The Experts below are selected from a list of 2934 Experts worldwide ranked by ideXlab platform

Eric B. Flynn - One of the best experts on this subject based on the ideXlab platform.

  • Three-Dimensional Acoustic Wavenumber Spectroscopy for Structural Health Monitoring
    Structural Health Monitoring 2019, 2019
    Co-Authors: Peter H. Fickenwirth, Matthew J. Adams, Eric B. Flynn
    Abstract:

    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 Spectroscopy
    2018 IEEE International Ultrasonics Symposium (IUS), 2018
    Co-Authors: Eric B. Flynn, Nicholas D. Stull
    Abstract:

    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 Monitoring
    Structural Health Monitoring 2017, 2017
    Co-Authors: Jacob Senecal, Abraham Jarque, Eric B. Flynn
    Abstract:

    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 [1]. 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.

  • Damage detection on composite structures with standing wave excitation and Wavenumber analysis
    Advanced Composite Materials, 2017
    Co-Authors: Jun-young Jeon, Eric B. Flynn, To Kang, Gyuhae Park, Sehyeok Gang, Soon-woo Han
    Abstract:

    This paper describes the use of Wavenumber filtering for damage detection with a signal-frequency standing wave excitation on composite structures. Using a single, fixed frequency excitation from a mounted piezoelectric transducer, the full steady-state wavefield could be obtained using a Laser Doppler Vibrometer with a mirror-tilting device. After completing the scanning, a Wavenumber filtering is applied to determine dominant Wavenumber components of the measured wavefield, which could be used for indicative of structural damage. Mapping processes based on local Wavenumber filtering is then carried out for damaged area visualization. Also introduced are the comparison of two methods for damage identification and visualization: the local Wavenumber mapping and Acoustic Wavenumber spectroscopy. To demonstrate the proposed techniques, several experiments are performed on composite structures with different types of damage, including debonding and delamination on composite plates. The results demonstrate th...

  • Nondestructive evaluation of composite materials via scanning laser ultrasound spectroscopy
    Nondestructive Characterization and Monitoring of Advanced Materials Aerospace and Civil Infrastructure 2017, 2017
    Co-Authors: Eliseanne Koskelo, Eric B. Flynn
    Abstract:

    Composite materials pose a complex problem for ultrasonic nondestructive evaluation due to their unique material properties, greater damping, and often complicated geometry. In this study, we explored Acoustic Wavenumber spectroscopy (AWS) as a means of rapid inspection of laminate and honeycomb composites. Each aerospace sample was tested at different ultrasonic frequencies using steady-state excitation via a piezo electric actuator. We measured the velocity response of the composite at each pixel via a raster scan using a laser Doppler vibrometer. We were able to detect radial inserts along corners, delamination, and facing-core separation by analyzing local amplitude and Wavenumber responses. For each honeycomb composite, we excited the sample at the first resonant frequency of the individual cells. The local mode shape for each cell was extracted from the local amplitude response. Analyzing local amplitude and phase responses for each cell provided an accurate indication as to the presence, size, shape, and type of defect present in the composite. We detected both delamination and deformation of cells within a honeycomb composite. For the laminar composites, we analyzed the non-resonance steady-state response at several excitation frequencies.

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, 2008
    Co-Authors: E. Capone, William K. Bonness
    Abstract:

    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 layer
    Journal of Fluids and Structures, 2008
    Co-Authors: Dean E. Capone, William K. Bonness
    Abstract:

    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 detection
    Journal of Mechanical Science and Technology, 2018
    Co-Authors: Seongin Moon, To Kang, Soon-woo Han, Jun-young Jeon, Gyuhae Park
    Abstract:

    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, 2018
    Co-Authors: Jun-young Jeon, To Kang, Gyuhae Park, Duhwan Kim, Soon-woo Han
    Abstract:

    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 Filtering
    Structural Health Monitoring 2017, 2017
    Co-Authors: To Kang, Seongin Moon, Soon-woo Han, Gyuhae Park, Jeong Han Lee, Jin-ho Park, Jun-young Jeon
    Abstract:

