Fatigue Analysis Of Step Type Wind Generator Foundation In Land

In the past decades,with the rapid development of large-scale wind generator,the number of newly installed wind generators had been increasing steadily.It provides considerable power generation.However,our country’s economy also suffers great losses due to the shutdown or repair caused by some minor faults and collapse of foundation caused by major accidents.As an important guarantee of the upper unit,the wind generator foundation not only provides the carrying capacity,but also provides enough anti-overtuning capacity.Therefore,once the foundation has weakness parts,long-term operation will cause great damage to the foundation itself.As a result,the main structure has a greater risk of collapse.In this paper,modal analysis,static analysis and dynamic analysis are carried out for the foundation of wind generator.The weakness parts of the foundation are determined,the failure form of the foundation is understood and the fatigue life of the foundation is predicted.The main research contents and results are as follows.Firstly,the finite element model of 3MW onshore wind generator is established and its modal analysis is carried out.After understanding the relevant concepts and properties of wind,based on the harmony superposition method,MATLAB software was used to simulate the pulsation wind speed.And use the time history of wind load obtained to analyze the foundation dynamic performance.Secondly,the concrete foundation of wind generator is studied.12 most unfavorable load combinations for each group are carried out by static analysis method in three working conditions.Representative results are selected for specific analysis to obtain the weakness parts and possible failure forms of the foundation.The relevant mechanical parameters and damage degree of the weakness parts are obtained by dynamic analysis method,which input two kinds of fatigue loads.To strengthen the weakness parts in foundation,some measures are taken to improve the strength grade of concrete in the weakness parts.The effectiveness of the improved method is validated by research.Finally,based on rain flow counting method,the concrete stress time history of wind generator foundation after dynamic action is extracted,and the stress time history is counted to obtain the hot spot stress result.Combined with S-N curve and fatigue cumulative damage principle,fatigue life of foundation concrete is predicted.The research shows that the wind generator is subjected to downwind force in operation,which exerts a drawing force on the foundation.The foundation failure is mainly caused by the stress concentration at the lower flange near the foundation ring,which leads to serious tensile damage of concrete.For the fatigue load of concrete,the results of the two forms of fatigue load show that high stress has a greater impact on the damage caused by fatigue load.By using the concrete with higher strength grade to improve the concrete in the weakness parts near the foundation ring,the tensile performance and fatigue life of static and dynamic loads are greatly improved.The concrete life N under three sets of dynamic loads was 147,282 and 6250.The concrete with higher strength grade in the weakness parts is 21 times higher than the original grade.