Um atuador planar de indução é um dispositivo baseado no mesmo princípio de funcionamento de um motor linear de indução, onde a interação de um campo magnético viajante produzido pelo primário do dispositivo com uma superfície de boa condutividade elétrica induz correntes parasitas que levam à produção de uma força de propulsão. O movimento planar sobre essa superfície é produzido através da movimentação linear em dois eixos ortogonais. Uma aplicação deste movimento é na propulsão de uma plataforma equipada com câmeras e sensores para a realização da inspeção em uma superfície metálica, que se beneficiaria da força normal que o motor planar de indução produz quando acionado sobre uma superfície ferromagnética para anexar a plataforma à superfície. Um modelo analítico que fornece equações para o campo elétrico e magnético é apresentado, e simulações numéricas baseadas no método dos elementos finitos são realizadas para avaliar o comportamento do dispositivo utilizando três tipos diferentes de superfícies como secundário: um secundário com duas camadas formadas por uma chapa de alumínio com outra de aço por baixo; apenas a chapa de alumínio; e apenas a chapa de aço. As distribuições de campo magnético calculadas por estes dois modelos teóricos mostram boa concordância entre si, e são utilizadas para calcular as forças de propulsão e normal produzidas pelo atuador. Medidas experimentais são realizadas em um protótipo de atuador planar de indução, e seus resultados são comparados com os resultados obtidos nos modelos teóricos, mostrando uma boa concordância e potencial para a aplicação do atuador planar de indução na inspeção de superfícies horizontais. / An induction planar actuator is a device that, based on the operating principle of a linear induction motor, in which the interaction between a travelling magnetic field produced by the primary of the device and a conducting surface generates eddy currents in the surface and leads to the generation of a thrust force. The device produces planar motion over this surface through movement on two orthogonal axis. An application of this movement is in a platform for the inspection of metallic surfaces, which is driven by the planar induction motor and equipped with cameras and sensors to inspect the surface. This application benefits from the normal force produced by the induction planar actuator operating over a ferromagnetic surface to attach the driving platform to it. An analytical model with equations for the electric and magnetic fields is presented, and numerical simulations based on the finite element method are carried out to assess the behaviour of the device using three different surfaces as secondary: a double-layered secondary formed by an aluminum plate over a steel plate; a aluminum only plate; and a single steel plate. The distributions for the magnetic field computed through these theoretical models show good agreement, and are employed to evaluate the thrust and normal forces produced by the planar induction actuator. Experimental measurements are made on a prototype of the device, and the results are compared to the results of the theoretical models, showing good agreement and potential in the application of the induction planar motor for the inspection of horizontal metallic surfaces.

Este trabalho apresenta um modelo analítico para a análise de vazão (throughput) da camada MAC do IEEE 802.11. A proposta se diferencia da maioria dos desenvolvimentos realizados na área por apresentar uma modelagem de ambientes com estações não-saturadas, levando em consideração o perfil do tráfego gerado pelas camadas superiores ao nível de enlace. Dessa maneira, o modelo permite uma análise do desempenho de aplicações reais sobre redes sem fio, a partir de resultados provenientes de um modelo matemático, enquanto diversos outros trabalhos avaliam somente situações de saturação das estações. Simulações utilizando Network Simulator 2 e comparações com resultados obtidos em trabalhos análogos desenvolvidos por outros pesquisadores validam o modelo proposto. Cenários com variações na quantidade de estações e carga oferecida à rede são avaliados utilizando o modelo teórico e comparados aos resultados simulados, provendo uma análise do comportamento dos limites de vazão do sistema. As estruturas do IEEE 802.11 MAC foram estudadas a fim de embasar o desenvolvimento do modelo proposto. Também foi realizada uma pesquisa a respeito de Cadeias de Markov, que serve como estrutura básica para a descrição do IEEE 802.11 DCF. / This work provides an analytical model to compute the IEEE 802.11 DCF throughput. The proposed analysis differs from most of the related work by presenting scenario modeling with unsaturated stations, accounting for the traffic characteristics generated by the upper layers to the data link layer. As a consequence, the proposed model allows for an accurate analysis of real applications over wireless networks, based on mathematical model results, while several other researches evaluate only saturate stations situations. Simulations ran using Network Simulator 2 and comparisons with results obtained on similar works developed by other researchers are used to validate the proposed model. Scenarios with different number of stations and offered loads are evaluated using the theoretical model and compared to the simulated results, providing an analysis on the behavior of the maximum throughput provided by the network. A study was made on the structures and mechanisms of IEEE 802.11 MAC in order to support the development of the proposed model. A research on Markov Chains was also done, since it is the basic structure used to describe the IEEE 802.11 DCF.

