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Stress intensity factor determination along a kinked crack path by DIC analyses
No full textInternational audienceSharp kinks may be observed under shear loading or in materials containing weak directions, such as those produced by additive manufacturing. A better understanding of the fracture of these materials, both theoretically and experimentally, is required to deploy them in structural applications. This study focuses on the measurement of stress intensity factors (SIFs) around a sharp kink using digital image correlation (DIC). The performances of two DIC-based techniques, namely, integrated-DIC and post-processing of DIC-measured displacement fields, are assessed on a benchmark test using fused deposit modeling capabilities, and are compared to a reference finite element solution. It is shown that Williams' expansion remains valid on a large enough region around the crack to extract reliable SIFs even very close to the crack kink. Both techniques are very trustworthy, provided the SIF identification zone is carefully defined to exclude the kink zone of influence
A coupled approach to compute approximate solutions of a compressible immiscible three-phase flow model with fast transient and stiff source terms
No full textInternational audienceThis paper aims at developing a new numerical coupled approach to compute solutions of a compressible immiscible three-phase flow model with stiff source terms. The targeted applications involve flows with fast transient and shock waves. Thus, a well-posed model with respect to the initial conditions that embarks an entropy inequality is considered. A preliminary work on the underlying relaxation process of the model is conducted. Then the new numerical scheme is presented and numerically tested
On the breathing of spectral bands in periodic quantum waveguides with inflating resonators
No full textInternational audienceWe are interested in the lower part of the spectrum of the Dirichlet Laplacian A^ε in a thin waveguide Π^ε obtained by repeating periodically a pattern, itself constructed by scaling an inner field geometry Ω by a small factor ε > 0. The Floquet-Bloch theory ensures that the spectrum of A^ε has a band-gap structure. Due to the Dirichlet boundary conditions, these bands all move to +∞ as O(ε^{-2}) when ε → 0^+. Concerning their widths, applying techniques of dimension reduction, we show that the results depend on the dimension of the so-called space of almost standing waves in Ω that we denote by X_†. Generically, i.e. for most Ω, there holds X_† = {0} and the lower part of the spectrum of A^ε is very sparse, made of bands of length at most O(ε) as ε → 0^+. For certain Ω however, we have dim X_† = 1 and then there are bands of length O(1) which allow for wave propagation in Π^ε. The main originality of this work lies in the study of the behaviour of the spectral bands when perturbing Ω around a particular Ω_⋆ where dim X_† = 1. We show a breathing phenomenon for the spectrum of A^ε : when inflating Ω around Ω_⋆ , the spectral bands rapidly expand before shrinking. In the process, a band dives below the normalized threshold π^2 /ε^2 , stops breathing and becomes extremely short as Ω continues to inflate
Impact of public policies on the dynamics of energy retrofit and fuel poverty in mainland France
No full textInternational audienceMost EU countries have introduced financial and fiscal instruments to accelerate investment in the energy renovation of buildings, which is needed to achieve carbon neutrality by 2050. However, in the absence of reliable data, it is difficult for some countries, such as France, to assess the impact of these instruments on both the dynamics of energy renovation and fuel poverty. To compensate for this lack of data, a tool has been developed. It is presented in this study. It takes into account the three predominant factors in the notion of fuel poverty, namely household resources, the price of energy and the quality of housing. It includes two multiple linear models for estimating: 1. disposable income and 2. energy expenditure. A life-cycle investment cost model is used to calculate the probability of an owner-occupier carrying out thermal renovation work. For tenant households, renovation is based on an annual renovation target. The model is tested in the French case with real values for variations in energy prices and disposable income. It has been calibrated to reproduce the distribution of dwellings according to their energy performance in 2017. The effects of different renovation subsidies on the dynamics of renovation and on fuel poverty are studied. Among the results of the simulations, it should be emphasised that financing the renovation of the least energy-efficient homes alone is not the most effective solution for reducing fuel povert
Machine Learning for Scientific Computing and Numerical Analysis
No full textMasterThese notes are for third-year students at École Polytechnique (Palaiseau, France), who have completed two years of classes préparatoires, making the material equivalent to a graduate-level course in the UK or US. The development of a Scientific Machine Learning (SciML) course for third-year students bridges the gap between scientific computing and machine learning. SciML, an emerging field, enables efficient methods for solving complex problems in science and engineering, like partial differential equations (PDEs). This course offers a new, valuable specialization, helping students stand out in the evolving job market, where demand for ML experts with specialized skills is growing
Effect of temperature and geometry on the brittle failure of an 18MND5 steel in the lower part of the ductile to brittle transition
No full textInternational audienc
Simulating synergism or antagonism in binary mixtures with different modeling approaches – A case study focused on the effect of disinfection by-products on algal growth
No full textInternational audienceThis paper aims to test several modeling approaches for predicting toxicity of binary mixtures with potential synergy and antagonism. The approach based on the construction of isoboles was first tested and criticized. In contrast to conventional approaches, and in order to be mathematically consistent with the additivity assumptions, non-linear isoboles have been constructed. This approach was compared with that proposed by Minto et al. (2000), which measures deviations from additivity by considering standardized variables and which considers the entire Hill concentration-response curves. The selected models were tested on a case study related to chlorine-based disinfectant by-products (DBPs), using experimental data describing the effect of five DBPs (monochloroacetic acid, dichloroacetic acid, trichloroacetic acid, bromochloroacetic acid and 1,1-dichloropropan-2-one) on a unicellular green algae Raphidocelis subcapitata. The approach based on the construction of isoboles has shown its limitations. Indeed, in cases where the individual substances involved have different slopes in terms of their Hill concentration-effect relationships, the so-called zone of indetermination can be large. Furthermore, conclusions drawn from isoboles based on EC50s or EC20s may not be consistent. Minto's approach makes it possible to construct interaction indicators that consider the entire Hill concentration-response curve. Response surfaces can be constructed to visualize the areas of concentration of the two substances involved that maximize the interaction effects
SVM-Based Approach Fault Detection for PMSG-Wind Energy Conversion System
No full textInternational audienc
Yes, there appear to be options to stop or control ASR in some dams !
No full textInternational audienceMany dam owners around the world have been faced with swelling concrete issues at their dams and hydro projects for the past 70 years or more. Several different management strategies have been adopted to allow continued operation, although the options so f ar appear limited and no technologies to stop or limit the reactions have been successfully implemented. In some cases, alkali-silica reactions (ASR) and its associated expansion appear to have diminished after 30 or so years, while in many other cases it continues with more or less vigour. In such cases the potential role of releasable alkalis from aggregates and recycling needs to be considered in order to reliably forecast future behaviour and develop a long-term management plan.In cases where the ASR continues, given the very long required service life of dams, a hundred years and more, there is a clear need to seek to identify some practical solutions to limit the ASR and its effects in these long-term cases. In such cases the roles of the key ingredients to the reactions, silica, alkalis and water must be clearly understood.Recent simulations by the authors have shown that, given the increasingly long required service lives of dams, and often the slow rate of expansion, some very long-term solutions, such as draining and drying the concrete to reduce the expansion rates in some parts of dams and associated structures, may be possible and worth considering in some cases. This paper reviews the issues involved in such notions and suggests some scenarios and technical solutions where very long-term sealing, draining and drying may be effective in existing dams with continuing ASR. In addition, we note that in some extreme cases of new dams or rehabilitation of existing dams where there is persistent uncertainty in performance testing of mix designs for ASR prevention, consideration could be given to applying such techniques immediately as a backup in case ASR occurs despite the testing.We suggest some practical options to achieve these objectives and identify issues that would need to be addressed to confirm their feasibility and practicability.</p