scholarly journals Analysis of Air-Coupled Transducer-Based Elastic Waves Generation in CFRP Plates

Sensors ◽  
2021 ◽  
Vol 21 (21) ◽  
pp. 7134
Author(s):  
Tomasz Wandowski ◽  
Damian Mindykowski ◽  
Pawel Kudela ◽  
Maciej Radzienski
Keyword(s):  
Wave Energy ◽  
Elastic Waves ◽  
Slope Angle ◽  
Excitation Frequency ◽  
Laser Doppler Vibrometer ◽  
Wave Mode ◽  
Unidirectional Composite ◽  
Signal Processing Algorithm ◽  
Reinforcing Fibers ◽  
Damage Maps

In this paper, the analysis of non-contact elastic waves generation in carbon fiber reinforced-polymer (CFRP) plate was conducted. Full non-contact elastic waves generation and sensing methods were also analyzed. Elastic waves generation was based on an air-coupled transducer (ACT) while waves sensing was based on a laser Doppler vibrometer. The excitation frequency was equal to 40 kHz. An optimal ACT slope angle for the generation of elastic waves mode was determined with the aid of dispersion curves calculated by using a semi-analytical model. Due to the stack sequence in the composite plate (unidirectional composite), ACT slope angles were different for waves generation in the direction along and across reinforcing fibers direction. Moreover, experimental verification of the optimal ACT slope angles was conducted. It was possible to generate A0 wave mode in the direction along and across the reinforcing fibers. Optimal angles determined using ACT were equal to 16° (along fibers) and 34° (across fibers). In the case of optimal angles, elastic waves amplitudes are almost two times higher than for the case of ACT oriented perpendicularly to the plate surface. Moreover, experimental results based on ACT showed that it was possible to generate the SH0 mode in the direction across the fiber for optimal angles equal to 10°. Finally, based on the A0 wave mode propagation, the process for localization of discontinuities was performed. Discontinuities in the form of additional mass simulating damage were investigated. A simple signal processing algorithm based on elastic wave energy was used for creating damage maps. Authors compared discontinuity localization for ACT oriented perpendicularly to the plate and at the optimal slope angle. The utilization of non-contact waves excitation at optimal ACT slope angles helped to focus the wave energy in the desired direction. Moreover, in this case, elastic waves with the highest amplitudes were generated.

Visualization of hidden damage from scattered wavefield reconstructed using an integrated high-speed camera system

2020 ◽  
pp. 147592172094080
Author(s):  
Huan-Yu Chang ◽  
Fuh-Gwo Yuan
Keyword(s):  
High Speed ◽  
Excitation Frequency ◽  
Laser Doppler Vibrometer ◽  
Wave Mode ◽  
Frame Rate ◽  
Image Correlation ◽  
Scanning System ◽  
Plate Boundaries ◽  
High Speed Camera ◽  
Camera System

In this article, a feasibility study for the visualization of hidden damage using an integrated high-speed camera system was carried out. A thin, planar, and low-modulus high-density polyethylene plate with surrogate damage was chosen to represent a damaged structure for the proof of concept, and two different damage scenarios (mimicked by attaching lightweight rectangular/circular masses to the back of the plate) were investigated. The acoustic/ultrasonic guided waves were generated in the plate by a surface-mounted piezoelectric actuator under continuous sinusoidal excitation, and in-plane wavefield displacements on the surface of the plate were captured using a high-speed camera. In order to reconstruct the scattered wavefield, these in-plane wavefields which primarily include the fundamental symmetric wave mode S0 and fundamental shear horizontal wave mode SH0 (induced due to reflection/scattering of the incident S0 wave mode from the damage and plate boundaries) were then extracted using digital image correlation image analysis software. All the experimental parameters (e.g. material properties of the plate, excitation frequency, selection of lens, field-of-view, speckle size) were carefully designed, integrated, and optimized. In order to overcome the current hardware limitations (insufficient spatial/temporal resolution), sample interleaving was implemented to artificially enhance the frame rate and image stitching techniques were used to increase the total effective camera resolution. Together, these techniques provided a nearly 250-fold enhancement in the data acquisition capability of the high-speed camera. In order to fully demonstrate the efficacy of the sample interleaving technique, two frequencies were excited: 14 and 28 kHz, below and above the original Nyquist frequency, respectively. The first fundamental SH0 and S0 wave modes for both frequencies were successfully detected and identified, and the disturbances at the damage region were clearly observed in the scattered wavefield reconstructed with the SH0 mode in particular, as the SH0 mode has a shorter wavelength making it better suited for detecting smaller damage. The hidden damage was then visualized by employing a modified version of the phase-based damage imaging condition, wavenumber index, that was previously developed for visualizing hidden delamination damage in composites with a laser Doppler vibrometer scanning system.

