Jill Bingham

Lamb wave characterization of corrosion-thinning in aircraft stringers: Experiment and three-dimensional simulation

The development of automatic guided wave interpretation for detecting corrosion in aluminum aircraft structural stringers is described. The dynamic wavelet fingerprint technique (DWFT) is used to render the guided wave mode information in two-dimensional binary images. Automatic algorithms then extract DWFT features that correspond to the distorted arrival times of the guided wave modes of interest, which give insight into changes of the structure in the propagation path. To better understand how the guided wave modes propagate through real structures, parallel-processing elastic wave simulations using the finite integration technique (EFIT) has been performed. Three-dimensional (3D) simulations are used to examine models too complex for analytical solutions. They produce informative visualizations of the guided wave modes in the structures and mimic the output from sensors placed in the simulation space. Using the previously developed mode extraction algorithms, the 3D EFIT results are compared directly to their experimental counterparts.

Simulation of guided waves in complex piping geometries using the elastodynamic finite integration technique

Although many technologies exist for inspecting piping systems, they are most successful on straight pipes and are often unable to accommodate the added complexities of pipe elbows, bends, twists, and branches, particularly if the region of interest is inaccessible. This paper presents a numerical technique based on the elastodynamic finite integration technique for simulating guided elastic wave propagation in piping systems. Comparisons show agreement between experimental and simulated data, and guided wave interaction with flaws, focusing, and propagation in pipe bends are presented. These examples demonstrate the ability of the simulation method to be used to study elastic wave propagation in piping systems which include three-dimensional pipe bends, and suggest its potential as a design tool for designing pipe inspection hardware and ultrasonic signal processing algorithms.

3D ELASTODYNAMIC FINITE INTEGRATION TECHNIQUE SIMULATION OF GUIDED WAVES IN EXTENDED BUILT-UP STRUCTURES CONTAINING FLAWS

In order to understand guided wave propagation through real structures containing flaws, a parallel processing, 3D elastic wave simulation using the elastodynamic finite integration technique (EFIT) has been developed. This full field, numeric simulation technique easily examines models too complex for analytical solutions, and is developed to handle built up 3D structures as well as layers with different material properties and complicated surface detail. The simulations produce informative visualizations of the guided wave modes in the structures as well as the output from sensors placed in the simulation space to mimic experiment.

Lamb wave detection of limpet mines on ship hulls

This paper describes the use of ultrasonic guided waves for identifying the mass loading due to underwater limpet mines on ship hulls. The Dynamic Wavelet Fingerprint Technique (DFWT) is used to render the guided wave mode information in two-dimensional binary images because the waveform features of interest are too subtle to identify in time domain. The use of wavelets allows both time and scale features from the original signals to be retained, and image processing can be used to automatically extract features that correspond to the arrival times of the guided wave modes. For further understanding of how the guided wave modes propagate through the real structures, a parallel processing, 3D elastic wave simulation is developed using the finite integration technique (EFIT). This full field, technique models situations that are too complex for analytical solutions, such as built up 3D structures. The simulations have produced informative visualizations of the guided wave modes in the structures as well as mimicking directly the output from sensors placed in the simulation space for direct comparison to experiments. Results from both drydock and in-water experiments with dummy mines are also shown.

Lamb Wave Detection of Delaminations in Large Diameter Pipe Coatings

This paper describes combined experiments and simulations to automate the extraction of ultrasonic guided wave mode arrivals in order to gain quantitative information about large-diameter pipeline coatings. The dynamic wavelet fingerprint technique (DWFT) is used to show differences between unknown coatings as well as to identify the presence of delamination and grinding flaws within the Lamb wave propagation path. Combined with complex multi-layered models to help interpret the guided wave feature changes, this extraction algorithm can be used for the detection of hidden flaws under a variety of protective coatings without having to disturb the coating or pipeline flow. High-resolution supercomputer simulations are developed using the elastodynamic finite integration technique (EFIT) accounting for the 3D interaction of realistic Lamb wave beams with finite-sized coating delaminations.

Wavelet Thumbprint Analysis of Time Domain Reflectometry Signals for Wiring Flaw Detection

We describe a signal processing technique for time‐domain reflectometry (TDR) detection of flaws in wiring. For subtle flaws the backscattered TDR voltage pulses are too slight to be identified by amplitude‐based peak‐detection methods. Here, a wavelet transform is used here to convert the 1D time traces into 2D binary “thumbprint” images. Flaws are then identified according to their unique 2D time‐scale patterns in these wavelet thumbprints. The method is demonstrated for RG58 coaxial cables with varying amounts of damage to the shielding.

Propagation of low‐frequency guided waves in three‐dimensional submerged heterogeneous pipes.

We numerically investigate the propagation of low‐frequency guided waves in a fluid‐filled elastic pipe submerged in a liquid. In a vacuum, axisymmetric modes travel through the pipe wall. When filled with a fluid of low sound speed, the pipe system can develop modes that are mainly supported by the interior fluid. As mode cut‐offs are approached, an increasing amount of energy penetrates the surrounding fluid. In order to determine these cut‐off frequencies, we have numerically obtained dispersion curves for the guided pipe modes from the characteristic equations for thick‐ or thin‐walled layered systems in cylindrical coordinates. As a complement to the separation of variable method, we also compute group speed curves from the propagation of interior source pulses through the medium using the time‐domain elastodynamic finite‐integration technique (EFIT). A time‐frequency analysis of the received signals at select probe locations reveals the group speed structure. We also compute the stability of the modes in the presence of heterogeneous contents such as gas or solid particulates using direct simulation with the EFIT code. Finally, we consider propagation through three‐dimensional structures such as valves.

Time‐domain numerical simulation of scattering by objects in the seafloor.

Numerical simulation of scattering in the time domain offers potential implementation advantages in comparison with frequency‐domain methods. By using explicit numerical time integration schemes, elastic stresses and velocities can typically be advanced using only spatially local information which makes parallelization by domain decomposition straightforward to implement in comparison with the solution of a large linear system of equations. On the other hand, incorporation of frequency‐dependent sound speed and attenuation appears more challenging in the time domain with the general need to compute convolutions under non‐FFT friendly conditions. This talk presents efficiency gains for the elastodynamic finite integration technique (EFIT) which is similar to the finite‐difference time‐domain method (FDTD). We present results on using explicit decomposition of scattered and incident wave fields and far‐field projection in the time domain with the discrete Helmholtz–Kirchhoff integral. We also present incorp...

Scattering of evanescent pipe modes form elastic spherical objects external to a fluid‐filled, submerged cylindrical waveguide.

Investigation into the interaction of low‐frequency fluid‐borne, radially decaying pipe modes with elastic objects exterior to a cylindrical waveguide using the elastodynamic finite integration technique (EFIT). The system is an oil‐filled steel pipe submerged in water. When the sound speed of the conveyed fluid is lower than the exterior fluid, there exist fluid/fluid modes possessing cutoff frequencies supported by both the interior and exterior fluids. These are in addition to the higher‐velocity, steel‐borne modes, and the low‐velocity internal‐fluid‐borne mode without a cutoff frequency. Excitation of a fluid/fluid mode near its cutoff frequency results in its further penetration into the exterior fluid. An object close to the pipe wall allows for scattering of this evanescent mode. An advantage of EFIT, direct manipulation of material properties, allows for easy inclusion of objects. Simulation results show the scattering from elastic objects with and without air pockets that are compared to analyti...