Many models have been proposed for software reliability prediction, but none of these models could capture a necessary amount of software characteristic. We have proposed a mixed approach using both analytical and data driven models for finding the accuracy in reliability prediction involving case study. This report includes qualitative research strategy. Data is collected from the case study conducted on three different companies. Based on the case study an analysis will be made on the approaches used by the companies and also by using some other data related to the organizations Software Quality Assurance (SQA) team. Out of the three organizations, the first two organizations used for the case study are working on reliability prediction and the third company is a growing company developing a product with less focus on quality. Data collection was by the means of interviewing an employee of the organization who leads a team and is in the managing position for at least last 2 years. / svra06@student.bth.se

Les doses secondaires neutroniques ne sont actuellement pas estimées lors de la planification de traitement dans les centres de protonthérapie puisque les logiciels de planification de traitement (TPS) ne le proposent pas tandis que les simulations Monte Carlo (MC) et les mesures sont inadaptées pour un environnement clinique. L’objectif de la thèse est de développer un modèle analytique dédié à l’estimation des doses secondaires neutroniques aux organes sains qui reste pratique et simple d’utilisation en routine clinique. Dans un premier temps, la géométrie existante de la gantry installée au Centre de protonthérapie d’Orsay (CPO) de l’institut Curie modélisée avec le code de calcul MCNPX a été étendue à trois configurations de traitement supplémentaires (énergie en entrée de ligne de 162, 192 et 220 MeV). Une approche comparative simulation-mesure a ensuite été entreprise afin de vérifier la capacité de ces modélisations à reproduire les distributions de doses (en profondeur et latérales) des protons primaires ainsi que le champ secondaire neutronique. Des écarts inférieurs à 2 mm ont été observés pour les protons primaires. Pour les neutrons secondaires, les écarts sont plus mitigés avec des rapports simulation sur mesure de ~2 et de ~6, respectivement pour la spectrométrie et les équivalents de dose dans un fantôme physique. L’analyse des résultats a permis d’identifier l’origine de ces écarts et de mettre en perspective la nécessité de conduire de nouvelles études pour améliorer à la fois les mesures expérimentales et les simulations MC. Dans un deuxième temps, une approche purement numérique a été considérée pour calculer les doses neutroniques aux organes sains de fantômes voxélisés représentant des patients d’un an, de dix ans et adulte, traités pour un craniopharyngiome. Une variation de chaque paramètre de traitement a été réalisée afin d’étudier leur influence respective sur les doses neutroniques. Ces paramètres ont pu être ordonnés par ordre décroissant d’influence : incidence de traitement, distance organe-collimateur et organe-champ de traitement, taille/âge des patients, énergie de traitement, largeur de modulation, ouverture du collimateur, etc. Des suggestions ont également été avancées pour réduire les doses neutroniques.Dans un troisième temps, un modèle analytique a été conçu de façon à être utilisable en routine clinique, pour tous les types de tumeur et toutes les installations de protonthérapie. Son entraînement séparé pour trois incidences de