Natural Vibration Characteristic Analysis Of Triple-piles Based Offshore Wind Power Structure

Compared to onshore wind power structure, the blades of offshore wind power structure are larger diameter, the tower is higher, the corresponding flexibility also has increased significantly; the basis structure of offshore wind power structure is more complex, and the sea-bed is soft ground, the bearing capacity is low; except for the effects of wind load, there is also wave load, current load, sea ice load and other marine environmental loads on the offshore wind power structure, these loads have added structural vibration source. This has put forward higher requirements for vibration resistance of offshore wind power structure. Offshore wind power structures are often rigid and flexible basis, the fundamental frequencies of the structural system is severely restricted, that must be between blade speed (IP) and3times the speed (3P). In addition, the natural frequency corresponding to the low order modes of structure need to maintain adequate staggered with the frequency of the waves, currents and sea ice and other marine environmental loads. In order to avoid structure resonance and ensure that the normal operation of offshore wind power overall structure, it will be a very meaningful that has researched the natural vibration characteristic of offshore wind power overall structure, and got the natural frequencies and mode shapes of offshore wind power overall structure. In this paper, the large-scale offshore wind power overall structure has been simulated by the ANSYS finite element software, and has analyzed the natural vibration characteristics of offshore wind power overall structure, and some factors that would affect the natural vibration characteristics of offshore wind power overall structure.Firstly, there were five finite element models of offshore wind power structure that was established by ANSYS software in the paper:basis model, basis-tower model, blade-hub-nacelle model, blade-hub-nacelle-tower model, basis-tower-nacelle-hub-blade model. The modal analysis results of five models were analyzed and compared. The results showed that the finite element model of offshore wind power structure could not be over-simplified, the low order modes of offshore wind power overall structure were mainly in the tower and blades.Secondly, the basic principle of m method and the calculation method of the P-y curve was introduced in the paper. This paper has investigated the impact on the natural vibration characteristic of the triple-piles based offshore wind power overall structure that the soil-structure interaction had by m method. The paper has used P-y curve to study the impact on the natural vibration characteristic of the offshore wind power overall structure that the mechanical properties of the soil has changed. The results showed that the consideration of soil-structure interaction could reduce the natural frequencies of offshore wind power overall structure on some extent, but it has a great influence on the basis’ local vibration of offshore wind power structure that the mechanical properties of the soil has changed.Then, the paper has researched the natural vibration characteristic of offshore wind power overall structure when the blades have iced in winter. There are two forms of blade icing:the glaze and the rime, their formation mechanism and characteristics were introduced respectively. The blades icing condition was set into three conditions, these conditions were analyzed and compared with no icing condition. The results showed that the blade icing could reduce the natural frequencies of offshore wind power overall structure.Finally, the resonance theory was introduced in the paper, combined with a practical project, the vibration source of offshore wind power overall structure was analyzed, the resonance analysis of the triple-piles based offshore wind power overall structure was carried out. The results showed that the various vibration source did not lead to resonance of offshore wind power overall structure.