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Influence of Microstructural Characteristics on the Tribological Performance of LPBF-Processed H13 Steel in Deposited and Heat-Treated States
No full textInternational audienceInfluence of Microstructural Characteristics on the Tribological Performance of LPBF-Processed H13 Steel in Deposited and Heat-Treated State
Monitoring and Control of Structures subject to Vibration and Damage using the Koopman operator
No full textInternational audienceDue to the effects of fatigue and excessive vibration, structures may present a different health condition than initially observed. The change in system behavior due to damage also causes the system to demand more energy, which can saturate the actuators and make the system unstable. In this context, this work proposes to estimate in real-time the dynamics of a structure and control the undesired effects of vibration and damage. A data-driven model will be developed based on the Koopman operator, analyzing only data from sensors and actuators already installed by the control system. The information obtained by this updated model can be used to monitor changes in structural health and adapt a controller to meet performance specifications, even if the system dynamics vary over time. Changes in the spectral characteristics of the Koopman operator can help identify damage in the structure. In addition, an adaptive model predictive controller can incorporate the possible changes in dynamics in real time, adjusting the optimization problem according to the current estimated model. Therefore, our results have demonstrated the benefits and limitations of this online monitoring and control strategy based on data already measured by the controller. REFERENCES [1] N. Mechbal and E. G. O. Nóbrega, Damage tolerant active control: Concept and state of art. IFAC Proceedings Volumes, vol. 45, no. 20, pp. 63–71, 2012. [2] M. Korda and I. Mezić, Linear predictors for nonlinear dynamical systems: Koopman operator meets model predictive control. Automatica, vol. 93, pp. 149–160, 2018
Towards Efficient Monitoring for WAAM Processes on a Robotized and Reconfigurable Manufacturing Cell
No full textInternational audienceWire Arc Additive Manufacturing (WAAM) is an efficient technology for producing metal parts. It offers high deposition rates, low material waste and reduced machining costs. However, the process's complex multi-physics nature presents several challenges, particularly with regard to residual stresses, deposition accuracy, and internal defects. Internal defects that occur during the WAAM process are difficult to detect in real time or immediately after fabrication without the use of non destructive testing methods. This study focuses on enhancing an experimental protocol that employs a monitoring method analysing the geometry of each deposited layer using a laser sensor. This approach, combined with segmentation techniques, aims to identify and locate internal defects. Specifically, the proposed method relies on segmenting individual layers and comparing normalised values to detect and localise defects. This paper presents the developed methodology and an initial validation of its effectiveness.</p
Rainfall Dynamics in Wind Energy Scenarios
No full textInternational audienceThe presence of rain in wind farms involves several modeling challenges, as the momentum exchanges between turbulent wakes and the particle phase present subtle phenomena. For instance, rain droplets are typically large enough to exhibit inertia relative to the air carrier phase. Under these conditions, it has been found that the gravitational settling of particles in turbulent flows may be either enhanced or hindered compared to stagnant conditions. While this has significant implications for rainfall transport, ash pollutants, and pollen dispersion, very few studies have been conducted in field conditions. Moreover, the scaling laws and non-dimensional parameters governing this phenomenon have not yet been properly identified, and determining which configurations result in the enhancement or hindrance of settling velocity remains an open question.We propose a hybrid experimental/numerical approach. Field data from a meteorological mast located at a wind farm in Pays d’Othe, 110 km South-East of Paris, France, were used to characterize the background turbulent flow through a set of sonic anemometers. Additionally, disdrometers were employed to characterize the settling velocity of raindrops, discriminating by particle size. Numerical simulations complement this data analysis. Specifically, 3D space and time vector fields that realistically reproduce the observed spatial and temporal variability of wind fields are generated using multifractal tools. Then, 3D trajectories of non-spherical particles are simulated and their settling velocity derived.Our findings indicate that the presence of turbulence significantly hinders the settling velocity of raindrops in turbulent environments. Our study covers several distinct rainfall events, allowing us to analyze the influence of turbulent flow properties on this phenomenon