scholarly journals Characterization of laser Doppler vibrometers using acousto-optic modulators

ACTA IMEKO ◽  
2020 ◽  
Vol 9 (5) ◽  
pp. 361
Author(s):  
Michael Gaitan ◽  
Jon Geist ◽  
Benjamin J. Reschovsky ◽  
Ako Chijioke
Keyword(s):  
Frequency Shift ◽  
Excitation Frequency ◽  
Laser Doppler Vibrometer ◽  
Laser Doppler ◽  
New Approach ◽  
Frequency Reference ◽  
Discrete Velocity ◽  
Velocity Shift ◽  
Vibration Excitation

We report on a new approach to characterize the performance of a laser Doppler vibrometer (LDV). The method uses two acousto-optic modulators (AOMs) to frequency shift the light from an LDV by a known quantity to create a synthetic velocity shift that is traceable to a frequency reference. Results are presented for discrete velocity shifts and for sinusoidal velocity shifts that would be equivalent to what would be observed in an ideal accelerometer vibration calibration. The method also enables the user to sweep the synthetic vibration excitation frequency to characterize the bandwidth of an LDV together with its associated electronics.

scholarly journals Wave and Jet Maintenance in Different Flow Regimes

2016 ◽  
Vol 73 (6) ◽  
pp. 2465-2484 ◽  
Author(s):  
Orli Lachmy ◽  
Nili Harnik
Keyword(s):  
Wave Energy ◽  
Wave Spectrum ◽  
Flow Regimes ◽  
Wave Mode ◽  
Hadley Cell ◽  
Model Parameters ◽  
Mean Flow ◽  
Eddy Heat Flux ◽  
Subtropical Jet ◽  
Zonal Wavenumber

Abstract The wave spectrum and zonal-mean-flow maintenance in different flow regimes of the jet stream are studied using a two-layer modified quasigeostrophic (QG) model. As the wave energy is increased by varying the model parameters, the flow transitions from a subtropical jet regime to a merged jet regime and then to an eddy-driven jet regime. The subtropical jet is maintained at the Hadley cell edge by zonal-mean advection of momentum, while eddy heat flux and eddy momentum flux convergence (EMFC) are weak and concentrated far poleward. The merged jet is narrow and persistent and is maintained by EMFC from a narrow wave spectrum, dominated by zonal wavenumber 5. The eddy-driven jet is wide and fluctuating and is maintained by EMFC from a wide wave spectrum. The wave–mean flow feedback mechanisms that maintain each regime are explained qualitatively. The regime transitions are related to transitions in the wave spectrum. An analysis of the wave energy spectrum budget and a comparison with a quasi-linear version of the model show that the balance maintaining the spectrum in the merged and subtropical jet regimes is mainly a quasi-linear balance, whereas in the eddy-driven jet regime nonlinear inverse energy cascade takes place. The amplitude and wavenumber of the dominant wave mode in the merged and subtropical jet regimes are determined by the constraint that this mode would produce the wave fluxes necessary for maintaining a mean flow that is close to neutrality. In contrast, the equilibrated mean flow in the eddy-driven jet regime is weakly unstable.

3D SPH Simulation of Wave Interaction Between Wave Energy Converters: Towards Optimum Wave Power Absorption in Wave Farms

2020 ◽  
Author(s):  
N. Sasikala ◽  
S. A. Sannasiraj ◽  
Richard Manasseh
Keyword(s):  
Wave Energy ◽  
Oscillation Amplitude ◽  
Excitation Frequency ◽  
Ocean Waves ◽  
Dynamic Responses ◽  
Q Factor ◽  
Floating Bodies ◽  
Sustainable Resources ◽  
Wave Energy Converters ◽  
Energy Converters

