Method For Identifying Transverse Gap Cracks Of Wind Turbine Blades Based On Modal Parameters

In recent years,as the global ecological environment is facing more and more serious damage,countries have begun to strongly advocate the use of green and clean energy.With the continuous development of the wind power industry,the problem of wind turbine failure will also follow.Turbine blades are key components of wind turbines and are expensive and expensive to manufacture.During the operation of the blade,the blade is in a harsh environment and the working conditions are complex.Due to the cyclic loading for a long time,the material will degenerate and fatigue and cracks will germinate;if not repaired in time,the cracks will rapidly expand and cause rotational imbalance,which may cause rotation imbalance.The collapse of the entire tower caused a major safety accident.Therefore,this paper takes 2WM wind turbine blades as the research object,and aims at Diagnosis of the cracks in the blade transverse gap through a combination of theoretical derivation and finite element analysis,and corresponding experimental research methods.Relevant research and experimental analysis have been performed on the diagnosis methods of the location and extent of single cracks and the location and extent of multiple cracks in the blade structure.The main research conclusions are as follows:1.Establish a 3-D finite element model of the blade,and perform modal analysis on it to study the effect of crack location and degree on the natural frequency of the blade.The natural frequency of the blade decreases as the degree of crack increases and at the same time as the distance of the crack from the root of the blade The farther,the natural frequency decreases;by comparing the effect of crack position and degree on natural frequency,it is found that the effect of crack position on natural frequency is the largest.2.The cracks will influence in the natural frequency of the blade.The natural frequency variation between the cracked blade and the intact blade is concerned.Taking the ratio of the adjacent two-order natural frequency variation,it is found that the ratio is only related to the crack position.Based on the ratio parameters,the blade is fictitiously divided into multiple connected regions.Implant the crack at each joint point of regions to establish the database of the ratio parameters for crack locating.Combining the database,the crack position criteria are proposed.The region where crack exists in can be ascertained.Then,a position parameter in the region is proposed,and the mapping between this parameter and the specific position within the region is established.The crack can be located more accurately in the region.The numerical simulation analysis of the blade model verifies the effectiveness of the method and the high positioning accuracy.The relevant crack localization test was carried out through a cantilever hollow tube.The test results verify the effectiveness of the single crack localization method and the localization accuracy is also high.3.A parameter of crack degree is proposed,that is,the ratio of the variation of the natural frequency to the natural frequency itself.For the same position,the correspondence between the parameter and the degree of crack is established.After crack locating,the degree of crack can be ascertained by the correspondence.The numerical simulation analysis of the blade model verifies the effectiveness of the method,and the recognition accuracy is high.The relevant crack degree recognition test was carried out through a cantilever hollow pipe.The test results verified the validity of the single crack degree recognition method,and the degree recognition accuracy was also high.4.Based on the natural frequency of the beam structure,a multi-crack diagnosis method is proposed.This method combines the sensitivity square matrix method with the element subdivision method.First,when the natural frequency order of the selected structure is equal to the number of elements divided by the beam,the sensitivity square matrix of the beam is determined.Next,combining the measured natural frequencies,solving the sensitivity square matrix equation to determine the cracked element,and the element subdivision method is used to reduce the crack area.Then,the other element elements are set to 0 to obtain the natural frequency parameter when there is only one crack.In this way,the multi-crack problem is transformed into multiple unrelated single-crack problems,and the natural frequency parameters of multiple groups of single-crack beams can be obtained in turn.Finally,according to the method of single crack localization and degree identification of beam structures,further locate the cracks in the single crack element,identify the degree of cracks,and finally realize the diagnosis of multiple cracks.Numerical simulation analysis and experiments verify the validity of the multi-crack diagnosis of the beam with good accuracy,which provides a strong basis for practical engineering applications.