| In recent years,the wind power industry is growing rapidly in China,and embedded-ring foundations are widely used in onshore power industry for its convenience in construction and great adaptability.However,the dynamic response characteristics and fatigue damage rules of embedded-ring foundations aren’t clear.Outflow-mortar phenomena are observed in part of foundations due to fatigue damage during service period,even lead to unit shutdown.Therefore,with the help of numerical simulation method,the dynamic response and fatigue damage characteristics of embedded-ring foundations are analyzed in this paper.The grouting reinforcement effect of outflow-mortar foundations is studied.The primary research contents and results are as follows:（1）Dynamic response characteristics of embedded-ring foundations under rated wind speed.Based on Abaqus software platform,an integrated finite element model of wind impeller-tower-foundation-soil is established.The concrete damaged plasticity model is introduced to simulate the cracking characteristics of concrete.The surface-to-surface contact model is introduced to simulate the contact behavior between concrete and embedded ring.Turb Sim software is used to simulate wind speed time history,and wind load of impeller is obtained by the thrust coefficient method.The dynamic response characteristics of foundation under rated wind speed is analyzed.Analysis results show that the stress of perforated rebars in the prevailing wind direction is much higher than that in other areas;At the initial stage of load action,the dynamic effect of the structure is obvious.Concrete cracks expand rapidly in prevailing wind direction,then the cracked areas remain stable.The tensile cracks are located near the upper row perforated and the bottom flange of embedded-ring,and there are no cracks in the orthogonal direction of prevailing wind direction.（2）Dynamic response characteristics of embedded-ring foundations under gust condition.Gust wind speed time history is obtained through the extreme operating gust model,and gust load is obtained by the thrust coefficient method.The dynamic response characteristics of foundations under the 50-year return of gust is analyzed,and the influence of gust duration is studied.Analysis results show that the concrete inside embedded ring is almost broken under extreme operating gusts,and local instability may occur;The detachment rate of foundations is obviously higher than theoretical result;Short-period gust may be more destructive.In order to control the gust load,reasonable pitch control strategies should be adopted,and partial load factors should be considered in gust conditions.（3）Fatigue analysis and fatigue life assessment of embedded-ring foundations.A set of time-domain-based fatigue life assessment process is designed for embedded-ring foundations.The S-N curve of steel and concrete is determined,the fatigue damage rules and mechanisms of embedded-ring foundations are analyzed,and the fatigue life of hot spot is assessed.Analysis results show that high cycle fatigue mode appears in the steels of the foundations,low cycle fatigue mode appears in concrete.The contribution of wind speed condition varies greatly for hot spot fatigue damage;The hot spot fatigue damage of perforated rebars in prevailing wind direction is most serious,and fatigue fracture maybe occur during term service period.It is suggested that fatigue design and test of upper perforated rebars in wind turbine foundation design.（4）Dynamic response characteristics and grouting reinforcement method of outflow-mortar foundations.The damage zones of foundation concrete are determined by measured data,and the safety indexes of foundation are defined.The dynamic response characteristics of outflow-mortar foundations are analyzed,and the influence of grouting material’s elastic modulus is discussed.Analysis results show that the safety indexes of outflow-mortar foundations are obviously deteriorated,and the dynamic response of the tower top doesn’t meet standard requirements;The grouting reinforcement effect increases when grouting material’s elastic modulus is larger,and the safety indexes of outflow-mortar foundations are close to healthy foundations after reinforcement.However,the safety indexes of foundation can’t be further promoted by improving grouting material’s elastic modulus,and it is suggested that elastic modulus of chemical grouting materials should be greater than 3 GPa in the project. |
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