Vibration Testing for Detecting Internal Corrosion

The vibration behavior of structures can be characterized in terms of resonance frequencies and mode shapes which describe properties of the tested object in a global way but do not in general provide information about structural details. We develop a simple method to address the inverse problem of identifying an internal corrosive part of small Hausdorff measure in a pipeline by vibration analysis. The viability of our reconstruction method is documented by a variety of numerical results from synthetic, noiseless and noisy data

Development and Validation of a Separation and Quantification Method for Residual Solvents in Active Substances by Headspace Gas Chromatography

The main objective was to develop and validate a method to assaying simultaneously nine residual solvents mentioned in the guidelines of the International Conference on Harmonization (ICH) Q3C: toluene, methanol, ethanol, acetone, propan-2-ol, ethyl acetate, tetrahydrofuran, dichloromethane and acetonitrile. Chromatographic separation was achieved on DB-624 column (30 m × 0.53 mm, 1.8 μm), nitrogen carrier gas and flame ionization detector. We have optimized the carrier gas flow, programming oven temperature and the split ratio. We have opted for the dimethyl sulfoxide as dissolution solvent. The developed method was validated for linearity, precision, accuracy and specificity and then applied for the research and quantification of residual solvents levels in two drug substances.  Excellent results were obtained. The developed method proved to be simple, producing symmetric peak shape, good resolution and reasonable retention time for solvents elution before seventeen minutes, specific, precise and linear in the range from the reporting level limit of quantification to 120% of the limit value, with a correlation coefficient greater than 0.999. The use of n-butyl acetate as internal solvent has improved the linearity and precision, compensating for the occurring variability. The quantification of residual solvents levels in two drug substances nefopam and enoxaparin, did not exceed the amount specified by the ICH guidelines.Thus, our method can be applied for the routine quantification of residual solvents levels in different active substances, for pharmaceutical companies and research laboratories

Modèles Mathématiques pour l'Inspection Nondestructive des Pipelines

The inverse problem of corrosion detection consists of the determination of the corrosion damage of an inaccessible part of the surface of a specimen when the available data are on the accessible part.Difficulties of this inverse problem result from its inherent ill-posedness and nonlinearity. Most of the techniques for detecting the corrosion are based on iterative algorithms:least-square algorithms and Newton-type iteration schemes. In these methods, one needs tremendous computational costs and timeto get a close image to the true solution, since these iterative algorithms may not converge to an approximate solution.The purpose of this work is to design a direct (non-iterative) technique for detecting corrosion in pipelines from voltage-to-current observations. Our new algorithm is of MUSIC-type (multiple signal classification) and is based on an accurate asymptotic representation formula for the steady state current perturbations.Following an asymptotic formalism, we develop in this thesis new non-iterative methods to address the inverse problem of identifying an internal corrosive part of small Hausdorff measure in a pipeline by (i) electrical impedance, (ii) vibration analysis, and (iii) ultrasonic waves. Our new algorithms are based on accurate asymptotic representation formulae for the data.In the first chapter, we establish an asymptotic representation formula for the steady state currents caused by internal corrosive parts of small Hausdorff measures. Based on this formula we designa non-iterative method of MUSIC (multiple signal classification) type for localizing the corrosive parts from voltage-to-curren observations.The vibration behavior of structures can be characterized in termsof resonance frequencies and mode shapes which describe properties of the tested object in a global way but do not in general provide information about structural details. Our aim in the secondchapter is to develop a simple method to address the inverse problem of identifying an internal corrosive part of small Hausdorff measure in a pipeline by vibration analysis. The viability of our reconstruction method is documented by a variety of numerical results from synthetic, noiseless and noisy data.In the third chapter, we develop three closely-related methods to address the inverse problem of identifying a collection of disjoint internal corrosive parts of small Hausdorff measures in pipelines from exterior ultrasonic boundary measurements. Our approaches also allow us to determine the actual number of corrosive parts present, as well as make use of one or multiple ultrasonic waves.In the fourth chapter, we consider the problem of determining the boundary perturbations of an object from far-field electric or acoustic measurements. Assuming that the unknown object boundary is a small perturbation of a circle, we develop a linearized relation between the far-field data that result from fixed Dirichlet boundary conditions, entering as parameters, and the shape of the object, entering as variables. This relation is used to find the Fourier coefficients of the perturbation of the shape and makes use of an expansion of the Dirichlet-to-Neumann operator.Dans les trois premiers chapitres de ce manuscrit de thèse, On propose trois nouvelles méthodes pour l'identification et la localisation des corrosions internes dans les pipelines. La première est par impédance électrique, la deuxième est par ondes guidées ultrasoniques et la troisième est par ultrasons.On jette les bases mathématiques de ces différentes méthodes et on présente quelques tests numériques qui montrent leur efficacité.Notre approche rentre dans la stratégie asymptotique développée au CMAP pour la résolution des problèmes inverses d'une manière robuste et stable. On exploite l'existence d'un petit paramètre (la mesure de Hausdorff de la partie corrosive) pour extraire des données la localisation de la partie corrosive et estimer son étendue. Le tout, d'abord, à travers des formules asymptotiques des mesures dépendantes du petit paramètre, rigoureusement établies à l'aide de la méthode des équations intégrales, et ensuite, par le biais de nouveaux algorithmes non-itératifs d'inversion. La plupart de ces algorithmes sont de type MUSIC (multiple signalclassification).Le dernier chapitre est indépendant des trois premiers. il est consacré à la reconstruction de la forme d'un objet perturbé connaissant le champ lointain électrique ou acoustique. On développe pour le cas acoustique et électrique une relation linéarisée entre le champ lointain, résultant des données sur le bord de conditions de Dirichlet comme paramètre, et la forme de la structure perturbée comme variable. Cette relation nous ouvre la voie à la reconstructiondes coefficients de Fourier de la perturbation et nous aide à la reconstruction des coefficients de Fourier de la perturbation ce qui nous mène à formuler un développement asymptotique complet del'opérateur Dirichlet-Neumann

Modèles mathémathiques pour l'inspection nondestructive des pipelines

PALAISEAU-Polytechnique (914772301) / SudocSudocFranceF

Development of an Analytical Method for the Plasma Determination of Five Anti-Epileptics and their Metabolites by HPLC: Comparison with Immunoanalytical Methods

International audienc

A MUSIC-type Algorithm for Detecting Internal Corrosion from Electrostatic Boundary Measurements

We establish an asymptotic representation formula for the steady state currents caused by internal corrosive parts of small Hausdorff measures. Based on this formula, we design a non-iterative method of MUSIC (multiple signal classification) type for localizing the corrosive parts from voltage-to-current observations