Generation Of Elastic Waves Research Articles

О рассеянии релеевских и продольных сейсмических волн на локальной неровности грунта

A three-dimensional (3D) numerical simulation of scattering of seismic surface Rayleigh and longitudinal waves propagating through the ground, the density and elasticity of which are typical of geomedium. At the soil boundary, there is local unevenness in the form of a hollow hemispherical notch (a truncated sphere). The dependence of the direction of the scattering field on the type of inhomogeneity is shown. From literature it is known that in the transition to another type of heterogeneity, for instance, to covering the boundary with a thin inert (massive) layer in the form of a circle, the forward scattering occurs. A pulsed mode of inhomogeneity probing is considered. As an emitter, it is proposed to use a short pulse source, e.g., a hydroacoustic emitter, or something similar - a pulsating monopole, shallowly immersed under the free boundary. This leads to the generation of such elastic waves as the surface Rayleigh and back-reflected longitudinal waves, which are usually recorded using an array of seismic receivers installed on the free boundary according to the grid pattern. The spatial amplitude distribution of the wave field is analyzed in the vertical (at the center of the inhomogeneity) and horizontal (at the free boundary) sections of the medium. The characteristic features of the wave field are caused by the influence of its scattering on the local inhomogeneity. The features in the image of wave reliefs that arise at the intersection of the wave fronts of longitudinal waves - reflected from the free boundary and scattered on the local inhomogeneity - are studied. Informative signs, indicating the presence of the local heterogeneity and enable diagnostics of its parameters are established. The ways to improve the validity and reliability of algorithms for detection and classification of inhomogeneities and for evaluation of their difficulties using the listed types of waves are discussed. Based on the use of increasingly shorter probing pulses, the possibility of a detailed representation of reliefs and, consequently, the potentially achievable spatial resolution in probing the local subsurface inhomogeneities are demonstrated.

Nonlinear elastic waves generated by surface wave interaction with local plasticity in thick-walled structures

Thick-walled structures (TWSs) are frequently utilized as primary load-bearing structures across diverse industrial sectors, illustrated by train axles. Proper health monitoring, particularly for early damage detection, is required to ensure the operational safety and structural integrity of such structures. Nonlinear elastic-wave-based structural health monitoring techniques present a potentially efficacious methodology, which relies heavily upon the understanding of nonlinear wave generation and propagation characteristics. Unfortunately, due to the complexity introduced by various wave modes in TWSs, a comprehensive understanding of nonlinear elastic waves is still lacking. Considering practical local plasticity on the surface of a TWS, this study investigates the characteristics of nonlinear elastic wave generation and propagation resulting from the fundamental surface wave-local plasticity interaction. Theoretical analyses were carried out to examine the scattering features of the generated nonlinear bulk waves based on Snell’s law. Finite element simulations were then performed to confirm the predicted scattering characteristics of the nonlinear bulk waves, with the introduction of a local material nonlinearity to replicate the plasticity in a TWS. Using the extrusion method, a local plastic zone was produced on an aluminum thick-walled beam. Experiments were finally carried out using a laser vibrometer to confirm the scattering features of nonlinear elastic waves. It was found that the nonlinear shear bulk waves are mainly generated due to the fundamental surface interaction with local plasticity. Furthermore, the generated nonlinear shear bulk waves propagate at a fixed angle towards the interior of the TWS, which can be measured on the opposite surface. The elucidation of the nonlinear elastic wave generation and propagation characteristics paves the way for an effective sensor arrangement in early damage detection applications.

Prediction of directivity characteristics of piezoelectric macro-fiber composite interdigital transducers: a semi-analytical approach

The employment of guided waves for structural health monitoring applications has attracted substantial attention in recent years. Piezoelectric transducers are frequently employed in these systems for elastic wave generation and acquisition. Their dynamic properties, i.e., direction-dependent frequency characteristics, are an important feature for designing a reliable monitoring strategy. Although analysis of the transducer directivity pattern can be performed using finite element models, these usually tend to be computationally very expensive, especially, for parametric and optimization studies. In this paper, a semi-analytical methodology is proposed that can predict the far-field responses of complex transducers of arbitrary shape and structure mounted on elastic plates. The approach reported here couples analytical far-field predictions with a local FE model evaluating the traction field generated by the transducer. Thus, the FE model captures the near-field responses, while the analytical part predicts the far-field responses. The implementation of this semi-analytical method requires development of analytical and numerical frameworks. The former includes computation of dispersion curves of the inspected plate, the stress and displacement profiles of wave modes and the excitability curves, while the latter includes estimation of the traction field between the transducer and the plate using the FE model. Owing to the popularity of piezoelectric macro-fiber composite (MFC) interdigital transducers, in this paper, we apply the proposed method to simulate the directivity patterns of the MFC IDTs of different configurations. To validate the reliability of the proposed method the simulated patterns are compared with experimental results obtained using Laser Doppler Vibrometer (LDV).

