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Experiments by Invited Researchers

 

Breaking wave impacts and non-breaking wave interactions with offshore wind turbine foundations

Project acronym: HyIII-DHI-10
Name of Group Leader: Dr. Jun Zang Dept. Architecture and Civil Enginee
User-Project Title: Breaking wave impacts and non-breaking wave interactions with offshore wind turbine foundations
Facility: Shallow water basin
Proceedings TA Project: Violent wave interactions with a vertical cylinder - applications to offshore wind turbine foundations and “ringing” re-visited
Data Management Report: Report

User-Project Objectives

Summary:

The primary aim of this research was to study steep wave and breaking wave impacts on offshore wind turbine foundations. Unique high quality data on wave impact pressures, free surface run-up, and total fluid loading on a vertical cylinder was obtained. Effects of caisson around the cylinder, sloping beach and directionality of spread wave on wave run-up and wave loading on the body have also been examined. These violent wave-structure interactions, triggered by localised wave groups, not only reveal physics, but also are ideal for numerical modellers to validate numerical simulations with a variety of numerical techniques.

In contrast to most previous experiments we concentrate on hitting the column with localised wave groups not on regular or random waves. By repeating the tests with both focused wave groups and the same wave groups inverted, so each tall crest in one is replaced by a deep trough in the inverted form, we are able to identify unambiguously the complete Stokes expansion type representation of the applied force: linear, second order two-frequency sum and difference, 3rd order triple-frequency sum etc. The cumulative effect of this relatively small but significant high frequency excitation is to produce dynamic response or ‘ringing’ of the column if the lowest resonant frequency is in the right range. Figure 1 shows two force time-histories for wave groups on constant depth hitting the cylinder.




FIGURE 1. Wave impact with the vertical cylinder: incident wave time histories (left) and horizontal forces on the cylinder (right), for unidirectional focused wave group (top) and bi-directional pair ±20° (middle). Bottom figures: incident wave spectrum (left), force spectrum (right), both for bi-directional pair only.

Keywords:

breaking wave impact, offshore wind turbine foundations, wave loading, wave run-up

Publication References
Steep wave and breaking wave impact on offshore wind turbine foundations - Ringing re-visited, IWWWFB 2010.
Zang J., Taylor P.H., Morgan G.C.J., Orszaghova J., Grice J., Tello M. and Stringer R. Submitted.

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