traitement a montré des écarts inferieurs à ~30% et ~60 µGy Gy⁻¹ entre les données d’apprentissage (doses neutroniques calculées aux organes sains) et les valeurs prédites par le modèle analytique. La validation a consisté à comparer les doses neutroniques estimées par le modèle analytique à celles calculées avec MCNPX pour des conditions différentes des données d’apprentissage. Globalement, un accord acceptable a été observé avec des écarts moyens de ~30% et ~100 µGy Gy⁻¹. La flexibilité et la fiabilité du modèle analytique ont ainsi été mises en évidence. L’entraînement du modèle analytique à partir d’équivalents de dose neutroniques mesurés dans un fantôme solide au Centre Antoine Lacassagne a confirmé son universalité, bien qu’il requière néanmoins quelques ajustements supplémentaires pour améliorer sa précision. / Stray neutron doses are currently not evaluated during treatment planning within proton therapy centers since treatment planning systems (TPS) do not allow this feature while Monte Carlo (MC) simulations and measurements are unsuitable for routine practice. The PhD aims at developing an analytical model dedicated to the estimation of stray neutron doses to healthy organs which remains easy-to-use in clinical routine. First, the existing MCNPX model of the gantry installed at the Curie institute - proton therapy center of Orsay (CPO) was extended to three additional treatment configurations (energy at the beam line entrance of 162, 192 and 220 MeV). Then, the comparison of simulations and measurements was carried out to verify the ability of the MC model to reproduce primary proton dose distributions (in depth and lateral) as well as the stray neutron field. Errors within 2 mm were observed for primary protons. For stray neutrons, simulations overestimated measurements by up to a factor of ~2 and ~6 for spectrometry and dose equivalent in a solid phantom, respectively. The result analysis enabled to identify the source of these errors and to put into perspective new studies in order to improve both experimental measurements and MC simulations. Secondly, MC simulations were used to calculate neutron doses to healthy organs of a one-year-old, a ten-year-old and an adult voxelized phantoms, treated for a carniopharyngioma. Treatment parameters were individually varied to study their respective influence on neutron doses. Parameters in decreasing order of influence are: beam incidence, organ-to-collimator and organ-to-treatment field distances, patient’ size/age, treatment energy, modulation width, collimator aperture, etc. Based on these calculations, recommendations were given to reduce neutron doses. Thirdly, an analytical model was developed complying with a use in clinical routine, for all tumor localizations and proton therapy facilities. The model was trained to reproduce calculated neutron doses to healthy organs and showed errors within ~30% and ~60 µGy Gy⁻¹ between learning data and predicted values; this was separately done for each beam incidence. Next, the analytical model was validated against neutron dose calculations not considered during the training step. Overall, satisfactory errors were observed within ~30% and ~100 µGy Gy⁻¹. This highlighted the flexibility and reliability of the analytical model. Finally, the training of the analytical model made using neutron dose equivalent measured in a solid phantom at the center Antoine Lacassagne confirmed its universality while also indicating that additional modifications are required to enhance its accuracy.

