Development of attenuation and diffraction corrections for linear and nonlinear Rayleigh surface waves radiating from a uniform line source

Effect of surface scratches on the characteristics of nonlinear Rayleigh surface waves in glass

Nonlinear ultrasonic waves have shown to be sensitive to various microstructural changes in metals including coherent precipitates; these precipitates introduce a strain field in the lattice structure. The thermal aging of certain alloy steels leads to the formation of coherent precipitates, which pin dislocations and contribute to the generation of a second harmonic component. A precipitate hardenable material namely 17–4 PH stainless steel is thermally treated in this research to obtain different precipitation stages, and then the influence of precipitates on the acoustic nonlinearity parameter is assessed. Conclusions about the microstrucutural changes in the material are drawn based on the results from a nonlinear Rayleigh surface wave measurement and complementary thermo-electric power, hardness and ultrasonic velocity measurements. The results show that the nonlinear parameter is sensitive to coherent precipitates in the material and moreover that precipitation characteristics can be characterized based on the obtained experimental data.

Estimation of near-surface shear-wave velocities and quality factors using multichannel analysis of surface-wave methods

Views Icon Views Article contents Figures & tables Video Audio Supplementary Data Peer Review Share Icon Share Twitter Facebook Reddit LinkedIn Tools Icon Tools Reprints and Permissions Cite Icon Cite Search Site Citation David Torello, Jin-Yeon Kim, Jianmin Qu, Laurence J. Jacobs; Measurement and fitting techniques for the assessment of material nonlinearity using nonlinear Rayleigh waves. AIP Conf. Proc. 31 March 2015; 1650 (1): 136–145. https://doi.org/10.1063/1.4914603 Download citation file: Ris (Zotero) Reference Manager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentAIP Publishing PortfolioAIP Conference Proceedings Search Advanced Search |Citation Search

Excitation of nonlinear surface waves is studied at the SBN-75 crystal — air interface. The SBN-75 crystal is characterised by the diffusion-type photorefractive nonlinearity, the surface wave being excited in the surface layer and the depth of its penetration into the crystal being determined by the nonlinear crystal parameters. Because of a large refraction coefficient in SBN-75, the penetration depth of the surface wave into the air is small; therefore, the nonlinear surface wave is localised in the surface crystal layer several micrometers in thickness. The oscillating intensity distribution of the surface wave at the output end of the crystal is measured. The oscillation period is determined by the angle of incidence of the exciting beam. The nonlinear wave is excited not only at the crystal — air interface but also in the case when the active surface of the crystal is covered by an electrode, for example, an aquadag layer. This circumstance opens up a possibility of studying new properties of the surface waves when an external electric field is applied to the crystal.

In this review we consider the propagation of nonlinear waves in magnetically structured plasmas. We start from studying nonlinear surface waves on magnetic interfaces and give a derivation of the equation governing propagation of these waves in incompressible plasmas. We present the results of a numerical solution of this equation. Then we discuss various generalizations of this equation.We proceed to study slow nonlinear waves in magnetic slabs. We present the Benjamin-Ono equation describing nonlinear slow sausage surface waves in magnetic slabs, and discuss its solutions in the form of algebraic solitons. Then we consider nonlinear slow body waves and write down the governing equation for these waves. We discuss its numerical solution which shows that the evolution of an initial perturbation results in a gradient catastrophe.After that we consider nonlinear slow sausage surface and slow body waves in magnetic tubes, which are similar to the corresponding counterparts in magnetic slabs. We present a system of two equations describing both types of waves. We briefly discuss the derivation of the Leibovich-Roberts equation for slow sausage surface waves from this system of equations, and present the results of its numerical study. Then we give a brief description of the derivation of the governing equation for slow body waves, which is very similar to its counterpart for slow body waves in magnetic slabs and has very similar properties. We complete this part of the review with presenting the governing equation for non-axisymmetric surface waves in a thin magnetic tube in an incompressible plasma.In the last part of the paper we consider the damping of nonlinear waves in weakly dissipative magnetically structured plasmas. We briefly discuss the application of the obtained results to the problem of heating of the solar corona.KeywordsSurface WaveSolitary WaveSolar PhysMagnetic TubeKink ModeThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

This paper describes the acoustic nonlinearity parameter (β) determination for fluids using a pulse-echo method with the stress-free boundary. A newly derived β formula requires the measurement of the fundamental and second harmonic displacements with appropriate corrections for attenuation, diffraction, and boundary reflection. Measurements are composed of two steps: receiver calibration and harmonic generation. The β values calculated for water at several distances between the planar transducer and the water-air interface are in good agreement with literature, providing a validation for the method.