Characteristic and mechanism of pollution by laser cleaning high-value vehicle parts with a complex structure in remanufacturing industry

Remanufacturing high-value vehicle parts is of substantial significance for the circular economy because it provides a second service life and reduces solid waste generation. Laser cleaning is a promising method in the remanufacturing industry owing to its high energy, precision, and efficiency. However, the pollution caused by laser cleaning remains unknown and has rarely been reported, limiting the application of this method. In this study, pollution removal and conversion using a high-energy laser were explored, and environmental life cycle and health risk assessments were conducted. The results showed that high-energy lasers might induce new organic pollutants, such as olefins, alkynes, and aldehydes. During laser cleaning, thermal elastic expansion and shock wave generation were the main mechanisms of rust removal, and evaporation and small-scope boiling were used for waste oil removal. The mean concentration of PM10 was above 7000 µg/m3 in laser rust removal, and the total concentration of volatile organic compounds (VOCs) was the highest in laser oil removal (∼ 2568 µg/m3). Particulate matter contained high amounts of Fe, Al, and Mn. An environmental life cycle assessment indicated that laser cleaning for stain removal significantly reduced the total environmental impact compared with that of traditional solvent-ultrasonic cleaning (∼ 40.0%) and sandblasting (∼ 83.3%). This study provides an environmental protection basis for increasing the use of laser cleaning in the remanufacturing industry.

Low-frequency air-coupled transducer based damage detection in composite materials

In this paper results of simulations of non-contact elastic wave generation in the composite panel based on acoustic to elastic wave transformation are presented. For this purpose simulations of acoustic wave generation and processing are based on the FEM method in COMSOL. Elastic wave generation and propagation are based on the spectral element method (SEM) in the time domain. The SEM model utilises time-varying acoustic pressure distributions calculated in the FEM. The SEM allows to simulate the interactions of elastic waves with the delamination. Damage localization is based on RMS elastic wave energy maps. In this research a panel made of carbon fibre-reinforced polymer composite is investigated. Research related to low-frequency air-coupled transducer (ACT) is presented. The utilisation of low-frequency waves allows for the reduction of the effects of the wave attenuation in composite material. The proposed combination of FEM and SEM gives an efficient tool for the simulation of non-contact wave generation for non-destructive testing analysis.

Mechanisms of elastic wave generation by EMAT in ferromagnetic media

The present paper deals with the problem of elastic wave generation mechanisms (WGMs) by an electromagnetic-acoustic transducer (EMAT) in ferromagnetic materials. The paper seeks to prove that taking into account all the WGMs must be a general rule to quantitatively predict the elastic waves generated by an EMAT in such materials. Existing models of the various physical phenomena involved, namely magnetic and magnetostrictive, electromagnetic, and ultrasonic, are combined to solve the multiphysics wave generation problem. The resulting model shows that WGMs (i.e., electromagnetic force, magnetostrictive strain, and magnetic traction) strongly depend on material properties and EMAT design and excitation. To illustrate this, four magnetic materials (nickel, AISI410, Z20C13, and low carbon steel) with similar elastic but contrasting electromagnetic properties are studied. A given EMAT of fixed excitation and geometry yields WGMs with highly different amplitudes in these materials, with a WGM dominant in one material being negligible in another. Experimental results make it possible to validate the accuracy of certain predictions of the model developed. In summary, the present work shows that considering all WGMs is the general rule when working with ferromagnetic materials. Furthermore, it offers a generic model that can be integrated into various numerical tools to help optimize EMAT design and give reliable data interpretation.

