Laurent Autrique

Sliding mode stabilization of the current profile in Tokamak plasmas

This paper deals with the robust stabilization of the spatial distribution of tokamak plasmas current profile using a sliding mode feedback control approach. The control design is based on the 1D resistive diffusion equation of the magnetic flux that governs the plasma current profile evolution. The feedback control law is derived in the infinite dimensional setting without spatial discretisation. Numerical simulations are provided and the tuning of the controller parameters that would reject uncertain perturbations is discussed.

Skin burns after laser exposure: histological analysis and predictive simulation.

Thermal effects of laser irradiation on skin are investigated in this paper. The main purpose is to determine the damage level induced by a laser exposure. Potential burns induced by two lasers (wavelength 808nm and 1940nm) are studied and animal experimentations are performed. Several exposure durations and laser powers are tested. Based on previous works, a mathematical model dedicated to temperature prediction is proposed and finite-element method is implemented. This numerical predictive tool based on the bioheat equation takes into account heat losses due to the convection on skin surface, blood circulatory and also evaporation. Thermal behavior of each skin layer is also described considering distinct thermal and optical properties. Since the mathematical model is able to estimate damage levels, histological analyses were also carried through. It is confirmed that the mathematical model is an efficient predictive tool for estimation of damage caused by lasers and that thermal effects sharply depend on laser wavelength.

Simultaneous determination of time-varying strength and location of a heating source in a three-dimensional domain

In this article, identification of heating source location and time-dependent surface heat flux is investigated considering point temperature measurements on a boundary of the studied three-dimensional geometry. Such Inverse Heat Conduction Problems are ill-posed, since solution stability is not satisfied when observations are noisy/disturbed. We propose a robust algorithm for a simultaneous estimation of location and time-varying strength of a plane heat source. This iterative regularization method based on the conjugate gradient method is tested in several numerical configurations.

Identification of influence factors in a thermal model of a plasma-assisted chemical vapor deposition process

This study is focused on several stages of an identification methodology and consists of selection of the parameters of influence and their identification considering state observations. A partial differential equations system describing the temperature evolution in a plasma-assisted chemical vapor deposition process is investigated. A preliminary study based upon the numerical design of experimental method leads to determination of the parameters which have to be carefully estimated since their uncertainties sharply reduce the adequacy of the model. Then, a sensitivity analysis is performed and the sensitivity problem derived from the direct problem is solved. Optimal observation strategy is briefly discussed in order to obtain state observations for the unknown parameters identification, and a conjugate gradient method is implemented for the resolution of the ill-posed inverse problem.

Parametric identification of a heating mobile source in a three-dimensional geometry

The resolution of an inverse problem of heat conduction in a three-dimensional plate using an iterative regularization method based on Alifanov’s iterative regularization method is investigated. Considering temperature observation on the upper face centre of a small thin steel plate, the time dependent strength of a plane heat source has to be identified. Two configurations are studied. For the first one, the heat source is fixed on the lower face centre. For the second one, the heat source is mobile and the trajectory is assumed to be known. For both situations, robustness of the approach is stated considering noisy measurements.

On-line identification of temperature-dependent thermal conductivity

In this communication, the investigated study deals with on-line parametric identification in a one-dimensional thermal system. The main objective is the determination of the temperature-dependent thermal conductivity considering noisy temperature measurements. In such a way, the identification problem is written as a minimization one. Since inverse heat conduction problems are ill-posed, a regularization method has to be numerically implemented. Thus, the conjugate gradient method (a well-known iterative regularization method) has been adapted for on-line purposes.

Feasibility Study and Optimal Design of an Experimental Bench for Identification of Liquid Thermal Diffusivity

Expertise of innovative materials by nondestructive techniques is a key goal in process engineering development. In this context, if identification of thermal diffusivity of liquid is a crucial requirement to develop a reliable mathematical model of knowledge, it is essential to propose a complete and valid methodology. Based on the analysis of thermal wave propagation (generated by a periodic excitation), an experimentation is developed in order to avoid the implementation of a pyroelectric sensor required in usual photopyroelectric techniques. The proposed approach is investigated in a trilayer system. Theoretical aspects of the identification of thermal parameters in the frequency domain are presented. A feasibility study is discussed in order to justify this approach for liquids. A sensitivity analysis is implemented in a particular case to provide an optimal experimental bench. Finally, experimental results for several liquids are presented and discussed.

Parametric identification using photothermal data inversion: application to a nonlinear thermal system

Military structures, devices and vehicles used on battlefields are likely to be exposed to heavy thermal aggressions, such as fires or explosions. Protection of personnel and material engaged in combat against such aggressions is a top priority, and needs the use of adapted and optimized systems. Intumescent paints have the ability to swell up when they are heated, building a thick multi-layered coating which provides efficient thermal insulation to the underlying material. In order to evaluate such coatings efficiency in a military framework and to identify its physical properties, experimental tests were carried out. A mathematical model describing intumescent paints behavior under several types of thermal aggressions was developed for system state evaluation in the case of long lasting fires. The model structure has been validated for thermal fluxes induced by several fire configurations and by brief, violent explosions. However, in order to supply the model with reliable input parameters, those must be identified. Thus, a whole identification process was carried out (modeling, sensitivity analysis, experiment, cost function minimization). The identification method is based on the frequency analysis of the heat waves generated by a modulated thermal excitation on the materials surface.

Microscale thermal characterization by inverse method in the frequency domain

Abstract In this communication, several aspects of the implementation of a finite element method for the resolution of inverse problems (occurring in parameter identification) are exposed. Identification of a thermal parameter (diffusivity) at micrometric scale is obtained from observations of output signal due to a periodic input. Resolution of this identification problem is facilitated by the formulation of a complex temperature in the Fourier space and a finite element analysis.

Heating Source Localization in a Reduced Time

Abstract Inverse three-dimensional heat conduction problems devoted to heating source localization are ill posed. Identification can be performed using an iterative regularization method based on the conjugate gradient algorithm. Such a method is usually implemented off-line, taking into account observations (temperature measurements, for example). However, in a practical context, if the source has to be located as fast as possible (e.g., for diagnosis), the observation horizon has to be reduced. To this end, several configurations are detailed and effects of noisy observations are investigated.