identifier: Bohlooli Arkhazloo, Nima  (2020). Optimization of furnace residence time and ingots positioning during the heat treatment process of large size forged ingots.  Thèse de doctorat électronique, Montréal, École de technologie supérieure.

subject:
traitement thermique
simulation CFD
four à gaz
mesure de température
uniformité de la température
modélisation du rayonnement
configuration du chargement
temps de résidence
mesures expérimentales
approche hybride
modélisation de la turbulence
modélisation de la combustion

abstract:
High-strength large size forgings which are widely used in the energy and transportation industries (e.g., turbine shaft, landing gears etc.) acquire significant mechanical properties (e.g., hardness) through a sequence of heat treatment processes, called Quench and Temper (Q&T). The heating process (tempering) that takes place inside gas-fired furnaces has a direct impact on the final properties of the product due to several major microstructural changes taking place at this step. Therefore, material properties are usually optimized by controlling the tempering process parameters such as time and temperature. A non-uniform temperature distribution around parts, as a result of thermal interactions inside the furnace or loading pattern, may result in the parts property variations from one end to another, changes in microstructure or even cracking. On the other hand, improvement of large products residence time inside the heat treatment furnace can minimize energy consumption and avoid undesirable microstructural changes. However, at the present time, the industrial production is mainly based on available empirical correlations which are costly and not always reliable. Accurate time-dependent temperature prediction of the large size forgings within gas-fired heat treatment furnaces requires a comprehensive quantitative examination of the heating process and an in-depth understanding of complex conjugate thermal interactions inside the furnace. Limitations in analytical studies and complexity and cost of experimentations have made numerical simulations such as computational fluid dynamics (CFD), effective methods in this field of study. However, among the rarely found studies on gas-fired furnaces, smallscale furnaces or those with shorter operation times were mainly considered (using different simplifications like steady-state calculations) because of complexity of the phenomena and large calculation times. Subsequently, there are very few studies on the improvement of the loading patterns of large-size steel parts inside the gas-fired furnaces and their relevant residence time optimization. Moreover, the limitation and strength of different numerical approaches to calculate thermal interactions in the turbulent reactive flow of the large size gas-fired batch type furnaces were addressed by few researchers in the literature. In this regard, the main objective of the present thesis is to provide a comprehensive quantitative analysis of transient heating and an understanding of thermal interactions inside the furnace so as to optimize the residence time and temperature uniformity of large size products during the heat treatment process. To attain this objective, the following milestones are pursued.

The first part of this study provides a comprehensive unsteady analysis of large size forgings heating characteristics in a gas-fired heat treatment furnace employing experimentally measured temperatures and CFD simulations. A three-dimensional CFD model of the gasfired furnace, including heat treating chamber and high momentum natural gas burners, was generated. The interactions between heat and fluid flow consisting of turbulence, combustion and radiation were simultaneously considered using the k -ε , EDM and DO models, respectively. The applicability of S2S radiation model to quantify the effect of participating medium and radiation view factor in the radiation heat transfer was also assessed. Temperature measurements at several locations of an instrumented large size forged block and within the heating chamber of the furnace were performed for experimental analysis of the heating process and validation of the CFD model. Good agreement with a maximum deviation of about 7% was obtained between the numerical predictions and the experimental measurements. The results showed that despite the temperature uniformity of the unloaded furnace, each surface of the product experienced different heating rates after loading (single loading) resulting in temperature differences of up to 200 K. Analysis of the results also revealed the reliability of the S2S model and highlighted the importance of radiation view factor for the optimization purposes in this application. Findings were correlated with the geometry of the furnace, formation of vortical structures and fluid flow circulations around the workpiece. The experimental data and CFD model predictions could directly be employed for optimization of the heat treatment process of large size steel components.

The second part of this study aims to determine the effect of loading pattern (in the multiple loading configurations) on the temperature distribution of large size forgings during the heat treatment process within a gas-fired furnace to attain more temperature uniformity and consequently homogenous mechanical properties. This part also focuses on the improvement of residence time of large size forged ingots within a tempering furnace proposing a novel hybrid methodology combining CFD numerical simulations and a series of experimental measurements with high-resolution dilatometer. Transient 3D CFD simulations validated by experimental temperature measurements were employed to assess the impact of loading patterns and skids on the temperature uniformity and residence time of heavy forgings within the furnace. Comprehensive transient analysis of forgings heating characteristics (including heat transfer modes analysis) at four different loading patterns allowed quantifying the impact of skids and their dimensions on the temperature distribution uniformity as well as products residence time. Results showed that temperature non-uniformities of up to 331 K persist for non-optimum conventional loading pattern. The positive influence of skids and spacers applications was approved and quantified using the developed approach. It was possible to reduce the identified non-uniformities of up to 32 % through changing the loading pattern inside the heat treatment furnace. This hybrid approach allowed to determine an optimum residence time of large size slabs improving by almost 15.5 % in comparison with the conventional non-optimized configuration. This approach was validated and it could be directly applied to the optimization of different heat treatment cycles of large size forgings.

The third part of the study addresses the details of the numerical simulation of heat treatment process of large size forgings within real scale gas-fired furnaces. Specifically, assessment of chemical equilibrium non-premix combustion model for accurate temperature prediction of heavy forgings, as well as performance of six different RANS based turbulence models for predictions of turbulent phenomenon were discussed in this context. In this regard, thermal interactions at different locations of the forged block as well as critical regions such as burner area, stagnation and wake region were performed using a one-third periodic 3D model of the furnace and validated by experimental measurements. Results showed that the one-third periodic model with chemical equilibrium non-premix combustion is reliable for the thermal analysis of the heat treatment process with a maximum deviation of about 3% with respect to the experimental measurements. It was also revealed that the choice of the turbulence model has a significant effect on the prediction of combustion and heat transfer around the block. Prediction of ɛ/k ratio by different turbulence models showed a significant relation to the turbulent combustion (such as burner flame length) and block temperature predictions, around the stagnation region. Standard and realizable k - ɛ models,  due to an unrealistic over prediction of turbulence kinetic energy (under-prediction of ɛ/k ratio), resulted in shorter flame length and under-prediction on the temperature of the forged block around the stagnation region; While, SST k - w model showed reasonable predictions in this region. RSM model was found as the most reliable turbulence model compared to the experimental measurements. Meanwhile, realizable k − ɛ model apart from some under-prediction on the stagnation region and flame length could effectively predict the overall temperature of the heavy forgings with reasonable accuracy with respect to the experimental data and RSM predictions.


identifier: Aidi, Saifeddine  (2020). Gestion de la disponibilité des services infonuagiques.  Mémoire de maîtrise électronique, Montréal, École de technologie supérieure.

type:
Mémoire ou thèse
Non évalué par les pairs

format: application/pdf application/pdf

subject:
cloud
SDN
virtualisation des fonctions réseaux
disponibilité des ressources

abstract:
Avec l’adoption croissante du réseau défini par logiciel (SDN) et de la virtualisation des fonctions du réseau (NFV), le déploiement d’infrastructure virtualisée à grande échelle prend de l’ampleur. Ces infrastructures hébergent des milliers de chaînes de service de réseau (SFC), chacune composée d’une chaîne de fonctions de réseau virtuelles (VNF) traitant les flux de trafic entrants. Malheureusement, dans de tels environnements, la défaillance d’un seul noeud peut entraîner la panne de plusieurs VNFs et, par conséquent, la rupture de nombreuses chaînes de service en même temps.

Dans ce travail, nous abordons ce problème particulier et examinons les solutions possibles pour garantir la disponibilité des chaînes de service affectées par les pannes en fournissant des VNFs de sauvegarde pouvant prendre le relais en cas de défaillance. Plus précisément, nous proposons un système de gestion de la disponibilité pour gérer efficacement les SFCs et les VNFs de sauvegarde. Nous formulons le problème de la disponibilité des SFCs en tant qu’un programme linéaire entier qui détermine le nombre minimal de sauvegardes nécessaires pour protéger tous les SFCs du système et identifier leur placement optimal dans l’infrastructure. Nous proposons également un nombre d’algorithmes heuristiques pour faire face au problème à grande échelle. Grâce à des simulations approfondies de différents scénarios de déploiement, nous montrons que ces algorithmes fournissent des solutions quasi optimales avec un temps de calcul minimal.


identifier: Khodaei, Hamid  (2020). Modeling of bulk and porous shape memory alloys.  Thèse de doctorat électronique, Montréal, École de technologie supérieure.

subject:
alliages à mémoire de forme
matériaux poreux
fabrication additive
modélisation des matériaux
analyse par éléments finis

abstract:
The unique properties of shape memory alloys (SMAs), including shape memory effect and superelasticity, have found applications in an increasing number of industries and engineering branches. A porous structure made of an SMA can offer the benefits associated with both porous metals and SMAs. With the recent progress in additive manufacturing technologies, it is now easier to produce lattice structures with customized unit cell geometries in order to meet certain mechanical requirement. A notable application for custom-designed porous SMA is in the field of human implants, where a biocompatible bone implant can be produced that has closer mechanical behavior to the bone, along with better bonding to the surrounding tissue.

A fundamental step in designing a porous SMA is the process of modeling and simulation of the part in order to predict its behavior. This includes material modeling of the SMA and reproducing its stress-strain behavior, as well as predicting the macroscopic response of the porous structure made of the SMA.

In the first part of this thesis, five different superelastic unit cells with porosities ranging from 0 to 90% were analyzed using FEM. The geometries were created and then analyzed under uniaxial tensile loads using Ansys APDL with its superelastic material model. Four major mechanical characteristics, namely, apparent reversible strain, apparent elastic modulus, volume fraction of transformed material, and strain energy absorption/dissipation were calculated. As a result, the dependency of these mechanical characteristics upon porosity and geometry of the unit cells were laid out. The procedures and methodology used for generating these data can be used as a framework that can also be expanded into a wider range of unit cell types and loading conditions.