A study on microcrack monitoring in concrete: discrete element method simulations of acoustic emission for non-destructive diagnostics

The research is focused on the monitoring of fracture evolution in concrete beams under three-point bending using the acoustic emission technique and the discrete element method. The main objective of the study was to numerically and experimentally investigate the mechanism behind the generation of elastic waves during acoustic emission events and their interaction with micro- and macro-cracking in concrete beams under monotonic quasi-static loading. This was achieved through the development of a DEM model and numerical modelling of AE effects. An improved 4-phase DEM model of concrete including real mesostructured specimens and the ability to simulate aggregate breakage was introduced. The propagation of elastic waves, recorded in both laboratory experiments and numerical calculations, was given particular attention. The results showed the high suitability of the developed DEM model for monitoring crack initiation, development and propagation, as well as for supporting the interpretation of diagnostic results obtained by acoustic emission techniques.

Damage localization using contact and non-contact narrow frequency band elastic wave generation

In this paper analyses of non-contact elastic wave generation based on an air-coupled transducer (ACT) are presented. Authors compared contact piezoelectric based (PZT) wave generation, with non-contact one using ACT for a narrow frequency band excitation. Elastic wave sensing was based in both cases on a scanning laser Doppler vibrometer. The problem of ACT slope angle for the effectiveness of elastic wave modes generation is analysed. It was shown that for an excitation frequency of 40 kHz it is possible to generate A0 wave mode both in the case of PZT and ACT. Both methods of wave generation are compared based on an analysis of damage localisation results. For this purpose wave irregularity mapping (WIM) algorithm was utilised together with two attenuation compensation methods (based on energy normalisation and weighting function). Specimens in the form of simple square GFRP panel and bonded GFRP aerospace structure with omega stiffeners were investigated. The authors investigated simulated damage (Teflon inserts) and real delamination. In this research very cheap and popular, low-frequency ACT was utilised giving the possibility of realisation of low-cost excitation method. ACTs connected with a laser vibrometry sensing allows of realisation of full non-contact damage localisation method. Authors presented also non typical but very useful application of SLDV allowing to visualise the effect of acoustic wave generation in the air and determination of the pattern of generated acoustic waves. This was based on the photo-acoustic effect.

Research on the evolution law of the seismic wave field based on the explosive source parameters

We present a numerical model for blast-induced seismic waves. This model is based on the transformation mechanism of the seismic wave field, and the process of the seismic wave’s generation is divided into two stages. The first stage is the generation of elastic waves. Due to the plastic deformation of the geotechnical medium in this stage, we have established the Euler model to describe it. The second stage is the prorogation of the elastic waves; we have established the Lagrange models to describe this stage. Finally, the influence of the main parameters of the explosive sources (detonation pressure and expansion index) on the seismic wave is analyzed by the established model. The results show that the proposed model in this paper can reasonably predict the evolution law of the seismic wave field based on the explosive source parameters.

Time-frequency simulation of ultrasonic longitudinal wave propagation in rocks

Ultrasound numerical simulation can be used as a powerful tool to investigate the generation, propagation, and interaction of elastic waves in solid materials for non-destructive evaluation (NDE). It has been widely applied in several domains such as medical, mechanical, construction, and geotechnical engineering, especially for the detection of cracks and defects in structures and for the identification of the characteristics of rock materials. The comprehension of the propagation of the ultrasonic wave in homogeneous and isotropic elastic materials is very important. This paper presents a method for simulating normal incidence ultrasonic waves (Longitudinal waves) propagating in rock structures. A mathematical model of the response of an ultrasonic wave in a submerged rock structure is introduced analytically based on the transfer matrix method (TMM), in which the layer is established in a quadrupole formalism. The simulation results of the ultrasonic response of rock structures are represented in a time–frequency representation. The results have been compared with the experimental data available in the literature and show good agreement. The numerical simulation method established in this work can be proposed as an effective complement to experiments and used for rock characterization by performing the simulation of ultrasonic responses for different thicknesses of rock structures.

