The Numberical Studies On Damage Detection In The Cracked Pipe

Damage detection for pipe has received more and more attentions.In this paper,numerical simulations on crack detection in pipe using ultrasonic guided waves were carried out.The main work includes:Firstly,some main studies and progresses in this field were reviewed,and the relative theoretical basis was introduced.Based on the theoretical analysis,the theory on ultrasonic guide waves and dispersion equation is studied.The dispersion curves were numerically calculated.By using the MATLAB code,the propagation of the guided-wave in plates is discussed.Secondly,guided wave modes in hollow circular cylinder were analyzed to choose the appropriate mode for guided wave detection in pipe.Comparison and analysis on different boundary conditions were made.The results show that the frequency of F mode increases with the increase of constraint,the difference of constraints in two ends has important effect on the frequency of L mode and T mode.Thirdly,by using finite element software ANSYS,a finite element model with single damage and double damages were simulated basing on pulsed echo principle and the crack detection formulas.The excitation is simulated by prescribing axial transient displacement at one end of pipe model.The echo can be received at the same end.The results of numerical simulation showed that the single crack position and the double crack positions could be accurately identified,and the thinning degree could be identified approximately.At last,a lot of research on the finite element model with oblique cracks had been done. Comparison and analysis on different inclined angle 0°,15°,30°,45°were made.Crack echo analysis,spectrum analysis and energy analysis also were studied.The results showed that the amplitude of F echo increases with the decrease of inclined angle.There is almost no effect of the increase of inclined angle on the frequency of signal,but the energy of echo waves showed a decrease trend.