Eulerian-Lagrangian scaling of the Lyapunov exponent in homogeneous turbulence
No full textInternational audienceWe present a heuristic derivation of the maximal Lyapunov exponent γ of homogeneous turbulence which yields two new relations, a sweeping relation and the scaling of the uncertainty field's integral length L∆. These relations and the maximal Lyapunov exponent's scaling that they imply are confirmed by periodic turbulence simulations. As the Reynolds number Re λ increases, L∆ and γ -1 decrease towards values smaller than the Kolmogorov length and time scales.</div
On the dependency of the extent of multiple solution zone around stability lobes on cutting law nonlinearity
No full textInternational audienceIn machining vibrations analyses, regenerative chatter stability boundaries aka stability lobes are known to be often accompanied by a multiple solution zone in process parameters space. In that zone the stable steady response coexists with a finite-amplitude oscillatory solution preceding cut interruption. Exploration of the oscillatory behavior requires accounting for finite nominal cut thickness and the condition of the tool exit from cut. In the present work we explore these conditions via a harmonic balancing framework, bringing forward the dependency of the extent of the unstable post-critical chatter domain on the cutting law nonlinearity
A New Multi-Parametric MRI-Based Scoring System for Degenerative Cervical Myelopathy: The Severity on Imaging Myelopathy Score (SIMS)
No full textInternational audienceBackground/Objectives: Degenerative cervical myelopathy (DCM) is the leading cause of functional disabilities of spinal origin in people over 50 years old. The objective of the present study was to establish a multi-parametric weighted scoring system that is easy to use in daily practice, based on the most significant MRI signs and correlated as strongly as possible with the clinical presentation (mJOA)—we call this system the SIMS or Severity on Imaging Myelopathy Score. Methods: Ninety-nine patients who underwent clinical and radiological evaluation by mJOA and MRI between January 2015 and March 2021 were retrospectively included. The variables included in the score were the Fujiwara ratio, the T2-weighted intramedullary hyperintensity, the aspect of the peri-medullary fluid cisterns, the Torg–Pavlov ratio, the local kyphosis and the number of stenotic levels. Each variable was first correlated to the mJOA score for each patient, making it possible to construct the final SIMS at the end, and validate it by comparison with mJOA scores. Results: The variables that were significantly correlated with one another were the T2-weighted intramedullary hyperintensity, the reduction in peri-medullary fluid spaces and the number of stenotic levels (p < 0.05). Then, points were assigned to each variable according to their relative importance and made it possible to construct the definitive SIMS. The final Spearman correlation coefficient between the SIMS and the mJOA score was −0.747. Conclusions: This work showed that this new multi-parametric MRI-based scoring system represents a consistent means to characterize the degree of severity of degenerative cervical myelopathy
MMC-Autotransformer : Impact of the Control on the Design and Efficiency
No full textInternational audienceTo increase flexibility and reliability of HVDC links and MTDC, it is likely that DC-DC converter will be employed. This paper specifically focuses on the DC-Auto-transformer. This study investigates its performance in relation to its parameters including: AC voltages, frequency and waveform characteristics. The analysis presented in this paper demonstrates that increasing the AC voltage within the converter reduces losses and minimizes capacitor size requirements. While, increasing the frequency reduces the losses as well as required size of capacitors. Furthermore, the results indicate that adopting a trapezoidal waveform improves both efficiency and capacitor size
Inversion-based Control Simplifications for a Cycling-mode Power Converter in Particle Accelerators
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Energy transition: an approach from scientific features to societal issues
No full textInternational audienceThis article presents the experience conducted by researchers at the University of Lille on the technical, scientific and societal issues of the energy transition. Thanks to an academic chair on Energy Transition and an «open laboratory», cross-disciplinary views from the academic world, industry, civil society, local authorities and associations were raised and encouraged. The objective is to identify methods for implementing the energy transition that take into account citizens' aspirations, environmental constraints and technological limitation altogether