Analysis of damage localisation results in GFRP panel for different configurations of air-coupled transducers

In this paper results of the damage assessment of fiber-reinforced composite panels using guided wave propagation phenomenon are presented. For this purpose, non-contact elastic wave generation based on an air-coupled transducer (ACT) is utilised. Elastic wave sensing was based on a scanning laser Doppler vibrometer (SLDV). The problem of ACT slope angle for the effectiveness of elastic wave modes generation is analysed. It was shown that for an excitation frequency of 40 kHz it is possible to generate A0 wave mode. The authors also investigated the damage sensitivity related to panel coverage area by elastic waves with large energy. An artificial damage in the form of Teflon inserts was utilised. Moreover, the influence of single and multiple acoustic wave sources on artificial damage localisation results was investigated. For this purpose RMS wave energy maps, statistical parameters, and damage indices are utilised. Different locations of ACTs and their influence on damage localisation results are investigated. A damage imaging algorithm based on wavefield irregularity mapping (WIM) has been proposed. In this research low-cost and popular, low-frequency ACT was utilised giving the possibility of realisation of the non-contact damage localisation method.

Dispersive higher harmonic generation and enhancement in mechanical metamaterials

Higher harmonic generation (HHG) of elastic waves is beneficial for various applications, including engineering nondestructive testing, imaging, therapy, etc. Due to the ubiquity of dispersion in most materials and structures, however, it is usually difficult to simultaneously satisfy the conditions of phase-matching and non-zero energy flux that are needed for high-efficient HHG. Here we propose a mechanical metamaterial with coupled translation-rotation motion and explore its rich dispersion property for the enhancement of two HHGs in arbitrary regions of the acoustic band, i.e., the dispersive second harmonic generation (SHG) and the dispersive third harmonic generation (THG). Besides the phase-matching condition for enhancing SHG, we analytically obtain two phase-matching conditions for THG and reveal that THG is a complex process involving the interaction of multiple waves. By tailoring the dispersion of the metamaterial, the enhanced dispersive SHG and HHG are shown to be able to propagate at an arbitrarily slow group velocity, or even zero velocity, giving rise to localization. The analytical predictions are validated by numerical simulations and experimental tests. This work shows that by combining nonlinearity, mechanical metamaterials can be designed to have advanced capabilities of wave manipulation.

Mass Transmission Regularities in CdTe under Nanosecond Laser Irradiation

In this paper, the mechanisms of mass transfer in the In/CdTe system under nanosecond pulsed laser irradiation, which are due to nonstationarity, nonequilibrium, physical and geometric nonlinearity, high speed and simultaneity of various physical processes; in particular, it is a change in the physical state of a solid body, the generation of elastic and shock waves, significant temperature and stress gradients, defect formation, diffusion, and others. The dominant mechanisms and regularities of indium mass transfer in CdTe under nanosecond laser irradiation of the In-CdTe structure have been established.

Acousto-optic devices using acoustic waves refraction

The methods of acousto-optics provide multiple techniques for controlling optical beam. The technical parameters of corresponding acousto-optic devices are largely determined by the efficiency of acoustic waves generation. In present work we examine the features of elastic waves generation in materials used in acousto-optics. In most of practical applications the elastic wave generation process is implemented through the refraction of elastic waves at the boundary between two anisotropic media. We present a detailed study of the refraction of elastic waves in strongly anisotropic media. We report new refractive effects such as “extraordinary” refraction. In the latter case the change in the direction of the incident acoustic wave does not influence the direction of the energy flow propagation for refracted elastic waves. The configuration of an acousto-optic device using the geometry of unusual refraction in an anisotropic medium is discussed.

Acoustic radiation force optical coherence elastography for ocular biomechanics

The mechanical properties of the cornea, limbus, and sclera provide important information regarding eye health. Optical coherence elastography (OCE) is highly suitable for assessing ocular tissues' mechanical properties due to its high resolution and superior displacement sensitivity. Typically, elastography involves an external mechanical excitation of the tissue. We recently adopted a method of Air-Coupled Acoustic Radiation Force for the generation of elastic waves in ocular tissues. This method shows several clear advantages other than the traditionally used air-puff excitation. However, the safety of this method needs to be studied before its clinical applications. Also, there is increased interest in passive elastography, where the mechanical response to natural physiological forces like heartbeat and respiration is measured. I will also demonstrate examples of using heartbeat for quantification of tissues' mechanical properties in vivo.

