Abstract
An alternating rotatory generator using an eddy current break is developed as a physical scale model of a direct-driven floating point absorber power take-off (PTO) for wave tank tests. It is shown that this design is a simple and cost-effective way to get an accurate linear damping PTO. The device shows some beneficial characteristics, making it an interesting option for full scale devices: For similar weights the inertia can be significantly higher than for linear generators, allowing it to operate with natural frequencies close to typical wave frequencies. The influence of the higher inertia on the power absorption is tested using both a numerical simulation and physical wave tank tests. With the increased inertia the PTO is able to absorb more than double the energy of a comparable direct-driven linear generator in some sea states. Moreover, the alternating rotatory generator allows the absorption characteristic to be tuned by changing the inertia and the generator damping.
Highlights
Physical wave tank tests play an important role in validating numerical results and testing devices under realistic and repeatable conditions
The power output of the high-inertia power take-off (PTO) were set in relation to a PTO with M = mw, which can be seen as a linear generator
The additional inertia allows to design the device for specific sea states and the PTO damping can be used to adjust the degree of specialisation
Summary
Physical wave tank tests play an important role in validating numerical results and testing devices under realistic and repeatable conditions. They are an important, while cost efficient, step in the development of a wave energy converter (WEC) before going to full scale. In this paper a new power take-off (PTO) design for floating point absorbers is presented which has been developed especially for wave tank tests. One way of lowering these costs is to simplify the mechanical design of the wave energy converter, and here especially the power take off (PTO) [3]. A disadvantage of most of these devices, is the high natural frequency, leading to a poor capture width for sea states with long wave energy periods, if no additional control [7] or similar mechanism [8,9] is applied
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