    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

  • Damage detection on composite structures with standing wave excitation and Wavenumber analysis
    Advanced Composite Materials, 2017
    Co-Authors: Jun-young Jeon, Eric B. Flynn, To Kang, Gyuhae Park, Sehyeok Gang, Soon-woo Han
    Abstract:

    This paper describes the use of Wavenumber filtering for damage detection with a signal-frequency standing wave excitation on composite structures. Using a single, fixed frequency excitation from a mounted piezoelectric transducer, the full steady-state wavefield could be obtained using a Laser Doppler Vibrometer with a mirror-tilting device. After completing the scanning, a Wavenumber filtering is applied to determine dominant Wavenumber components of the measured wavefield, which could be used for indicative of structural damage. Mapping processes based on local Wavenumber filtering is then carried out for damaged area visualization. Also introduced are the comparison of two methods for damage identification and visualization: the local Wavenumber mapping and Acoustic Wavenumber spectroscopy. To demonstrate the proposed techniques, several experiments are performed on composite structures with different types of damage, including debonding and delamination on composite plates. The results demonstrate th...

William L. Siegmann - One of the best experts on this subject based on the ideXlab platform.

  • Parameter dependence of Acoustic mode quantities in an idealized model for shallow-water nonlinear internal wave ducts.
    The Journal of the Acoustical Society of America, 2019
    Co-Authors: Matthew A. Milone, Brendan J. Decourcy, Ying-tsong Lin, William L. Siegmann
    Abstract:

    Nonlinear internal waves in shallow water have significant Acoustic impacts and cause three-dimensional ducting effects, for example, energy trapping in a duct between curved wavefronts that propagates over long distances. A normal mode approach applied to a three-dimensional idealized parametric model [Lin, McMahon, Lynch, and Siegmann, J. Acoust. Soc. Am. 133(1), 37–49 (2013)] determines the dependence of such effects on parameters of the features. Specifically, an extension of mode number conservation leads to convenient analytical formulas for along-duct (angular) Acoustic Wavenumbers. The radial modes are classified into five types depending on geometric characteristics, resulting in five distinct formulas to obtain Wavenumber approximations. Examples of their dependence on wavefront curvature and duct width, along with benchmark comparisons, demonstrate approximation accuracy over a broad range of physical values, even including situations where transitions in mode types occur with parameter changes. Horizontal-mode transmission loss contours found from approximate and numerically exact Wavenumbers agree well in structure and location of intensity features. Cross-sectional plots show only small differences between pattern phases and amplitudes of the two calculations. The efficiency and accuracy of Acoustic Wavenumber and field approximations, in combination with the mode-type classifications, suggest their application to determining parameter sensitivity and also to other feature models.Nonlinear internal waves in shallow water have significant Acoustic impacts and cause three-dimensional ducting effects, for example, energy trapping in a duct between curved wavefronts that propagates over long distances. A normal mode approach applied to a three-dimensional idealized parametric model [Lin, McMahon, Lynch, and Siegmann, J. Acoust. Soc. Am. 133(1), 37–49 (2013)] determines the dependence of such effects on parameters of the features. Specifically, an extension of mode number conservation leads to convenient analytical formulas for along-duct (angular) Acoustic Wavenumbers. The radial modes are classified into five types depending on geometric characteristics, resulting in five distinct formulas to obtain Wavenumber approximations. Examples of their dependence on wavefront curvature and duct width, along with benchmark comparisons, demonstrate approximation accuracy over a broad range of physical values, even including situations where transitions in mode types occur with parameter changes...

  • Influence of random nonlinear internal wave parameters on resonant Acoustic mode coupling
    The Journal of the Acoustical Society of America, 2005
    Co-Authors: Scott D. Frank, William L. Siegmann
    Abstract:

    Shallow water transmissions sometimes suffer anomalous amplification or loss caused by mode coupling due to the presence of nonlinear internal wave packets. The possibility of coupling between two Acoustic modes is specified by an internal wave‐Acoustic resonance condition, which relates Acoustic Wavenumber differences to peak locations of the packet spectrum. This mechanism is critical in a recent analysis [S. D. Frank et al., J. Acoust. Soc. Am. 116, 3404–3422 (2004)] of some broadband intensity variations from the SWARM 95 experiment. That investigation used regularly spaced, evenly‐sized nonlinear internal wave packets and it is important to determine how random variations in the wave widths and inter‐wave spacings affect propagation results. An analytic expression for the Wavenumber spectrum of an idealized packet is obtained in terms of these parameters. This expression predicts spectral peak locations for parameters from the SWARM 95 model that correspond with observed data. Estimates of peak locat...

