Dynamic Characteristic Analysis Of Fluid-Filled Cylindrical Shells In Viscoelastic Medium

In this thesis, the waves'free vibration, dispersion and dynamic characteristics of fluid-filled cylindrical shells in infinite (visco)elastic medium are studied theoretically and experimentally. The effects of elastic medium, cylindrical shell's geometry parameter and fluid in shells on the dynamic characteristics are discussed as well, and the results offers theory guidance for the anti-seismic design and non-destructive detection of seabed pipelines and underground pipelines. The major work of this paper is presented as follow. First, construct a free vibration analysis model of fluid-filled cylindrical shells; use theory of shell and equations of elastic-dynamics to derive the coupling equation of the model; and solve the transcendental equation by Muller root-finding method. Case studies show that the non-dimension have been more affected by rigidity of elastic medium, and the non-dimension frequencies of cylindrical shells increase with the rigidity ratio of elastic medium increasing, while fluid in shells has little effect to the non-dimension frequency of cylindrical shells.Secondly, the contour integration method in complex plane is put forward to solve the dispersion equation of complicated coupling system. All the complex roots of dispersion equation are derived by using the contour integration method in complex plane, which overcomes the shortcomings of traditional method which can only get the real root and approximate disposal method which can't derived all the complex roots in the whole complex plane. The complex roots of dispersion equation of submerged cylindrical shells are solved out.Sequentially, based on the above analysis, the complicated coupling system dispersion equation of fluid-filled cylindrical shells in infinite elastic medium is resolved, and thus get the dispersion curves of free propagation waves and attenuating wave of fluid-filled cylindrical shells in infinite elastic medium. Case studies show that the numbers of propagation wave are more affected by the fluid in shells; original frequency of propagation waves are affected by the rigidity of elastic medium; when the rigidity of elastic medium is small, the coupling of fluid and structure is strong, and the coupling decreases with the increase of rigidity of elastic medium.Then, dynamic responses of both fluid-filled and empty cylindrical shells in viscoelastic are analyzed by concentrating harmonic load. Case studies show that displacement response of cylindrical shells in viscoelastic medium is smaller than fluid-filled cylindrical shells by concentrating harmonic force. The displacement response decreases with the increase of rigidity of elastic medium and with the increase of rigidity of elastic medium, the displacement response is less affected by fluid. Because of the damping of the viscoelastic medium, the displacement response of cylindrical shells surrounding by viscoelastic medium decrease in low and middle frequency bands; response peaks fall and the response curves become smooth, and the effects of damping of viscoelastic medium decreases with the increase of frequency,.Finally, dynamic response of fluid-filled cylindrical shells in viscoelastic is analyzed experimentally under concentrating harmonic load. The results show that displacement response attenuates with the increase of distance because of damping of soil. The speed of vibration decaying of high frequency signal is faster than low frequency signal.The work presented in this paper is part of the contents of the project"Acoustic Signal Characteristics of Leak by Buried Water Supply Pipelines and the Leak Detection Equipment"(No 60002005), which is supported by the National Natural Science Foundation of China.