| Offshore wind energy accounts for the largest proportion in the generalized Marine renewable Energy structure,and under the guidance of the”Maritime Power”and”One Belt,One Road”,which are national top-level strategies and the marine economic development policies of various coastal economic provinces,it has ushered in the golden age of barbaric development.However,Chinese current offshore wind turbines are mainly built in the nearshore shallow waters within the depth of fifty meters,and with the improvement of the wind turbines' rated power,the diameter of upper blades has been breakthrough one hundred meters,thus they need strong and reliable support of the bottom structure.At present,the support of the offshore wind turbines are mainly various types of pile foundations.The intense ocean dynamic loads made the cost of the foundations' design,construction and installation account for more than half of the entire cost,so it is of great engineering significance to analyze the structural response to the static and dynamic characteristics of the offshore wind turbines subjected to marine environmental dynamic loads.At present,the main dynamic loads of marine environment on the pile foundations of offshore wind turbine with current sizes and in the current depth of water environment is wave load,especially those kinds of strong nonlinear wave loads produced by the extreme wave are more important.In this paper,a special kind of extreme random wave named freak wave is selected as the marine environmental load on the offshore wind turbines firstly,and according to actual engineering hydrologicl datas in the engineering background of the offshore wind farm project in Rudong County,Jiangsu Province,the wave parameters are identified.With the secondary development function of the Fluent software,the numerical wave flume used to simulate the freak wave is established,and then it is respectively used to simulate the wave load produced by freak wave on two kinds of offshore wind turbines' foundations commonly used in projects,which are single-pile foundations and three-pile foundations.By comparing the numerical test results and the calculation results of Morison equation,the accuracy and reliability of Fluent in simulating the freak wave and its effect on the offshore wind turbines' foundations are verified.Then according to the actual geological datas and based on the relationship between the deflection of offshore wind turbines and the resistance of foundation soil,the pile-soil interaction was simulated by p-y curve method.Based on the ANSYS Workbench platform,the generalized three-dimensional finite element models of the offshore wind turbines' foundations are established,and the fluid-soild coupling analysis of Fluent+ANSYS APDL is realized,the static strength and dynamic response analyses of single-pile foundation and three-pile foundation subjected to freak wave are carried out respectively.The combined effects of wind load,transfer load of superstructure and the freak wave load are considered comprehensively in static strength analysis.In order to highlight the difference between freak wave action and regular wave action,regardless of the additional effects of wind load and transfer load of superstructure,the transient dynamic analysis only considering the freak wave action is carried out,and the results are compared with those only considering the regular wave action.The results show that the responses of two kinds of pile foundation structures subjected to freak wave are similar in two respects.One is that the maximum displacement of the structure occurs at the flange plate,in which the upper and lower structures of the wind turbine connect,while the maximum stress of the structure occurs at the mud surface where the pile foundation and the seabed meet.Compared with the regular wave action,the response curves of two kinds of pile foundations show strong nonlinearity.Secondly,the structural response of two kinds of pile foundation structures under the action of a freak wave alone is much higher than that under the action of regular waves of the same scale.There are three main different respects between the structural responses of two kinds of pile foundation structures.One is that the performance of single pile foundation resisting low-frequency wave load is better from the modal analysis;Secondly,regardless of the additional effects caused by the interaction of other loads,the structural response of three-pile foundation structure is smaller than that of single-pile foundation under the action of freak wave alone.Thirdly,the structural response of three-pile foundation is smaller than that of single-pile foundation under various working conditions,which shows that the safety and stability of three-pile foundation are better while resisting the freak wave action.In this paper,aimed at two common types of pile foundation structures for offshore wind turbines,a three-dimensional finite element fluid-solid coupling generalized model of offshore wind turbines' foundation is established by use of Fluent platform and ANSYS Workbench platform.By means of numerical simulation analysis,the extreme wave force of freak waves on offshore wind turbines' pile foundations and their structural static and dynamic response characteristics are analyzed and studied.The research and results of this paper have important scientific reference significance and engineering practical significance for the design of offshore wind turbines' foundations and ensuring the safety and stability of the foundation structures during the operation and maintenance of wind farms. |
PDF Full Text Request