Backward waves with double zero-group-velocity points in a liquid-filled pipe.

Area of Science:

• Solid mechanics
• Acoustics
• Non-destructive testing

Background:

• Hollow cylinders exhibit backward propagation modes with unique zero-group-velocity (ZGV) points.
• ZGV points signify resonant conditions and are foundational to laser ultrasound techniques for measuring elastic constants.
• The suitability of ZGV for liquid-filled pipes requires investigation.

Purpose of the Study:

• To theoretically and numerically investigate the influence of contained liquid on backward waves and ZGV modes in hollow pipes.
• To assess the applicability of the ZGV technique for in-service non-destructive evaluation of liquid-filled pipes.

Main Methods:

• Analysis of dispersion spectra and excitation properties of backward waves in fluid-filled pipes.
• Theoretical and numerical modeling to understand wave propagation phenomena.

Main Results:

• The presence of liquid increases the number of backward modes and ZGV points, enhancing excitability by point sources.
• Several guided modes exhibit double ZGV points due to strong mode repulsions, a phenomenon observed in fluid-filled pipes but not in dry ones.
• These double ZGV points arise from sign changes in the dispersion curve slopes.

Conclusions:

• The ZGV technique shows potential for non-destructive evaluation of liquid-filled pipes.
• The presence of liquid significantly alters wave propagation, leading to new ZGV phenomena.
• Further research can leverage these findings for advanced pipe inspection.