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Eric B. Flynn – One of the best experts on this subject based on the ideXlab platform.
Three-Dimensional Acoustic Wavenumber Spectroscopy for Structural Health MonitoringStructural Health Monitoring 2019, 2019Co-Authors: Peter H. Fickenwirth, Matthew J. Adams, Eric B. FlynnAbstract:
Acoustic Wavenumber spectroscopy (AWS) is an effective technique for the assessment of millimeter-scale damage on large thin-walled structures such as airplanes, wind turbine blades, ship hulls, and water tanks. To date, Acoustic Wavenumber spectroscopy remains a nondestructive evaluation technology, as it requires significant human intervention. This research demonstrates how including automated three-dimensional geometry scanning in 360-degrees can work to extend the capabilities of AWS to structural health monitoring. First, we collect threedimensional geometry for our Wavenumber analysis over complex geometries. We perform this for three different samples: 1) A large plate oriented normal to the scanner, 2) Two plates clamped at an angle, and 3) An intentionally bowed plate. Then we perform Wavenumber estimation on the structures correcting for perspective errors based on the geometry information. In the future, we plan to reduce human involvement during the data collection process.
Toward Utilizing Full-Field Laser-Ultrasound for Practical Nondestructive Inspection with Acoustic Wavenumber Spectroscopy2018 IEEE International Ultrasonics Symposium (IUS), 2018Co-Authors: Eric B. Flynn, Nicholas D. StullAbstract:
This study concerns the use of steady, harmonic excitation in place of repeated transient excitation for full-field laser ultrasound inspection. With harmonic excitation, we realized several orders of magnitude improvement in signal level in ultrasonic laser Doppler vibrometer measurements, enabling scans with eye safe lasers on unmodified inspection surfaces at speeds of up to five square meters per minute. We’ve found that two classes of full-field analysis techniques to be especially effective when properly modified for harmonic response measurements: Wavenumber spectroscopy and local gradient estimation. This paper focuses on the former. Wavenumber spectroscopy, which is effective at detecting in-plane defects, involves local analysis of the wavelengths of the ultrasonic waves in order to quantify changes in effective thickness using the Rayleigh-Lamb equations. Using the techniques briefly described in this paper, we achieved effective nondestructive evaluation with scan rates of up to 320 square centimeters per second on metallic samples and 80 square centimeters per second on carbon-fiber-reinforced polymer composites.
Compact Laser Ultrasound Scanner for Wide-Area Persistent MonitoringStructural Health Monitoring 2017, 2017Co-Authors: Jacob Senecal, Abraham Jarque, Eric B. FlynnAbstract:
In this study we evaluate the feasibility of using a simple, unstabilized, homodyne interferometer configuration for local Wavenumber estimation of guided waves, a process known as Acoustic Wavenumber spectroscopy . Acoustic Wavenumber spectroscopy identifies damage in a two-dimensional scan on a pixel by pixel basis, by estimating the Wavenumber of a structure’s response to a steady-state, single frequency, ultrasonic excitation. By leveraging the requirement to measure only a single known frequency it may be possible to use a simplified laser doppler vibrometer (LDV). A simple and inexpensive laser ultrasound scanning device would provide convenient and rapid stand-off inspection for evaluating structural damage in a variety of settings. Due to the typical cost, complexity, and size of commercial LDV systems, they are often only used for one-off measurements in the laboratory. A simplified system could enable permanent deployment of LDV technology for persistent structural health monitoring applications.
William K. Bonness – One of the best experts on this subject based on the ideXlab platform.
Turbulent boundary layer shear stress transmitted through a viscoelastic layer.The Journal of the Acoustical Society of America, 2008Co-Authors: E. Capone, William K. BonnessAbstract:
Transfer functions are developed for the transmission of unsteady shear stress, generated by a turbulent boundary layer in water, through a viscoelastic layer backed by a rigid plate. Existing analytical models are used to estimate the unsteady wall pressure and shear stress from 10–1000 Hz for a flat plate boundary layer with zero pressure gradient. A new model is developed for the transmission of unsteady shear stress through the viscoelastic layer. The model is used to predict the unsteady pressure fluctuations, or flow noise (due to the unsteady shear stress), which would be seen by a finite size sensor embedded under the elastomer layer. The calculated unsteady pressure and shear stress levels are in good agreement with recent experimental measurements. The unsteady shear stress transfer functions are found to have a peak at the Acoustic Wavenumber.
