Numerical investigation of leaky modes in helical structural waveguides embedded into a solid medium

Area of Science:

• Civil Engineering
• Materials Science
• Non-Destructive Evaluation

Background:

• Helical multi-wire cables are vital in bridges and retaining walls but susceptible to corrosion and fatigue.
• Non-destructive evaluation (NDE) is essential for detecting internal defects in these structures.
• Elastic guided waves offer long-distance propagation but suffer attenuation in unbounded media, especially in helical designs.

Purpose of the Study:

• To develop a numerical approach for computing wave modes in embedded helical structures.
• To investigate wave propagation characteristics and attenuation in such complex geometries.
• To enhance the effectiveness of guided wave-based NDE for civil engineering cables.

Main Methods:

• Combined the semi-analytical finite element method (FEM) with a radial perfectly matched layer (PML) technique.
• Implemented a twisting coordinate system to maintain translational invariance.
• Validated the centered PML configuration with a twisted cylinder test case and investigated an off-centered configuration for embedded helical wires and seven-wire strands in concrete.

Main Results:

• The numerical approach successfully computes modes in embedded helical structures.
• The study analyzed the effect of twist on the eigenspectrum and modal attenuation.
• Both centered and off-centered radial PML configurations yielded comparable results.

Conclusions:

• The proposed numerical method is effective for analyzing wave propagation in embedded helical cables.
• Understanding modal attenuation is key to optimizing guided wave inspection techniques.
• This research contributes to improved defect detection in critical civil engineering infrastructure.