Vibration Analysis And Damage Detection Of Rotating Tapered Beams

Rotating mechanical structures are widely used in aerospace engineering such as helicopter rotor blades,turbine blades.These mechanical structures are prone to failure due to the harsh working environment.Therefore,it is necessary to study the damage detection of mechanical structures.The method of structural damage detection based on vibration has the advantages of non-destructiveness,globality,high efficiency and real-time online monitoring.The analysis of dynamic characteristics of the structure is the precondition for damage identification.This paper first summarizes the domestic and international research status of the analysis for the vibration characteristics of rotating beams,and mainly introduces several methods including assumption mode method,power series solution method,Adomian modified decomposition method,dynamic stiffness method,the research status and development trend of vibration-based damage detection.Several types of the methods are mainly reviewed,including natural frequency-based method,moving mass method,mode shape-based method,neural network-based method.Secondly,the natural vibration characteristics of rotating beams are analyzed by the dynamic stiffness method,and the effects of the rotation speed,the offset length and the taper ratios on the natural frequencies and mode shapes are considered.Lumped crack model of rotating cracked beams is established.The natural vibration characteristics of rotating beams is studied when crack damage occurs.The joint effect of crack damage and rotation speed on vibration characteristics is emphatically expounded.The results show that the natural frequency of the rotating beam decreases due to crack damage.When the crack is located near the fixed end of the beam,the natural frequency decays the most.The crack damage degree and rotation speed does not independently affect the vibration characteristics of the beam,there is a coupling effect.Afterwards,the method of curvature mode and flexibility curvature were used to identify the crack damage.Two kinds of detection indexes(curvature mode difference and flexibility difference curvature)are introduced.The sensitivity of each damage index to crack position and depth is analyzed and compared.And the effect of rotating speed on damage detection is also considered.The results show that both the curvaturemode difference index and the flexibility difference curvature index are very sensitive to crack damage,and all of them have great damage recognition ability,and they are also effective for multi-crack damage.Finally,a moving mass-crack beam model is established.The natural frequency curve is calculated by the moving mass method and the fractal dimension curves(HFD,KFD)are obtained combining with Higuchi and Katz's fractal dimension theories.The sensitivity of the curve to the location and depth of the crack,the effect of the moving mass are discussed.And the effect of rotating speed to crack detection is also considered.The results show that the HFD and KFD curves of the natural frequency curve can effectively detect the location of the damage,and they are very sensitive to the degree of damage.They also has certain validity for the identification of multi-crack damage.