Steep wave loads from irregular waves on an offshore wind turbine foundation: Computation and experiment

Bo Terp Paulsen, Harry B. Bingham, Henrik Bredmose, Signe Schløer

    Research output: Chapter in Book/Report/Conference proceedingArticle in proceedingsResearchpeer-review

    Abstract

    Two-dimensional irregular waves on a sloping bed and their impact on a bottom mounted circular cylinder is modeled by three different numerical methods and the results are validated against laboratory experiments. We here consider the performance of a linear-, a fully nonlinear potential flow solver and a fully nonlinear Navier-Stokes/VOF solver. The validation is carried out in terms of both the free surface elevation and the inline force. Special attention is paid to the ultimate load in case of a single wave event and the general ability of the numerical models to capture the higher harmonic forcing. The test case is representative for monopile foundations at intermediate water depths. The potential flow computations are carried out in a two-dimensional vertical plane and the inline force on the cylinder is evaluated by the Morison equation. The Navier-Stokes/VOF computations are carried out in three-dimensions and the force is obtained by spatial pressure integration over the wettet area of the cylinder. In terms of both the free surface elevation and inline force, the linear potential flow model is shown to be of limited accuracy and large deviations are generally seen when compared to the experimental measurements. The fully nonlinear Navier-Stokes/VOF computations are accurately predicting both the free surface elevation and the inline force. However, the computational cost is high relative to the potential flow solvers. Despite the fact that the nonlinear potential flow model is carried out in two-dimensions it is shown to perform just as good as the three-dimensional Navier-Stokes/VOF solver. This is observed for both the free surface elevation and the inline force, where both the ultimate load and the higher harmonic forces are accurately predicted. This shows that for moderately steep irregular waves a Morison equation combined with a fully nonlinear two-dimensional potential flow solver can be a good approximation.
    Original languageEnglish
    Title of host publicationProceedings of ASME 2013 32st International Conference on Ocean, Offshore and Arctic Engineering
    Number of pages10
    Volume9
    PublisherAmerican Society of Mechanical Engineers
    Publication date2013
    Article numberOMAE2013-10727
    Publication statusPublished - 2013
    Event32nd International Conference on Ocean, Offshore and Arctic Engineering (OMAE 2013) - Nantes, France
    Duration: 9 Jun 201314 Jun 2013
    Conference number: 32

    Conference

    Conference32nd International Conference on Ocean, Offshore and Arctic Engineering (OMAE 2013)
    Number32
    Country/TerritoryFrance
    CityNantes
    Period09/06/201314/06/2013

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