Research Of The Characteristics Of Acoustical Response Induced By Eddy Current In Matal Tube

As one of the five transportations,pipeline has the advantages over transportation of low cost,less energy consumption,long distance all-weather continuous transmission etc.In the long-term work,however,it's easy for pipeline to product stress corrosion cracking influenced by the working environment and transport material scouring and corrosion,so carrying out the research of pipeline crack detection method is very urgent and important.Using COMSOL Multiphysics simulation software,this paper carried out the simulation of the pipeline EMAT in circumferential and axial direction and studies the characteristic of detection.The main research content is as follows:1)Based on the research on the working mechanism of the EMAT,this paper establishes the finite element model of pipeline circumferential surface wave based on the Lorentz force mechanism,implements electromagnetic field coupling force field in the EMAT,the whole process of sound field.On this basis,the paper observes the effect on signal amplitude made by the exciting current amplitude,static magnetic field intensity,lift-off distance and the size of the coil,which lay the groundwork for pipeline EMAT optimization design.At the same time,the paper studies the response characteristics of circumferential surface wave to crack defects,and analyzes signal characteristics in influence of the crack depth,the buried depth.2)Based on the dispersion equation of pipeline circumferential Lamb,the paper analyzes the circumferential mode and dispersion properties of Lamb.Based on the frequency-selection characteristic of inflexion coil,the paper determines the parameters of the circumferential Lamb ultrasonic transducer,and builds the model of the two-dimensional circumferential Lamb.The paper analyzes the eddy current effect of circumferential Lamb transducer and the results of magnetic field and sound field.By the application of finite element method,the paper gets the propagation characteristics of structure of circumferential Lamb wave.Detection feature of cLamb0 mode is studied in defect,at the same time the paper analyzes how the clamb0 mode effects the reflection and transmission and the mode conversion coefficient.3)Aiming at 3D model of pipeline has some problems such as longer computing time and low accuracy of calculation.Based on the analysis stress-strain relationship of L guided wave and geometric symmetry structure,this paper establishes a two-dimensional ax symmetric L guided wave simulation model of electromagnetic ultrasonic transducer.This paper verifies the correctness of the L guided wave form three aspects: the group velocity of wave model,vibration modes of wave and the curve of the structure of wave.On this basis,L guided wave is studied on the response characteristics of axisymmetric defects and analyzes the influence of different defect depth on the reflection and transmission coefficients.