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Comparative study of tubular composite structure subjected to internal pressure loading: Analytical and numerical investigation
No full textInternational audienceThe purpose of this paper is to study the mechanical behaviour of a multi-layered composite tubular structure with various orientations subjected to internal hydrostatic pressure. The first part of this paper is devoted to studying stress analysis using the analytical approach. The 3 D analysis of the composite pipe originally made with carbon/epoxy is studied and compared with a pipe made of E-glass/epoxy; each layer is examined with five orientations. The hoop, axial, longitudinal, transversal, and shear stresses are obtained for each layer of the composite pipe simultaneously. The hybrid composite pipe is done to take advantage of the properties of each fiber and the studied hybridisation. `To validate some cases of the presented results, a numerical model is developed in ANSYS workbench software; this particular model is characterized by very close to the theoretical results. Throughout the investigation, it is observed that the behaviour of composite carbon/epoxy is the most resistant compared to glass/epoxy, and the results obtained in the case of hybrid shows that the variability of the stacking sequences generates the variation of the behaviour on composite hybrid pipe. It can be increased the design material utilisation and working pressure level by winding angle variation or hybridized between stacking sequences. The ability of this new 3 D model to simulate the stress evolution in the full-scale composite tubular structure under internal pressure events were demonstrated
Numerical investigation of the radial cold rolling process of the grooves
No full textInternational audienceThe radial cold rolling process is widely used in industry due to the advantages of chip removing processing. In this study, circular complex profiles were formed by cold-rolling with radial feed, using a patented device with two roller-tools. By achieving several numerical simulations of the radial rolling process, the study aimed to establish the influence that the maximum set force and the diameter of the workpiece have on the productivity of the process and the quality of the formed trapezoidal and metric grooves. The numerical simulations were performed with ABAQUS/Explicit software and by using a previously validated finite element model. The penetration curve of the roller-tools in the material was introduced in the simulation as an analytical function and was determined based on experimental researches. To express the dependency of the penetration curve coefficients on other rolling conditions, a multivariable analysis using a design of experiments technique was performed. The parameters that result from numerical simulations and were analyzed in this study are the profile forming time, the maximum radial force, the distribution of the equivalent strains in the axial section of the profiles, and the profile dimensions. The conclusions that were drawn from the analysis of the results regarding the influence of the set maximum force and the workpiece diameter on the analyzed parameters of the numerical simulations, together with the definition of efficient process criteria, allowed also the identification of the optimal conditions of the rolling process
Numerical investigation of ice accretion on an offshore composite wind turbine under critical loads
No full textInternational audienceIn northern regions, wind turbines are affected by the formation of ice on the surface of their structures, which usually occurs on moving blades, resulting in a significant decrease in aerodynamic performance and then the output power tends to reduce. This research evaluates the mechanical behavior and damage of the proposed composite blade structure under icing conditions. A comparative evaluation was carried out considering three ice configurations and three blade positions. The results are then examined and analysed. During this study, the blade in service was subjected to three different critical loads. A numerical simulation is adopted using finite element method (FEM) with ABAQUS software to localize damage in the composite wind turbine blade. The method developed is based on the failure criteria of HASHIN to detect failure modes in large structures and to identify the most sensitive zones. Major damage appeared in the transition region and was the principal reason for the composite blade failure. Furthermore, greater strength and stiffness were found with Carbon (CC) fibers blade designs, whereas configuration 3 was found to be the best one, and the optimal blade position was when the ice structure was placed vertically
Two new in-plane torsion tests for the investigation of self-heating under pure shear cyclic loading
