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L @'échographie comme moyen de surveillance instrumentale préanesthésique de la fonction cardiovasculaire - revue bibliographique chez l'homme et l'animal de compagnie
Get PDFEn anesthésie, que ce soit en médecine humaine ou vétérinaire, il est essentiel de monitorer la fonction cardiovasculaire afin de maintenir le patient en vie, mais également d'éviter toutes les complications liées à cette perturbation cardiovasculaire. Il est ainsi important de détecter et de monitorer d'éventuelles hypotensions, hypovolémies, surcharges volémiques ou encore des pertes sanguines. Il est également intéressant de prédire la capacité de réponse à la fluidothérapie d'un patient, afin d'adapter au mieux le remplissage vasculaire. De plus, l'utilisation des ultrasons comme moyen de monitoring s'est développé afin d'éviter l'utilisation de méthodes invasives. Ainsi, de nombreuses méthodes échographiques ont été décrites en médecine humaine afin de surveiller ces différents paramètres. La méthode la plus étudiée est l'évaluation de la veine cave inférieure, mais l'échocardiographie est également sujet d'étude. D'autres vaisseaux plus accessibles comme la veine jugulaire et l'artère carotide, ou encore la veine fémorale sont également analysé dans les cas où la veine cave n'est pas visualisable. En médecine vétérinaire, les mêmes paramètres sont étudiés mais de manière beaucoup plus récente. Ainsi, la plupart des études portent plus sur la faisabilité de la méthode, que sur la détermination de valeur seuil et la précision de la technique. Les études sont également centrées sur la veine cave caudale et l'échocardiographie, il n'existe que peu d'étude sur des vaisseaux plus périphériques. Il est important de noter que les travaux sont principalement réalisés chez le chien, le chat et le cheval étant très peu représentés. Ce travail résume ainsi les différentes méthodes utilisable en médecine humaine et vétérinaire pour le monitoring cardiovasculaire en per-anesthésique
Morphing électroactif hybride par la conception d'actionneurs-capteurs intégrés pour l'augmentation des performances aérodynamiques - application aux ailes de l'Airbus A320.
Get PDFFor the next 20 years, the quantity of air travelers in the world is expected to rise to almost the double of the current number. This growth is followed by the eminent increase of greenhouse gas emissions linked to climate change. Another obvious consequence is the higher operation cost for airline companies. These factors explain the need for better efficiency for modern aircrafts. Among these studies there is the Smart Morphing and Sensing European Project. The goal of the project is to design a system of electroactive actuators for two different time scales. Shape Memory Alloys (SMA) are used for low-frequency camber control of an A320 wing prototype at reduced scale, developed by LAPLACE, while piezoelectric based actuators are responsible for high frequency vibration of its trailing-edge. The experiments have been carried out in the S4 subsonic windtunnel at the IMFT facilities in Toulouse to analyze shear-layer dynamics. TR-PIV results were acquired at Reynolds Number of 700k and 1 million. In addition, lift and unsteady pressure measurements were obtained at different upstream velocities. Spectral analysis were computed to investigate the effects of morphing on vortices manipulation and turbulence reduction
Chemical weathering and CO2 consumption in a multi-lithological karstic critical zone: Long term hydrochemical trends and isotopic survey
Get PDFThe chemical weathering (CW) of rocks at the Earth's surface plays a key role in the global carbon cycle along multiple pathways. Although karst systems are hotspot carbonated areas, they are not always monolithological. It is therefore challenging to estimate the CW of these complex areas. The interannual, seasonal, and spatial variations of CW rates and CO2 consumption were investigated using a long-term hydrogeochemical database (1994–2019) from a mountainous karstic catchment in southwestern France (Baget Catchment). A geochemical and isotopic spatial sampling allowed the identification of the main mineral or lithological sources in the catchment, which controlled the water chemistry. The CW budget showed that the (Ca2+ + Mg2+) fluxes originated from carbonate dissolution (1.14 mol·m−2·yr−1 equivalent to 74%) and silicate weathering (18%) by carbonic acid solutions. Gypsum dissolution and carbonate weathering by sulphuric acid from pyrite oxidation contribute equally to 4%, although the former accounts for 66% of the dissolved sulphate fluxes. During a summer sampling survey, an innovative sulphur isotopic approach based on δ34SSO4, allowed us to demonstrate that the ore-nature sulphuric acid drove 9.0% of total carbonate dissolution and represented only 16.8% of the dissolved sulphate stream fluxes. Hydrological conditions, temperature, vegetation, the epikarst (quasi-permanent shallow and discontinuous saturated layer under the soil), and the water dynamics were the key factors influencing the inter-annual and inter-seasonal variations of the CW rates and CO2 consumption. In addition, the carbon isotopic signature evidenced geochemical processes such as CO2 outgassing and calcite precipitation processes. The latter could remove up to 74% of HCO3− from streamwaters, depending on the hydrological conditions at the outlet between 2016 and 2019. Finally, this study highlights that CW rates and CO2 consumption may vary over inter-annual and inter-seasonal scales, and spatially even for a small catchment. Furthermore, the global CO2 consumption appears to be mainly driven by the runoff intensity in karst hydrosystems, where carbonate dissolution was found to consume 71% of the total weathering CO2 uptake
Impedance control for a flexible robot enhanced with energy tanks in the port-hamiltonian framework