Solicitud de envío manuscrito de artículo científico. / Este estudio focalizado en la problemática de la deserción en el contexto de los institutos de educación superior, específicamente aquellos que imparten programas de formación técnica profesional en el Perú, que esta tomando cada vez más auge en la agenda pública nacional, fenómeno de carácter social que impacta el ámbito educativo y desarrollo de las fuerzas socioproductivas, que se ha visibilizado mediante el incremento sistemático del abandono de los estudiantes de las aulas de clases en las distintas, fases o etapas del proceso de formación educativa, disminuyendo significativamente los ingresos por los servicios académicos que ofertan en el mercado este tipo de centros, que se encuentran en riesgo e incertidumbre ante la posibilidad de cierre técnico por la reducción de los recursos para sostener el funcionamiento y operatividad. El objetivo general es proponer un modelo analítico administrativo eficiente para la reducción del índice de deserción en la educación técnica en el Perú. El trabajo se sustenta metodológicamente en el enfoque cualitativo propio de la corriente del paradigma interpretativo, mediante un diseño no experimental de campo de corte transversal, un tipo de investigación descriptiva con un nivel analítico-comparativo. Los informantes claves lo integran (10) sujetos que proporcionarán información intersubjetiva a partir de las experiencias y conocimientos cultivados, a los cuales se les aplicó un guión de entrevista como instrumento, que fue sometido al proceso de categorización, triangulación e interpretación de la información. Los resultados evidenciaron que la deserción está vinculada con factores económicos, laboral, académico, personal y familiar. El estatus económico de los estudiantes que desertan en los centros de educación técnica del Perú, provienen en la gran mayoría del segmento C o D, situándola como media a baja con menor proporción en el segmento B, luego él E y A. Las causas de la deserción, son por los aspectos económicos, laborales, académicos, personales y familiares. De allí que se diseñó un modelo analítico administrativo innovador y eficiente para contribuir con la reducción de índice de deserción. / This study focused on the problem of dropout in the context of higher education institutes, specifically those that provide vocational technical training programs in Peru, which is increasingly booming on the national public agenda, a social phenomenon that impacts the educational field and development of socio-productive forces, which has become visible through the systematic increase in the abandonment of students from classrooms in the various phases or stages of the educational training process, significantly reducing the revenue from the academic services offered on the market by such centres, which are at risk and uncertainty at the possibility of technical closure by reducing resources to sustain the operation. The overall objective is to propose an efficient administrative analytical model for the reduction of the attrition rate at technical education in Peru. The work is methodologically based on the qualitative approach typical of the current of the interpretative paradigm, through a non-experimental cross-sectional field design, a type of descriptive research with an analytical-comparative level. Key informants integrate it (10) subjects who will provide intersubjective information based on cultivated experiences and knowledge, to which an interview script will be applied as an instrument, which will be subjected to the process of categorization, triangulation and interpretation of the information. The results showed that the desertation is linked to economic, labor, academic, personal and family factors. The economic status of students who defect at technical education in Peru, come in the vast majority of segment C or D, placing it as average down with lower proportion in segment B, then he E and A. The causes of the desertion are because of the economic, labor, academic, personal and family aspects. From there, an innovative and efficient administrative analytical model was designed to contribute to the reduction of the attrition rate. / Trabajo de investigación

La présence d’harmoniques de forces électromagnétiques dans les machines électriques est généralement source de bruit acoustique et de vibrations (B&V). Ce phénomène doit être considéré dès les premières phases de conception pour respecter les normes en matière de B&V, en particulier dans le secteur automobile. Le niveau de B&V s’obtient à partir d’une simulation multi-physique basée sur des modèles électromagnétiques, mécaniques et acoustiques, de préférence rapides et précis de manière à l’inclure le plus tôt possible dans la phase de conception. Cette thèse CIFRE est partie intégrante du programme de recherche interne de la société EOMYS ENGINEERING, qui développe et commercialise son logiciel MANATEE dédié à la simulation électromagnétique et vibroacoustique des machines électriques. Dans ce contexte de modélisation, cette thèse porte sur la méthode électromagnétique semi-analytique des sous-domaines pour le calcul des harmoniques de forces 2D dans l’entrefer d’une large variété de machines électriques, et se concentre particulièrement sur la Machine Synchrone à Aimant Permanents en Surface (MSAPS) et la machine asynchrone à cage d’écureuil. La thèse s’intéresse également à deux verrous scientifiques concernant la contribution des forces tangentielles au niveau de vibration global, et l’effet de modulation des dents qui apparaît dans les machines avec un nombre proche d’encoches et de pôles. A cet effet, un banc d’essai comprenant une machine bruyante particulière (une MSAPS avec 12 encoches et 10 pôles) et l’instrumentation nécessaire a été