Hydroelastic Analysis Of The Floating Structure For The Very Large Offshore Wind Farm

It is well known that the 21th century is the time of developing the oceanic resources and the wind energy is the cleaner one among all kinds of energy. Nowadays most of the wind power generations are of pile foundation and locate offshore. With the quick pace of wind power generation in the ocean, the very large offshore floating wind farm is inevitable to be developed in the future. The development process of wind power from coastal waters to high ocean will definitely lead to a fatal technology reform. An apparent work that needs to be done is to redesign the upholding platform of wind mill.Since the very large offshore floating wind farm belongs to the very large floating structures, the deformation of the platform resulted from the waves should be considered, namely fluid-structure interaction. Therefore, the hydroelastic theories derived in the past five decades are adopted to solve the problem. At present, the methods of hydroelastic research mainly cover two means, the direct calculation method and the mode analysis method. In this dissertation, the latter is used. The floating structures are simplified as beams, and the dry mode in the air is figured while the potential flow theory is employed to solve the hydrodynamic issue. Based on the different boundary condition between the three dimensional hydroelastic theory and three dimensional potential flow theory, the three-dimensional hydroelastic theory is devolved into three-dimensional rigid theory by changing the boundary condition of the object surface. In this way, the hydroelastic response of structures in the waves could be solved quickly and effectively and the engineering practicability of this simplification method is discussed afterwards.Firstly, the theory of structural dynamics is introduced to find a proper quick method, which could solve the dry mode of the structures. With abundant relative research experience, the structure attributes of large beam-form structures could be obtained with simple analytic solutions of beams.Secondly, a particular description of the mature three-dimensional rigid potential flow theory and the three-dimensional linear hydroelastic theory considering the effect of the structural elastic deformation is given, and the difference between the two theories is approached. And the difference is mainly focused on the ways of dealing with the boundary condition of the object surface. The hydroelastic theory need take the generalized fluid-structure interaction boundary condition into consideration. By changing the boundary condition of the object surface and modifying the motion response functions, the three-dimensional hydroelastic theory becomes three-dimensional rigid theory. Hereby, the principal coordinate is obtained and the elastic modal amplitudes of all orders are expressed with the rigid displacement amplitude.Moreover, the ideal design form of the offshore wind power farm platform is brought forward. Then the calculation of hydroelastic and rigid theory is proposed. Many results are approached, such as the response transfer function of the rigid body, the vertical bending mode response amplitude of the structure and the vertical displacement amplitude distribution and bending distribution of the whole structure in axial direction. By contrasting the bending distribution plot of three-dimensional rigid body and hydroelasticity theory, it is proved that the three-dimensional hydroelastic simplification method proposed in this paper could satisfy the actual engineering need.Lastly, the loads obtained by the two different wave theories are imposed to the structure to carry out the static analysis. Some results, such as the vertical displacement and axial stress are contrasted, seeking for the similarities and differences of the three-dimensional rigid body method and three-dimensional hydroelastic simplification method in this paper.