| 1. |
- Argatov, Ivan, et al.
(författare)
-
Resonance spectrum for a continuously stratified layer : application to ultrasonic testing
- 2013
-
Ingår i: Waves in Random and Complex Media. - : Taylor & Francis. - 1745-5030 .- 1745-5049. ; 23:1, s. 24-42
-
Tidskriftsartikel (refereegranskat)abstract
- Ultrasound wave propagation in a nonhomogeneous linearly elastic layer of constant thickness immersed between homogeneous fluid and solid media is considered. The resonances (scattering poles) for the corresponding acoustic propagator are studied. It is shown that the distribution of the resonances depends on the smoothness of the coefficients that characterize physical properties of the layer and the ambient media. Namely, if the coefficients have jump discontinuities at the boundaries, then the resonances are asymptotically distributed along a straight line parallel to the real axis on the unphysical sheet of the complex frequency plane. On the contrary, if the coefficients are continuous, then it is shown that the resonances are asymptotically distributed along a logarithmic curve. The developed mathematical model is applied to the ultrasonic testing of the articular cartilage (AC) layer attached to the subchondral bone from one side and being in contact with a solution on the other side. It is conjectured that the spacing between two successive resonances may be sensitive to AC degeneration. The application of the obtained results to the development of ultrasonic testing for quantitative evaluation of AC is discussed.
|
|
| 2. |
- Goryashko, Vitaliy O., et al.
(författare)
-
The sharpness-induced mode stopping and spectrum rarefication in waveguides with periodically corrugated walls
- 2013
-
Ingår i: Waves in Random and Complex Media. - : Informa UK Limited. - 1745-5030 .- 1745-5049. ; 23:2, s. 89-113
-
Tidskriftsartikel (refereegranskat)abstract
- Starting from the rigorous excitation equation, the propagation of waves through a 2D waveguide with the periodically corrugated finite-length insert is examined in detail. The corrugation profile is chosen to obey the property that its amplitude is small as compared to the waveguide width, whereas the sharpness of the asperities is arbitrarily large. With the aid of the method of mode separation, which was developed earlier for inhomogeneous-in-bulk waveguide systems [Waves Random Media 2000; 10: 395], the corrugated segment of the waveguide is shown to serve as the effective scattering barrier whose width is coincident with the length of the insert and the average height is controlled by the sharpness of boundary asperities. Due to this barrier, the mode spectrum of the waveguide can be substantially rarefied and adjusted so as to reduce the number of extended modes to the value arbitrarily less than that in the absence of corrugation (up to zero), without changing considerably the waveguide average width.
|
|
| 3. |
|
|
| 4. |
- Kvasha, O. V., et al.
(författare)
-
The propagation of in-plane P-SV waves in a layered elastic plate with periodic interface cracks: exact versus spring boundary conditions
- 2011
-
Ingår i: Waves in Random and Complex Media. - : Informa UK Limited. - 1745-5030 .- 1745-5049. ; 21:3, s. 515-528
-
Tidskriftsartikel (refereegranskat)abstract
- The propagation of in-plane (P-SV) waves in a symmetrically three-layered thick plate with a periodic array of interface cracks is investigated. The exact dispersion relation is derived based on an integral equation approach and Floquet's theorem. The interface cracks can be a model for interface damage, but a much simpler model is a recently developed spring boundary condition. This boundary condition is used for the thick plate and also in the derivation of plate equations with the help of power series expansions in the thickness coordinate. For low frequencies (cracks small compared to the wavelength) the three approaches give more or less coinciding dispersion curves, and this is a confirmation that the spring boundary condition is a reasonable approximation at low frequencies.
|
|
| 5. |
- Lindgren, Georg
(författare)
-
Horseshoe-like patterns in first-order 3D Gauss-Lagrange waves with directional spreading
- 2015
-
Ingår i: Waves in Random and Complex Media. - : Informa UK Limited. - 1745-5030 .- 1745-5049. ; 25:4, s. 729-745
-
Tidskriftsartikel (refereegranskat)abstract
- The Gauss–Lagrange model for ocean waves describes the vertical and horizontal movements of water particles as three correlated Gaussian fields. The model can produce irregular waves, asymmetric in both vertical and horizontal direction, and by judicious choice of a single skewness parameter the front–back asymmetry can be regulated to realistic values. In this paper, it is shown that this additive model for shallow waters can also produce horseshoe-like patterns around moderate to high wave crests. Such phenomena are usually analyzed and described as nonlinear interaction effects between different frequencies. The tool in the paper is a Slepian model for the three-dimensional movements conditioned on a wave crest
|
|
| 6. |
- Matus, V. V., et al.