No full textInternational audienceThe fatigue limit under a pure shear loading is very complex to determine for thin sheet materials. In this paper, two new specimen geometries are proposed to assess the fatigue limit under this condition using self-heating measurements for isotropic material. Both new geometries are disc-shaped with particular designs to promote a homogeneous stress field. Strain gauge measurements confirmed that the applied strain fields correspond to a pure shear condition. The thermal fields were imaged by an infrared camera, demonstrating the validity of using a 0D thermal approach. In this way, fatigue limits under pure shear loading could be determined
Distributed Multistage Optimization of Large-Scale Microgrids under Stochasticity
No full textInternational audienceMicrogrids are recognized as a relevant tool to absorb decentralized renewable energies in the energy mix. However, the sequential handling of multiple stochastic productions and demands, and of storage, make their management a delicate issue. We add another layer of complexity by considering microgrids where different buildings stand at the nodes of a network and are connected by the arcs; some buildings host local production and storage capabilities, and can exchange with others their energy surplus. We formulate the problem as a multistage stochastic optimization problem, corresponding to the minimization of the expected temporal sum of operational costs, while satisfying the energy demand at each node, for all time. The resulting mathematical problem has a large-scale nature, exhibiting both spatial and temporal couplings. However, the problem displays a network structure that makes it amenable to a mix of spatial decomposition-coordination with temporal decomposition methods. We conduct numerical simulations on microgrids of different sizes and topologies, with up to 48~nodes and 64~state variables. Decomposition methods are faster and provide more efficient policies than a state-of-the-art Stochastic Dual Dynamic Programming algorithm. Moreover, they scale almost linearly with the state dimension, making them a promising tool to address more complex microgrid optimal management problems
An unscented transformation approach to stochastic analysis of measurement uncertainty in magnet resonance imaging with applications in engineering
No full textInternational audienceIn the frame of stochastic filtering for nonlinear (discrete-time) dynamic systems, the unscented transformation plays a vital role in predicting state information from one time step to another and correcting a priori knowledge of uncertain state estimates by available measured data corrupted by random noise. In contrast to linearization-based techniques, such as the extended Kalman filter, the use of an unscented transformation not only allows an approximation of a nonlinear process or measurement model in terms of a first-order Taylor series expansion at a single operating point, but it also leads to an enhanced quantification of the first two moments of a stochastic probability distribution by a large signal-like sampling of the state space at the so-called sigma points which are chosen in a deterministic manner. In this paper, a novel application of the unscented transformation technique is presented for the stochastic analysis of measurement uncertainty in magnet resonance imaging (MRI). A representative benchmark scenario from the field of velocimetry for engineering applications which is based on measured data gathered at an MRI scanner concludes this contribution
Study of mechanical performance of polymer nanocomposites reinforced with exfoliated graphite of different mesh sizes using micro-indentation
No full textInternational audienceThe first phase of this work aims to use the right additive nano-fillers choices, such as exfoliated Graphite (ExG), increasing the mechanical, electrical, and thermal performances. In this work, we are interested in quantifying the effect particles' size on a polymer matrix's performance. For this, three sets of exfoliated polymers filled with Graphite, characterized by three particle sizes, called meshes 50, 100, and 150, were investigated. In this analysis, exfoliated Graphite reinforced polymers were subjected to indentation tests to define local mechanical properties. The sample is an epoxy 862 matrix reinforced with exfoliated graphite additives. For each specific size, the additives are mixed in percentages of 0% in the act of control, 0.5%, 4%, 8%, and 16% by weight. Matching pure polymers, polymers reinforced by exfoliated Graphite have proven to have significant improvements in local elastic properties (such as modulus, hardness, stiffness, etc.). Results showed that the reinforced epoxy's local mechanical properties are affected by the size and the percentage of nano-additives. Through the inspection of the load-displacement curve, it can be concluded that the nano-additive has a significant influence on the plastic mechanical properties of the sample. Therefore, the size of nanoparticles has significantly improved in material properties
