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  • Articles  (576)
  • 2010-2014  (576)
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  • Articles  (576)
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  • 1
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    A closed form solution method for rapid calculation of guided wave dispersion curves for pipes (2014)
    Elsevier
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    Publication Date: 2014-12-24
    Description: Publication date: March 2015 Source: Wave Motion, Volume 53 Author(s): Ruth Sanderson Guided wave inspection is a fast growing technology for screening pipelines for corrosion. The technique is capable of inspecting tens of metres from a single test location and examining otherwise inaccessible regions of pipeline such as cased road crossings. However, enhancements to the technique are needed if inspections are to be transformed from a screening procedure to a more quantitative assessment of the condition of the pipeline. A rapid calculation procedure to determine the dispersion curves for guided wave modes is important if enhancements are to be automatically incorporated into the technique. Commercial code for dispersion curve calculation is available but it is proprietary and typically uses an iterative procedure to calculate curves which can be unreliable and slow. Other methods for calculating dispersion curves have been published including semi-analytical finite element solutions but these require extensive programming. In this paper, a closed form solution based on known trigonometric behaviour in the circumferential and axial directions and a standard polynomial solution through the thickness is presented. The method allows rapid computation of dispersion curves for typical guided wave inspection scenarios with minimal programming required. In addition, a tracing algorithm is also presented which allows the computed points to be joined to form curves and therefore fully identify the dispersive behaviour of each wave mode. The new method has been successfully verified against the well-established software, Disperse ® , for a range of pipe sizes, materials and frequencies typical to guided wave inspection.
    Print ISSN: 0165-2125
    Electronic ISSN: 1878-433X
    Topics: Geosciences , Physics
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  • 2
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    Modeling of elastic waves in a blocky medium based on equations of the Cosserat continuum (2014)
    Elsevier
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    Publication Date: 2014-12-18
    Description: Publication date: January 2015 Source: Wave Motion, Volume 52 Author(s): V.M. Sadovskii , O.V. Sadovskaya Based on the equations of the dynamics of piecewise-homogeneous elastic material, parallel computational algorithms are developed to simulate the process of stress and strain wave propagation in a medium consisting of a large number of blocks interacting through compliant interlayers. Computations of waves caused by localized impulse perturbations show that such a medium can be considered as isotropic only in the case of sufficiently thin interlayers. In the case of relatively thick interlayers, the anisotropy effects are observed which consist in the appearance of elongated wave fronts along the coordinate directions and characteristic oscillations of velocities and stresses because of the rotational motion of blocks. For the description of waves in a blocky medium with thin interlayers, the equations of the isotropic Cosserat continuum are applicable. As the thickness of interlayers increases, the orthotropic Cosserat continuum theory which takes into account the symmetry of elastic properties relative to the coordinate planes can be applied. By comparing the elastic wave velocities in the framework of piecewise-homogeneous model and continuum model, a simple method is obtained to estimate the mechanical parameters of the orthotropic Cosserat continuum modeling a blocky medium. In two-dimensional formulation of the orthotropic model the computational algorithm and the program system are worked out for the analysis of propagation of elastic waves. The comparison showed good qualitative agreement between the results of computations of waves caused by localized impulses, in the framework of the model of a blocky medium with compliant interlayers and the model of orthotropic Cosserat continuum.
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    Electronic ISSN: 1878-433X
    Topics: Geosciences , Physics
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  • 3
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    Improving spatio-temporal focusing and source reconstruction through deconvolution (2014)
    Elsevier
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    Publication Date: 2014-12-18
    Description: Publication date: January 2015 Source: Wave Motion, Volume 52 Author(s): Brian E. Anderson , Johannes Douma , T.J. Ulrich , Roel Snieder In this study, a technique is demonstrated to improve the ability of time reversal to both spatially and temporally focus, or compress, elastic wave energy, or to improve the quality of the reconstruction of the source signal. This method utilizes the deconvolution, or inverse filter, in single channel time reversal experiments in solids. Special attention is given to the necessary procedure for improving source signal reconstruction in real experimental conditions. It is also demonstrated theoretically and numerically that good temporal focusing implies that the radius in the spherically symmetric part of the spatial focus is small.