In the second part, the accuracy of Auricchio’s SMA material model implemented in the current FE programs such as Ansys and Abaqus was investigated. A series of experimental tests were performed on superelastic thin-walled tube samples made of NiTi. Uniaxial, as well as multiaxial path-varying loads were applied to characterize mechanical behavior of the NiTi samples. The experimental tests demonstrated a distinct path-dependent behavior Under
multiaxial load cases. To validate the Auricchio’s model, the test sample geometry was created and analyzed in Ansys under the load cases similar to the experimental tests. It was shown that while this material model was able to closely reproduce the uniaxial response of the SMA, it was not able to predict the multiaxial and path-dependent behavior of NiTi samples accurately.

In the third part, Likhachev’s model was investigated as an alternative SMA material model that has the potential to provide a better prediction of the SMA response under multiaxial loading conditions. By implementing this model in Matlab, it was shown that, under multiaxial load cases, Likhachev’s model could predict the SMA behavior more closely to the experimental curves, compared to the Auricchio’s model. To adapt this model for FE implementation, two strain-driven formulations of Likhachev’s model were proposed. The first one was a non-iterative reformulation with short calculation time that was limited to 1D loadings only. The second one was an iterative scheme with a PID control concept for achieving convergence, which was functional in all load cases. An attempt was made to derive the tangent modulus numerically, but it did not produce consistent results. As a future work, it will be valuable to devise an analytical formulation of the tangent modulus for this model.


identifier: Paz Loboguerrero, Andrés Felipe  (2020). A DO-178C-compliant model-driven approach to support the development and certification of safety-critical avionics software.  Thèse de doctorat électronique, Montréal, École de technologie supérieure.

subject:
ingénierie dirigée par les modèles
systèmes critiques
systèmes d’avionique
conception hétérogène
spécification des exigences
certification
DO-178C

abstract:
Increasingly complex software is nowadays engineered to cater to safety-critical domains, like aircraft. However, engineering software for avionics systems is not a straightforward task. On one hand, consumer demands have spurred the need to pack features in, often intricate ones that will make systems smarter. On the other hand is the safety-critical nature of their operational environments. Because of this, their engineering is highly regulated in order to ensure they are developed appropriately to avoid, or at least mitigate, posing undue harm to anyone or anything in their operational environments. Avionics systems manufacturers are, thus, obliged to provide the appropriate software safety assurance in compliance with the applicable regulatory norm DO-178C. These two factors have pointed toward the need of engineering techniques that aid in reducing development complexities and support certification endeavours. Model-Driven Engineering (MDE) has been proposed as a cost- and time-effective alternative. The main rationale behind MDE is that models represent information at the right levels of abstraction to enable reasoning and ease information manipulation throughout the entire engineering life cycle. Nonetheless, significant challenges must still be overcome for MDE to comprehensively support the development and certification of avionics systems, and experience widespread adoption.

This thesis focuses on the investigation of MDE for supporting the use of different modelling languages for describing the same system while ensuring 1) consistency between the different system models, 2) traceability of the elements in such models back to requirements, and 3) all of this information explicitly relates to DO-178C regulatory objectives. Given these challenges, the main contribution of this thesis is a systematic and automated method, based on MDE, for assisting engineering teams in ensuring consistency of heterogeneous design models and providing such teams with a requirements specification infrastructure. All outputs of the method are explicitly traceable to DO-178C regulatory objectives.

To arrive at this contribution, we reviewed various heterogeneous design modelling and consistency management approaches. We derived a systematic and automated method that can be applied to various design scenarios involving different modelling languages and different design guidelines. Existing heterogeneous design modelling approaches can be leveraged within our proposed method. Furthermore, we studied several requirements modelling languages used in the context of safety-critical systems and characterized their support toward enforcing information for DO-178C certification and capturing structured semantically-rich information to enable requirements-based analyses and testing. Based on the results from such a survey we advocated for the combination of several of these languages to build a modelling language that could be integrated into the proposed method. We followed a systematic approach to build such a modelling language. We undertook empirical evaluations of our proposal by applying it in two case studies. As part of the evaluations we also include assessment workshops with practitioners from industry to examine their perceptions about it.

The results from the empirical evaluations show that our proposal can be effectively used to support the development and certification of avionics software in accordance with DO-178C. Practitioners from industry consider the proposal to be easy to understand and gave it an overall likelihood of adoption within the contexts of their work.


identifier: Ouanouki, Rafik  (2020). Extracting rules to help in the conversion of a relational database to NoSQL (column-oriented) database technology.  Thèse de doctorat électronique, Montréal, École de technologie supérieure.

subject: règles de conversion de bases de données relationnelle

subject: NoSQL

subject: définition infonuagique

subject: mégadonnées

abstract:
This research aims to support software engineers in their first attempt at a conversion of relational databases to a database technology recognized as better suited to cloud computing (NoSQL), which in this particular case study is HBase. To do this, an initial research activity aims to understand and clarify the notions of essential and optional characteristics in the cloud computing definition. This discussion is considered by taking the perspective of this research (i.e. a database conversion from RDB to NoSQL). Subsequently, the main contribution of this research explores the possibility of extracting database conversion rules.

Two experiments were carried out to identify an initial list of conversion rules:

1. The first experiment consisted of asking participants (engineers from École de technologie supérieure) to convert a particular schema, without the use of a guide or conversion rules. Several questionnaires were completed by the participants during the experiment. The main goal of this experiment was to evaluate the need for conversion rules to help software engineers in the conversion of relational schemas to non-relational schemas.

2. The second experiment consisted of dividing the participants into sub-groups tasked to convert a single RDB relation (i.e. one-to-one) to a possible schema in HBase. The goal was to test the results of a basic relationship compared with all the schematic conversion possibilities in HBase, a particular non-relational database, and then extract the conversion rules. This experiment would show why one particular schema is better than another and would allow for the identification of conversion rules based on facts (e.g., performance measurement of a query on each of the resulting schemas).

The main contributions of this thesis are:

1. A list of rules for converting relational database schemas to the schema of a non-relational database:
a. Rules on data proximity;
b. Rules on column families;
c. Rules on data quantity;
d. Rules on access patterns.

2. Clarification to the term cloud computing is also proposed by introducing the notion of mandatory and optional characteristics excluded from the most popular definition.


identifier: Rony, Jérôme  (2020). Feed-forward weakly supervised deep learning models for breast cancer diagnosis from histological images.  Mémoire de maîtrise électronique, Montréal, École de technologie supérieure.

subject:
diagnostic du cancer du sein
apprentissage faiblement supervisé
apprentissage profond

abstract:
Breast cancer screening has become one of the top priorities to reduce the number of deaths from breast cancer and treat it as soon as possible. When making a diagnosis for breast cancer, the gold standard is histological image analysis. However, these images are very large and require both time and expertise to be correctly interpreted. Research in computer vision algorithms has shown great potential to assist practitioners in making faster and more accurate diagnoses. However, to use these kinds of algorithms, large amounts of data with high quality annotations are often required.

In this thesis, we propose to approach this problem from the perspective of weakly supervised learning. In this scenario, we consider that we only have weak annotations such as image-level labels for each sample. With these weak annotations, we seek to train accurate models to accurately predict both image-level (classification) and pixel-level labels (segmentation).

As a first contribution, we identify, analyze and evaluate several weakly supervised techniques proposed for natural images with the intent of identifying which one are the most promising for our application.

As a second contribution, we generalize a technique proposed for binary classification to the more general settings of multi-class and multi-label classification. We show that this technique scales well to widely used natural image datasets and further evaluate it on histological image datasets.

As a third contribution, we study the impact of adding size constraints to train a model. This corresponds to a scenario where an annotator would only estimate the size of the cancerous regions in histological images, reducing the time needed to annotate images when doing a segmentation. We propose a formulation to take advantage of the size information and show that it significantly improves the segmentation performance compared to training with image-level labels only.


identifier: Bouchet, Mélusine  (2020). Conception et évaluation in vivo de prothèses vasculaires compliantes de petit diamètre par électrofilage avec revêtement bioactif.  Thèse de doctorat électronique, Montréal, École de technologie supérieure.

subject:
prothèse vasculaire
électrofilage
compliance
revêtement bioactif
adhésion

abstract:
Dans le traitement des maladies cardiovasculaires, l’utilisation des prothèses synthétiques est actuellement limitée par d’importantes complications cliniques, particulièrement pour le remplacement des vaisseaux de petit diamètre (< 6 mm). La faible compliance des implants et leurs propriétés de surface inadéquates sont à l’origine du manque d’endothélialisation et des processus biologiques entraînant un taux d’occlusion des conduits inacceptable.

L’hypothèse à la base de ce projet est que la combinaison d’une structure tubulaire compliante avec une couche interne non thrombogène ayant la capacité de stimuler la formation d’une monocouche de cellules endothéliales aurait le potentiel d’améliorer les résultats cliniques. Dans ce contexte, la technique d’électrofilage a été sélectionnée car elle permet de fabriquer des structures fibreuses modulables dans le but de reproduire la morphologie de la matrice extracellulaire des vaisseaux natifs et d’en imiter les propriétés mécaniques. De plus, un revêtement bioactif composé d’un dépôt plasma riche en amines primaires (L-PPE:N) sur lequel est greffé du sulfate de chondroïtine (CS) a démontré un potentiel de réduction de l’adsorption de protéines impliquées dans la formation d’un thrombus, tout en favorisant l’endothélialisation des surfaces. Cette thèse propose ainsi d’élaborer une nouvelle génération de prothèses vasculaires afin d’améliorer la perméabilité des conduits in vivo, tout d’abord par la conception de structures tubulaires électrofilées compliantes, puis leur évaluation in vivo dans un modèle ovin suite à leur combinaison avec un revêtement bioactif.