Get PDFIn modern robotics, the manipulators are no longer isolated under fully controlled conditions but rather conceived to work in unconstrained environments. Under these operations, compliant control and passivity properties of the robot are of great importance, and thus the system’s energy function plays a crucial role in the control design. In this work, we propose a new design of cartesian impedance control for a flexible robot whose dynamics is represented within the port-Hamiltonian framework. To improve the performance of the system and maximize the capabilities of the robot, the robotic control system is enhanced with energy tanks that allow for temporarily non-passive operations, but ensure the passivity of the extended system. In addition, a secondary controller is designed using the port-Hamiltonian approach to cover the case of redundant robotic manipulators. The performance of the full control system is tested via simulations of the Kuka iiwa manipulator in closed loop with the proposed passivity-based controller. The results show a satisfactory performance of the control system for set-point regulation, external forces, time-varying reference trajectories, and parametric uncertainty
Quantification of the transposition error for CFD computations of the heat transfer coefficient.
Get PDFThis dissertation deals with the use of RANS CFD commercial solvers for heat transfer computations of nuclear reactor components. The validation of two codes has been previously performed on reduced scale mock-ups at smaller Reynolds number scale in experimental facilities. The objective of this work has been to verify if the accuracy of calculation of the heat transfer coefficient with CFD evolves when approaching the real reactor scale Reynolds number. Experiments and CFD computations have been conducted for this purpose. The first step has been to lay down the basics of CFD and uncertainty quantification. The latter subject provides a working environment which consolidates the validation approach, as the comparisons are given by taking into consideration the different sources of uncertainty in heat transfer simulations and experiments. An important aspect of this work has been to develop a measurement methodology to retrieve heat transfer coefficient maps for water exchanging with a heated smooth wall with reasonable uncertainty. The method that has been chosen is based on the gypsum dissolution and the heat and mass transfer analogy. The measured mass transfer coefficient has been transposed to smooth wall heat transfer coefficient by considering the roughness of the gypsum surface after dissolution and the difference of heat and mass diffusion in water. The values of the heat transfer coefficient obtained have been compared to literature for Reynolds number in the range [10^4,10^5] on the well documented case of heat exchange in a rectangular channel for turbulent flow, showing good agreement. Then, two commercial softwares were tested for computations of the heat transfer coefficient by reproducing the experiments. In the rectangular channel, the boundary conditions uncertainty during the experiments were propagated through the CFD simulations with two different methods: the deterministic sampling which uses a limited number of sigma points to propagate the covariance of the inputs and Monte Carlo method which relies on the estimation of large samples of the boundary conditions with a surrogate model based on gaussian process. These two methods have been found to yield identic results indicating that the boundary conditions uncertainty is negligible in comparison to the experimental uncertainty. Finally, the comparison between CFD and experiments has been done and combined to the experimental uncertainty to estimate the model error which has been found to decrease for increasing Reynolds numbers. The process has then been reproduced for comparisons of CFD and experiments in a 1/5th reduced scale mock-up of a steam generator water box. The measurement methodology has been adapted and combined both heat and mass transfer measurements. The 2D mass transfer data has been processed with the Proper Orthogonal Decomposition and the heat transfer measurements were used to measure the transposition factor. Heat and mass transfer data showed consistent values indicating good confidence on the heat and mass transfer analogy. The heat and mass transfer measurements were then combined to proceed to the uncertainty quantification of CFD on the Reynolds number range [10^5,10^6]. The numerical error has been estimated with a grid convergence method (GCM) using Richardson extrapolation and was shown to be negligible. The same conclusion was drawn for the boundary conditions uncertainty which has been estimated with Monte-Carlo method. Finally, the comparison between CFD and experiments has been found to depend on the turbulence model, depend on near wall meshing and depend on software. It has also been concluded that the type of cells had an impact on simulations of the steam generator mock-up flow where tetrahedral cells yielded higher Nusselt number. The overall comparison between CFD computations and experiments finally showed the non-evolution of the model error with increasing Reynolds number
Cislunar CubeSats to Measure Radiation in Support for Human Space Exploration
Get PDFThe intentions of space agencies and private entities alike are clear: humankind wants to establish its presence on and around the Moon. Plans for the exploration of the surface of Earth’s only natural satellite are established, with international accords and partnership being created around the globe. A new opportunity arises for the space community as national agencies are currently collaborating in the conception of a lunar orbiting station, symbolic successor of the International Space Station (ISS) currently on a Low Earth Orbit (LEO). This “Gateway” station, will serve multiple purposes, including supporting human and robotic activity on the lunar surface and scientific research in Lunar vicinity. It will be placed on a Near Rectilinear Halo Orbit around the second Earth Moon Lagrange point (EML), with its apoapsis over the lunar south pole [1]. In this zone, the radiation environment is not yet very well known: the station will be equipped with the ERSA and HERMES sensors suites to measure doses absorbed by the crews on the NRHO. Nevertheless, a complete cartography of the larger cislunar space is not yet available, but it would prove very useful for all future missions to the Moon.
