Abstract
A point absorbing wave energy converter (WEC) is a complicated dynamical system. A semi-submerged buoy drives a power take-off device (PTO), which acts as a linear or non-linear damper of the WEC system. The buoy motion depends on the buoy geometry and dimensions, the mass of the moving parts of the system and on the damping force from the generator. The electromagnetic damping in the generator depends on both the generator specifications, the connected load and the buoy velocity. In this paper a velocity ratio has been used to study how the geometric parameters buoy draft and radius, assuming constant generator damping coefficient, affects the motion and the energy absorption of a WEC. It have been concluded that an optimal buoy geometry can be identified for a specific generator damping. The simulated WEC performance have been compared with experimental values from two WECs with similar generators but different buoys. Conclusions have been drawn about their behaviour.
Highlights
In the Lysekil project a wave energy converter (WEC) concept, developed by Uppsala University, is being tested at the test site offshore Lysekil on the Swedish west coast
capture width ratio (CWR) is derived as the ratio between the power absorbed by the WEC’s generator and the total time average incident wave power that is traveling through the buoy
The study presented in this paper aims to investigate how the buoy geometry and dimensions affect the power absorption, which should be expressed as independent of buoy dimensions
Summary
In the Lysekil project a wave energy converter (WEC) concept, developed by Uppsala University, is being tested at the test site offshore Lysekil on the Swedish west coast. The electromagnetic damping in the generator can to some extent be controlled with power electronics during operation, but in this study a constant resistive load is assumed in the simulations and have been used in the experiments. The most accurate method available to analyze the dynamics of this system is to use a computational fluid dynamics (CFD) tool coupled with a generator model which should be applied in the time domain [1]. This is very time consuming and demands high computational power, which does not make it suitable when dealing with large amounts of experimental data. The incident wave power is assumed to be the wave energy transport per meter wave front multiplied by the buoy diameter [5,13,14]
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