Mechanical Response Of Multi-pile Offshore Wind Turbine Under Environmental Load

As a kind of renewable energy,wind energy resources have become the key global new energy development object.It is of great significance to study the structural characteristics of offshore wind turbines applicable to the middle and deep sea areas.The previous research on the dynamical properties of the offshore wind turbine structure mostly concentrated on the basic structure of wind turbine,which did not have an adequate study on the overall structural characteristics.In this paper,the overall structure of six-pile offshore wind turbine will be taken as the research object;and dynamical response of the offshore wind turbine overall structure under marine environmental loads will be analyzed under the consideration of pile-soil interaction.This research aims to provide support for developing and taking advantage of offshore wind energy resources.The specific work is done as follows:Firstly,the computing theory and method of the overall offshore wind turbines' structure subjected to sea winds,ocean currents and wave loads in a complex marine environment will be elaborated.And three working conditions of the structure under different load combinations can be determined according to the load combination principle.Subsequently,the interaction between pile foundation below the seabed mud surface and soil around the pile foundation will be classified and discussed from the aspects of action mechanism,boundary conditions,computational solution.Secondly,five types of simulation units will be selected by using ANSYS finite element software,particularly using BEAM188 to simulate variable diameter and variable cross-section components,and using COMBIN39 to simulate pile-soil interaction.Combined with the APDL command flow programming language,two different finite element analysis models will be established for the overall structure of the six-pile offshore wind turbines.In addition,the dynamical properties of the offshore wind turbine structurewill be analyzed based on the six-fold pile diameter method constrainingthe fan pile foundation.And then,the effect of each load on the overall structure of the offshore wind turbine will be obtained by applying different loads to the fan structure.Moreover,the quasi-static analysis of the overall structure of offshore wind turbines under different environmental load combinations will be conducted to obtain the results of static response of the overall structure of the six-pile offshore wind turbines for strength verification.Based on the results of structural modal analysis,it can also be judged whether the natural vibration frequency of the fan's overall structure has a resonance effect on the external excitation frequency.As a result of the transient dynamics analysis,the change regularity of structural nodes displacement and element stress with wave cycle can be concluded.Finally,the dynamical response of the offshore wind turbine structure under marine environmental loads will be analyzed by using the soil-spring method to simulate pile-soil interaction.In addition,its results will be compared with the six-fold pile diameter method.The mainly factor for the discrepancy will be that the two methods have different constraints on the pile foundation below the seabed mud surface.Furthermore,the soil-spring method will be more in line with the pile-soil interaction relationship,and can better reflect the actual stress of the foundation structure below the seafloor mud surface.