Oscillating properties of jacket support structures subjected to extreme wave events

Abstract

The paper presents laboratory measurements involving the response of a jacket structure scaled to represent the support structure of an offshore wind turbine. The full-scale structure was assumed to be installed in water depth ranging between 50-60m. To simulate the flexibility of the foundation system and test the dynamic soil-wave-structure interaction, the jacket model is placed on top of a set of novel special devices (bearings), consisting of spring assemblies, allowing relatively small but realistic horizontal and vertical motions of the structure. The experimental data presented herein involve the model subjected to extreme waves. Both regular and long-crested irregular waves were tested; the latter associated with nearly focused wave events. It is shown that the structure moves as expected (and designed) in surge and pitch. The displacements were analogous to the wave steepness. Focused events yielded larger displacements than regular waves of similar wave steepness. Nonlinear effects were more evident when focused events were introduced. The above preceding observations imply that such structures must be examined under realistic sea-states. © 2019, National Technical University of Athens. All rights reserved.