Abstract
In this study, the cyclic responses of an offshore wind turbine with a tripod foundation installed on an actual site were evaluated in a centrifuge. To understand the behavior of the turbine at the site, the site soil conditions, environmental loads, and real offshore wind turbine structure installed at the actual site were modeled by considering the centrifuge scaling law. From a series of cyclic loading tests, the cyclic responses of the tripod foundation were evaluated in terms of temporary/permanent displacements and cyclic stiffness. Moreover, the long-term behavior of the tripod foundation was predicted from the experimental results. The test results showed that the initial stiffness of the soil–foundation system decreased as the loading amplitude increased and that the stiffness increased with the number of cycles due to soil densification. The findings revealed that the cyclic behaviors of the tripod were more affected by the load amplitude than the number of cycles. In addition, the permanent rotation increased logarithmically with the number of cycles. A simple method to predict the displacement and change in the foundation stiffness of the actual wind turbine is proposed based on the results of the model tests. The results of this study also provide key insights into the long-term cyclic behavior of tripod foundations for offshore wind turbines.
Highlights
Many countries are attempting to reduce environmental pollution due to fossil fuels by utilizing alternative renewable energy sources such as water, wind, solar, and tidal power.In particular, wind power—one of the cleanest energy sources—has shown potential in meeting international renewable energy targets [1,2,3]
We investigated the cyclic behavior of a tripod foundation for offshore wind turbines (OWTs), in terms of the permanent displacement and soil stiffness
It was found that the increase in permanent displacement was affected more by the loading level than the number of cycles; The initial rotational stiffness of the tripod foundation decreased as the cyclic loading amplitude increased
Summary
Many countries are attempting to reduce environmental pollution due to fossil fuels by utilizing alternative renewable energy sources such as water, wind, solar, and tidal power.In particular, wind power—one of the cleanest energy sources—has shown potential in meeting international renewable energy targets [1,2,3]. Many countries are attempting to reduce environmental pollution due to fossil fuels by utilizing alternative renewable energy sources such as water, wind, solar, and tidal power. Because the levelized cost of energy of wind power has steadily decreased, offshore wind turbines (OWTs) have attracted considerable attention [4]. To secure the competitiveness of offshore wind–energy production, a safe and economical OWT foundation design is crucial because the foundation-construction cost constitutes a large portion of the total OWT cost [5]. Monopiles are frequently used as conventional OWT foundations. The suction bucket foundation has been regarded as a highly competitive alternative to the conventional monopile foundation owing to its convenient installation without heavy equipment for penetration and no hammer noise from driving and shorter installation and construction times, leading to reduced cost of the overall installation operation. Tripod foundations, which consist of three suction buckets placed in a triangular shape, can increase the bearing capacity and overturning resistance of the foundation for OWTs
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