Features of semiconductor irradiation with low-energy caesium ions

The paper considers the emission of secondary cluster ions when Si and GaAs surfaces are simultaneously sputtered with low-energy caesium ions (0.5–2 keV) and a pulsing beam of bismuth ions with an energy of 30 keV. It is shown that the observed mass spectra can be obtained if the caesium atoms implanted during irradiation form nano-islands (nanoparticles) at the irradiated surface. It was found that these Cs nanoparticles are formed under the surface due to the so-called Ostwald ripening process and come to the surface during the ongoing sputtering. The composition of the experimental mass spectra with 6–7 target and caesium atoms of a sufficiently high intensity leads to the conclusion that neither the recombination model nor the direct emission model can explain the observed emission. We explain the observed yield of cluster ions by the sputtering mode with the formation of “thermal spots”. These high-temperature spots resulting from collisions of primary bismuth ions with target atoms give rise to the generation of elastic waves in the target. These waves reach the surface and lead to a simultaneous escape of several atoms from the surface layer, or, in other words, to the formation of a secondary cluster.

Quasi-static secondary flow regions formed by microfluidic contraction flows of wormlike micellar solutions

This study investigates the effects of yield stress (τ0) and shear banding on the fluidic behaviors of cetyltrimethylammonium bromide/sodium salicylate wormlike micellar solutions flowing through a microfluidic planar contraction (8:1) geometry. Test solutions with different surfactant concentrations (Cd = 75, 87.5, and 100 mM) at a fixed molar ratio of salt to surfactant (R = 0.32) were characterized by shear and extensional rheometry. While the lower concentrated test solution (Cd = 75 mM) with low τ0 (≈ 0.02 Pa) and no shear banding showed a Newtonian-like flow behavior for Mach number, Ma < 1, the flow with corner vortices was formed when Ma exceeds unity. For higher Cd (87.5 and 100 mM), new fluidic phenomena are documented: (i) even at a low volumetric flow rate (Q), the fluid velocity at upstream corners was slower than that of Newtonian-like flows and (ii) at higher Q, the secondary flow with a quasi-static condition was formed at Ma well lower than unity. Micro-particle image velocimetry showed the lower shear rates at upstream corners, which can be understood by the effects of contraction entry, shear thinning, and high yield stress. The quasi-static secondary flow region was not induced by generation of elastic shock waves; instead the shear banding was found to be the underlying mechanism for the separation of the region from the main flow. In addition, the length of secondary flow regions showed a close correlation with the Deborah number, which was calculated using the extensional relaxation time.

Технические средства волнового воздействия на продуктивные пласты

The article is devoted to the problem of hydrocarbon extraction through the use of wave technologies and technical means of influencing reservoirs, which underlines its urgency. A classification of main processes that occur in productive formations during wave action, as well as design features and operating principles of oil recovery enhancement techniques, is proposed. A critical review of field testing the technical means of wave action in oil fields allows us to identify their fundamental advantages and disadvantages. Theoretical and experimental research of some devices of elastic wave generation and results of their laboratory tests are presented.

Confocal air-coupled ultrasonic optical coherence elastography probe for quantitative biomechanics.

We present an air-coupled ultrasonic radiation force probe co-focused with a phase-sensitive optical coherence tomography (OCT) system for quantitative wave-based elastography. A custom-made 1 MHz spherically focused piezoelectric transducer with a concentric 10 mm wide circular opening allowed for confocal micro-excitation of waves and phase-sensitive OCT imaging. Phantom studies demonstrated the capabilities of this probe to produce quasi-harmonic excitation up to 4 kHz for generation of elastic waves. Experimental results in ocular tissues showed highly detailed 2D and 3D elasticity mapping using this approach with great potential for clinical translation.

Strength of upstream and downstream chambers, collectors, heat exchange tubes of gas aerial cooler apparatus, and assessment of life extension

The gas aerial cooler apparatus (ACA) were characterized. These ACA serves for cooling the service gas. The analysis of engineering documentation was carried out in order to establish the range of amenable to control parameters of the engineering status, to carry out the recognition of failures (if ever) and damages that could led to a failure. The applied method of acoustic emission (AE) yielded total and direct information on the defect growth (hazard rate) in materials of operational facilities. The AE control might be used as a determinative procedure for the selection of criteria needed for assessing the status of diverse structures as well as for release to continued operation the production facilities (with providing a necessary level of safety during the enterprise operation) because the AE control enables to detect a fault at early stage of its growth. By applying the AE method for elaboration of a control of specific objectives, complicated problems related to generation of elastic waves from growing cracks and their transformation during propagation up to sensors were successively resolved.