.

The highest loads for mooring-lines and internal PTO-force, was found in irregular waves in WS5. The highest internal PTO peak heave load, was found to be 1618kN in tension, full scale. The highest mooring-line forces was in the order of only 30% of the internal peak PTO-force, and found to be 495kN calculated to full scale.

Due to time limitations and problems in mechanical interface and mass, the planned phase control testing was not possible to run, though previous numerical simulation [3] has indicated that the concept is well suited for phase control.

The work carried out has put up a very good platform for further work, where several focus areas as development of float geometry -and size and implementation of phase control, should further increase the power output and the general efficiency of the concept.

References

[3] Study of the Intentium wave energy converter, PhD Jørgen Hals, Sintef MARINTEK, 2011. Report for Intentium. (remember you have to be loged in to access this):

icon 2011-1109_iowep_Marintek_Report-580306

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