A hybrid numerical method for the prediction of free surface flows including both nonlinear wave and viscous effects is presented. In this method, a zonal approach that combines a potential flow method for fully nonlinear free surface waves and a Reynolds-averaged Navier-Stokes (RANS) method for turbulent incompressible flow is used. The potential flow equation is solved in the far field to provide the nonlinear waves generated by the body motion. The RANS method is used in the near field to resolve the turbulent boundary layer and wake flows around the body. Extensive results are presented for a submerged hydrofoil with and without the presence of free surface waves. The coupled RANS and potential flow method successfully resolves the body boundary layer, the viscous wake, and the nonlinear free surface waves. The results clearly demonstrate the feasibility of the coupling approach and therefore enables the use of a rather small RANS solution domain for efficient and accurate resolution of free surface flows including both the viscous and nonlinear wave effects.

The nonlinear TE-polarized surface waves localized at the interface between a nonlinear uniform material and a semi-infinite one-dimensional photonic crystal are investigated. We assume that the nonlinear material is right handed and the photonic crystal is made of alternate left-handed metamaterial and right-handed material. We study the intensity-dependent properties of the nonlinear surface waves for both self-focusing and defocusing Kerr-like nonlinearity. Unlike the linear regime, it is shown that in the case of self-focusing nonlinearity the dispersion curve has two branches corresponding to two types of surface mode structures (one structure with a hump at the interface and the other one with two humps). While, in the case of defocusing nonlinearity the dispersion curve has a single branch. We also show that the existence region of the surface waves is intensity dependent (independent) in the case of self-focusing (defocusing) nonlinear regime and the presence of left-handed materials and nonlinear medium provides a possibility for forward or backward waves selection in the given structure by adjusting the intensity parameter at the interface.

The Turkish plate is covered by hundreds of accelerometer and broadband seismic stations with less than 50 km inter-station distance providing high-quality earthquake recordings within the last decade. We utilize part of these stations to extract the fundamental mode Rayleigh and Love surface wave phase and group velocity data in the period range 5–20 s to determine the crust structure beneath the Aegean region in southwest Turkey. The observed surface wave signals are interpreted using both single-station and two-station techniques. A tomographic inversion technique is employed to obtain the two-dimensional group velocity maps from the single-station group velocities. One-dimensional velocity–depth profiles under each two-dimensional mesh point, which are jointly interpreted to acquire the three-dimensional image of the shear-wave velocities underneath the study area, are attained by utilizing the least-squares inversion technique, which is repeated for both Rayleigh and Love surface waves. The isotropic crust structure cannot jointly invert the observed Rayleigh and Love surface waves where the radial anisotropic crust better describes the observed surface wave data. The intrusive magmatic activity related to the northward subducting African plate under the Turkish plate results the crust structure deformations, which we think, causing the observed radial anisotropy throughout complex pattern of dykes and sills. The magma flow resulting in the mineral alignment within dykes and sills contributes to the observed anisotropy. Due to the existence of dykes, the radial anisotropy in the upper crust is generally negative, i.e., vertically polarized S-waves (Vsv) are faster than horizontally polarized S-waves (Vsh). Due to the existence of sills, the radial anisotropy in the middle-to-lower crust is generally positive, i.e., horizontally polarized S-waves (Vsh) are faster than vertically polarized S-waves (Vsv). Similar radial anisotropic results to those of the single-station analyses are obtained by the two-station analyses utilizing the cross-correlograms. The widespread volcanic and plutonic rocks in the region are consistent with the current seismic interpretations of the crustal deformations.

