Applying Model Based Techniques for Early Safety Evaluation of an Automotive Architecture in Compliance with the ISO 26262 Standard

International audienceIn 2011, the automotive industry introduced the application of a standardized process for functional safety-related development of automotive electronic products. The related international standard, ISO 26262 functional safety for road vehicles, has high demands on process documentation and analysis. Within an engineering context this challenges the tremendous increase of complexity for modern automotive systems and high productivity demands for industrial competiveness purpose. Model based development techniques based on an Architecture Description Language (ADL) has been identified as the best candidate to manage the system complexity and the related safety analysis with the benefit of formal description and capabilities for test automation. The proposed concept relies on the definition of a compositional error modeling approach tightly coupled with the system architecture model, capable to analyze the software and hardware architectures and implementations. This paper explains the results of the language extension based on the EAST-ADL and AUTOSAR domain model in terms of early safety evaluation of an automotive architecture, automating the qualitative and quantitative assessment of road vehicle products as claimed by the application of the ISO 26262

On the interaction of vortices with mixing layers

We describe the perturbations introduced by two counter-rotating vortices - in a two-dimensional configuration - or by a vortex ring - in an axisymmetric configuration - to the mixing layer between two counterflowing gaseous fuel and air streams of the same density. The analysis is confined to the near stagnation point region, where the strain rate of the unperturbed velocity field, A0, is uniform. We restrict our attention to cases where the typical distance 2r0 between the vortices - or the characteristic vortex ring radius r0 - is large compared to both the thickness, δv, of the vorticity core and the thickness, δm∼(ν/A0)1/2, of the mixing layer. In addition, we consider that the ratio, Γ/ν, of the vortex circulation, Γ, to the kinematic viscosity, ν, is large compared to unity. Then, during the interaction time, A0,-1, the viscous and diffusion effects are confined to the thin vorticity core and the thin mixing layer, which, when seen with the scale r0, appears as a passive interface between the two counterflowing streams when they have the same density. In this case, the analysis provides a simple procedure to describe the displacement and distortion of the interface, as well as the time evolution of the strain rate imposed on the mixing layer, which are needed to calculate the inner structure of the reacting mixing layer as well as the conditions for diffusion flame extinction and edge-flame propagation along the mixing layer. Although in the reacting case variable density effects due to heat release play an important role inside the mixing layer, in this paper the analysis of the inner structure is carried out using the constant density model, which provides good qualitative understanding of the mixing layer response

Simulation aux grandes échelles: instabilités thermo-acoustiques, combustion diphasique et couplages multi-physiques

La combustion turbulente, que ce soit dans des configurations de laboratoire ou dans des configurations réelles industrielles, met en oeuvre un nombre important de physiques fortement couplées: chimie, turbulence, multi-phasique, thermique, etc. Pour répondre aux demandes de plus en plus exigeantes des concepteurs, qui doivent proposer des solutions concurrentielles tout en respectant les contraintes environnementales de bruit et d'émission de polluants, la simulation numérique est devenue incontournable. Plus précisément, la simulation maintenant utilisée comme outil de conception, doit être fiable et précise. Dans le domaine de la combustion turbulente, à fort caractère instationnaire, la Simulation aux Grandes Echelles (SGE) s'est récemment imposée. Cette technique s'est en effet avérée capable de prédire finement le comportement des brûleurs dans des environnements complexes, et permet aujourd'hui d'aborder des problématiques encore mal maîtrisées telles que les instabilités thermo-acoustiques ou la combustion diphasique. On donne ici quelques exemples de problèmes encore ouverts dans ce domaine

Applying a science‐based systems perspective to dispel misconceptions about climate effects of forest bioenergy

The scientific literature contains contrasting findings about the climate effects of forest bioenergy, partly due to the wide diversity of bioenergy systems and associated contexts, but also due to differences in assessment methods. The climate effects of bioenergy must be accurately assessed to inform policy-making, but the complexity of bioenergy systems and associated land, industry and energy systems raises challenges for assessment. We examine misconceptions about climate effects of forest bioenergy and discuss important considerations in assessing these effects and devising measures to incentivize sustainable bioenergy as a component of climate policy. The temporal and spatial system boundary and the reference (counterfactual) scenarios are key methodology choices that strongly influence results. Focussing on carbon balances of individual forest stands and comparing emissions at the point of combustion neglect system-level interactions that influence the climate effects of forest bioenergy. We highlight the need for a systems approach, in assessing options and developing policy for forest bioenergy that: (1) considers the whole life cycle of bioenergy systems, including effects of the associated forest management and harvesting on landscape carbon balances; (2) identifies how forest bioenergy can best be deployed to support energy system transformation required to achieve climate goals; and (3) incentivizes those forest bioenergy systems that augment the mitigation value of the forest sector as a whole. Emphasis on short-term emissions reduction targets can lead to decisions that make medium- to long-term climate goals more difficult to achieve. The most important climate change mitigation measure is the transformation of energy, industry and transport systems so that fossil carbon remains underground. Narrow perspectives obscure the significant role that bioenergy can play by displacing fossil fuels now, and supporting energy system transition. Greater transparency and consistency is needed in greenhouse gas reporting and accounting related to bioenergy

Ship plume dispersion rates in convective boundary layers for chemistry models

Detailed ship plume simulations in various convective boundary layer situations have been performed using a Lagrangian Dispersion Model driven by a Large Eddy Simulation Model. The simulations focus on the early stage (1–2 h) of plume dispersion regime and take into account the effects of plume rise on dispersion. Results are presented in an attempt to provide to atmospheric chemistry modellers a realistic description of characteristic dispersion impact on exhaust ship plume chemistry. Plume dispersion simulations are used to derive analytical dilution rate functions. Even though results exhibit striking effects of plume rise parameter on dispersion patterns, it is shown that initial buoyancy fluxes at ship stack have a minor effect on plume dilution rate. After initial high dispersion regimes a simple characteristic dilution time scale can be used to parameterize the subgrid plume dilution effect in large-scale chemistry models. The results show that this parameter is directly related to the typical turn-over time scale of the convective boundary layer

The prospect for modal shifts in passenger transport worldwide and impacts on energy use and CO2

Travel statistics for most countries are subject to numerous uncertainties. But as presented in this paper, the IEA has developed a sufficient database to estimate passenger travel by mode for major countries and regions around the world, and produce consistent travel and energy use estimates, perhaps the first of their kind. For example, we estimate that in 2005 total global passenger travel using motorised modes was about 40 trillion kilometres, or about 6000 per person. The IEA has also developed a set of travel projections to 2050, including a Baseline and a "Modal Shift" scenario. This paper provides the result of this analysis and estimates the potential impacts on CO2 from a 25% reduction in car and air travel by 2050 relative to the Baseline in that year. The modelling effort and policy analysis used to support the findings are also described