En raison du manque de directives dans les pratiques de conception des implants vasculaires, nous avons tout d’abord employé un modèle analytique pour sélectionner un matériau pouvant obtenir une compliance et une pression à la rupture semblables à des artères natives de petit diamètre (0,0725 %/mmHg et 2031 mmHg, respectivement). Afin d’établir une preuve de concept, nous avons démontré qu’une structure électrofilée en polyuréthane (PU) et polycaprolactone (PCL) était plus compliante qu’un implant commercial en polytétrafluoroéthylène expansé (ePTFE). Avec la sélection d’une épaisseur de 145 μm, il a alors été possible de construire une prothèse vasculaire de petit diamètre avec un bon équilibre entre les importantes propriétés suivantes : la compliance, la pression à la rupture, l’étanchéité au sang et la maniabilité.

Suite au transfert du revêtement bioactif à base de L-PPE:N et CS sur les implants électrofilés en PU/PCL, des expérimentations animales ont démontré leur infériorité par rapport à des implants en ePTFE, avec l’observation de sténoses et occlusions au sein de nos conduits. Les causes de ces échecs concernent, d’une part, des altérations structurelles pariétales pour les implants électrofilés thrombosés, et d’autre part, la thrombogénicité de la surface luminale des prothèses potentiellement engendrée par un mauvais greffage de la CS.

Le bénéfice de la compliance de nos conduits n’a ainsi pas pu être vérifié. Des recommandations ont été proposées pour chacune des hypothèses d’échec à une visée d’améliorations de travaux futurs.

À cet effet, un essai de pelage a été adapté afin de caractériser la force d’adhésion à leur interface pour optimiser la cohésion entre deux matrices électrofilées, et différents paramètres de fabrication ont été explorés. Les travaux ont notamment mis ici en évidence l’augmentation de la force d’adhésion avec le diamètre des fibres entre deux matrices électrofilées. Ces résultats permettent d’apporter des éléments de réflexion dans l’optimisation des implants, et de viser le développement de prothèses multicouches.

Les travaux menés ont permis de développer un nouvel implant électrofilé en PU/PCL, établi selon une démarche de conception simple et raisonnée qu’est le modèle analytique, et ayant de meilleures propriétés mécaniques que des implants commerciaux en ePTFE. Malgré les résultats insatisfaisants de l’étude animale sur ces conduits avec revêtement bioactif, ces travaux constituent une avancée des connaissances sur la combinaison de ces types de matériau et molécule active dans un modèle de grand animal. L’étude exploratoire sur la force d’adhésion permet également l’avancement de la compréhension des propriétés d’adhésion entre des matrices électrofilées. Le potentiel de la technique d’électrofilage est ainsi mis en valeur dans ce projet et ouvre la voie au développement d’une nouvelle génération de prothèses vasculaires de petit diamètre.


identifier: Pham, Minh Nha  (2020). Numerical and experimental study of dynamics and vibration control of flexible joint robots.  Thèse de doctorat électronique, Montréal, École de technologie supérieure.

subject: robot articulation flexible

subject: contrôle des vibrations

subject: contrôleur à deux étages

subject: observateur de perturbation

subject: observateur d'état

subject: formation d’entrée variant dans le temps

subject: prédicteur de Smith

abstract:
Serial robots are recently one of the most effective methods to realize several industrial applications including precision positioning and inspection tasks. They can provide a large working envelope, access to restricted areas, operations in hazardous environments, and precision works with high degree of reliability. A major issue of serial robots is vibration, due to flexible modes dynamics that are excited. The vibration causes deterioration of motion control accuracy, large stress in the joint gearboxes, and deformations or damages of the robot manipulator. The flexible modes dynamics are introduced due to the low rigidity of robot manipulators, which may be caused by the flexibility of joints or links. Regardless of size and design, most serial robots are still quite flexible with the first resonance in low frequencies of about 10 Hz. To avoid the consequences caused by vibrations, vibration control becomes very important and needs to be taken into account in control design.

The main objective of this study is to design control algorithms to reduce vibration of flexible joint robots. The proposed controller design procedure can be applied for various industrial robots and is tested experimentally on an industrial six-joint robot namely SCOMPI, developed at Hydro-Québec’s Research Institute. In order to achieve that end, two phases of study are proposed.

The objective of the first phase is to study the dynamics of a single flexible joint robot and design a control algorithm to reduce the vibration. Decentralized dynamic model of flexible joint robot is studied. Control concepts are tested on a simple experimental setup consisting of only one joint and one link. All parts of the system are considered rigid except for one element that is the flexible joint. The single flexible joint model is placed in a fully-controlled environment, in which access to motor torque command, motor reference, or feedback states are available. For this objective, an enhanced two-stage feedback controller is proposed, which combines two parts. The first is a two-stage feedback loop based on back stepping control, which considers the motor position as a virtual control input for the link side dynamics. The second is a disturbance-state observer, which compensates disturbances and reconstructs indirect measurements. Numerical simulation and experimental results validate that the proposed controller effectively improves control performance in terms of reducing link vibration, extending control bandwidth, and attenuating the kinematic error from the joint’s harmonic drive reducer. Limitations of the proposed controller are also discussed. The control performance relies on system parameters, which need to be properly identified. It also requires effort to manually tune controller gains. And most importantly, the proposed controller needs access to motor torque command to implement its algorithm. However, it is worth mentioning that the results of the first phase validate the underlying modelling assumption for the flexible joint and that the two-stage architecture is feasible for vibration control purpose.

Based on promising results of vibration control on single flexible joint test bench, the second phase is to adapt the acquired knowledge for a much more general case, industrial serial robot with multiple joints. There is a decision to make, either a multi joint experimental setup is built or an existing serial robot is used as a test bench. With the former option, the controller developed in the first phase can be directly applied. However, building a new multi-joint experimental setup costs a lot of effort and time. The latter option, using an existing industrial robot as a test bench, has a big advantage. It costs much less since man power, material to build things are saved and all mechanical or electronic elements are included. However, a new controller must be designed to comply with the existing robot control interface. One of the constraints is that the industrial robot is controlled in position mode and that the access to the motor torque command is not provided. Without access to the motor torque command, the controller proposed for single joint test bench in the first phase can not to be directly applied.

Considering these two options, an existing industrial multiple joint serial robot is used to develop vibration control algorithms. Although a new controller needs to be developed, it still shares some aspects of the dynamic model of flexible joint robot developed in the first phase. Also, it can be easily industrialized afterward since all constrains are already taken into account. Note that, due to the fact that access to motor torque command is unavailable, the proposed controller needs to be based on the access to motor position command.

The objective of the second phase is to design vibration control algorithms for industrial robots with multiple flexible joints. A two-stage flexible joint discrete controller is presented, where the decentralized approach is extended with a lumped stiffness to take into account the dominant coupling mode. In the first stage, a time-varying input shaping feedforward shapes the rigid closed-loop dynamics into a desired dynamics that does not produce link vibrations. A second stage is added to increase disturbance rejection. A generalized Smith predictor is developed to compensate for delay and link feedback sensor filtering. Numerical simulations and experiments on a six-joint robot manipulator SCOMPI confirm that the proposed controller improves control performances in terms of bandwidth, vibration attenuation, and disturbance rejection.


identifier: Cisse, Moussa  (2020). Analyse multivariée et optimisation par la méthode des surfaces de réponses (MSR) de l’électro-conversion de l’azote ammoniacal en condition saline.  Mémoire de maîtrise électronique, Montréal, École de technologie supérieure.

subject:
azote ammoniacal
électrochimie
zéolite
ACP
rendement
optimisation
MSR
modélisation

abstract: Les concentrations élevées d’azote ammoniacal dans le lieu naturel liées aux activités anthropiques, affectent de façon néfaste les qualités physiques et biologiques de l’environnement. Les techniques de traitement physique, biologique et géochimique de ce polluant sont contraignantes sur le plan opérationnel, économique et parfois environnemental. La méthode électrochimique est de plus en plus prospectée dans un contexte d’amélioration du procédé pour un meilleur impact environnemental et économique. L’objectif de cette étude consiste à évaluer la performance d’une combinaison du dispositif électrochimique monopolaire avec la chabazite en milieu salin pour l’électro-conversion de l’azote ammoniacal. Après des essais préliminaires qui ont permis de choisir les sels MgCl2·6H2O et NaCl, des essais électrochimiques à 3 V ont offert une performance supérieure en présence de 3 g Cl-/L de NaCl avec 49,6% de rendement et moins de 1% de nitrate et de nitrite. L’analyse des paramètres électrochimiques et chimiques et l’Analyse en Composantes Principales (ACP) ont mis en évidence les effets négatifs de la variation du pH et ceux des réactions d’acidification et de complexation en présence du sel MgCl2·6H2O sur le rendement d’électro-conversion de N-NH4+. L’ACP a identifié la salinité et l’énergie comme étant les facteurs prépondérants à cette électro-conversion. Sur cette base, l’analyse factorielle avec la méthode de rotation par VARIMAX a permis de sélectionner la Tension Électrique (TE), la Concentration en ions Chlorures (CC) et la concentration Finale en ions Hydrogènes (HF) pour la construction du modèle de Rendement Électro-conversion de N-NH4+ (RE). L’analyse des variances (ANOVA) a par la suite montré que la concentration Finale en ions Hydrogènes (HF) n’est pas significative à la réponse du modèle. Ce modèle d’optimisation par la Méthode des Surfaces de Réponses (MSR) a donc été construit à l’aide d’un plan factoriel à trois niveaux par facteur avec les variables Tension Électrique (TE) et Concentration en ions Chlorures (CC). Le modèle de rendement d’électro-conversion de N-NH4+ obtenu, avec 94 % de coefficient de détermination, indique un rendement de 68 % dans les conditions optimales de 12 V et de 3,97 g Cl-/L. L’analyse économique a permis d’évaluer un coût de 5,6 $/kg de N-NH4+ traité. Ce coût pourrait être diminué en évaluant les conditions de réutilisation de la solution de régénération et de la zéolite ainsi que, de remplacement des électrodes.


identifier: Zhang, Chunping  (2020). Influence of casting process parameters on macrosegregation in large size steel ingots using experimentation and simulation.  Thèse de doctorat électronique, Montréal, École de technologie supérieure.

subject:
macroségrégation
grands lingots d’acier
expérimentation
modélisation

abstract:
The present project aims to develop a reliable numerical model to predict the extent and severity of macrosegregation in a 40MT (metric ton) medium-carbon high strength steel ingot as a function of casting parameters with the view to minimize the occurrence of the macro-scale defect. For this purpose, the commercial finite element modeling (FEM) code Thercast® was at first determined to be used for the simulation work. This basis of such a decision rested on the critical literature review on the evolution of solidification modeling technique in the past 60 years, the powerful computing capability of the software and its performance of the three-dimensional simulations of mold filling and solidification based on a volume-averaged solid-liquid two-phase model.

