Defect Evaluation In A Pipe Based On Poincare Section Sudden Changes

Ultrasonic guided wave detection technology is very suitable for long-distance pipeline detection because of its advantages of long detection distance and wide range.However,in the process of ultrasonic guided wave propagation,there are some phenomena such as dispersion,attenuation,mode conversion and so on.Combined with the influence of environmental noise,when detecting small defects,because the defect echo is very weak,it is very likely to be submerged in the noise,resulting in the risk of missing detection.In order to improve the detection sensitivity of small defects,based on the parameter sensitivity and noise immunity of chaotic system,a weak guided wave signal detection method based on Poincare section mutation characteristics is proposed.Firstly,the period doubling evolution process and anti-noise ability of Duffing system are analyzed,which provides a theoretical basis for the construction of detection system.;Then,by analyzing the bifurcation diagram and Poincare section,the chaotic threshold is quickly obtained,and the detection system is constructed;Further,the influence of noise on Poincare section is analyzed.Finally,we carried out the experimental study of small defects in pipeline.The echo signal of small defect is intercepted and input into the detection model.Through the mutation characteristics of Poincare section,the small defect recognition is successfully identified.In order to locate and evaluate defects,a fast dichotomy method is proposed in this paper.Based on the intermittent chaos characteristics,the cell space is constructed on the Poincare section,and the number of cells occupied by the phase points on the Poincare section is calculated,which is defined as the damage index.Experiments show that the damage index has a simple linear relationship with the damage degree in a certain range.In order to identify the size of defects more accurately,a weak guided wave amplitude detection method based on Poincare section mutation characteristics is proposed.The influence of the number of cycles on the detection results is discussed in detail,and the theoretical derivation is verified by numerical simulation.The results show that when the guided wave period number n ≤30,the amplitude identification result is A;when the guided wave period number n＞150,the amplitude identification result is 2A,where A is the amplitude of the guided wave signal.Finally,the amplitude of the ultrasonic guided wave in the pipeline with defects is detected,and the reflection coefficient is constructed.The results show that the reflection coefficient measured by the experiment has a high corresponding accuracy with the theoretical value,which indicates that the defect quantitative evaluation method based on the reflection coefficient has a high detection accuracy.Since the method is applicable to the detection of defects in any waveguide structure with vertical incidence of ultrasonic guided waves,it is highly universal and has certain engineering application value.