conçu et réalisé. Le banc d’essai vise enfin à comparer les différents modèles utilisés couramment dans les simulations B&V / The presence of magnetic stress harmonics inside the electrical machine is generally responsible for vibrations and acoustic noise generation. This phenomenon is called e-NVH (Noise, Vibrations and Harshness due to electromagnetic excitations) and has to be considered in the machine design to meet with NVH standard requirements, especially in automotive applications. The e-NVH assertion requires a multiphysics simulation including electromagnetic, mechanical and acoustic models, which must be fast and accurate especially for early design stages. This industrial PhD thesis takes part of the internal research program of EOMYS ENGINEERING company, which develops and commercializes MANATEE software, dedicated to the e-NVH simulation of electrical machines. In this modeling context, the present thesis investigates and extends the semi-analytical electromagnetic model, called Subdomain Method (SDM), for the computation of two-dimensional airgap magnetic stress harmonics in various topologies of electrical machines, mainly focusing on Surface Permanent Magnet Synchronous Machines (SPMSMs) and Squirrel Cage Induction Machines (SCIMs). The thesis also investigates two scientific open questions concerning the contribution of circumferential excitations to the overall vibration level and the slotting modulation effect, which appears in electrical machines with a close number of poles and teeth. For this purpose, an experimental test rig including a particular noisy machine (a SPMSM with 12 slots and 10 poles) and appropriate sensors has been designed and built. The test rig also aims at benchmarking the different multiphysics models currently used in e-NVH simulation workflow

Interlocking Cross Laminated Timber (ICLT) wall panels are a new wood construction product similar to Cross Laminated Timber panels. Besides being an innovative structural system, they also utilize beetle killed timber from many of the forests that have been devastated by the Mountain Pine Beetle. Three tests were performed on three ply ICLT panels measuring 8 feet (2.44m) wide, 8 feet (2.44m) tall and 8.5 inches (21.6cm) thick to determine the racking, flexural and axial strengths of the wall panels. After each test was performed the walls were disassembled and investigated for cause of failure. Using the data from the tests as a benchmark, simple analytical models to predict the design capacities of the walls for racking, flexural, and axial strengths were established. The analytical models for racking strength, flexural strength and axial strength predicted reasonably well the measured strength values. Additional testing is necessary to increase the available database, further validate the analytical models developed, better understand the structural performance of ICLT panels, and establish acceptable design methodology for ICLT wall panels.

Tire, or in its primitive form, Wheel, an important invention for the transportation sector, has evolved from a circular block of hard and durable material to one of the most complex and influential components of an automobile. It is the only means of contact between the vehicle and the road and is responsible for generating forces and moments that impact vehicle performance, stability, and control. Tire tribology is the study of interacting surfaces in relative motion which includes friction and wear. Tire friction is an essential concept for estimating the tractive effort/ traction at the tire-road interface that further helps to determine the control and stability of the vehicle. In contrary, it also results in rolling resistance and wear. Tire and vehicle engineers are henceforth interested in a robust and efficient approach towards estimation of friction and wear. Past experimental observations using tread compound samples have revealed the different factors influencing the friction at the contacting interface. In addition, different mechanisms or components resulting in frictional losses, being Hysteretic, Adhesive and Viscous, and wear being abrasive, fatigue, adhesive and corrosive were also observed. Although experimental and empirical observations have provided us with an accurate estimation of friction and wear parameters, it is very tedious and expensive approach. Recent developments in the computational power encouraged researchers and engineers towards evolution of analytical and numerical models considering the underlying physical mechanisms at the contact interface. Past research studies developed multiscale techniques for estimation of friction coefficient due to hysteretic losses from internal damping of the rubber material because of oscillation from surface undulations. Later, contact mechanics models developed using Hertzian technique or stochastic approach were considered in conjunction with frictional losses to obtain the hysteretic component of friction to consider the effect of surface roughness. Previous studies at CenTiRe focused on surface characterization techniques and estimation of friction for dry surfaces using Persson and Klüppel's approach. Comparative studies unveiled the importance of considering pressure/ normal load towards friction estimation. In addition, it was found that effect of adhesion for estimation of contact mechanics parameters must be considered. The present work focusses on obtaining a conceptual framework to model a comprehensive friction model considering the effect of surface roughness, substrate condition and asperity interaction. A finite element simulation of rubber block sliding on a rough substrate is performed using a multiscale technique for estimation of friction and contact mechanics under dry condition. The estimated contact