The Wide shallow bucket foundation has been successfully used for offshore wind turbines in city of Xiangshui in Jiangsu Province, China, and has a promising application prospect. Stiffness of shallow bucket foundation and natural frequencies of wind turbine are key parameters in dynamic analyses of the offshore wind turbine. However, the effects of scour on the stiffness of wide shallow bucket foundation and the natural frequencies of offshore wind turbine are not studied sufficiently. Numerical models of the wind turbine considering bucket-soil-interaction by using finite element method are established. The influences of scouring depth on static stiffness of wide shallow bucket foundation and the first order natural frequency of wind turbine are analyzed. The results show that scouring depth has a more distinct impact on rocking static stiffness than horizontal stiffness. Due to the large rocking and horizontal stiffness of wide shallow bucket foundation, scouring has little influence on the 1st natural frequency of the offshore wind turbine.
Due to the growing demand of resources, offshore wind turbine (OWT) developed rapidly in the past several decades for its advantages of clean and high efficiency to produce power. A series of policies have been established by Chinese government to encourage further developments of offshore wind energy in the coast of China. However, the cost of offshore wind turbine is still high especially in construction of foundation. Generally, the cost of the foundation accounts for nearly 30% of total costs (Thornley et al., 2009; Arshad and Kelly, 2013). Accordingly, optimizations of the foundation have raised concerns related to offshore wind farm investment (Wang et al., 2017). There are several typical types of the fixed foundations for offshore wind turbine including monopile, gravity base, suction bucket and jacket structures (Bhattacharya, 2014). Suction bucket has become better alternatives to driven piles because of technical challenges and costs associated with the installation equipment, the process of installation of suction buckets involve little noises and are friendly to environments. Besides, suction buckets also provide a greater resistance to lateral loads than driven piles because of the larger diameters typically used. In this background, wide-shallow composite bucket foundation (WSCBF) has been proposed and successfully examined (Lian et al., 2012; Liu et al., 2015; Zhang et al., 2016) (Fig.1). In fact, a fully operational wind turbine equipped with WSCBF was successfully applied in city of Xiangshui in Jiangsu Province, China.