In this work, the concept of generalized topological sensitivity, developed recently to deal with inverse elastodynamic scattering by penetrable obstacles in the frequency domain, is extended to permit non-invasive defect reconstruction and material characterization by means of transient elastic waves. This quantity, which signifies the first-order perturbation of a given cost functional due to nucleation of an infinitesimal elastic defect in the reference (defect-free) solid, is intended to be used as an obstacle indicator though an assembly of interior sampling points where it attains pronounced negative values. From an asymptotic analysis of the transient scattered field emanating from a defect with vanishing size in the reference elastic solid, the expression for topological sensitivity, explicit in terms of (i) the Green's function and (ii) the free (i.e. incident) field for the reference domain, is obtained by employing the so-called direct approach and a convolution-based boundary integral representation of the featured elastodynamic wavefields. For generality, the proposed formula is recast in terms of its adjoint-field counterpart that caters for general reference domains where the Green's function may not be available. Through numerical simulations, it is shown that the generalized topological sensitivity in the time domain provides an effective preliminary tool for the 3D reconstruction and material identification of discrete internal heterogeneities. The results also demonstrate that the defect "illumination" by transient elastic waveforms results in a higher quality of reconstruction relative to its time-harmonic (monotonal) counterpart.
|Original language||English (US)|
|Number of pages||18|
|Journal||Computer Methods in Applied Mechanics and Engineering|
|State||Published - Sep 15 2008|
Bibliographical noteFunding Information:
The support provided by the National Science Foundation through Award Nos. CMMI-0324348 and OISE-0350590 to B. Guzina and the University of Minnesota Supercomputing Institute during the course of this investigation is gratefully acknowledged.
Copyright 2008 Elsevier B.V., All rights reserved.
- Elastic waves
- Inverse scattering
- Material identification
- Penetrable defects
- Topological sensitivity
- Transmission problem