mechanics and friction is compared with analytical models and experimental measurements obtained using Linear sliding friction tester developed in collaboration with other members of the group. In addition, a FE model is developed to measure the wear properties of rubber material based on continuum damage mechanics and further obtain the wear profile of a rubber block sliding on a rough substrate. / Doctor of Philosophy / Tribology, a recent terminology for an age-old concept of friction, wear, and lubrication. the study of interacting surfaces in relative motion which includes friction and wear. Friction is the resisting force at the contact interface leading to heat build-up and material loss at the contact interface which is known as flash temperature and wear respectively. Tire is one of the most complex and influential components of a vehicle that helps in optimizing its performance for better stability and control. Knowledge of tire friction and wear is important for tire engineering and vehicle dynamics engineers as it helps in characterizing the handling characteristics of the vehicle, characterizing the tire material compounds to understand the tire durability. Rubber is a viscoelastic material, the friction and wear in rubber is intricate as opposed to other elastic materials. Based on experimental observations in the past, friction and wear are influenced by factors like material properties, normal load/ pressure, sliding velocity, temperature, surface characteristics, and environmental conditions. In addition, the frictional losses at the contact interface are considered to compose of adhesion, hysteresis and viscous components and wear is categorized as – adhesive, abrasive, fatigue, corrosive and erosive. Recent developments in computational power encouraged researchers and engineers in developing analytical and computational models that consider the physical mechanisms occurring at the contact interface. The present research focuses on obtaining a comprehensive friction and contact mechanics model considering the effect of surface roughness at different length scales, surface condition (dry/ wet) and asperity interaction. In addition, the developed model in conjunction with a brush model is considered for estimating the tire traction characteristics such as the forces and moments. A finite element simulation of rubber block sliding on a rough substrate is performed using a multiscale technique for estimation of friction, contact mechanics and abrasion parameters under dry condition. The results thus obtained are compared with the analytical model that is developed for wet conditions. Experimental validation of the friction estimated using the analytical and numerical methods will be performed using a linear sliding friction tester developed in collaboration with other members of the group.

L'émergence et le développement des systèmes électriques de ces vingt dernières années nous ont conduits à l'élaboration d'architectures de plus en plus complexes. Nous les retrouvons notamment au niveau d'applications embarquées ainsi qu'au cœur de réseaux de distribution isolés. L'intégration de nombreux équipements de différentes natures soulève la problématique de la stabilité. C'est dans ce contexte que s'insèrent ces travaux de thèse, qui aboutissent sur la mise en œuvre de méthodes d'analyse de la stabilité et de la qualité des réseaux distribués de puissance. Les études menées au cours de ces travaux reposent sur des expressions analytiques représentant le comportement fréquentiel de réseaux continus. Ces modèles sont ensuite associés au critère de Routh-Hurwitz, afin de permettre les études de stabilité selon les évolutions de leurs paramètres. L'analyse des résultats obtenus au niveau d'architectures présentant plusieurs équipements permet d'affiner nos connaissances sur le fonctionnement de ces systèmes. Les phénomènes de couplage, la disposition d'un réseau en fonction du nombre et de la puissance des charges, du point de vue de la stabilité, sont notamment développés. Les recherches de dimensionnements optimaux de plusieurs éléments indéterminés, combinant les notions de stabilité et de qualité et réalisées à l'aide d'algorithmes d'optimisation, sont également présentées. Enfin, les parties fondamentales de ces travaux, que constituent la modélisation ainsi que l'étude de la stabilité, sont validés par une approche expérimentale. / The emergence and the development of electrical systems during these last twenty years have led us to the elaboration of more and more complex architectures. They can be particularly found on embedded applications as well as in the heart of isolated distribution networks. The integration of several equipments with various natures raises the problem of stability. Thesis work presented here fits in with this context, leading to the implementation of stability and quality analysis methods, applied to distributed power networks. Studies led during this work are based on analytical expressions representing the continuous networks frequency behaviour. These models are then associated to the Routh-Hurwitz criterion in order to allow stability studies, according to their parameter values evolution. Analysis of results obtained on networks architectures using several equipments allows the refinement of our knowledge on these systems operation. Coupling phenomena, network layout according the loads number and power from a stability point of view, are particularly developed. Optimal sizing research for several undetermined elements, merging stability and quality criteria and carried out using optimization algorithms, is also presented. Finally, fundamental parts of this work which correspond to models building as well as stability studies are validated by an experimental approach.