Sidescan sonar mosaicing improvements using a tracking algorithm combining forward looking sonar images and ship heading oscillations
No full textInternational audienceTo offer optimal data quality, devices like magnetometers or sidescan sonars (SSS) are traditionally deployed near the seabed, often put on a towfish, linked to the ship by a cable. Unfortunately, this line implies imprecision in the towfish locations. In order to obtain a positioning of the towfish with respect to the vessel, a forward looking sonar (FLS) is used to track the different towfish location during the time. A bespoke experiment, realized for this study in Brest Harbor in an area of about 500x100 meters, is first presented. Then, a tracking algorithm is performed to find the SSS reflector in the FLS images. This algorithm uses a Kalman filter to link ship heading oscillations to FLS images to give SSS positions during the time. At that time, the image sonar mosaicing is carried out in a geographical information system (GIS), with the help of the tracking results and the GPS positions of the ship. The last part of this work is to compare the different SSS mosaics results (with or without layback corrections) to the digital terrain models (DTM) of the same area, in order to estimate the benefits of these corrections
Frequency and Amplitude Modulations of a Moving Structure in Unsteady Non-Homogeneous Density Fluid Flow
No full textInternational audienceA fluid-structure interaction’s effects on the dynamics of a hydrofoil immersed in a fluid flow of non-homogeneous density is presented and analyzed. A linearized model is applied to solve the fluid-structure coupled problem. Fluid density variations along the hydrofoil upper surface, based on the sinusoidal cavity oscillations, are used. It is shown that for the steady cavity case, the value of cavity length Lp does not affect the amplitude of the hydrofoil displacements. However, the natural frequency of the structure increases according to Lp. In the unsteady cavity case, the variations of the added mass and added damping (induced by the fluid density rate of change) generate frequency and amplitude modulations in the hydrofoil dynamics. To analyse this phenomena, the empirical mode decomposition, a well established data-driven method to handle such modulations, is used
Systèmes d'antennes ultra-large-bande pour applications in-band full-duplex
No full textIn-band full-duplex technology aims to mitigate the scarcity of spectral resources by allowing two radios to communicate simultaneously in the same frequency band. The main challenge for full-duplex radios is to cancel the self-interference signals, which couple from the transmitter of one radio to its own receiver, by implementing various self-interference cancellation circuitry at the antenna, analog, and digital stages of the radio front-end. Conventional self-interference cancellation techniques were dedicated for narrowband systems and little work has been conducted to extend their performance for wideband operation. Thus, in this work, we focus on studying the wideband potential of the available cancellation techniques and implementing wideband full-duplex systems based on those techniques. The implemented systems are based on the near-field cancellation technique which uses four antennas and two baluns. The systems' merits vary from extremely wide bandwidth to higher mechanical solidity and dual-polarization, but they all can maintain a decent amount of cancellation.La technologie in-band full-duplex a pour objectif d’augmenter l'efficacité spectrale des liaisons sans-fils en permettant à deux systèmes de communiquer simultanément dans la même bande de fréquence. Dans cette configuration in-band full-duplex, le principal défi consiste à annuler ou réduire les signaux d’auto-interférence, qui se couplent de l'émetteur vers son propre récepteur. Divers circuits d'annulation d'auto-interférence peuvent alors être mis en oeuvre : au niveau de l’antenne, de l'étage analogique et/ou numérique. Les techniques classiques d'annulation d'auto-interférence sont majoritairement dédiées aux systèmes à bande étroite et peu de travaux ont été menés pour étendre leurs performances à un fonctionnement en large-bande et encore moins en ultra-large-bande. Dans ce travail, nous nous focalisons sur l'étude des techniques d'annulation compatibles avec un fonctionnement ultra-large-bande et sur leurs mises en oeuvre. Les systèmes antennaires proposés sont basés sur une technique d'annulation en champ proche qui utilise quatre antennes et deux baluns. Les avantages des systèmes développés sont multiples, ils proposent tous une bande passante extrêmement large tout en maintenant un niveau d'annulation d'auto-interférence au moins supérieur à 55-60 dB sur cette bande avec des configurations permettant soit d'en augmenter la solidité mécanique, soit d'obtenir une double polarisation ou encore avec une alimentation innovante des antennes