This paper discusses the preliminary design of a lunar CubeSat mission, developed by the Space Advanced Concepts Laboratory at the Institut Supérieur de l’Aéronautique et de l’Espace (ISAE-SUPAERO) in Toulouse, France. The mission, named DRACO (Detection of RAdiation in Cislunar space Orbit), considers two CubeSats deployed in the cislunar space to study its radiation environment, gaining knowledge for future crewed missions near the Earth-Moon Lagrange (EML) points, and proving the ability of nanosatellites to operate in this environment. Moreover, one of the key functions of the Gateway station will be the deployment of smaller spacecraft. This assumption will simplify the mission design for the DRACO CubeSats’ reduced propulsion and control capabilities, avoiding performing a lunar insertion manoeuvre.
Once deployed from the Gateway, the two spacecraft will transfer to a neighbouring Near Rectilinear Halo Orbit, where they will remain for a calibration phase. They will then transfer to their science orbit, each reaching a larger Halo orbit around EML1 and EML2. The orbit choice was done considering multiple parameters such as stability, station keeping costs etc., to determine the most cost efficient and goal-oriented orbit. Transfers have been studied within the Circular Restricted Three-Body Problem (CR3BP) model, which introduces some simplifications in the relative motion between the Earth and the Moon, while maintaining the fundamental dynamical behaviours of a multibody system. A search for a transfer sequence was carried out, to find the best design with respect to the mission requirements, also considering the limited amount of fuel available and the mission lifetime. Moreover, the advantage of invariant manifolds, natural dynamical structures that provide low-cost transfer in the cislunar space, was evaluated. Finally, the disposal of spacecraft was discussed, in search for a feasible solution, sustainable for the future debris environment.
The main DRACO mission objective is to characterise the radiation environment around the Moon. To achieve this, CubeSats were equipped with a suitable payload to perform full field ion measurements, observing the ion spectra to potentially validate different Galactic Cosmic Rays (GCRs) and Solar Particle Events (SPEs) models. Environmental models available in the literature were considered as basis for this analysis [2]. The performance of the CubeSats in the radiation environment is also assessed performing a sectoral analysis on the different subsystems of the nanosatellites. A complete Computer Aided Design (CAD) model with all required components was analysed with the advanced radiation dose analysis and shielding optimization software, FASTRAD [3]. The results of these studies led to the creation of a preliminary design of the two CubeSats. Moreover, different widths for the external panels of the spacecraft were considered, to provide the best trade-off between radiation protection and mass.
References
[1] J. Williams, D. E. Lee, R. J. Whitley, K. A. Bokelmann, D. C. Davis, and C. F. Berry, ‘Targeting Cislunar Near Rectilinear Halo Orbits for Human Space Exploration’, presented at the 27th AAS/AIAA Space Flight Mechanics Meeting, San Antonio, Texas, Feb. 2017.
[2] M. A. Xapsos, P. M. O'Neill and T. P. O'Brien, "Near-Earth Space Radiation Models," in IEEE Transactions on Nuclear Science, vol. 60, no. 3, pp. 1691-1705, Jun. 2013, doi: 10.1109/TNS.2012.2225846.
