Study On Chaos Oscillator System In Pipes Using Ultrasonic Guided Waves

The pipeline transportation is one of the important modern transport modes, which has some irreplaceable advantages to the other modes. The pipeline transportation, with more and more extensive applications in economic construction, and more and more profound influence on the modern lives of urban residents, possesses wide development prospects. However, with the largely creasing laying and service time of oil and gas pipelines, damage failure accidents occur fluently, which cause huge losses to people's life and property. Therefore, it is particularly important to detect the damage of pipelines. As a new non-destructive detection technique developed in recent years, ultrasonic guided wave technique has some advantages, such as high-efficiency, long-distance, large-range and low-cost, etc. As a result, it has attracted an extensive attention in the non-destructive detection fields.In the thesis, a new ultrasonic guided wave technique is proposed based on the chaotic oscillator system. Firstly, Duffing equation is validated to be feasible for damage detection in pipelines. Several numerical examples of different amplitude of pure noise and supersonic guided wave signal shows that the chaotic oscillator system has good immunity to the noise, which can detect the guided wave signals.Secondly, by numerical simulations and experiments, the influence of the noise in undamaged pipelines as well as the defect signals in the damaged pipelines, which are submerged in noises, on the chaotic oscillator system is investigated. The numerical results show that, according to the phase trajectory of the chaotic oscillator system, the change of spectrum and the maximum Lyapunov exponent can distinguish the damaged and undamaged pipelines obviously. Furthermore, it is proved that, only the phase trajectory becomes unsmooth, with its characteristic unchanged, when the intensity of the noise is less than some threshold.Finally, the experimental results shows that the chaotic oscillator system is available for the ultrasonic guided wave detection, even if the noise is enough intense to submerge the defect guided wave signals. The existence of cracks in pipelines can be detected definitely according to the change of phase trajectory, spectrum and the maximum Lyapunov exponent of the chaotic oscillator system.