Since the field of computer networks has rapidly grown in the last two decades, congestion control of traffic loads within networks has become a high priority. Congestion occurs in network routers when the number of incoming packets exceeds the available network resources, such as buffer space and bandwidth allocation. This may result in a poor network performance with reference to average packet queueing delay, packet loss rate and throughput. To enhance the performance when the network becomes congested, several different active queue management (AQM) methods have been proposed and some of these are discussed in this thesis. Specifically, these AQM methods are surveyed in detail and their strengths and limitations are highlighted. A comparison is conducted between five known AQM methods, Random Early Detection (RED), Gentle Random Early Detection (GRED), Adaptive Random Early Detection (ARED), Dynamic Random Early Drop (DRED) and BLUE, based on several performance measures, including mean queue length, throughput, average queueing delay, overflow packet loss probability, packet dropping probability and the total of overflow loss and dropping probabilities for packets, with the aim of identifying which AQM method gives the most satisfactory results of the performance measures. This thesis presents a new AQM approach based on the RED algorithm that determines and controls the congested router buffers in an early stage. This approach is called Dynamic RED (REDD), which stabilises the average queue length between minimum and maximum threshold positions at a certain level called the target level to prevent building up the queues in the router buffers. A comparison is made between the proposed REDD, RED and ARED approaches regarding the above performance measures. Moreover, three methods based on RED and fuzzy logic are proposed to control the congested router buffers incipiently. These methods are named REDD1, REDD2, and REDD3 and their performances are also compared with RED using the above performance measures to identify which method achieves the most satisfactory results. Furthermore, a set of discrete-time queue analytical models are developed based on the following approaches: RED, GRED, DRED and BLUE, to detect the congestion at router buffers in an early stage. The proposed analytical models use the instantaneous queue length as a congestion measure to capture short term changes in the input and prevent packet loss due to overflow. The proposed analytical models are experimentally compared with their corresponding AQM simulations with reference to the above performance measures to identify which approach gives the most satisfactory results. The simulations for RED, GRED, ARED, DRED, BLUE, REDD, REDD1, REDD2 and REDD3 are run ten times, each time with a change of seed and the results of each run are used to obtain mean values, variance, standard deviation and 95% confidence intervals. The performance measures are calculated based on data collected only after the system has reached a steady state. After extensive experimentation, the results show that the proposed REDD, REDD1, REDD2 and REDD3 algorithms and some of the proposed analytical models such as DRED-Alpha, RED and GRED models offer somewhat better results of mean queue length and average queueing delay than these achieved by RED and its variants when the values of packet arrival probability are greater than the value of packet departure probability, i.e. in a congestion situation. This suggests that when traffic is largely of a non bursty nature, instantaneous queue length might be a better congestion measure to use rather than the average queue length as in the more traditional models.