Stewart A L Glegg - One of the best experts on this subject based on the ideXlab platform.

  • the far field sound from rough wall boundary layers
    Proceedings of The Royal Society A: Mathematical Physical and Engineering Sciences, 2009
    Co-Authors: Stewart A L Glegg, William J Devenport
    Abstract:

    The noise radiated by a turbulent boundary layer over a rough wall is shown to be characterized by a dipole surface source that, if the surface pressure is spatially homogeneous, can be specified by a convolution integral combining the surface pressure Wavenumber spectrum and the Wavenumber spectrum of the surface roughness slope. For random roughness elements with almost vertical sides, the surface slope has a Wavenumber white spectrum and the radiated sound is directly proportional to the surface pressure spectrum multiplied by an Acoustic efficiency factor ( k o h ) 2 , where k o is the Acoustic Wavenumber and h is the geometrical r.m.s. roughness height. The theoretical result agrees with the roughness noise measurements of Smith et al . (Smith et al. 2008 AIAA paper no. 2008-2904) for all flow speeds and roughness element heights (in wall units) of k g +

  • High Frequency Sound Radiation From Fans With Transonic Tip Speeds
    11th AIAA CEAS Aeroacoustics Conference, 2005
    Co-Authors: Stewart A L Glegg
    Abstract:

    This paper discusses the Acoustic field generated by trailing edge noise sources in ducted fans with transonic tip speeds. A solution is developed for the sound field in the fan duct and the blade passages by assuming a high frequency limit. An analytical expression is derived for the amplitude of the Acoustic modes in the blade passages. I. Introduction Most aero engine fans operate with tip speeds that are well into the transonic range. The presence of transonic flow complicates the coupling between sound generated downstream of the fan face and Acoustic modes propagating upstream in the fan inlet duct. This paper will consider this problem, in the high frequency limit that is applicable to the fan noise sources of interest in large diameter high by pass ratio aero engines. In a previous study a numerical method was developed for the solution of Goldstein’s equation for sound propagation in non uniform flows [1]. The method was based on solving for the complex phase of the velocity potential in the high frequency limit, and ignored terms which were of order 1/ko 2 (where ko is the Acoustic Wavenumber). The Eikonal equation was solved on a specified grid to obtain a first order approximation to the real part of the phase, and the result was used in a second order equation to obtain the imaginary part of the phase. Accurate solutions were obtained for specific idealized examples, such as radiation from monopole and dipole sources. The paper also considered an idealized two dimensional trailing edge noise source, and was able to predict it’s radiated sound field in a subsonic flow. Some initial results were presented of a two dimensional problem which includes the primary effects of propagation from a source in a duct with non uniform flow. Of specific interest was the radial variation of the Acoustic field as the sound propagated upstream through a blade passage. For simplicity a two dimensional model was considered in which the flow in the horizontal direction increases linearly from M=0.5 at the lower boundary to M=0.95 at the upper boundary. This model was proposed to illustrate the effects of the radial variation of the flow speed in a rotor blade passage. The study considered whether sources close to the lower boundary in slower flow generate more sound upstream than sources close to the outer boundary where the flow speed is almost sonic. The calculations showed that for the source in slower flow, the field upstream is stronger than the field downstream. In general however the modal structure gives a relatively uniform level across the duct. In contrast for the case when the source is in higher speed flow significant refraction effects were apparent. A caustic appeared in the direct field which gave a high level on the upper duct wall just upstream of the source. Interestingly this was manifested in the reflected field * Professor, Dept. of Ocean Engineering, Senior member of AIAA