Daniel Marceau

NEW DEVELOPMENTS IN FREQUENCY DOMAIN OPTICAL TOMOGRAPHY. PART II. APPLICATION WITH A L-BFGS ASSOCIATED TO AN INEXACT LINE SEARCH

This second part deals with the application of the presented formulations for the reconstruction of optical properties in frequency domain optical tomography with the finite element method. We use the Limited memory BFGS algorithm with an inexact line search in order to avoid numerous evaluations of the objective function. Normalization of the objective function with measurements and independent scaling of its gradient are used to improve the quality of the reconstruction. The results show a better recovering of both the absorption and scattering coefficients.

Advanced numerical simulation of the thermo-electro-chemo-mechanical behaviour of hall-héroult cells under electrical preheating

In today’s context, aluminum producers strive to improve their position regarding energy consumption and production costs. To do so, mathematical modeling offers a good way to study the behavior of the cell during its life. This paper deals with the numerical simulation of the electrical preheating of a Hall-Heroult cell using a quarter model of the cell. The fully coupled thermo-electro-mechanical model includes material non linearities and multiphysical behavior at interfaces allowing accurate evaluation of the stress distribution in the cathode blocks and surrounding components. The baking of the ramming paste as well as the evolution of its thermo-electro-mechanical properties are updated via the baking index computed using a kinetic of reaction. The model is initially calibrated with in situ measurements and then used to estimate the effect of preheating on the behavior of the cell including temperature, current, deformations as well as the contact conditions at critical interfaces.

Development of an Analytical Dynamic Model of a Vibro-Compactor Used in Carbon Anode Production

The carbon anode quality has a significant impact on the production of primary aluminum. Their performance can be evaluated by their various mechanical, electrical, physical, and chemical, properties such as density, electric resistivity, CO2 and air reactivities. The focus of this work is to study the various parameters of the vibro-compaction, which is one of the critical steps in the process of anode manufacturing. In this work, a dynamic model of a vibro-compactor is developed. The vibro-compactor is modeled as a rigid mass suspended on springs and dampers and subjected to harmonic external excitation. This model is used to identify the optimal conditions of the vibro-compacting process. These conditions are obtained through a correlation between the analytical vibro-compaction parameters and data from an industrial vibro-compactor. The use of optimum parameters will help improve the anode performance and, consequently, lead to better productivity and reduction on environmental impact.

NEW DEVELOPMENTS IN FREQUENCY DOMAIN OPTICAL TOMOGRAPHY. PART I. FORWARD MODEL AND GRADIENT COMPUTATION

This paper deals with a gradient-based frequency domain optical tomography method where the collimated source direction is taken into account in the computation of both the forward and the adjoint models. The forward model is based on the least square finite element method associated to the discrete ordinates method where no empirical stabilization is needed. In this first part of the study, the forward model is highlighted with an easy handling of complex boundary condition through a penalization method. Gradient computation from an adjoint method is developed rigorously in a continuous manner through a Lagrangian formalism for the deduction of the adjoint equation and the gradient of the objective function. The proposed formulation can be easily generalized to stationary and time domain optical tomography by keeping the same expressions.

Determination of the Microstructural Creep Properties of Cast Iron Connector at High Temperatures for the Prediction of the Thermo-Mechanical Behavior of Anodic Assemblies

The prediction of the air gap at the cast iron to carbon interface in the anodic assemblies as well as its closing and pressure build-up during the operation remain a complex task. It is therefore very difficult to predict the electrical performance of anodic assemblies. This main difficulty comes from the evolution of the thermophysical and thermo-mechanical properties of the microstructure mapping during these stages. To overcome this difficulty, a natural approach is to characterize this mapping of microstructures.

Effects of High Temperatures and Pressures on Cathode and Anode Interfaces in a Hall‐Heroult Electrolytic Cell

This paper deals with the physical modifications occurring at high temperatures and pressures at the interfaces found in the anode and cathode of a Hall-Heroult electrolytic cell. The anode and the cathode are fabricated from carbon blocks, with steel bars inserted and sealed with cast iron. Consequently, two different types of interface are found in the anode and the cathode assembly: cast-iron with steel and cast-iron with carbon. For the investigation presented here, an experimental setup was built to heat and load anode and cathode samples. Specific attention was put on the sample preparation, to reproduce real cathode/anode sealing conditions. During the heating and the loading of the samples, fluctuations of electrical and thermal contact resistances were observed and related to physical transformation at the interfaces. These transformations could potentially explain the non-homogeneities of voltage and current distribution occurring in a Hall-Heroult electrolytic cell.

Optical Tomography With a Least Square Finite Element Formulation of the Collimated Irradiation in Frequency Domain

This paper presents a numerical study of optical tomography in frequency domain for the reconstruction of optical properties of scattering and absorbing media with collimated irradiation light sources. The forward model is a least square finite element formulation of the collimated irradiation problem where the intensity is separated into its collimated and scattered parts. This model does not use any empirical stabilization and moreover the collimated source direction is taken into account. The inversion uses a gradient type minimization method where the gradient is computed through an adjoint formulation. Scaling is used to avoid numerical round errors, as the output readings at detectors are very low. Numerical reconstructions of optical properties of absorbing and scattering media with simulated data (noised and noise-free) are achieved in a complex geometry with satisfactory results. The results show that complex geometries are well handled with the proposed method.Copyright