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    Electronic ISSN: 1878-433X
    Topics: Geosciences , Physics
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  • 4
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    Regular wave integral approach to numerical simulation of radiation and diffraction of surface waves (2014)
    Elsevier
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    Publication Date: 2014-12-18
    Description: Publication date: January 2015 Source: Wave Motion, Volume 52 Author(s): Zhi-Min Chen A regular wave integral method is developed in the discretisation of a linear hydrodynamic problem on radiation and diffraction of surface waves by a floating or submerged body. The velocity potential of the problem is expressed as a solution of a body boundary integral equation involving the pulsating free surface Green function or pulsating free surface sources distributed on the body surface. With the use of a discretisation on the regular wave integral rather than discretisations on the singular wave integral of the Green function as in earlier investigations, the singular wave integral is approximated as an expansion of regular (or nonirregular) wave potentials. Influence coefficients between pulsating free surface source points are computed by the approximate expansion together with Hess–Smith panel integral formulas. Thus the velocity potential solution is evaluated by a boundary element algorithm. The numerical results produced from the proposed method agree well with semi-analytic solution results.
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    Electronic ISSN: 1878-433X
    Topics: Geosciences , Physics
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  • 5
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    Wave propagation in graded rings with rectangular cross-sections (2014)
    Elsevier
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    Publication Date: 2014-12-18
    Description: Publication date: January 2015 Source: Wave Motion, Volume 52 Author(s): J.G. Yu , X.D. Yang , J.E. Lefebvre , Ch. Zhang In this paper, a double orthogonal polynomial series method is proposed to investigate the guided wave propagation in a two-dimensional (2-D) structure, namely, a FGM ring with a rectangular cross-section. Two kinds of graded rings are considered: material gradient directions being in the radial direction and in the axial direction respectively. Numerical comparison with available reference results for a straightly homogeneous rectangular bar illustrates the validity of the proposed method. The dispersion curves and displacement distributions of various FGM rings, which have different radius to thickness ratios, different material gradient directions and different thickness to height ratios, are calculated to reveal the guided wave characteristics.
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    Electronic ISSN: 1878-433X
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  • 6
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    On optical Airy beams in integrable and non-integrable systems (2014)
    Elsevier
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    Publication Date: 2014-12-18
    Description: Publication date: January 2015 Source: Wave Motion, Volume 52 Author(s): Gaetano Assanto , Antonmaria A. Minzoni , Noel F. Smyth The interaction of an accelerating Airy beam and a solitary wave is investigated for integrable and non-integrable equations governing nonlinear optical propagation in various media. For the integrable nonlinear Schrödinger equation, by way of a Bäcklund transformation, we show that no momentum exchange takes place, as the only effect of the interaction is to modulate the amplitude of the solitary wave. The latter result also holds for propagation in anisotropic media with birefringent walkoff and nonlocality, as specifically addressed with reference to uniaxial nematic liquid crystals in the absence of beam curvature. When the wavefront curvature characteristic of accelerating Airy beams is accounted for, both asymptotic and numerical solutions show that a small amount of momentum is initially exchanged, with the solitary wave rapidly settling to a state of constant momentum.
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  • 7
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    Numerical solution of the Benjamin equation (2014)
    Elsevier
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    Publication Date: 2014-12-18
    Description: Publication date: January 2015 Source: Wave Motion, Volume 52 Author(s): V.A. Dougalis , A. Duran , D. Mitsotakis In this paper we consider the Benjamin equation, a partial differential equation that models one-way propagation of long internal waves of small amplitude along the interface of two fluid layers under the effects of gravity and surface tension. We solve the periodic initial-value problem for the Benjamin equation numerically by a new fully discrete hybrid finite-element/spectral scheme, which we first validate by pinning down its accuracy and stability properties. After testing the evolution properties of the scheme in a study of propagation of single- and multi-pulse solitary waves of the Benjamin equation, we use it in an exploratory mode to illuminate phenomena such as overtaking collisions of solitary waves, and the stability of single-pulse, multi-pulse and ‘depression’ solitary waves.
