Study On Magnetostrictive Torsional Wave Excitation Model And Its Influence Factors

As the main transportation way of oil and gas,pipeline plays an important role in production and transportation.Under the long-term use and the special environment,pipeline will product many kinds of defects which is the main problem in oil,gas and petrochemical industry.With the rapid development of the national economy,the number of pipeline to be used will also increase,and the corresponding service safety status and service life prediction of the pipeline is also in urgent need of strengthening,which is in order to ensure the normal production operation.Therefore,how to quickly and accurately achieve the detection of pipeline status in service,as the current non-destructive testing of the primary task.This dissertation was supported by the National Natural Science Foundation of China(No.51675258,51075372),National key R & D program(No.2016YFF0203000),the Science and Technology Project of Jiangxi Provincial Education Department(No.GJJ150699)and the Key Laboratory of Digital Signal and Image Processing of Guangdong Province(2014GDDSIPL-01).The use of magnetostrictive torsional mode guided wave sensor for non-contact and non-destructive testing.The propagation characteristics of the torsional mode guided waves are not affected by the presence of the liquid in the duct,and the modal is non-dispersive at all frequencies.This type of sensor can achieve a single point of detection,and the resulting wave propagation distance,fast.However,the low signal-to-noise ratio of the detection signal is the main drawback of the magnetostrictive ultrasonic guided wave detection.Therefore,it is very important to study the excitation of the magnetostrictive torsional guided wave and its influencing factors under the force-magnetic coupling The In this paper,we study the magnetostrictive torsion mode guided wave sensor by combining the simulation theory and the experimental study.First of all,the basic theory of magnetostrictive guided wave detection technology is described in detail.Introduces the basic characteristics of the magnetostrictive effect of ferromagnetic materials and the guided wave detection system mechanism are described in detail,and then giving torsional guided wave dispersion equation according to the guided wave characteristics of multi-mode and dispersion.At the same time,proposing the nonlinear model of multi-field coupling combined with the literature.Secondly,the detection principle and the structure of the magnetostrictive torsional mode guided waves are introduced,and including the propagation of torsional waves in the circular tube and the control equations of the excitation process of the torsional mode guided waves.The three-dimensional force magnetic coupling numerical simulation model of the torsional mode guided wave sensor is established by the finite element software COMSOL,and the magnetic field distribution inside the pipeline is obtained by loading and solution.On this basis,the displacement analysis of the magnetostrictive force on a particle where is internal the pipeline and near the magnetic field,and the characteristics of guided wave which is encouraged by the numerical model are analyzed by means of the law of the particles in the circumferential and axial vibration,and compared with the propagation characteristics of torsional mode guided waves in ferromagnetic materials.The results show that the direction of bias and dynamic resultant magnetic field is single in terms of the ferromagnetic pipeline,and the magnetostrictive effect dominates.According to the simulation results,it is concluded that the guided waves generated by the proposed model are consistent with the propagation characteristics of the torsional mode guided waves in ferromagnetic materials,that is to say,the circumferential vibration is the main one,the generated wave propagates along the axial direction of the pipeline and perpendicular to the direction of particle vibration.The simulation results show that the strain produced by force-magnetic-sound multi field coupling can be obtained,can truly reflect the torsional mode of magnetostrictive guided waves,It provides the basis for further research on the influence factors of guided waves and the guided waves enhancement.Thirdly,an experimental platform is built for the magnetostrictive torsional mode guided wave detection system,By calculating the velocity of the guided wave and comparing with the theoretical wave velocity,Thus determined the guided wave mode is torsional wave.Be aimed at the simulation model for the excitation of torsional waves in ferromagnetic pipelines is established under the influence of circumferential bias magnetic field,from the three aspects of excitation signal frequency current intensity and periodic analyzed the influence of magnetostrictive actuator sensor on the pipeline particle vibration displacement.In order to verify the validity of the simulation results,experiments were carried out under different influence factors,and the experimental waveforms are analyzed.The results show that the excitation signal with the change of condition,peak particle vibration amplitude and echo were changed,and the optimal excitation conditions can be selected,the change trend is consistent between the simulation results and experimental results,so the simulation model can be used as the reference study on magnetostrictive guided wave excitation detection.Finally,the structure of the magnetostrictive torsion mode guided waveguide sensor is optimized,and the ultrasonic inspection of the pipeline is carried out by using the cross-coil magnetostrictive torsional waveguide structure.Firstly,the influence and effect of bias magnetic field on magnetostrictive guided wave sensor are introduced.Secondly,the principle and characteristics of the cross-coil excitation sensor are introduced.The numerical simulation shows that the cross-coil magnetostrictive sensor can effectively stimulate the torsional wave and prove that the direction of the synthetic magnetic field intensity vector in the pipeline is affected by the amplitude of the vibration.The results show that there is always an optimal direction in the different materials to make the vibration amplitude of the particles the best.The results show that the excitation energy of the cross coil sensor can be used to generate the torsional wave,and the simulation results are verified by experiments,and the two are in good agreement with each other.Therefore,the magnetostrictive sensor of the cross-coil technology is a useful and effective tool for pipeline inspection.Under the experimental conditions,when the dynamic magnetic field strength is constant,the magnetic field strength of the bias coil is obtained When the vector direction is close to a certain optimal direction,the amplitude of the guided wave is the best,which is helpful to enhance the signal-to-noise ratio and the sensitivity to the defect.