The transmission of turbulent boundary layer unsteady pressure and shear stress through a viscoelastic layerJournal of Fluids and Structures, 2008Co-Authors: Dean E. Capone, William K. BonnessAbstract:
The transmission of unsteady pressure and shear stress, generated by a turbulent boundary layer in water, through a viscoelastic layer backed by a rigid plate is investigated. Analytical models are used to estimate the unsteady pressure and shear stress from 10 to 1000 Hz for a flat plate boundary layer with zero pressure gradient. Additionally, models for the transfer of the unsteady pressures and shear stress through the viscoelastic layer are developed. The models are used to predict the unsteady pressure fluctuations, or flow noise, which would be seen by a finite size sensor embedded under the elastomer layer. The unsteady pressure levels are found to be 20 dB greater than the unsteady shear stress levels across all frequency ranges computed, in agreement with recent measurements. The unsteady pressure transfer functions have a peak at the shear Wavenumber and are larger than the shear stress transfer magnitudes from 10 to 50 Hz. The unsteady shear stress transfer functions have a peak at the Acoustic Wavenumber and are larger than the pressure transfer magnitudes from 50 to 1000 Hz. Over the frequency range examined, the unsteady pressures were found to be the dominant contributor to the sensor flow noise due to the considerably larger magnitude of the unsteady pressures on the top of the viscoelastic layer.
Jun-young Jeon – One of the best experts on this subject based on the ideXlab platform.
Optimization of excitation frequency and guided wave mode in Acoustic Wavenumber spectroscopy for shallow wall-thinning defect detectionJournal of Mechanical Science and Technology, 2018Co-Authors: Seongin Moon, To Kang, Soon-woo Han, Jun-young Jeon, Gyuhae ParkAbstract:
In plate-like structures, wall-thinning defects resulting from corrosion may not be accompanied by any indication of damage on the surface. Thus, inspections are required to ensure that wall-thinning defects are within allowable limits. However, conventional ultrasonic techniques require physical contact to the structure. Alternatively, Acoustic Wavenumber spectroscopy (AWS) may be used for detecting, locating, and characterizing defects. This paper describes the performance of AWS in the estimation of a wall-thinning defect size in thinplate structures using finite element analysis (FEA). Through a series of FEAs, the structure’s steady-state response to a single-tone ultrasonic excitation is simulated, and the wall-thinning defect-size effect on the Wavenumber-estimation accuracy is investigated. In general, the A0 guided wave mode is widely used to visualize defects because of the nature of the wave speed variation in relation to the plate thickness. However, it is not appropriate for the detection of relatively shallow wall-thinning defects, because the rate of change in wave speed with the thickness decreases with increasing plate thickness. To overcome this limitation, we propose a method to optimize excitation frequency and effective guided wave mode instead of utilizing the A0 mode. The results can be used to determine the size of shallow wall-thinning defects in plate-like structures.
Comparison of guided and standing waves based full field laser scanning techniques for damage detection using Wavenumber analysis (Conference Presentation)Smart Structures and NDE for Industry 4.0, 2018Co-Authors: Jun-young Jeon, Gyuhae Park, To Kang, Duhwan Kim, Soon-woo HanAbstract:
This paper presents the comparison study of Wavenumber-based defect detection performance in full field laser scanning techniques. Two types of wave excitation are used for damage detection; guided waves and standing waves. A piezoelectric actuator is mounted on surface of the thin plate to generate guided and standing waves with a single excitation frequency. Subsequent responses on each grid point are measured using a Laser doppler vibrometer (LDV) with a mirror tilting device. Full field wave image is then generated from the measured wave signals. After the laser scanning, Wavenumber based processing is applied to the measurements to generate two types of full wave field images and to detect structural damage. Three Wavenumber based signal processing are applied to the wave filed images to estimate damage size and depth, including the Local Wavenumber mapping, Acoustic Wavenumber Spectroscopy, 2D wavelet based Wavenumber spectroscopy. For the comparison of these two techniques, several experiments are performed on thin walled structures with several different types of damage, including corrosion in an aluminum plate and debonding on composite plates. This paper outlines pros and cons of these two excitation techniques in terms of several parameters, including damage sensitivity, processing time and their applicability.
Measurement of Thickness of Wall-Thinned Plate using Acoustic Wavenumber Spectroscopy and Spatial Local Wavenumber FilteringStructural Health Monitoring 2017, 2017Co-Authors: To Kang, Seongin Moon, Gyuhae Park, Soon-woo Han, Jeong Han Lee, Jin-ho Park, Jun-young JeonAbstract:
The surface of a structure can generate cracks or wall-thinning, due to corrosion. This can eventually lead to the fracture of the structure, which can trigger enormous fatality and property loss. Thereby, a laser imaging technology on such structures as thin plate structure, or piping which thickness is relatively thin in comparison to the area, has been steadily studied for the past 10 years. The most typical among the laser imaging technology is the pulse laser imaging. By using the same, a new technology for inspecting and imaging a desired area within a relatively short period of time was developed, so as to scan various structures including the thin-plate structure and piping. However, this method builds images by measuring waves reflected from defects, and have a time delay of a few milliseconds at each scanning point. Moreover, complexity of the systems is so high due to additional components such as laser focusing parts. This paper proposes laser imaging method with increased scanning speed based on excitation and measurement of standing waves in structures. Wavenumber of standing waves changes at sections with geometrical discontinuity such as thickness. It is shown that defects in a structure can be visualized by generating standing waves with single frequency and scanning the waves at each point by the laser scanning system suggested in this work. The proposed technique is validated by a wall-thinned plate that has a linear thickness variation