Guided circumferential wave propagation characteristics for porous cylinder immersed in infinite fluid

Abstract

Underground water, gas and oil all exist in the fractured or porous strata. Waves that propagate through porous cylinder immersed in infinite fluid are of considerable interest in the estimation of porous parameter, such as an underwater concrete column may present pore characteristics after a long time water immersion. Compared with longitudinal guided wave, circumferential guided wave has its advantages in the ultrasonic nondestructive inspection of porous cylinder. In order to investigate the propagation characteristics of guided waves in a porous cylinder immersed in infinite fluid and analyze the effects of the porous medium parameters on the dispersion characteristic, a model of porous cylinder surrounded by fluid is built. Based on the elastic-dynamic theory and modified liquid-saturated porous theory, the characteristic equation of guided wave is established, and the dispersion curves are obtained numerically. The effects of cylindrical radius and pore parameters on the propagation characteristics of guided waves are discussed; the attenuation characteristics of guided waves are also analyzed; the time domain waveforms of the guided circumferential waves are obtained by numerical inversion, and the influence of porous parameters on waveforms is simulated. It is found that the dispersion curves are similar to that of elastic cylinder in the fluid, there exist multiple mode guided waves and approximate shear velocity of medium for higher modes, and higher order modes are more affected by the radius, but it does not change the tendency of curve. The phase velocity decreases with porosity increasing at the same frequency and the effect of porosity on higher order modes is greater than that on mode 1; due to the dissipation in the medium, the attenuation increases porosity increasing. It can be seen from the transient responses that the wave packets move backward and the displacement amplitude decreases with the porosity increasing. The characteristics of the inversed transient response are in good agreement with theoretical dispersion and attenuation. The results show that the propagation of guided circumferential wave is affected by the pore parameters, especially for porosity, which can provide a theoretical reference for the non-destructive evaluation of the porous cylinder surrounded by infinite fluid.