The paper deals with the presentation of a model to predict performance characteristics of a tightly moored piston-like wave energy converter which is allowed to move in heave, pitch and sway modes of motion. The WEC’s piston-like arrangement consists of two floating concentric cylinders, the geometry of which allow the existence of a cylindrical moonpool between the external cylinder, the ‘torus’ and the inner cylinder, the ‘piston’. The first-order hydrodynamic characteristics of the floating device, i.e. exciting wave forces and hydrodynamic parameters, are evaluated using a linearized diffraction-radiation semi-analytical method of analysis that is suited for the type of bodies under consideration. According to the analysis method used, matched axisymmetric eigenfunction expansions of the velocity potentials in properly defined fluid regions around the body are introduced to solve the respective diffraction and radiation problems and to calculate the floats’ hydrodynamic characteristics in the frequency domain (Mavrakos et al. 2004, 2005). Based on these characteristics, the retardation forcing terms are calculated, which account for the memory effects of the motion. In this procedure, the coupling terms between the different modes of motion are properly formulated and taken into account (Cummins, 1962; Faltinsen, 1990). The floating WEC is connected to an underwater hydraulic cylinder that feeds a hydraulic system with pressurized oil. The performance of the system under the combined excitation of both first- and second order wave loads is here analyzed. To this end, the diffraction forces originated from the second order wave potentials are computed using a semi-analytical formulation which, by extension of the associated first-order solution, is based on matched axisymmetric eigenfunction expansions.
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ASME 2008 27th International Conference on Offshore Mechanics and Arctic Engineering
June 15–20, 2008
Estoril, Portugal
Conference Sponsors:
- Ocean, Offshore and Arctic Engineering Division
ISBN:
978-0-7918-4823-4
PROCEEDINGS PAPER
Performance Characteristics of a Tightly Moored Piston-Like Wave Energy Converter Under First- and Second-Order Wave Loads
Spyros A. Mavrakos,
Spyros A. Mavrakos
National Technical University of Athens, Athens, Greece
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George M. Katsaounis,
George M. Katsaounis
National Technical University of Athens, Athens, Greece
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Ioannis K. Chatjigeorgiou
Ioannis K. Chatjigeorgiou
National Technical University of Athens, Athens, Greece
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Spyros A. Mavrakos
National Technical University of Athens, Athens, Greece
George M. Katsaounis
National Technical University of Athens, Athens, Greece
Ioannis K. Chatjigeorgiou
National Technical University of Athens, Athens, Greece
Paper No:
OMAE2008-57867, pp. 783-792; 10 pages
Published Online:
July 27, 2009
Citation
Mavrakos, SA, Katsaounis, GM, & Chatjigeorgiou, IK. "Performance Characteristics of a Tightly Moored Piston-Like Wave Energy Converter Under First- and Second-Order Wave Loads." Proceedings of the ASME 2008 27th International Conference on Offshore Mechanics and Arctic Engineering. Volume 6: Nick Newman Symposium on Marine Hydrodynamics; Yoshida and Maeda Special Symposium on Ocean Space Utilization; Special Symposium on Offshore Renewable Energy. Estoril, Portugal. June 15–20, 2008. pp. 783-792. ASME. https://doi.org/10.1115/OMAE2008-57867
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