The factors influencing model accuracies were eliminated one by one. For instance, an axisymmetric model in the dimension of 1/24 of the actual casting system was determined to be representative enough for the necessary simulation work. An average general cell size of 35 mm was identified to be the discretization parameter for its realization of the compromise between computational accuracy and efficiency based on series of sensitivity studies of solidification to mesh size. Modeling boundary conditions were set based on industrial practice, which took into account the local friction and the thermal exchange between the steel and the mold components, as well as the mutual exchange between mold components themselves in the casting system. Input temperature-dependent parameters of all concerned materials, reflecting their thermodynamic, thermomechanic and thermodiffusion behaviors, were identified by means of combined approaches of computational thermodynamics program Thermo-Calc® software, literature reports, published empirical equations, Thercast® software material database, industry sources, theoretic calculations, as well as room and high temperature tension tests in laboratory. The applicability of the used softwares and models was verified before applying them to the investigated steel. The experimental planning was strictly formulated based on simulation tests. Lever rule microsegregation model was ascertained to be the most reasonable depiction of the physical behavior of the steel in study in large-size cast ingot. This selection was made after comparative examinations of various microsegregation schemes against experimental measurements, together with subsequent adoption to the regions formed in different stages of the solidification process. A thermomechanical model was finally deemed as the baseline formulation for all the parametric studies in terms of the impact study of thermomechanical shrinkage on macrosegregation and its reproductions of experimental findings.

The dependence of the solidification behavior on the variations of filling rate, melt superheat and initial mold temperature was then investigated, respectively, using the established reliable model. The three casting control parameters were selected due to the shortness or confliction of relevant data in the literature, as well as the complication, high-cost or impossibility of the employment of other macrosegregation control techniques. The studied casting variables included the filling rates of 0.084, 0.107 and 0.145 m/min (with filling times of 38, 30 and 22 min), the initial melt superheats of 75, 65 and 55 °C, the initial mold temperatures of 50, 120 and 250 °C. These casting parameters represented the conditions the most commonly encountered in industry during casting of large size ingot. The results indicated that a quicker filling operation, a lower melt superheat and a colder mold condition tended to decrease the macrosegregation intensity in the upper section of the casting, along the centerline, and in the mid-radius solute-enriched bands. The alleviation effect was associated with the changes in flows induced by pouring jet, thermosolutal convection, thermomechanical deformation of the phases, along with the variations of the temperature gradient in the casting and the solidification speed. The predictions of the studied cases were verified with experimental characterizations on the macro-/micro-structures, solutal distributions, dimensional change of the casting and the temperature variations on mold outside surface.

The findings in the dissertation allow for a better understanding of the underlying mechanisms responsible for the occurrence of macrosegregation in ingot casting process. They should also be helpful for the casting process design of a given ingot and could be used in industry to improve the quality of large size ingot production and the productivity of high value-added steels or other alloys which are prone to macrosegregation.


identifier: Huot, Mickael  (2020). La méthode ARIV : une nouvelle approche pour propulser la performance des organisations.  Mémoire de maîtrise électronique, Montréal, École de technologie supérieure.

subject:
amélioration continue
lean
six sigma
échec
succès

abstract:
La performance des organisations est une composante clé pour assurer la prospérité d’une nation. Se faisant, la performance doit continuellement augmenter par le biais de nouveaux procédés et processus ou dans l’amélioration de ceux-ci. Cependant, beaucoup d’initiatives en ce sens tendent à échouer dans l’industrie. Cette réalité mine la performance des entreprises et la qualité de vie des individus. De plus, ceci génère un gaspillage de ressources humaines, financières et matérielles qui est profitable pour aucune des parties prenantes.

Selon la littérature, dans l’industrie, les méthodes d’amélioration tel que le lean six sigma et le lean manufacturing ont des taux d’échec élevés. La recherche a permis de répertorier les facteurs qui font en sorte qu’un projet réussi ou échoue. Les chercheurs situés à divers endroits sur la planète ont répertorié des facteurs communs et une compilation de ceux-ci a été effectué. Un de ces facteurs a un effet domino majeur sur les autres éléments soit la priorisation et la sélection des projets.

La méthode ARIV a donc été développée en prenant compte de ces différents facteurs et ce à chacune des étapes des projets pour maximiser les probabilités de succès. La formation, la priorisation et la sélection des projets, l’engagement des dirigeants, la communication et l’engagement des employés sont tous des facteurs pris en compte, au moment opportun, dans la méthode ARIV.

À travers nos mandats de consultation chez ARIV, nous avons documenté des cas d’étude et discuter de l’application de la méthode. À chaque étape de la méthode, nous avons mesuré les probabilités de succès en fonction des facteurs de succès répertoriés dans la littérature. En comparant les résultats des indicateurs de performance des projets avec les probabilités de succès, nous pouvons conclure que les moyens employés pour assurer le succès des projets sont robustes.


identifier: Le, Phuoc Luong  (2020). Optimization of integrated construction supply chain and BIM-based logistics planning.  Thèse de doctorat électronique, Montréal, École de technologie supérieure.

subject: gestion de la chaîne d'approvisionnement

subject: secteur de la construction

subject: logistique

subject: modèle d'optimization

subject: planification de l'aménagement du site

subject: logistique tierce partie

subject: modélisation des informations sur le bâtiment

abstract:
Improving the performances of logistics activities is an important reason for applying the concept of supply chain management in the construction industry. Based on the systematic literature review, we find the key decisions, which are presently focused on construction logistics and supply chain management. These decisions are identified for three main stages of a construction supply chain project: planning and design, procurement, and construction execution. In the scope of this thesis, we focus on logistics improvement for the construction projects; thus, decisions related to construction logistics are taken into account to model and optimize the construction supply chain operations. In order to achieve efficiency in construction logistics, the four decisions are commonly conducted: transportation, material purchasing and storage, site layout, and material handling. In this thesis, issues related to material transportation and material purchasing and storage are considered to model and optimize the integrated construction supply chain network with a Third-party logistics partnership, which minimizes the total supply chain costs, including transportation cost, material purchasing cost, and material storage cost. Meanwhile, site layout planning and material handling are concurrently considered to generate an efficient layout of temporary facilities in the construction site, which aims to minimize the material handling cost and maximize the adjacency score between the facilities.

Based on the identified present focuses of decision making in construction logistics and supply chain management, we found that the development of supply chain integration in the construction industry has been limited and at a slower speed in comparison to that of other industrial sectors. Thus, we recommend the supply chain integration as a key factor for the efficiency in construction logistics. Besides the integration of relevant supply chain actors, it is also important to leverage the focal role of the supply chain driver acting as the coordinator for the construction logistics activities. In this thesis, the Third-party logistics partnership is proposed to achieve the supply chain integration in the construction logistics network. The integration of relevant actors is also important for construction operations. Building information modeling (BIM)-based platform is suggested to facilitate the collaboration of construction actors in the logistics execution.

Third-party logistics partnership can be used as a strategic tool for improving construction site logistics since it supports the construction supply chain operations with the integration of relevant actors. Recently, the use of third-party logistics providers has been considered as a business opportunity for the construction industry where many problems in logistics management exist. This thesis presents an optimal decision-making model for construction supply chain operations with the Third-party logistics partnership, which promotes the role of Third-party logistics provider as the logistics coordinator. The proposed model aims to create an optimal logistics plan for material purchasing, transportation, and storage. The model has distinctive contributions since it supports the determination of the operational strategies for common tasks in construction supply chain management: supplier selection, determination of order quantity, and consideration of the efficiency in using Third-party logistics under the considerations of material types and uncertainties price, demand and supply. The model is especially useful for the construction owner and General contractor to consider the material procurement from remote suppliers who require large purchasing amounts to offer low prices and transportation costs. Using the numerical case example, we find that the proposed model performs better results in total supply chain cost in comparison with the construction supply chain model without Third-party logistics. This implies that the optimization model for the integrated construction supply chain operations with a Third-party logistics partnership can be used to improve the construction logistics performance and deal with the practical requirements of the current issues in the construction industry.