Abstract Ocean waves are one of the sustainable resources of renewable energy for carbon-free electricity. For cost-effective commercial-scale projects, Wave Energy Converters (WECs) are deployed in arrays with optimum spacing as an alternative for a large (oscillatory) device in isolation. It has been found that when the wave excitation frequency is close to the resonant frequency of the WEC, the efficiency factor of energy farms, called q-factor, increases with the oscillation amplitude of the device. It has been found that the maximum absorbed energy of WECs depends directly on array configuration as that the radiated and incident wave fields interfere to direct the energy flux in the ocean towards the floating bodies. In this paper, the fully nonlinear interaction between two 3D floating bodies in close proximity and excited near its’ resonance is studied using Weakly Compressible Smoothed Particle Hydrodynamics (WCSPH). Apart from the calculations of q factor, hydrodynamic forces acting on the floating bodies and their dynamic responses are also calculated. An optimum array of WECs is proposed.

scholarly journals A novel control method to maximize the energy-harvesting capability of an adjustable slope angle wave energy converter

2016 ◽  
Vol 97 ◽  
pp. 518-531 ◽  
Author(s):  
Nguyen Minh Tri ◽  
Dinh Quang Truong ◽  
Do Hoang Thinh ◽  
Phan Cong Binh ◽  
Dang Tri Dung ◽  
...  
Keyword(s):  
Energy Harvesting ◽  
Wave Energy ◽  
Control Method ◽  
Slope Angle ◽  
Wave Energy Converter ◽  
Energy Converter

Damage Identification Using a Continuously Scanning Laser Doppler Vibrometer System

2016 ◽  
Author(s):  
Da-Ming Chen ◽  
Y. F. Xu ◽  
W. D. Zhu
Keyword(s):  
Damage Identification ◽  
Excitation Frequency ◽  
Damage Index ◽  
Laser Doppler Vibrometer ◽  
Its Region ◽  
Laser Doppler ◽  
Scanning Laser ◽  
Scanning Laser Doppler Vibrometer ◽  
Baseline Information ◽  
The Difference

A continuously scanning laser Doppler vibrometer (CSLDV) system is capable of rapidly obtaining spatially dense operating deflection shapes (ODSs) by continuously sweeping a laser spot from the system over a structure surface. This paper presents a new damage identification methodology for beams that uses their ODSs under sinusoidal excitation obtained by a CSLDV system, where baseline information of associated undamaged beams is not needed. A curvature damage index (CDI) is proposed to identify damage near a region with high values of the CDI at an excitation frequency. The CDI uses the difference between curvatures of ODSs associated with ODSs that are obtained by two different CSLDV measurement methods, i.e., demodulation and polynomial methods; the former provides rapid and spatially dense ODSs of beams, and the latter provides ODSs that can be considered as those of associated undamaged beams. Phase variables are introduced to the two methods for damage identification purposes. The proposed damage identification methodology was experimentally validated on a beam with damage in the form of machined thickness reduction. The damage and its region were successfully identified in neighborhoods of prominent peaks of CDIs at different excitation frequencies.

Measurement of defects in a plate using dry-coupled interdigital transducer–based scanning laser Doppler vibrometer

2020 ◽  
pp. 147592172096024
Author(s):  
To Kang ◽  
Seong-Jin Han ◽  
Seongin Moon ◽  
Soonwoo Han ◽  
Jun Young Jeon ◽  
...  
Keyword(s):  
Steel Plate ◽  
Excitation Frequency ◽  
Laser Doppler Vibrometer ◽  
Laser Doppler ◽  
Scanning Laser ◽  
Lead Zirconium Titanate ◽  
Thick Plates ◽  
Scanning Laser Doppler Vibrometer ◽  
Degree Of Separation ◽  
Interdigital Transducer

The interdigital transducer–based scanning laser Doppler vibrometer has recently been introduced to efficiently generate the symmetric mode for damage detection of shallow defects in thick plates. To measure shallow defects in a carbon steel plate, the excitation frequency is optimized based on the analysis of wavenumber sensitivity and degree of separation between modes. Even though the interdigital transducer–based scanning laser Doppler vibrometer method using continuous excitation is a promising method for visualizing defects in plate-like structures, the interdigital transducer has to be coupled to media, such as oil or water, to minimize the variation in acoustic impedance between the lead zirconium titanate and the plate-like structures. In this study, we develop a dry-coupled interdigital transducer–based scanning laser Doppler vibrometer system for the detection of shallow defects in a plate to facilitate easy mounting and demounting from the plate. To verify the proposed dry-coupled interdigital transducer–based scanning laser Doppler vibrometer, plates with four and eight different depth defects are introduced, and it is demonstrated that the defects in thick plates measured by dry-coupled interdigital transducer–based scanning laser Doppler vibrometer are visualized compared to those measured by interdigital transducer–based scanning laser Doppler vibrometer.

