ABSTRACT

Wide-shallow composite bucket foundation (WSCBF) can be adapted to the development need of offshore wind farms due to its special structural form. A finite element model for nonlinear dynamic analysis of large - scale ship and composite bucket foundation was established. And the most suitable model was determined. Applying the improved and more objective finite element model using mesh automatic remove technique to analyze soil-structure interaction problems was reasonable and successful. A collision risk was analyzed and evaluated the crashworthiness of WSCBF to vary parameters like wall material properties, impact position, different number of pre-stressed tendons in concrete transition section.

INTRODUCTION

The wind energy is playing a more and more important role in the renewable energy market. Compared with land-based wind energy, there is more available space, more stable and higher wind speed, and less visual disturbance and noise for offshore wind energy (Dong et al.,2011). Offshore wind energy is a rapidly growing industry. With the development of offshore wind energy, the foundations for offshore wind turbines (OWTs) have caused wide public concerns. When the operations and maintenance ship is berthing, the ship and the infrastructure of the wind turbine are likely to collide (Jia et al., 2020). The OWT foundations' development triggers some new challenges, including the impact between the foundation for offshore wind turbines and ships, environmental pollution and security risk. Therefore, the crashworthiness designs of bottom supported structures or foundations for offshore wind turbines are very necessary and should be considered and developed.

Some researchers in Tianjin University have developed and examined a new OWT foundation type, named wide-shallow composite bucket foundation (WSCBF) (Ding et al., 2012; Wang et al., 2017). It has low cost, convenient construction, high reusable and bearing capacity, self-floating towing and one step installation in the appointed sea area and other merits (Zhang et al., 2013; Wang et al., 2019). As shown in Figure 1, it is the construction process of one-step installation of composite bucket foundation. WSCBF is composed of the upper pre-stressed concrete arc transition structure and the steel bucket at the bottom. An arc transition structure has been designed on the top of the bucket foundation to ensure that the heavy loading from the upper tower structure is successfully transmitted to the foundation. It is the reason for designing an arc transition structure that the diameter of tower is less than the diameter of the bucket. Arc transition structure is the key part which links the upper high-flexible tower and the lower rigid bucket. OWTs are usually suffered to the wind, wave and flow loads as well as the weight of the structure above. They also suffer the erosion because of sea water, and are likely to be accidentally damaged due to the collisions by ships that are out of control or berthing in construction process. Dynamic simulation on collision between a ship and the large pre-stressed concrete bucket foundation (LPCBF) was executed by Ding et al. (2014). However, the WSCBF is different from the LPCBF, because the LPCBF is mainly made of reinforced concrete while the WSCBF is made of pre-stressed concrete and steel. Additionally, previous researches have not involved the optimization and crashworthiness behavior of the WSCBF, especially for the arc transition structure. Figure 2 is the composite bucket foundation application example of Jiangsu Daoda Wind Power Plant of China in 2017.

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