This thesis also focuses on developing a hybrid site layout framework, which combines the two well-known approaches – mathematical and systematic layout planning – to generate the step-by-step procedure for site layout planning. Site layout planning needs the expertise from the relevant actors for the assessment of facility relationships or the selection of the best solutions. Meanwhile, mathematical techniques are necessary for the optimization of productive objectives in site layout planning. Therefore, it is suggested that knowledge-based techniques should be integrated with mathematical techniques to deal with site layout problems. It is also important to ensure the data correction and updating for site layout planning. It is suggested that advanced technologies, especially the BIM platform, should be used to facilitate the data provision and automation for the systematic site layout process. Hence, this thesis proposes a framework, which systematically integrates qualitative and quantitative data for dynamic site layout planning using a cloud-enabled BIM platform and the knowledge-based rules. The proposed framework takes advantage of emerging BIM technology to support quantitative data collection and sharing. Besides, the qualitative data are generated on the managers’ expertise through knowledge-based rules. All the data used for parameters in the site layout model are collected and processed in a systematic procedure, instead of being predetermined as in many previous studies. The validations show that the proposed framework performs better results in both terms of cost reduction and adjacency improvement. This implies that the hybrid approach, which integrates the mathematical and systematic site layout methods, can be used to create productive site layout plans.


identifier: Poulin-Masson, Jean-René  (2020). Application de l’approche de mécanique de la rupture pour la tolérance aux dommages et la prédiction de la vie en fatigue de composants obtenus par fusion sélective au laser.  Thèse de doctorat électronique, Montréal, École de technologie supérieure.

subject:
fabrication additive
fatigue
mécanique de la rupture
propagation de fissure
superalliage
tomographie à rayons X
porosité
défauts de fabrication

abstract:
Les procédés de fabrication additive de matériaux métalliques suscitent de plus en plus d’intérêt dans différents secteurs industriels pour la fabrication de composants à forte valeur ajoutée. Parmi ces procédés, la fusion sélective au laser (LPBF pour laser powder bed fusion) permet de mettre en forme des alliages dont les propriétés mécaniques statiques sont similaires à celles de leurs contreparties corroyées. Toutefois, les défauts de fabrication leur confèrent un comportement moins enviable pour les applications en fatigue. En ce sens, pour élargir le champ d’application aux composants soumis à des chargements cycliques, il est nécessaire de développer une meilleure compréhension de l’impact de ces défauts sur le comportement en fatigue.

Cette thèse présente, en trois articles scientifiques, une proposition de démarche visant à établir une zone de conception sécuritaire pour des composants obtenus par LPBF, et ce, en considérant les défauts qui résultent de leur mise en forme. La démarche en question fait appel à la mécanique de la rupture et au modèle d’El-Haddad pour mettre en relation la taille de défaut tolérable à diverses amplitudes de contraintes.

Dans un premier temps, le comportement en fatigue de l’alliage d’Inconel 625 obtenu par fabrication additive est évalué selon l’approche de la mécanique de la rupture. L’effet de l’anisotropie résultant de la mise en forme est considéré et une comparaison avec un alliage corroyé de même composition est réalisée. La résistance à la propagation de fissure longue a été montrée dépendante de l’orientation de fabrication et de l’orientation de propagation de la fissure relativement à l’axe de fabrication. Toutefois, en excluant les mécanismes de fermeture de fissure, celle-ci s’est montrée comparable à celle de l’alliage corroyé de même composition (Inconel 625).

Par la suite, une méthode de création de défauts a été développée. Pour ce faire, des paramètres d’exposition laser non optimaux ont été développés. Dans le second article, des échantillons sont fabriqués en modifiant la vitesse du laser, ce qui a permis de générer différents taux de porosité (0.1 à 2.7%) et d’en évaluer l’impact sur le comportement quasi statique et en fatigue de l’Inconel 625. Les résultats obtenus mettent en évidence l’impact limité des défauts de fabrication sur les propriétés élastiques du matériau, mais une grande sensibilité de la ductilité de la présence de ces défauts. De plus, l’impact des défauts a été montré fortement dépendant de l’orientation de fabrication. En propagation de fissure, la présence de défaut s’est avérée particulièrement importante lorsque le facteur d’intensité de contrainte est élevé, alors que l’impact sur le seuil de propagation de fissure est négligeable.

Dans un troisième temps, des échantillons de fatigue sont fabriqués avec des défauts induits dans la section de test en utilisant les paramètres laser déterminés au chapitre précédent lors de l’exposition des couches correspondantes. Un total de 4 ensembles d’échantillons sont étudiés, lesquels ont des taux de porosités compris entre ~0.1 et ~2.7%. La caractérisation des défauts sur un nombre restreint d’éprouvettes est réalisée et à partir de la taille mesurée, une prédiction de la limite de fatigue en vie infinie est effectuée en utilisant le modèle de El-Haddad. Pour valider la prédiction du modèle, des essais de fatigue sous force contrôlée sont réalisés et la limite de fatigue résultante est comparée à la prédiction du modèle d’El-Haddad. Les résultats expérimentaux montrent que le modèle est légèrement conservateur. L’erreur maximale entre la résistance en fatigue prédite par El-Haddad et celle estimée au moyen d’essais sous force contrôlée est d’environ 7%, ce qui est jugé acceptable.

Afin d’aller plus loin dans cette démarche et de manière préalable à l’application a une pièce, il est suggéré de réaliser des essais analogues sur des échantillons de tailles variables et de valider la possibilité de prédire la taille des défauts en utilisant les statistiques de l’extrême. Pour ce qui est des applications en vie finie, les résultats expérimentaux suggèrent qu’il est important de considérer la phase d’initiation de fissure, ainsi que celle de propagation afin d’avoir une prédiction adéquate puisqu’en présence de défauts, la phase de propagation s’étend sur un plus grand nombre de cycles.


identifier: Mokhayyeri, Faniya  (2020). Domain-specific face synthesis for still-to-video face recognition.  Thèse de doctorat électronique, Montréal, École de technologie.

subject:
Reconnaissance de visage
synthèse de visage
reconstruction du visage en 3D
surveillance vidéo
adaptation de domaine
représentation clairsemée
apprentissage générique

abstract:
Face recognition (FR) has attracted a considerable amount of interest from both academia and industry due to the wide range of applications as found in surveillance and security. Despite the recent progress in computer vision and machine learning, designing a robust system for video-based FR in real-world surveillance applications has been a long-standing challenge. One key issue is the visual domain shift between faces from source domain, where high-quality reference faces are captured under controlled conditions from still cameras, and those from the target domain, where video frames are captured with video cameras under uncontrolled conditions with variations in pose, illumination, expression, etc. The appearance of the faces captured in the videos corresponds to multiple non-stationary data distributions can differ considerably from faces captured during enrollment. Another challenge in video-based FR is the limited number of reference stills that are available per target individual to design facial models. This is a common scenario in security and surveillance applications, as found in, e.g., biometric authentication and watch-list screening. The performance of video-based FR systems can decline significantly due to the limited information available to represent the intra-class variations seen in video frames. This thesis proposes 3 data augmentation techniques based on face synthesis to overcome the challenges of such visual domain shift and limited training set. The main advantage of the proposed approaches is the ability to provide a compact set that can accurately represent the original reference face with relevant intra-class variations corresponding to the capture conditions in the target domain. In particular, this thesis presents new systems for domain-invariant still-to-video FR that are based on augmenting the reference gallery set synthetically which are described with more details in the following.

As a first contribution, a face synthesis approach is proposed that exploits the representative intra-class variational information available from the generic set in target domain. The proposed approach, called domain-specific face synthesis, generates a set of synthetic faces that resemble individuals of interest under the capture conditions relevant to the target domain. In a particular implementation based on sparse representation, the generated synthetic faces are employed to form a cross-domain dictionary that accounts for structured sparsity where the dictionary blocks combine the original and synthetic faces of each individual. Experimental results obtained with videos from the Chokepoint and COX-S2V datasets reveal that augmenting the reference gallery set of still-to-video FR systems using the proposed face synthesizing approach can provide a significantly higher level of accuracy compared to state-of-the-art approaches.

As a second contribution, a paired sparse representation model is proposed allowing for joint use of generic variational information and synthetic face images. The proposed model, called synthetic plus variational model, reconstructs a probe image by jointly using (1) a variational dictionary designed with generic set and (2) a gallery dictionary augmented with a set of synthetic images generated over a wide diversity of pose angles. The augmented gallery dictionary is then encouraged to share the same sparsity pattern with the variational dictionary for similar pose angles by solving a simultaneous sparsity-based optimization problem. Experimental results obtained on Chokepoint and COX-S2V datasets, indicate that the proposed approach can outperform state-of-the-art methods for still-to-video FR with a single sample per person.

As a third contribution, a deep Siamese network, referred as SiamSRC, is proposed where performs face matching using sparse coding. The proposed approach extends the gallery using a set of synthetic face images and exploits sparse representation with a block structure for pairwise face matching that finds the representation of a probe image that requires the minimum number of blocks from the gallery. Experimental results obtained using the Chokepoint and COX-S2V datasets suggest that the proposed SiamSRC network allows for efficient representation of intra-class variations with only a moderate increase in time complexity. Results show that the performance of still-to-video FR systems based on SiamSRC can improve through face synthesis, with no need to collect a large amount of training data.

Results indicate that our proposed techniques which are the integration of face synthesis and generic learning can effectively resolve the challenges of the visual domain shift and limited number of reference stills and provide a higher level of accuracy compared to state-of-the-art approaches under unconstrained surveillance conditions.


identifier: Mostafavi Toroqi, Moeedreza  (2020). Privacy-preserving algorithm for outsourcing matrix multiplication based on Strassen’s algorithm.  Mémoire de maîtrise électronique, Montréal, École de technologie supérieure.

subject:
multiplication de matrices
schéma de Strassen

abstract:
Matrix Multiplication is a fundamental mathematical tool and basic problem with various applications in many domains such as data mining and data analyzing. Most of the time, limited-resource clients cannot afford the cost of heavy computations and needs to outsource the information and computations to a powerful and efficient cloud system. In this data exchanging, security and privacy concerning become a significant issue due to the value of some sensitive data such as private personal information or industrial data. The untrusted cloud servers beside malicious adversaries are always a kind of hazard for the clients and increase the risk of information leakage in data outsourcing. There exist many secure algorithms with creative data masking methods which are already usable in the industry, but due to numerous system and treat models, and the importance of the level of the security, new algorithms always emerge to improve the existing schemes.

