Interaction between mooring line damping and response frequency as a result of stiffness alteration in surge

Lars Johanning, George H. Smith, Julian Wolfram

    Research output: Chapter in Book/Report/Conference proceedingConference contribution

    9 Citations (Scopus)

    Abstract

    The design and operation of a chain mooring for a wave energy converter (WEC) is considered. Experimental measurements of a mooring line were conducted in the Heriot-Watt University wave basin at a scale of 1:10. The laboratory procedures were designed to resemble tests undertaken earlier in the year at 'full' scale in 24 m water depth. This paper describes and compares these measurements and relates the results to earlier work on mooring lines by Webster [1]. Measurements of both the damping and response frequencies of the mooring are described. Although the present results support partly the conclusions of the earlier work, care must be taken in how these are applied when one is considering mooring line design for WECs. It is concluded that there are significant differences for a WEC for both operational and limit state design in comparison with a more conventional offshore system such as an FPSO or CALM. Although the primary requirement is still one of station-keeping two further considerations may be of great importance. Firstly if a 'farm' of devices is to be considered then limitations in sea space may necessitate that the devices be relatively densely packed. This will mean that the 'footprint' of the mooring should be constrained, to ensure that the moorings from each device do not interfere with one another and this will have great significance for the loading experienced by the line. This can be exacerbated by variations in tidal range which will have a larger effect in comparison with a conventional deepwater mooring. A second factor may arise if the mooring system response is critical to the WEC energy extraction process. If the mooring becomes part of the 'tuned' system then changes in the mooring properties of damping and natural frequency could seriously affect energy conversion efficiencies. Copyright © 2006 by ASME.

    Original languageEnglish
    Title of host publicationProceedings of 25TH International Conference on Offshore Mechanics and Arctic Engineering, OMAE 2006
    Volume2006
    Publication statusPublished - 2006
    Event25th International Conference on Offshore Mechanics and Arctic Engineering 2006 - Hamburg, Germany
    Duration: 4 Jun 20069 Jun 2006

    Conference

    Conference25th International Conference on Offshore Mechanics and Arctic Engineering 2006
    Abbreviated titleOMAE 2006
    CountryGermany
    CityHamburg
    Period4/06/069/06/06

    Keywords

    • Floating wave energy converter
    • Mooring line damping
    • Mooring response frequency
    • Stiffness characteristics

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  • Cite this

    Johanning, L., Smith, G. H., & Wolfram, J. (2006). Interaction between mooring line damping and response frequency as a result of stiffness alteration in surge. In Proceedings of 25TH International Conference on Offshore Mechanics and Arctic Engineering, OMAE 2006 (Vol. 2006)