GEL: CLEAN ENERGY FROM THE SEA

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The system for the exploitation of energy from waves has been developed by Seapower SCRL in collaboration with Umbra Group, a world leader in the production of linear actuators with recirculating ball bearings. The wave system is constituted by a pivoted floating body, connected to a support structure, free to oscillate around a horizontal axis under the action of the waves. The permanent magnet electric generator, integrated in the Power Take Off (PTO)actuator/generator, allows the transformation of linear motion induced by waves into rotary motion of the generator rotor. A floating body of about 5 m beam can produce power of around 60 kW out of a wave of heights of 1.5 meters. In an Italian site with enough energy (eg west coast of Sardinia), the system can produce approximately 150,000 kWh per year. A 1:5 scale model of the system has already been tested in the towing tank of Department of Industrial Engineering (DII) of University of Naples “Federico II”, and the next steps will be the floating body geometry optimization followed by the manufacture and testing of a full-scale prototype of 60 kW.

 

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The generator uses the principle of electromagnetic induction to produce electricity. The linear 

motion, caused by the external load, is converted into rotary motion through a screw (VT) of recirculating ball; rotary motion is given to the rotor of the permanent magnet generator.

Tests in towing tank

The tests were executed on a 1:5 scale model in the towing/wave tank of DII. The tests were performed on different possible configurations of the buoy and also in the presence of a vertical wall simulating the fixed structure to which the buoy is anchored. The wave generator of the towing tank is able to reproduce waves of different given amplitudes and frequencies. Each test has been performed at fixed wave amplitude and frequency searching for the optimum value of the damping coefficient of the PTO system.

Scaled model tested in the towing tank
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Numerical simulation

gel(3) copia.jpgBoth potential as well as CFD based codes have been used to simulate the system behavior. As far as It concerns CFD codes we have used STAR CCM + commercial code;it is a finite volume code for the integration of the equations of motion. The calculation model includes approximately 6 million cubic cells; a single unsteady computation takes on average more than 3 days of supercomputing infrastructure. In the calculation model, the system is practically identical to the real system being hinged about a horizontal axis. The presence of the PTO system was simulated by an external force, proportional to the instantaneous velocity of the buoy.

 

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