In this thesis, we propose four privacy-preserving algorithms based on Strassen’s scheme to provide the desirable result of matrix multiplication for the clients who are not able to process the regular matrix multiplication algorithms because of lake of powerful resources.


identifier: Cao, Hongliu  (2019). Random forest for dissimilarity based multi-view learning : application to radiomics.  Thèse de doctorat électronique, Montréal, École de technologie supérieure.

subject:
espace de dissimilarité
forêt aléatoire
apprentissage multi-vue
dimension élevée
taille réduite de l’échantillon
apprentissage de dissimilarité
sélection dynamique

abstract:
The work of this thesis was initiated by a Radiomic learning problem. Radiomics is a medical discipline that aims at the large-scale analysis of data from traditional medical imaging to assist in the diagnosis and treatment of cancer. The main hypothesis of this discipline is that by extracting a large amount of information from the images, we can characterize the specificities of this pathology in a much better way than the human eye. To achieve this, Radiomics data are generally based on several types of images and/or several types of features (from images, clinical, genomic).

This thesis approaches this problem from the perspective of Machine Learning (ML) and aims to propose a generic solution, adapted to any similar learning problem. To do this, we identify two types of ML problems behind Radiomics: (i) learning from high dimension, low sample size (HDLSS) and (ii) multiview learning. The solutions proposed in this manuscript exploit dissimilarity representations obtained using the Random Forest method. The use of dissimilarity representations makes it possible to overcome the well-known difficulties of learning high dimensional data, and to facilitate the joint analysis of the multiple descriptions, i.e. the views.

The contributions of this thesis focus on the use of the dissimilarity measurement embedded in the Random Forest method for HDLSS multi-view learning. In particular, we present three main results: (i) the demonstration and analysis of the effectiveness of this measure for HDLSS multi-view learning; (ii) a new method for measuring dissimilarities from Random Forests, better adapted to this type of learning problem; and (iii) a new way to exploit the heterogeneity of views, using a dynamic combination mechanism. These results have been obtained on radiomic data but also on classical multi-view learning problems.


identifier: Ferjani, Amel  (2020). Modélisation de la performance à la fissuration des chaussées réhabilitées par les techniques de retraitement type I et type II.  Thèse de doctorat électronique, Montréal, École de technologie supérieure.

subject:
enrobés recyclés à froid
chaussées réhabilitées
comportement viscoélastique
résistance à la fissuration
méthode des éléments finis étendus
propagation des fissures

abstract:
Le passage répété du poids lourd et les conditions climatiques extrêmes entrainent la dégradation des structures de chaussées, ce qui impose parfois le recours à des techniques de réhabilitation permettant de maintenir la route en état sécuritaire et prolonger sa durée de vie. Depuis les années 1980, les techniques de recyclage, notamment les techniques de retraitement type I et type II, ont commencé à gagner en popularité au Québec. Ces méthodes permettent d’améliorer l’état structural et fonctionnel de la chaussée et répondent aux exigences du développement durable. Bien que ces techniques soient considérées performantes, certains aspects relatifs à la prédiction de leurs performances restent peu maitrisés.

La fissuration est l’un des modes de dégradation les plus fréquents dans les chaussées réhabilitées, cependant les méthodes de dimensionnement actuelles ne tiennent pas compte de l’existence des fissures dans les structures dégradées. En outre, la compréhension du comportement des matériaux recyclés à froid est nécessaire pour prédire le comportement de ces chaussées. C’est dans ce cadre que s’inscrit cette thèse qui vise à modéliser et évaluer la performance des chaussées réhabilitées par retraitement type I et type II à la fissuration.

Afin d’atteindre l’objectif de cette thèse, l’étude s’est divisée en trois volets. La première partie concerne la caractérisation, en laboratoire, du comportement des matériaux recyclés à froid utilisés dans les chaussées réhabilitées par retraitement type I et type II (MR7 et MR5, respectivement). L’essai de module complexe a été utilisé pour caractériser le comportement viscoélastique alors que l’essai de flexion semi-circulaire pour déterminer la résistance à la fissuration des MR5 et MR7. La deuxième partie a été consacrée pour modéliser le comportement de ces matériaux en utilisant la méthode des éléments finis. Pour ce faire, un modèle 2D de l’essai SCB a été développé à l’aide du logiciel ABAQUS et calibré selon les résultats expérimentaux. L’initiation et la propagation des fissures ont été modélisées par la méthode des éléments finis étendus. Les résultats numériques ont montré un bon accord avec la propagation des fissures observée en laboratoire. La dernière partie est destinée pour développer des modèles en éléments finis des structures de chaussées et évaluer leurs comportements. Afin de valider l’approche de modélisation, une structure réelle disponible dans la base de données LTPP a été modélisée par la méthode des éléments finis. La comparaison des résultats de modélisation et les mesures de déflexions sur la chaussée a permis de valider cette approche. Finalement, les structures réhabilitées ont été modélisées et évaluées vis-à-vis à la fissuration. Les résultats ont montré que la technique de retraitement type I est sensible à la remontée des fissures existantes alors que la performance du retraitement type II est liée au comportement des MR5.


identifier: Verdier, François  (2020). Développement d'une méthodologie d'optimisation du profil d'aile de l'UAS-S45 en utilisant les algorithmes ABC et PSO.  Mémoire de maîtrise électronique, Montréal, École de technologie supérieure.

subject: aérodynamique optimisation algorithmes PSO ABC CST NURBS

abstract:
Afin de réduire l’impact sur l’environnement et améliorer les performances aérodynamiques d’un aéronef, l’aile déformable est un moyen qui semble très prometteur pour le développement des technologies des avions verts. Cependant afin d’obtenir les meilleurs résultats possibles et ainsi de justifier les coûts investis dans la recherche et l’industrialisation de ce système il est important d’être certain que la meilleure méthode est employée.

Dans ce mémoire une étude est réalisée et un programme est développé afin d’obtenir la meilleure optimisation possible d’un profil d’aile. Pour cela deux aspects sont étudiés : dans un premier temps, la méthode de représentation du profil est analysée. C’est une étape cruciale de l’optimisation car c’est la base de tous les calculs qui suivent, il est donc important que la méthode employée soit la plus adaptée à la résolution de notre problème. C’est pour cette raison que les résultats obtenus par deux méthodes très répandues et reconnues, les Non-Uniform Rational Basis Splines (Piegl & Tiller) et la méthode Classe/Shape Transformation (Ceze, Hayashi, & Volpe), sont comparés dans la première partie du mémoire.

Afin de réaliser l’optimisation en elle-même, deux algorithmes évolutifs sont ensuite comparés, l’algorithme ABC et le PSO, dans les mêmes conditions, afin de déterminer lequel fournit les meilleurs résultats.

Pour le faire le profil du drone S45 Balaam est tracé et ses coefficients aérodynamiques sont obtenus grâce au solveur aérodynamique XFoil intégré dans le programme Matlab et les coefficients aérodynamiques ainsi que les coordonnées du profil optimisés sont ensuite obtenus.


identifier: Mackowsi, Victor  (2020). Transformation dynamique dans l’alliage de titane IMI 834.  Mémoire de maîtrise électronique, Montréal, École de technologie supérieure.

subject:
transformation dynamique
alliage de titane
déformation
microstructure

abstract:
Lors de déformation à des températures proches du transus dans le domaine biphasé, la transformation dynamique a lieu et une fraction de phase alpha se transforme en phase bêta. Ce phénomène a été étudié dans cette recherche pour l’alliage de titane de grade aéronautique IMI834 et son influence sur l’évolution de la microstructure a été quantifiée.

Dans cette étude, les effets de la température, de la déformation, de la vitesse de déformation et de la taille de grains bêta ont été observés par des essais de compression uniaxiale sur l’intégralité de la tranche centrale du matériau. Les analyses microstructurales réalisées en microscopie optique ont permis de mettre en évidence la modification de la fraction de phase alpha. Les paramètres ont des impacts différents, avec toujours une augmentation de la phase alpha au centre et une diminution sur les bords. Un modèle de prédiction pour cet alliage est proposé.

Il est conclu que la transformation dynamique influence de façon hétérogène la microstructure au sein d’une pièce compressée créant des différences de propriétés mécaniques au sein de la pièce forgée.


identifier: Bouchard-Roy, Jacob  (2020). Évaluation du potentiel énergétique lié à l’activité temporo-mandibulaire.  Mémoire de maîtrise électronique, Montréal, École de technologie supérieure.

subject:
récupération d’énergie
conduit auditif
déformation
dynamique
articulation temporo-mandibulaire

abstract:
La récupération de l’énergie que dégage le corps humain semble une source d’énergie intéressante pour alimenter les wearables. L’énergie dynamique des mouvements des parties du corps humain est entre autres l’une des sources d’énergie les plus prometteuses. Un endroit insoupçonné où l’on retrouve une telle dynamique est le conduit auditif externe. La proximité entre le conduit auditif et le condyle mandibulaire entraîne des déformations dans le conduit auditif lorsque la mâchoire est en mouvement, par exemple, lorsqu’une personne parle ou mange. Cela ouvre donc la possibilité d’utiliser cette énergie pour alimenter divers appareils portés à l’oreille comme les appareils auditifs ou les écouteurs intra-auriculaires intelligents. Cela permettrait de réduire leur dépendance aux piles à usage unique qui sont actuellement la source d’énergie la plus utilisée par ce type d’appareil.

La conception d’un microrécupérateur d’énergie intra-auriculaire est une tâche complexe. C’est pourquoi il est primordial de bien définir l’environnement dynamique du conduit auditif au préalable. L’objectif de ce mémoire est de développer un capteur capable mesurer la puissance disponible provenant du conduit auditif en fonction de l’activité temporo-mandibulaire.

Le capteur conçu est constitué d’un bouchon rempli d’eau, d’un transducteur de pression hydraulique et d’un système d’acquisition. Huit participants ont porté le capteur, sur des périodes de test allant de dix minutes à trois heures. La pression enregistrée est transformée en puissance instantanée, puis est évaluée pour différentes activités temporo-mandibulaires. Pour détecter ces activités, un enregistrement audio est pris simultanément à l’intérieur et à l’extérieur d’une oreille occluse. Par la suite, un algorithme de classification d’événements verbaux et non verbaux permet de détecter les activités telles que manger, parler et avaler.

