Nonlinear Coda Wave Interferometry: Sensitivity to wave-induced material property changes analyzed via numerical simulations in 2D.

Affiliation

IFSTTAR, Dep. GERS, Lab. GeoEND, CS4, F-44344 Bouguenais Cedex, France; Laboratoire d'Acoustique de l'Universitédu Mans, LAUM, UMR 6613 CNRS, Le Mans Université, Avenue Olivier Messiaen, 72085 Le Mans Cedex 9, France; Acoustic Science and Technology Laboratory, Harbin Engineering University, Harbin 150001, China; Key Laboratory of Marine Information Acquisition and Security (Harbin Engineering University), Ministry of Industry and Information Technology, Harbin 150001, China; College of Underwater Acoustic Engineering, Harbin Engineering University, Harbin 150001, China. Electronic address: [Email]

Abstract

The numerical studies conducted in this paper are based on our previous research (Chen et al., 2017); through use of the spectral element method, parametric sensitivity studies of Nonlinear Coda Wave Interferometry (NCWI) are established here and divided into two parts. In the first part, CWI observables are found to be proportional to the product of the changes in elastic modulus within the Effective Damaged Zone (EDZ) and the EDZ surface area. The modifications to intrinsic properties are quantified via an overall wave velocity variation, as probed by a reverberated coda wave. However, for high-level changes, CWI may fail due to meaningless decorrelation values. In this context, parametric studies are conducted to yield a maximum range for EDZ contrast and area. To further validate these observations using a more realistic numerical model, instead of introducing a homogeneous EDZ model, the second part of this paper adds random cracks with random orientations into the EDZ of a material sample. The influence of a strong pump wave on localized nonlinear damage is reestablished; results show that the cracks added into the EDZ reduce the property changes required to match the previous experimental dataset.

Keywords

Effective Damaged Zone (EDZ),Nonlinear Coda Wave Interferometry (NCWI),Numerical modelling,Spectral Element Method (SEM),

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