Evaluation on the Capability of Revealing Ocean Swells from Sentinel-1A Wave Spectra Measurements

2020 ◽  
Vol 37 (7) ◽  
pp. 1289-1304
Author(s):  
Xuan Wang ◽  
Romain Husson ◽  
Haoyu Jiang ◽  
Ge Chen ◽  
Guoping Gao
Keyword(s):  
Wave Energy ◽  
Wave Spectrum ◽  
Wave Mode ◽  
Wave Frequency ◽  
Wave Parameter ◽  
Wave System ◽  
Wave Spectra ◽  
Wave Measurements ◽  
The Difference ◽  
Level 2

AbstractWave measurements retrieved by Sentinel-1A level-2 ocean (OCN) products are sensitive to swells other than wind seas, and are considered to provide a finer resolution of ocean swells. To assess the capability of swell retrieval globally, OCN products are validated against WAVEWATCH III (WW3) wave spectra for two available incidence angles [“wave mode” (WV); WV1: 23°; WV2: 36°], focused on the integral wave parameters and most energetic wave system of Sentinel-1A. The wave parameter difference between Sentinel-1A and WW3 along antenna look angles for WV1 demonstrates the obvious impact of the nonlinearity influence in the azimuth direction, resulting in an unrealistically high wave height at the low wave frequency, and the spurious split of wave systems in the range direction, due to the vanishing of velocity bunching modulation. WV2 is less pronounced in these two aspects, but tends to shift wave energy to a higher wave frequency in the range direction. The inside discrepancy of wave energy has two noticeable features: the difference in peak wavelengths in the wave spectrum is positively clustered in the azimuth direction and negatively clustered in the range direction; some of the most energetic partitions derived from Sentinel-1A are difficult to assign to any wave systems in WW3. This phenomenon could be related to wind-wave coupling as the azimuth cutoff/WW3 peak wavelength is confined to a ratio below 0.5 for the negative difference between Sentinel-1A and WW3 peak wavelengths and the spectral distance of most energetic wave system in Sentinel-1A highly resembles “swell pools.”

scholarly journals Mixed Rossby–Gravity Wave–Wave Interactions

2019 ◽  
Vol 49 (1) ◽  
pp. 291-308 ◽  
Author(s):  
Carsten Eden ◽  
Manita Chouksey ◽  
Dirk Olbers
Keyword(s):  
Kinetic Equation ◽  
Wave Field ◽  
Gravity Wave ◽  
Rossby Wave ◽  
Wave Energy ◽  
Wave Mode ◽  
Linear Wave ◽  
Wave Interactions ◽  
First Case ◽  
Linear Gravity

AbstractMixed triad wave–wave interactions between Rossby and gravity waves are analytically derived using the kinetic equation for models of different complexity. Two examples are considered: initially vanishing linear gravity wave energy in the presence of a fully developed Rossby wave field and the reversed case of initially vanishing linear Rossby wave energy in the presence of a realistic gravity wave field. The kinetic equation in both cases is numerically evaluated, for which energy is conserved within numerical precision. The results are validated by a corresponding ensemble of numerical model simulations supporting the validity of the weak-interaction assumption necessary to derive the kinetic equation. Since they are generated by nonresonant interactions only, the energy transfers toward the respective linear wave mode with vanishing energy are small in both cases. The total generation of energy of the linear gravity wave mode in the first case scales to leading order as the square of the Rossby number in agreement with independent estimates from laboratory experiments, although a part of the linear gravity wave mode is slaved to the Rossby wave mode without wavelike temporal behavior.

Band Gaps of SH Wave in Piezoelectric Phononic Crystal

2011 ◽  
Vol 239-242 ◽  
pp. 1486-1489
Author(s):  
Man Lan ◽  
Pei Jun Wei
Keyword(s):  
Dispersion Equation ◽  
Elastic Waves ◽  
Phononic Crystal ◽  
Stop Band ◽  
Slope Angle ◽  
Band Gaps ◽  
Pass Band ◽  
Wave Band ◽  
Sh Wave ◽  
Plane Sh Wave

The dispersive characteristic of anti-plane elastic waves propagating through laminated piezoelectric phononic crystal is studied in this paper. First, the transfer matrix method (TMM) and the Bloch theorem are used to derive the dispersion equation. Next, the dispersion equation is solved numerically and the dispersive curves are shown in Brillouin zone. The pass band and the stop band of anti-plane SH wave propagating perpendicular to and oblique to the laminated periodic structure are compared. The effects of the slope angle on the wave band structure are discussed.

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