Review of progress, QNDE

Efficient finite element modelling of ultrasound waves in elastic media

Using finite element and ultrasonic method to evaluate welding longitudinal residual stress through the thickness in austenitic stainless steel plates

CIVA: an expertise platform for simulation and processing NDT data.

We present a method for high-resolution imaging of lithospheric structures based on full waveform inversion of teleseismic waveforms. We model the propagation of seismic waves using our recently developed direct solution method/spectral-element method hybrid technique, which allows us to simulate the propagation of short-period teleseismic waves through a regional 3-D model. We implement an iterative quasi-Newton method based upon the L-BFGS algorithm, where the gradient of the misfit function is computed using the adjoint-state method. Compared to gradient or conjugate-gradient methods, the L-BFGS algorithm has a much faster convergence rate. We illustrate the potential of this method on a synthetic test case that consists of a crustal model with a crustal discontinuity at 25 km depth and a sharp Moho jump. This model contains short- and long-wavelength heterogeneities along the lateral and vertical directions. The iterative inversion starts from a smooth 1-D model derived from the IASP91 reference Earth model. We invert both radial and vertical component waveforms, starting from long-period signals filtered at 10 s and gradually decreasing the cut-off period down to 1.25 s. This multiscale algorithm quickly converges towards a model that is very close to the true model, in contrast to inversions involving short-period waveforms only, which always get trapped into a local minimum of the cost function.

https://hal.archives-ouvertes.fr/hal-01265155/document

Three-dimensional full waveform inversion of short-period teleseismic wavefields based upon the SEM–DSM hybrid method

Pencil method in elastodynamics: application to ultrasonic field computation

Modeling of ultrasonic fields radiated by contact transducer in a component of irregular surface.

Ultrasonic nondestructive testing may be operated on pieces of complex structure, such as welded components in nuclear plants. Crystallographic analyses of these structures display both anisotropic and heterogeneous characteristics, so that the material may be modeled as a succession of anisotropic media separated with interfaces of arbitrary shape. The aim of this paper is to describe the extension of the model Champ-Sons developed at the French Atomic Energy Commission to predict transient fields radiated from arbitrarily shaped sources into such pieces, for which numerical efficiency is required. This model is based on two models that have been presented at 1997 and 1998 QNDE conferences. A pencil description is used. Each pencil propagating from an elementary source on the transducer to a calculation point into the solid and following a geometrical path is described by means of a 4×4 matrix, which is the product of elementary ones, describing either the propagation into a homogeneous medium or the tra...

Calculation of wideband ultrasonic fields radiated by water-coupled transducers into heterogeneous and anisotropic media

A hybrid model is developed combining advantages of both semi‐analytical and numerical methods. Most of the propagation is computed semi‐analytically (pencil method, code Civa), while wave — defect interaction is computed numerically (FEM, code Athena) in a small region surrounding the defect. Both codes exchange results required to predict responses from defects through an integral formula extending Auld’s principle to the transient case. The theory and its implementation are discussed. Examples illustrate its interest in UT simulations involving complicated interactions.

A Semi‐Analytic‐FEM Hybrid Model for Simulating UT Configurations Involving Complicated Interactions of Waves with Defects

Sensitivity of UT methods in materials such as coarse‐grained steels depends on attenuation and noise, due to scattering by microstructural heterogeneities. Here, existing UT simulation tools developed at CEA are modified to account for experimental observations of noise and attenuation. A model‐based inversion tool is developed to estimate from experiments the parameters to input into the forward models. Example of application is given, showing the quantitative importance of these phenomena in terms of performance demonstration.

Nicolas Gengembre

Papers

Pencil method in elastodynamics: application to ultrasonic field computation

Modeling of ultrasonic fields radiated by contact transducer in a component of irregular surface.

Calculation of wideband ultrasonic fields radiated by water-coupled transducers into heterogeneous and anisotropic media

A Semi‐Analytic‐FEM Hybrid Model for Simulating UT Configurations Involving Complicated Interactions of Waves with Defects

Simplified Modeling of Backscattered Noise and Attenuation Phenomena for Quantitative Performance Demonstration of UT Methods