La puissance instantanée moyenne trouvée est de 26.2mW pour l’activité de mastication. De même, le capteur de puissance a mesuré 3.8mW pour l’activité de parler. Ces connaissances pourront aider la conception d’un micro-récupérateurs d’énergie intra-auriculaire efficace. Cette étude montre que la déformation du conduit auditif représente une source d’énergie suffisante et disponible durant la période d’utilisation de tels appareils.


identifier: Tout, Hanine  (2017). Context and resource aware cloud-based solution for efficient and scalable multi-persona mobile computing.  Thèse de doctorat électronique, Montréal, École de technologie supérieure.

subject:
multi-persona
appareil mobile
virtualisation mobile
infonuagique
gestion des ressources
migration
optimisation multi-objectif
heuristique
programmation dynamique
apprentissage automatique

abstract: Fueled by changes in professional application models, personal interests and desires, and technological advances in mobile devices, multi-persona mobile computing has emerged recently to keep balance between different aspects, in our daily life, on a single mobile terminal. In this context, mobile virtualization technology has turned the corner and currently heading towards widespread adoption to realize multi-persona. Although recent lightweight virtualization techniques were able to maintain balance between security and scalability of personas, the limited CPU power and insufficient memory and battery capacities, still threaten personas performance and physical device viability. Throughout the last few years, cloud computing has cultivated and refined the concept of outsourcing computing resources, and nowadays, in the coming age of smartphones and tablets, the prerequisites are met for importing cloud computing to support resource constrained mobiles. From these premises, we propose in this thesis a novel mobile cloud-based solution for efficient multi-persona mobile computing support, which includes (1) profiling means for device, network and program monitoring; (2) generic, adaptable and lightweight optimization techniques for resource and performance management; (3) proactive methods with advanced manageability strategies; and (4) efficient algorithms to automatically find the adequate strategies to be applied by the end terminal while meeting with personas requirements and system survivability. Various prototypes have been built and evaluated via extensive experiments through which the results have proved the efficiency of the proposed solutions.


identifier: Abdallah, Bashar  (2020). Computer based technique to detect depression in Alzheimer patients.  Mémoire de maîtrise électronique, Montréal, École de technologie supérieure.

subject:
alzheimer
déficience cognitive légère
dépression
détection automatique

abstract:
Depression is common among Alzheimer's patients in the early and middle stages of Alzheimer, it is estimated that 30% of Alzheimer patients are suffering from depression. Depression in Alzheimer patients can lead to more cognitive decline. There is no official test that diagnoses depression in Alzheimer patients which is a challenge for the medical communities. This research aimed to help the medical communities in this challenge, by presenting machine  learning models that classify AD and MCI patients into two classes (depressive and non-depressive). 276 participants (mean age 70.9) are selected from the Pitt Corpus of Dementia Bank.

The interviewer’s voice and the silences are removed from the audio records as a preprocessing task. Different features are extracted from the patient's speech to achieve this task. For instance, MFCC’s, Spectral Centroid, Spectral Roll-Off Point, and others. We used three traditional classification techniques (SVM, Random Tree, and Random Forest). The Artifical Neural Networks (ANN) is used also to provide an idea of how this project can be extended. Bootstrapping method is used to solve the sampling bias – 70% of the patients are not suffering from depression.

From the results, MFCC’s features set is more appropriate with tree-based classifiers than SVM, where the Random Tree classifier achieved the highest classification accuracy (91.3%). While the other features set are more appropriate with SVM than tree-based classifiers, where SVM achieved 89.1% accuracy, 91.1% recall, and 89.1% precision. As a conclusion of the research results, the Random Tree classifier performed the highest classification performance rates – with 91.3% for accuracy, recall, and precision - using MFCC’s features (Standard Deviation and Kurtosis).


identifier: El-Atrash, Khlifa  (2020). Modified marshall mix design method for asphalt roads in hot and arid climate.  Thèse de doctorat électronique, Montréal, École de technologie supérieure.

subject:
presse à cisaillement giratoire (PCG)
superpave
Marshall
laboratoire
climat
enrobé
formulation

abstract:
Rheological properties of asphalt mix materials, prevailing temperatures, level and rate of loading time have substantial effects on the performance of asphalt concrete pavements. Thus, they must be given appropriate consideration during asphalt mix design.

Most of all developing countries rely on the empirical Marshall mix design (MMD) method to obtain homogeneous mixtures for asphalt roads. However, the MMD method does not take into account the climatic conditions, the level of compaction, and the asphalt binder properties required for hot and arid climates.

The migration to more appropriate asphalt mix design methods such as the Superpave method, requires the purchase of expensive equipment, training of operators, and excludes all the laboratories, and the equipment currently used in these countries for asphalt mix design.

The solution proposed in this thesis is to resort to a hybrid approach whereby the traditional MMD method is enhanced to also consider the environmental conditions of these regions. This approach is based on the integration of the characteristics of new asphalt binders (performance grade or modified asphalt) and the compaction test performed with the gyratory compactor as associated to the Superpave mix design (SMD) method.

This proposed Modified Marshall Method (3M) is cost-effective because it does not require expensive equipment and tools (except the gyratory compactor), is relatively easy-to-use, and does not require substantial training for operators and engineers.

The results of the laboratory investigations conducted as part of this thesis show substantial improvement of the properties of asphalt mixtures and an equally substantial increase in performance, indicative of extended pavement life in hot and arid (HA) climates with minimal additional equipment as proposed in modified Marshall method.


identifier: Arunachalam, Shiva Ram  (2020). Suspended carbon nanotube beams fabricated by a low temperature surface micromachined process for humidity and gas sensing.  Thèse de doctorat électronique, Montréal, École de technologie supérieure.

subject:
nanotubes de carbone
suspendu
humidité
ionisation

abstract:
The world we live in today is connected in more ways than we can imagine. Smart devices and networks form the core of our everyday lives. The advent of the Internet of Things and Industry 4.0, which are terms defined to make the world around us more connected via the internet at a domestic and industrial setting respectively, necessitates various kinds of sensors working in conjunction with each other. Keeping this in mind, this thesis explores the application of Suspended Single walled Carbon Nanotubes for Gas Sensing. Gas Sensors are used in a variety of environments such as hospitals, space shuttles and domestic kitchens to detect and prevent the leakage of hazardous gases. A variety of materials such as Polymers, ceramics and metal oxides and detection mechanisms have been used to identify various gases. More recently, Carbon nanotubes have garnered considerable attention for gas sensing applications due to their excellent electrical properties and ease of surface modification. With advancements in production techniques, the cost of Carbon Nanotube production has reduced significantly which has enabled the development of Carbon Nanotube based gas sensors. Although multiple Carbon Nanotube based gas sensors have been studied in the past, the overall device structure remains broadly similar. Additionally, these devices offer suffer from large hysteretic effects, often because of the effect of the substrate on the overall sensing mechanism, which can lead to unreliable measurement outputs.

This work aims to solve the issue of hysteresis by using suspended Carbon Nanotubes and thereby isolating the sensing element from the effects of the substrate. To do this, first, a low temperature surface micromachining process is developed to obtain suspended devices. Once the process is well developed, the suspended device is used to detect humidity. The performance of the suspended device is compared to a non-suspended device to demonstrate the advantages of suspended Carbon nanotubes.

Next, the performance metrics of the suspended sensor are improved by chemically functionalizing the nanotubes to make them more sensitive to water vapor. The nanotubes are obtained commercially, pre-functionalized, and used in the fabrication process. A comparative study between suspended and non-suspended functionalized nanotube-based sensors is also done. Lastly, the device design has been modified to fabricate an ionization gas sensor based on horizontally aligned suspended carbon nanotubes. The ionization potential of various gases is identified and other parameters such as the repeatability, long term stability, etc. have been studied.


identifier: Pourzadi, Aref  (2020). Novel dual-band LTCC bandpass filters for microwave applications.  Thèse de doctorat électronique, Montréal, École de technologie supéreure.

subject:
filtre à deux bandes passantes
LTCC
éléments localisés
schéma de circuit
DNBPF
SNBPF
ADS
HFSS
masque physique
réalisation de circuit

abstract:
The idea of using a single wireless communication system for multiple frequency bands simultaneously, has directed part of wireless communication researches towards the design of dual-band microwave components. This dual functionality of components bring low power consumption, system size reduction and more efficient in cost minimizing. Beside all of these advantages, specifications such as type of circuit, Implementation platform, frequency, dimension, performance and etc. have created stringent challenges in this field.

In many dual-band communication systems, one of the essential components is microwave dual-band bandpass filter (DBPF). Filtering networks allow signals to pass between two specific frequencies whereas block unwanted signals or make attenuation. In our study, we focus on design, physical realization and fabrication of very compact size of dual-band bandpass filters using low temperature co-fired ceramic technology (LTCC). Among commonly used strategies for building filters, lumped-elements are used to reach compact circuit size at frequencies less than 6 GHz. Out of different options for realizing lumped-elements, LTCC technology is highly recommended due to high circuit integration with size and loss reduction through the use of multilayer of low loss dielectrics.

Initially, we present a new schematic for dual-band LTCC second-order Chebyshev bandpass filter. Using even and odd mode analysis, working mechanism of the proposed schematic is fully analyzed mathematically and a direct synthesis procedure is presented to calculate the values of the schematic elements for given center frequencies and bandwidth. This design procedure leverages as much as possible, analytical formulas. The nature of the frequency response of the circuit is established by combination of four poles and four zeros and specific sequencing between them. Four transmission zeros are generated to clean out of band frequencies and reject spurious signals. The limitations on the proposed schematic and design procedure are completely discussed and two appendixes are provided for demonstration process of analytical formulas. Then, the filter topology and synthesis technique are applied for designing of a dual-band bandpass filter (D-BPF) operating in Industrial, scientific and medical (ISM) bands 0.9 and 2.45 GHz and fabricated in LTCC technology. The measurement results show an excellent agreement between the electromagnetic (EM) simulated and fabricated prototype.