In this paper we present frequency and transient analysis of a thin tabular conductive slab in lossy Earth due to a uniform magnetic line source excitation. The line source is parallel to the slab, and thus the problem is two dimensional. Under these conditions the frequency domain solution can be expressed in the form of a series which has an exact time domain representation. Our results are checked against two well‐known limiting cases. This problem can model ore slabs and fluid‐filled cracks in geophysical applications. The analytical and numerical results give a diagnosis of the thickness and conductivity of the slab and provide physical insight in the interpretation of actual field data.

The white-lipped frog, Leptodactylusalbilabris, exhibits the greatest sensitivity to substrate-borne vibrations (seismic stimuli) reported to date for any terrestrial animal. Nerve fibers from the sacculus, the source of this extraordinary sensitivity, show clear responses to sinusoidal seismic stimuli with peak accelerations less than 0.001 cm/s2. In addition, this animal generates substrate-borne vibrational signals during calling. As the male’s vocal sac expands, it strikes the substrate impulsively, generating a vertically polarized surface (Rayleigh) wave that is detected by neighboring males. These Rayleigh waves are used as intraspecific communication signals to coordinate chorus behavior in this species. Recently, a particularly unusual behavior has been described for one species of Malaysian treefrog (Polypedates). During nocturnal courtship, females living in dense mats of floating vegetation perch conspicuously on a reed or blade of grass and tap their rear toes rhythmically. Males on neighboring reeds were observed to quickly locate and mate with the tapping female. Thus it is likely that toe tapping functions as a vibrational signal indicating the female’s presence to neighboring males. It is becoming clear that seismic communication and sensitivity to whole-body vibrations are more ubiquitous among the vertebrates than had been previously imagined. [Work supported by NIH.]

Magnetomechanical materials such as ferromagnetic elastic polycrystals exhibit magnetostrictive couplings and can be used in a variety of signal processing devices, although perhaps not to the same extent as piezoelectric materials. The nonlinear characteristics of these devices may be benefical or undesirable. After some preliminary results on nonlinear rotationally invariant equations and the nonlinear bulk, coupled magnetoacoustic waves, perturbations and multiple-scale techniques are used to study two particularly relevant problems. One of these concerns the nonlinear propagation of generalized (magnetoacoustic) Rayleigh waves on a magnetostrictive substrate. The second one concerns the vibrations of a magnetostrictive elastic resonator. In the first case exhibiting mode couplings, the generation of harmonics and the anisochronism of nonlinear surface waves are studied by means of a multiple-scale technique in which the secularity condition is shown to be provided by a system of complex coupled-amplitude equations in the manner of nonlinear optics. In the second case a Galerkin representation is followed by a multiple-scale technique. In both cases the influences of magnetostriction and nonlinear elasticity are clearly delineated.

A non-destructive method for characterizing the depth of artificial surface-breaking flaws (slots) using Rayleigh surface waves is described. Dynamic photoelasticity was used to obtain a full-field visualization of the waves generated on interaction of a Rayleigh wave with a slot. This visualization showed that for slot lengths of the same order of size as the predominant wavelengths in the incident Rayleigh wave, there is a significant interaction of the subsurface Rayleigh disturbance with the slot tip, producing transmitted surface disturbances that were quantitatively analyzed. Specifically, the frequency content of these transmitted waves was found for four different slot depths. The high frequency components of these transmitted signals exhibited a maximum frequency which decreased with increasing slot depth. This was attributed to the fact that the maximum frequencies of the subsurface field of the incident Rayleigh wave decrease with increasing depth. Ultrasonic testing was also done on surface slots in steel blocks, using commercial Rayleigh wave transducers. A relationship similar to the photoelastic results was obtained for the frequency components of the transmitted waves at the surface relative to the slot depth. However, in the ultrasonic case, there was a definite high frequency cut off point which could be directly related to the slot depth for slots perpendicular to the surface. This relationship was shown to also accurately predict the depth of inclined slots.

A mathematical model for the movement of a conducting liquid through a conducting porous medium: I. Excitation of oscillations of the magnetic field by the surface Rayleigh wave