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    Electronic ISSN: 1878-433X
    Topics: Geosciences , Physics
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  • 8
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    Propagation of guided waves in pressure vessel (2014)
    Elsevier
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    Publication Date: 2014-12-18
    Description: Publication date: January 2015 Source: Wave Motion, Volume 52 Author(s): Fucai Li , Zhiqiang Liu , Xuewei Sun , Hongguang Li , Guang Meng Pressure vessels usually operate under extremes of high/low temperatures and high pressures. Defect, such as crack and corrosion, can result in leakage or rupture failures, even catastrophic incidents. Guided wave-based structural health monitoring (SHM) technology is one of the most prominent options in non-destructive evaluation and testing (NDE/NDT) techniques. Propagation of guided waves in a typical pressure vessel is systematically investigated in this study for the application of guided wave-based SHM. Shape of the pressure vessel is a cylinder with two end caps. Because of geometric similarity, theory of guided wave propagation in the cylinderical structure is analyzed to study dispersive features of guided waves in the pressure vessel. Dispersion curves of three different types of guided wave modes, viz. the longitudinal, torsional and flexural modes, are calculated using theoretical method. Based on the analyses and experimental wave signals, central frequency and wave parameters of incident wave are optimized. Effect of contained liquid on propagation of guided waves, especially the L(0, 2) mode, in the pressure vessel is further investigated to minimize energy leakage of the wave to the contained liquid. The analytical method, finite element analysis (FEA) and experiments are applied to study propagation characteristics of guided waves in the pressure vessel, so as to demonstrate the feasibility of guided wave-based non-destructive evaluation and testing (NDE/NDT) for such kind of complex structures.
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  • 9
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    Omnidirectional two-dimensional acoustic cloak by axisymmetric cylindrical lattices (2014)
    Elsevier
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    Publication Date: 2014-12-18
    Description: Publication date: Available online 16 December 2014 Source: Wave Motion Author(s): Choonghee Jo , Jihoon Jeong , Byung-Jin Kwon , Kwang-Chun Park , Il-Kwon Oh We report a two-dimensional acoustic cloak designed with axisymmetric cylindrical lattices. The proposed axisymmetric lattice layers are optimized such that acoustic cloaking can be effectively realized within realistic material properties regardless of the incoming direction of plane waves. The cylindrical shape of lattice structures consists of five layers and each layer is composed of the same number of circular cylinders to form an axisymmetric lattice structure. The present results show that acoustic cloaking with axisymmetric cylindrical lattices can be realized with many advantages such as use of realistic material properties, simplified geometry, omnidirectional cloaking and controllable cloaking degrees.
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    Topics: Geosciences , Physics
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  • 10
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    Explicit formulas for the reflection and transmission coefficients of one-component waves through a stack of an arbitrary number of layers (2014)
    Elsevier
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    Publication Date: 2014-12-18
    Description: Publication date: Available online 12 December 2014 Source: Wave Motion Author(s): Pham Chi Vinh , Tran Thanh Tuan , Marcos A. Capistran The transmission and reflection of one-component elastic, acoustic, optical waves on a stack of arbitrary number of different homogeneous layers have been intensively studied in the literature. However, all obtained formulas for the reflection and transmission coefficients are in implicit form. In this paper, we provide the explicit formulas for them. From these formulas we immediately arrive at the explicit formulas for the reflection and transmission coefficients of one-component waves through an FGM layer. Based on the obtained exact formulas, approximate formulas for the reflection and transmission coefficients are established for a stack of thin layers and for a thin FGM layer. It is numerically shown that they are good approximations. Since the obtained formulas are totally explicit, they are useful in evaluating, not only numerically but also analytically, the transmission and reflection coefficients of one-component waves.
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