| Transportation pipelines have excellent characteristics such as safety and stability,and are widely used in various industries such as construction,HVAC,municipal,and marine industries.They have become one of the five major transportation methods.In actual use,the pipeline structure will be damaged by external force,self-aging,environmental corrosion and other influences,which can easily cause safety problems and property losses.Therefore,how to conduct convenient and efficient inspections for transportation pipelines to ensure industrial The safety and reliability of pipelines and urban pipe networks are particularly necessary.Ultrasonic guided wave nondestructive testing technology has broad application prospects in the field of pipeline structure nondestructive testing due to its fast,efficient and safe characteristics.In this paper,by analyzing the propagation law of guided waves in the pipeline,the damage location and imaging of the circumferential defects of the straight pipe structure are carried out.Firstly,based on the hollow cylindrical guided wave theory,introduce the related concepts of guided waves and the phenomenon of guided wave attenuation,derive the guided wave dispersion equation of the pipe section structure,and draw the dispersion curve;solve the longitudinal mode,flexural mode and torsion of the guided wave in the pipe section structure The characteristics of the modal;draw the radial displacement distribution of the guided wave to show which mode of guided wave is the most efficient when determining the defect type;introduce the ultrasonic guided wave detection and time reversal method in the pipe section structure The basic principle.Secondly,based on ANSYS software,a finite element model of the pipe section was established,explaining the element type and the principle of grid division,explaining the basis for determining the time step,and comparing and selecting the number of excitation signal cycles that are most sensitive to pipe section damage identification.Third,the guided wave propagation process in the pipeline is simulated by ANSYS software,and the guided wave propagation velocity is calculated;the circumferential damage is set on the pipeline model,combined with Hilbert transform and other methods,and the defect location is located on the axis to improve the accuracy of damage signal identification;Change the size of the damage circumferential angle to obtain the relationship between the reflection coefficient and the size of the circumferential damage;study the components of the defect echo modal and separate them;draw the circumferential displacement distribution of the echo signals of different damages,and The Fourier transform is performed on it,and the relationship between the proportion of the symmetrical modal component in the damage echo signal and the magnitude of the circumferential damage is obtained.Finally,two damage imaging methods are introduced.The first is damage imaging based on the wave field structure of the flexural mode: the wave structure and propagation characteristics of the flexural mode guided wave are analyzed,combined with the finite element calculation results,and the F(1,3)guided wave propagation law in the damage echo signal is inferred.Based on the distribution characteristics of the sound field,the inclination angle of the signal wave front is obtained,the wave front is drawn,and the defect boundary is determined according to the calculated actual propagation distance of the guided wave.The second is damage imaging based on the time reversal method: according to the basic theory of the time reversal method,the damage echo signal received by each receiving point is time-reversed as an excitation and then acted on the corresponding node of a non-damaged pipeline.When the guided wave propagates to the axial position of the defect,the guided wave is focused at the damaged area,and the displacement of the damaged area is significantly larger than that of the non-damaged area,so as to determine the circumferential position of the damage. |
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