Sensor fault detection and isolation filter for polytopic LPV systems: A winding machine application

In this paper, a fault diagnosis method is developed for a particular class of nonlinear systems described by a polytopic linear parameter varying (LPV) formulation. The main contribution consists in the synthesis of an accurate fault detection and isolation (FDI) filter and also a sensor fault magnitude estimation with a quality factor. This quality factor of the filter underlines if the fault estimation can be used or not. Stability conditions of the polytopic LPV filter are studied by ensuring poly-quadratic stability with Linear Matrix Inequality (LMI) representation. The effectiveness of this global FDI scheme through LPV modelization, filter design and stability analysis, is illustrated on a real winding machine under multiple sensor faults.     

Polynomial algorithms for subisomorphism of nD open combinatorial maps

Combinatorial maps describe the subdivision of objects in cells, and incidence and adjacency relations between cells, and they are widely used to model 2D and 3D images. However, there is no algorithm for comparing combinatorial maps, which is an important issue for image processing and analysis. In this paper, we address two basic comparison problems, i.e., map isomorphism, which involves deciding if two maps are equivalent, and submap isomorphism, which involves deciding if a copy of a pattern map may be found in a target map. We formally define these two problems for nD open combinatorial maps, we give polynomial time algorithms for solving them, and we illustrate their interest and feasibility for searching patterns in 2D and 3D images, as any child would aim to do when he searches Wally in Martin Handford’s books.     

Global and local characterization of the thermal diffusivities of SiCf/SiC composites with infrared thermography and flash method

Two types of SiC_f/SiC composites with different matrix quantities are prepared by CVR from pyrolyzed Carbon/resin composites. Experiments based on transient, space-resolved infrared thermography are developed; various assessment methods are implemented to measure simultaneously transverse and in-plane thermal diffusivities, globally and locally; the emphasis is set on the accuracy of the estimations. The material anisotropy is revealed and the influence of matrix volume fraction on the global thermal diffusivities is evaluated. Gradients of the properties are clearly visible in the samples, by use of the local analysis. The global heat conductivity values are discussed with respect to previous works.     

Evaluation of three-dimensional and two-dimensional full displacement fields of a single edge notch fracture mechanics specimen, in light of experimental data using X-ray tomography

The aim of this study is to show the validity of a 3D numerical approach and the 2D theoretical approaches from 3D experimental results on a single edge notch cracked specimen loaded in mode I. The three displacement components all over the volume were measured by means of Digital Volume Correlation coupled with X-ray computed tomography. The numerical approach and the experimental one give similar results with differences equivalent to the accuracy of the method of measurements. The theoretical approach provides higher results and is not relevant to experimental results, but this approach allows an evaluation of the 3D effect zone.     

Segmenting and tracking fluorescent cells in dynamic 3-D microscopy with coupled active surfaces.

Cell migrations and deformations play essential roles in biological processes, such as parasite invasion, immune response, embryonic development, and cancer. We describe a fully automatic segmentation and tracking method designed to enable quantitative analyses of cellular shape and motion from dynamic three-dimensional microscopy data. The method uses multiple active surfaces with or without edges, coupled by a penalty for overlaps, and a volume conservation constraint that improves outlining of cell/cell boundaries. Its main advantages are robustness to low signal-to-noise ratios and the ability to handle multiple cells that may touch, divide, enter, or leave the observation volume. We give quantitative validation results based on synthetic images and show two examples of applications to real biological data.     

Temperature, pore pressure and mass variation of concrete subjected to high temperature — Experimental and numerical discussion on spalling risk

Spalling at high temperature is a phenomenon that can be observed in different materials such as ceramics, rocks and bricks. For concrete, this phenomenon, considered as a thermal instability of the material, can seriously jeopardize the integrity of a whole structure during fire and can even constitute a risk for people. Many explanations to the spalling risk exist but still no model can accurately predict it. Among them, models based on thermo-hydral behaviour of concrete have been proposed and developed by several authors. In particular, an important role is given to the pore vapour pressure, considered by many authors as the main mechanism for the trigger of such a thermal instability. However, pore vapour pressure is not easy to measure and numerical works still need more experimental results to validate their assumptions regarding the spalling risk. This paper presents the results of an experimental study carried out on five different concrete mixtures. We used a device intended for measuring temperature, pore vapour pressure and mass loss of concrete specimens. The aim of the study was to better understand the thermo-hydral behaviour of concrete exposed to high temperature and the possible link to spalling risk. In particular, we focused on the influence of matrix compactness on the transfer properties of concrete and we discussed about the importance of pore vapour pressure on spalling risk. Moreover, based on our experimental observations, a numerical analysis of the influence of water content on the thermomechanical behaviour of concrete during heating is done.     

Numerical Modeling of Vacuum Heat Treatment of Nickel-based Superalloys

Numerical modeling is carried out of the heat transfer effects arising during heat treatment of single-crystal nickel-based superalloys, of the type used for high pressure turbine blades in jet engines. For these components, fine control of the thermal history during processing is needed to avoid incipient melting and to develop the properties needed for service applications. Computational fluid dynamics methods are employed for the analysis. The modeling is used to predict the temporal evolution of the temperature distribution inside the treated component, to calculate heat transfer coefficients, and to analyze the homogeneity of heat transfer. The impact of the boundary conditions is investigated with particular emphasis on the temperature of the heating elements. Its value was derived from an analytical model of the furnace using effective view factors. The predictions of the modeling are tested against measurements made on laboratory-scale apparatus containing features of production-scale equipment.     

On the mechanism of porosity formation during welding of titanium alloys

The mechanism of porosity formation during the fusion welding of titanium and its alloys is studied. Porosity formed during the electron beam welding of titanium is characterized using high-resolution X-ray tomography, residual gas analysis and metallographic sectioning; the results confirm that porosity formation is associated with evolution of gas, especially hydrogen. A model for hydrogen diffusion-controlled bubble growth is proposed, to aid in the interpretation of these findings. To investigate further the effect of hydrogen on porosity formation, hydrogen charging is used to achieve different hydrogen levels prior to welding. The results confirm that porosity can be suppressed even at every high hydrogen levels, when welding is carried out with optimized welding parameters and perfect joint alignment; on the other hand, porosity is exacerbated when a small beam offset is employed. This is because any beam offset alters the size of the liquid zone at the melting front, where the joint edges first become melted. It is proposed that the thickness of the liquid film at the melting front is crucial for bubble nucleation and bubble survival in the weld pool; bubbles can escape through the keyhole by breaking through this liquid film, when it is too thin. This challenges the common assumption of bubble escape by flotation to the weld pool surface. Thus the nucleation rate in the liquid zone at the melting front determines the likelihood of porosity occurring. This suggests that the beam offset is likely to be one factor influencing porosity formation in these circumstances. The paper provides fundamental insights into the mechanism of porosity formation during the welding of titanium alloys and guidance to aid in its elimination.