Study On Guided Wave Responses To Stress In Circular Tube Structure Based On Acoustoelastic Theory

Pipeline transportation is the main transportation mode of oil and gas resources,while most pipelines are in harsh natural environment and often suffer from stress.If stress can be detected before pipeline damage and preventive measures can be taken,huge economic losses can be avoided.Among many pipeline inspection methods,ultrasonic guided wave inspection method has many advantages,such as long propagation range,sensitivity to stress and damage,and need less energy excitation.Ultrasonic guided wave detection method has been successfully applied to practical engineering as a process for monitoring pipeline damage or detecting pipeline defects,but there is little research on stress detection by using the propagation characteristics of guided waves in pipelines.Therefore,it is necessary to study the propagation characteristics of ultrasonic guided waves in tubular structures under stress.In the past,the semi-analytical finite element method was generally used to analyze the propagation characteristics of ultrasonic guided waves in pipes,while the stress response analysis of guided waves in circular pipe structures under axial stress was rarely reported by the solution method based on acoustoelastic theory.Based on the acoustoelastic theory,the medium of circular pipe structure will become equivalent transversely isotropic medium under axial stress.Therefore,based on the acoustoelastic theory,this paper studies the stress response of guided waves in circular tube structures,and solves and calculates the propagation characteristics of guided waves in circular tube structures under axial stress by analytical method.The research in this paper will help to understand the guided wave propagation characteristics of circular tube structures under stress,and have guiding significance for stress detection of circular tube structures.Ultrasonic guided waves have complex wave field components in circular tube structure,and there are many propagation modes at certain frequencies,which will become more complex under stress.In this paper,the pipe model with air inside and outside,water inside and oil outside is air inside,and the specific modes under stress are analyzed through the frequency dispersion curve and the speed change curve with frequency,which is beneficial to select the detection modes reasonably according to the actual engineering specific detection requirements and theoretical analysis,and has guiding significance for the application of ultrasonic guided waves in pipeline stress detection.In this paper,firstly,the sound field of circular tube structure under axial stress is solved theoretically,and the theoretical solution of isotropic circular tube structure under axial stress is given in terms of potential function,which provides a basis for theoretical analysis of wave field of isotropic circular tube structure under axial stress.Then,according to the boundary conditions of three models(pipe model with air inside and outside,pipe model with air inside and water outside,and pipe model with oil inside and air outside),the dispersion equation is obtained respectively.After the undetermined coefficient of potential function is obtained,the sound wave expression of pipe structure with oil inside and air outside can be obtained.In this paper,Newton iteration is used to calculate dispersion curves,and the dispersion curves of longitudinal mode and torsional mode of the three models and the curves of velocity variation with frequency under different stresses are calculated and investigated.Fourier transform algorithm is used to simulate the full-wave waveform excited by a liquid point sound source in the tube.The research results of guided wave dispersion show that under the pipeline model with both inside and outside air,the multimode of longitudinal mode guided waves can be known by dispersion curve,and each propagation mode has cut-off frequency,which can be obtained by the curve of velocity variation with frequency,and the velocity of longitudinal mode changes uniformly with the magnitude of applied stress;There is little difference between the dispersion curve and velocity variation curve with frequency of the pipeline model with air inside and water outside and the pipeline model with air inside and outside Under the pipeline model with oil inside and air outside,through dispersion analysis and the curve of velocity variation with frequency,it can be found that the velocity variation of longitudinal mode also changes uniformly with the magnitude of applied stress,and all of them are in specific areas with velocity variation,and the velocity variation in other frequency bands tends to zero,that is,they are hardly affected by stress.The results of the full-wave waveform excited by the liquid point sound source in the pipe show that the full-wave in the pipe model with oil inside and air outside is calculated,and the first wave moves backward when it arrives,indicating that the velocity of the first wave decreases under the action of tensile stress,and it is difficult to analyze the change when it arrives in other modes due to aliasing,which requires further extraction and analysis by means of signal processing.The research in this paper not only helps to deepen the understanding of the propagation mechanism of ultrasonic guided waves in stressed circular pipe structures,but also provides theoretical basis for new stress detection methods of circular pipe structures,and provides meaningful guidance for guided wave nondestructive testing of circular pipe structures..