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J. Mar. Sci. Eng. 2017, 5(4), 45;

Validation of a Tool for the Initial Dynamic Design of Mooring Systems for Large Floating Wave Energy Converters

Department of Civil Engineering, Aalborg University, Thomas Manns Vej 23, 9220 Aalborg Ø, Denmark
Author to whom correspondence should be addressed.
Received: 11 May 2017 / Revised: 14 August 2017 / Accepted: 13 September 2017 / Published: 22 September 2017
(This article belongs to the Section Ocean Engineering)
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Mooring of floating wave energy converters is an important topic in renewable research since it highly influences the overall cost of the wave energy converter and thereby the cost of energy. In addition, several wave energy converter failures have been observed due to insufficient mooring systems. When designing these systems, it is necessary to ensure the applicability of the design tool and to establish an understanding of the error between model and prototype. The present paper presents the outcome of an experimental test campaign and construction of a numerical model using the open-source boundary element method code NEMOH and the commercial time-domain mooring analysis tool OrcaFlex. The work used the wind/wave energy converter Floating Power Plant as a case study, which is defined as a large floating structure with a passive mooring system. The investigated mooring consists of a three-legged turret system with synthetic lines, and it was tested for both operational and extreme events. In order to understand the difference between the model and experimental results, no tuning of the model was done, besides adding drag elements with values found from a simplified methodology. This resembles initial design cases where no experimental data are available. Generally good agreement was found for the tensions in the lines when the drag element was applied, with some overestimation of the motions. The main cause of difference was found to be underestimation of linear damping. A model was tested with additional linear damping, and it illustrated that a final analysis needs to use experimental data to achieve the best results. However, the analyses showed that the investigated model can be used without tuning in initial investigations of mooring systems, and it is expected that this approach can be applied to other similar systems. View Full-Text
Keywords: wave energy; mooring; numerical; NEMOH; OrcaFlex; validation wave energy; mooring; numerical; NEMOH; OrcaFlex; validation

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Thomsen, J.B.; Ferri, F.; Kofoed, J.P. Validation of a Tool for the Initial Dynamic Design of Mooring Systems for Large Floating Wave Energy Converters. J. Mar. Sci. Eng. 2017, 5, 45.

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