Dispersion Characteristics And Experimental Study Of Lamb Waves In Solid Plates

In the evaluation of cementing quality,the characteristics of acoustic wave are often used to evaluate the cementing quality.Schlumberger company's cementing quality evaluation instrument Isolation Scanner uses ultrasonic technology to measure the lamb wave signal in the casing,and has achieved good results in the evaluation of cementing quality of oil well cement.The dispersion characteristics of lamb waves in solid plates are studied theoretically and the dispersion properties are designed and tested.In the study,the propagation model of ultrasonic in the cement ring of casing well is simplified into the lamb wave propagation model in plane solid plate.The Lamb wave dispersion equation is deduced,and the solution program is compiled to draw the phase velocity curve of the lamb wave propagating in a certain thickness plate.When the frequency thick product increases to a certain value,not only the 0-order mode is stimulated,but also the first-order and higher-order mode wave can be stimulated.The experimental scheme of measuring the waveform of Lamb Wave array is designed,and used the method of oblique incidence to measure the waveform of the Lamb wave in the low-frequency and high frequency bands respectively,and used the matrix beam method to deal with the waveform.Processing results show that in the low frequency band,only the A₀ mode and the S₀ mode wave can be stimulated,and the dispersion analysis and the theoretical curve can match well.In the high-frequency segment,the 0-order,first-order and higher-order mode waves of A₀,S₀,A₁ and S₁ can be stimulated,and in the dispersion analysis,the tendency of each mode to change phase velocity with frequency is observed.Under the same frequency condition,the influence of different incident angles on the excited lamb wave shape is studied,and the smaller the angle is,the better the modal of the phase velocity can be excited when the frequency thick product is determined.The experimental results are of great significance to the research of lamb wave dispersion characteristics.