[3] P. Pourrouquet, J.-C. Thomas, P.-F. Peyrard, R. Ecoffet, and G. Rolland, ‘FASTRAD 3.2: Radiation Shielding Tool with a New Monte Carlo Module’, presented at the 2011 IEEE Radiation Effects Data Workshop, Las Vegas, NV, Jul. 2011. doi: 10.1109/REDW.2010.6062530
Preparation and characterisation of green nano-sized ceramic pigments with the spinel structure AB2O4 (A = Co, Ni and B = Cr, Al)
Get PDFInorganic pigments based on AB2O4 (A = Co, Ni; B = Cr, Al) spinel structures with green colour were successfully synthesised by the polymeric route. The effect of the substitution of trivalent and divalent cations on the structural, optical and morphological properties of the pigments was investigated. The synthesised nanopowders were examined using thermogravimetry-differential thermal analysis (TG-DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer–Emmett–Teller analysis (BET), UV–vis diffuse reflectance measurements, and CIEL*a*b* colorimetric analyses. The results show that the CoCr2O4 spinel and the spinels substituted by nickel and aluminium cations were obtained with a single phase after heat treatment at 900 °C. The produced powders present shades of the green colour with improvement in morphology for the substituted samples. The Ni0·5Co0·5CrAlO4 nanoparticles consisted of grains of quasi-spherical shape with sizes between 50 and 75 nm. This powder was used in small quantities with glazes for colouring tests on the surfaces of ceramic substrate
Datadriven emulation models for Rocket Engines Injector design
No full textOver the last decade a change in paradigm has been experienced in the development of rocket engines with an enhanced focus in cost effectiveness. Additionally, new mission requirements are expected in the future, thus posing a threat for vectors with inadequate propulsive elasticity. Future estimates hence predict a competitive commercial launch and space transportation sector. Design of new rocket propulsion systems is therefore under growing pressure of reduc ing development costs while satisfying performance through a wide range of scenarios. Validated computational fluid dynamics (CFD) codes for the simulation of combustion chambers can play an important role in this context. These provide an alternative to experimentdriven design. Nonetheless, a holistic approach for design optimization is not yet practical as exploration of the entire engine design space through fullscale CFD evaluations is too expensive in terms of computational time. Surrogate models may avoid this conundrum through fast inference times, without significant loss in predictive accuracy. The aim of the present work is to use an artificial intelligence algorithm trained on data from Reynolds Averaged Navier Stokes (RANS) numerical simulations to generate datadriven surrogate models for a shear coaxial injector GOx/Methane combustion chamber. A single element combustion chamber experimentally tested at the Technische Universität München (TUM) is taken as reference case. A Design of Experiments (DOE) considering 9 pa rameters (geometrical and operating conditions) serves as departing point for this study. More than 3500 axisymmetric simulations are carried out to cover the design of experiments. Scalar and average quantities (0D), wall quantities (1D) and field quantities (2D) are considered to extract different surrogate models. As a first step, depending on the size of the output, different machine learning techniques are employed to extract surrogate models of different dimensions: gaussian processes, fully connected neural networks (FCNN) and convolutional neural networks (CNN). A comparison between different approaches is developed and carried out. A posteriori, a scrutiny of the quantities predicted by the surrogate models (0D, 1D and 2D) is carried out including validation through analysis of conservation and physical consistency. Cross model consistency, where possible, and error sources are also evaluated
Hydrostatic pressure wheel for regulation of open channel networks and for the energy supply of isolated sites
Get PDFThe Hydrostatic Pressure Wheel is an innovative solution to regulate flow discharges and waters heights in open channel networks. Indeed, they can maintain a water depth while producing energy for supplying sensors and a regulation system. To prove the feasibility of this solution, a complete model of water depth–discharge rotational speed relationship has been elaborated. The latter takes into account the different energy losses present in the turbine. Experimental measurements achieved in IMFT laboratory allowed to calibrate the coefficients of head losses relevant for a large range of operating conditions. Once the model had been validated, an extrapolation to a real case showed the possibility of maintaining upstream water level but also of being able to produce sufficient energy for supplying in energy isolated sites. The solution thus makes it possible to satisfy primary energy needs while respecting the principles of frugal innovation: simplicity, robustness, reduced environmental impact
Effect of powder size and processing parameters on surface, density and mechanical properties of 316L elaborated by Laser Powder Bed Fusion
Get PDFDespite the attractive capabilities of additive manufacturing (AM) technology, the industrialization of these processes remains very low. This is attributed to the complexes physical phenomena involved in the AM process and the layered structure of the produced parts. Intense research work is still needed for the prediction and optimization of AM parts mechanical properties. In this study, the influence of particle size distribution (PSD) of stainless steel 316L (SS 316L) powders on AM parts properties was investigated. Four PSD were used to produce test parts and compare the resulting porosity, surface roughness and macro-hardness. The SS 316L specimens were fabricated by Laser Powder Bed Fusion process (LPBF) on a SLM 125HL machine using variations in laser power and scan velocity. Computed scan tomography (CT) was used to characterize the defects. Lack of fusion and keyhole defects were detected. Defects were detected even in nearly dense parts. The powder size distribution was found to affect the porosity. Results from CT tests were used to identify the minimum achievable porosities for each powder, through the appropriate selection of process parameters. The macro-hardness and surface roughness were found to vary with the powder properties