Further, a new schematic of LTCC narrow bandpass filter containing two poles and two transmission zeros (TZs) is presented for industrial narrowband applications (SNBPF). The bandpass frequency response is established by the two poles, and two TZs are appointed in the both sides of passband to reject spurious signals. Due to symmetry of the network, similar to DBPF, even and mode analysis is used to explain working mechanism. Also, a design procedure is provided to apply the new topology in different frequencies of spectrum. Then, we demonstrate that the single bandpass is generalized to a dual-band frequency response (DNBPF) by manipulating the schematic of SNBPF filter. The working mechanism and design procedure of the DNBPF are provided. To validate the theory of proposed schematics, two design examples are synthesized and prototyped in LTCC.

Finally, we propose a fast technique for realization of lumped-elemet values into 3D physical layout on LTCC. Depending on number of elements, physical dimension, mutual coupling and parasitic effects, the circuits require time consuming optimizations and this stage can be very frustrating for designers. In this technique, using correlation strategy between simulators Advanced Design Simulators (ADS) and High frequency structure simulator (HFSS), processing time of physical realization is reduced significantly because of elimination of tuning steps. The usefulness of this technique is demonstrated through a fully synthesized D-BPF.


identifier: Rokooie, Marzieh  (2020). Visualizing large medical image datasets using the 3D scale-invariant feature transform (SIFT).  Mémoire de maîtrise électronique, Montréal, École de technologie supérieure.

subject:
visualisation d’images médicales
apprentissage automatique
classification
données massives
images cérébrales

abstract: This thesis proposes an image classification paradigm where instead of fully automatic classification, the goal is to generate a highly-informative visual summary of class-related information for human interpretation. Rather than providing a single classification, we provide a visualisation highlighting the information relevant to group differences. In this particular research, we provide a survey of instance-based classification and visualization. A probabilistic framework is developed for classification and visualization, based on the 3D scale-invariant feature transform (SIFT) format. We propose a novel kernel density bandwidth estimator for SIFT feature densities, based on hypothesis testing, where the bandwidth minimizes the p-value of Fisher’s exact test. We also propose a method of of ranking features based on the false discovery rate (FDR). An existing implementation of the SIFT-Rank method Toews & Wells (2013) is used for feature extraction, and classification and visualization are implemented in MATLAB. We validate our approach on 3D magnetic resonance image (MRI) data of the adult human brain from the Open Access Series of Imaging Studies (OASIS) dataset Marcus et al. (2007). Experiments investigated classification and visualisation of three binary categories: age (young, old), gender (male, female), and disease (Alzheimer’s disease vs. healthy). The highest classification accuracy was 94.71% for age (old vs. young), and the method may prove useful for understanding the aging process. The method is generally applicable to arbitrary 3D medical image modalities and conditions, for example computed tomography (CT) lung scans.


identifier: Kaba, Emmanuel Kossè  (2020). Développement d’une approche pour la préservation et le développement d’un sous-réseau routier en Afrique subsaharienne.  Thèse de doctorat électronique, Montréal, École de technologie supérieure.

subject:
Afrique Subsaharienne
projet de construction et d’entretien
priorisation
analyse économique
analyse multicritère
indice composite
indicateurs techniques
économiques
sociaux et environnementaux

abstract:
Les investissements des bailleurs de fonds et des gouvernements demeurent clairement insuffisants pour assurer le développement et la préservation des réseaux routiers dans les pays d’Afrique subsaharienne (ASS). Les outils de gestion qui pourraient faciliter la prise de décisions économiquement viables et socialement acceptables pour la construction, la préservation et la réhabilitation durables des routes manquent. Les effets directs de ces lacunes sont la faible densité de routes revêtues et la détérioration avancée des routes existantes.

Dans les pays d’Afrique subsaharienne, la prise en compte des aspects sociaux et environnementaux dans la prise de décision en gestion des chaussées est en effet très limitée, voire inexistante.

C’est dans ce cadre, que cette thèse a pour objectif de proposer une approche qui permet de prioriser les projets de construction et de préservation de routes, en intégrant les aspects techniques, économiques, sociaux et environnementaux, au niveau réseau puis au niveau projet.

Cette approche est basée sur l’indice de priorité de financement des routes (IPFR) pour la priorisation et la sélection adéquates des projets routiers au niveau réseau. Cet indice se base sur la saisie et l’analyse en composantes principales de données routières pour en dégager des indicateurs techniques, économiques, sociaux et environnementaux.

Dans la première partie de cette thèse, un IPFR est proposé pour classer conjointement les deux types de projets routiers par priorité de financement. Par la suite, quatre projets de construction (bitumage de routes non-revêtues) et six projets de préservation, totalisant 330 km de routes, ont été sélectionnés selon leur admissibilité au programme du bailleur de fonds et sur la base de leur IPFR. Ces projets prioritaires nécessitent des investigations et des analyses approfondies au niveau projet, d’où l’importance de développer des méthodes rationnelles intégrées.

Au niveau projet, deux méthodes rationnelles intégrées permettent de déterminer respectivement les meilleures interventions de bitumage et d’entretien périodique.

Une première méthode rationnelle intégrée est proposée dans la seconde partie de cette thèse afin de choisir les meilleures options de bitumage pour les routes non revêtues. Cette méthode est fondée sur le dimensionnement mécaniste-empirique et l’intégration des aspects environnementaux et sociaux dans l’analyse économique conventionnelle via une analyse multicritère. L’option de bitumage en enrobé dense (ED), sélectionnée grâce à cette méthode, permet de maximiser la valeur actuelle nette et les avantages sociaux, d’améliorer le confort au roulement et de réduire le risque d’accident ainsi que de réduire la pollution atmosphérique.

Une deuxième méthode rationnelle est présentée dans la troisième partie de cette thèse pour déterminer les meilleures interventions d’entretien de routes candidates selon la réduction de consommation d’énergie, la réduction des quantités et des coûts des émissions polluantes (CCVEE), des coûts totaux de transports (CTCV) et des contraintes budgétaires sur une période de 20 ans. Les meilleures interventions choisies à l’aide de cette deuxième méthode sont des options d’entretien périodique permettant de réduire d’environ 23% la consommation d’énergie, d’économiser environ 23 % des CCVEE et 30 % des CTCV.

En conclusion, cette thèse démontre l’importance et la possibilité d’utiliser le concept des routes durables par l’intégration quantitative et qualitative des facteurs techniques, économiques, sociaux et environnementaux pour la gestion durable des routes en ASS aux niveaux réseau et projet.


identifier: Nasiri, Behnaz  (2020). Modeling information flow through deep convolutional neural networks.  Mémoire de maîtrise électronique, Montréal, École de technologie supérieure.

subject:
apprentissage automatique
réseau de neurones convolutionnels
classification
apprentissage par transfert

abstract: In this work we investigate methods for optimizing deep convolutional neural networks (CNN) by 1) reducing the computational complexity and 2) improving classification performance for the task of transfer learning. Based on the work of Chaddad et al. (2019, 2017), the CNN is modeled as a Markov chain, where the filter output at a layer is conditionally independent of the rest of the network, given a set of previous layers. Filter banks at each layer are compressed using principal component analysis (PCA), where a reduced set of orthogonal basis filters are used to reduce the number of convolutions required while preserving classification accuracy. Information theory is then used to quantify the flow of image information through the network. Filter responses with low conditional entropy (CENT) are shown to be highly effective in image classification, and can be used as generic features for effective, noise resistant transfer learning. CENT feature analysis is demonstrated in various contexts including computer-assisted diagnosis of Alzheimer’s disease (AD) from 3D magnetic resonance images (MRI) of the human brain, and object classification in 2D photographs.


identifier: Champagne, Olivier  (2020). Simulation numérique d’une source de chaleur mobile par la méthode Element-Free Galerkin.  Mémoire de maîtrise électronique, Montréal, École de technologie supérieure.

subject:
source de chaleur
soudage MIG
validation expérimentale
méthode Element-Free Galerkin
méthode des éléments finis
domaine de support
fonction de pondération
points de
quadrature

abstract:
Les applications impliquant des sources de chaleur mobiles, telles que le soudage, sont courantes dans l’industrie. Dans le but de contrôler et de maîtriser ces procédés, les ingénieurs ont recours à la simulation numérique et, la plupart du temps, c’est la méthode des éléments finis (MÉF) qui est utilisée. Toutefois, cette dernière possède plusieurs inconvénients principalement liés au maillage, qui est un concept clef de la MÉF. Une alternative de plus en plus envisageable pour surmonter ces inconvénients est l’utilisation des méthodes sans maillage (meshless methods). Relativement nouvelles, certaines connaissances techniques relatives à leur utilisation sont encore limitées.

Dans ce mémoire, un code de calcul basé sur la méthode sans maillage Element-Free Galerkin (EFG) a été développé pour résoudre un problème tridimensionnel de conduction impliquant une source de chaleur mobile en régime transitoire. Le code a ensuite été validé numériquement en comparant avec la MÉF et un logiciel commercial. Un excellent accord a été obtenu entre les résultats des différentes méthodes.

Par la suite, des essais expérimentaux de soudage MIG sur des échantillons d’aluminium 6061-T6 ont été effectués. Grâce à des thermocouples situés à différentes distances du cordon de soudure, le cycle thermique du procédé a été enregistré et comparé avec les résultats de la simulation. Il a été convenu que la méthode permet de bien prédire les températures maximales et le taux de refroidissement du procédé, malgré l’utilisation de propriétés de matériau constantes.

Finalement, une étude paramétrique a été menée pour déterminer les paramètres optimaux à utiliser, c’est-à-dire la taille et la forme des domaines de support, les différentes fonctions de pondération et la quantité de points de quadrature requise. Il a été conclu que l’utilisation d’un domaine en forme de sphère ou de brique (parallélépipède droit) avec un nombre de points de quadrature 10 fois plus élevé que le nombre de noeuds représentent un choix approprié.