(författare)
-
Wave propagation in 2D elastic composites with partially debonded fibres by the null field appraoch
- 2009
-
Ingår i: Waves in Random and Complex Media. - : Informa UK Limited. - 1745-5030 .- 1745-5049. ; 19:4, s. 654-669
-
Tidskriftsartikel (refereegranskat)abstract
- Time-harmonic plane wave propagation in a two-dimensional (2D) elastic matrix with partially debonded elastic fibres of nonclassical cross-section is investigated. The modified null field approach, taking into account the asymptotic behaviour of the solution at the interface crack-tips, is exploited to obtain the numerical results for a single scatterer. The effective medium approach based on Foldy's approximation is applied to estimate the average dynamic parameters of the composites containing randomly distributed partially debonded fibres of dilute concentration. Numerical results concern the longitudinal wave dispersion and attenuation owing to scattering by both randomly oriented and aligned fibres. The effects of the fibre shape, debonding (interface crack) size and direction of wave incidence on the effective P-wave velocity and attenuation coefficient are analysed.
|
|
| 7. |
- Mykhas'kiv, V. V., et al.
(författare)
-
Effective dynamic properties of 3D composite materials containing rigid penny-shaped inclusions
- 2010
-
Ingår i: Waves in Random and Complex Media. - : Informa UK Limited. - 1745-5030 .- 1745-5049. ; 20:3, s. 491-510
-
Tidskriftsartikel (refereegranskat)abstract
- The propagation of time-harmonic plane elastic waves in infinite elastic composite materials consisting of linear elastic matrix and rigid penny-shaped inclusions is investigated in this paper. The inclusions are allowed to translate and rotate in the matrix. First, the three-dimensional (3D) wave scattering problem by a single inclusion is reduced to a system of boundary integral equations for the stress jumps across the inclusion surfaces. A boundary element method (BEM) is developed for solving the boundary integral equations numerically. Far-field scattering amplitudes and complex wavenumbers are computed by using the stress jumps. Then the solution of the single scattering problem is applied to estimate the effective dynamic parameters of the composite materials containing randomly distributed inclusions of dilute concentration. Numerical results for the attenuation coefficient and the effective velocity of longitudinal and transverse waves in infinite elastic composites containing parallel and randomly oriented rigid penny-shaped inclusions of equal size and equal mass are presented and discussed. The effects of the wave frequency, the inclusion mass, the inclusion density, and the inclusion orientation or the direction of the wave incidence on the attenuation coefficient and the effective wave velocities are analysed. The results presented in this paper are compared with the available analytical results in the low-frequency range.
|
|
| 8. |
- Zhang, Y., et al.
(författare)
-
Polarization-independent 2D omni-directional photonic band gaps in a 1D periodic metal-dielectric (anisotropic) structure
- 2009
-
Ingår i: Waves in Random and Complex Media. - : Informa UK Limited. - 1745-5030 .- 1745-5049. ; 19:1, s. 39-48
-
Tidskriftsartikel (refereegranskat)abstract
- It is shown that there is no polarization-independent two-dimensionally (2D) omni-directional photonic band gap (PBG) for any conventional one-dimensional (1D) metal-dielectric (isotropic) structure. Through the study of band diagrams and some asymptotic analysis, a 1D periodic metal-dielectric (anisotropic) structure is proposed to achieve a polarization-independent 2D omni-directional PBG. Theoretical predictions for both the lossless and lossy cases are verified with finite element method (FEM) simulation of a point source in such a structure.
|
|
