Simulation And Research On The Propagation Mechanism Of Electromagnetiom Ultrasonic Guided Waves In Pipeline

The pipeline takes an important role in the oil industry, chemical industry, thermoelectricity, water supply industry and so on. The security of pipeline relates to national economy, ecological environment and other aspects, therefore, the non-destructive inspection technologies of pipeline have been focused on all the time. Supersonic guided waves examination technology is one of the non-destructive inspection technologies. Compared with the traditional technologies, it has no demand of the coupling medium and the surround peeling, far propagation distance, a quick speed and other merits. Because of theses merits, the non-destructive inspection was extended to the high temperature and high-speed online examination. The supersonic guided waves technology is one of important methods in long distance pipeline flaw examination detected by electromagnetism supersonic examination.This article does a further research on the electromagnetism ultrasonic theory, theoretically it inferred three physical fields-the electromagnetic field, mechanical field and supersonic wave field that involved by working process of the electromagnetism ultrasonic transducer. EMAT was simulated by using finite element simulation software ANSYS. EMAT has been divided into three switching processes according to the process of theory inferential reasoning-the high-frequency coil has response of eddy of same frequency in the test sample surface, it was influenced by Lorentz force in the biased magnetic field produced by the permanent magnet, under the Lorentz force, the test sample's interior produced the mechanical vibrations and disseminated in the medium and formed the ultrasonic wave, and formed the guided waves while disseminating in the wave guide. To make a further study of guided wave's dissemination characteristic in pipeline, this article did a further research of the elastic dynamic theory and had a conclusion that the guided waves have the multimode and frequency dispersion characteristic in the spreading process. Introduced finite element method in research supersonic guided waves dissemination question validity, and dissemination in pipeline has conducted the simulation to the longitudinal guided waves L (0,1) modality and L(0,2) modality using finite element software ANSYS/LS-DYNA.Through the schematic drawing of the dissemination of guided waves, the decay and frequency dispersion phenomenon had been directly reflected when the guided waves spread, Wave velocity calculated by the receiving time of the echo signal matched well with frequency dispersion curves. Through watching the node's shifting time course curve, the characteristics of frequency dispersion and attenuation of guided waves were explained by the data and graph again.