486 research outputs found
Low intrusive coupling of implicit and explicit integration schemes for structural dynamics: application to low energy impacts on composite structures
Simulation of low energy impacts on composite structures is a key feature in
aeronautics. Unfortunately they are very expensive: on the one side, the structures of
interest have large dimensions and need fine volumic meshes (at least locally) in order to
capture damages. On the other side small time steps are required to ensure the explicit
algorithms stability which are commonly used in these kind of simulations [4]. Implicit
algorithms are in fact rarely used in this situation because of the roughness of the solutions
that leads to prohibitive expensive time steps or even to non convergence of Newtonlike
iterative processes. It is also observed that rough phenomenons are localized in
space and time (near the impacted zone). It may therefore be advantageous to adopt
a multiscale space/time approach by splitting the structure into several substructures
owning there own space/time discretization and their own integration schemes. The
purpose of this decomposition is to take advantage of the specificities of both algorithms
families: explicit scheme focuses on rough areas while smoother (actually linear) parts of
the solutions are computed with larger time steps with an implicit scheme. We propose
here an implementation of the Gravouil-Combescure method (GC) [1] by the mean of low
intrusive coupling between the implicit finite element analysis (FEA) code Z-set and the
explicit FEA code Europlexus. Simulations of low energy impacts on composite stiffened
panels are presented. It is shown on this application that time step ratios up to 5000 can be reached. However, computations related to the explicit domain still remain a
bottleneck in terms of cpu time
Oxidation Resistance of Thermal Barrier Coatings Based on Hollow Alumina Particles
International audienc
Discovery of carbon monoxide in the upper atmosphere of Pluto
Pluto's icy surface has changed colour and its atmosphere has swelled since
its last closest approach to the Sun in 1989. The thin atmosphere is produced
by evaporating ices, and so can also change rapidly, and in particular carbon
monoxide should be present as an active thermostat. Here we report the
discovery of gaseous CO via the 1.3mm wavelength J=2-1 rotational transition,
and find that the line-centre signal is more than twice as bright as a
tentative result obtained by Bockelee-Morvan et al. in 2000. Greater
surface-ice evaporation over the last decade could explain this, or increased
pressure could have caused the atmosphere to expand. The gas must be cold, with
a narrow line-width consistent with temperatures around 50 K, as predicted for
the very high atmosphere, and the line brightness implies that CO molecules
extend up to approximately 3 Pluto radii above the surface. The upper
atmosphere must have changed markedly over only a decade since the prior
search, and more alterations could occur by the arrival of the New Horizons
mission in 2015.Comment: 5 pages; accepted for publication in MNRAS Letter
Quantum Computing of Classical Chaos: Smile of the Arnold-Schrodinger Cat
We show on the example of the Arnold cat map that classical chaotic systems
can be simulated with exponential efficiency on a quantum computer. Although
classical computer errors grow exponentially with time, the quantum algorithm
with moderate imperfections is able to simulate accurately the unstable chaotic
classical dynamics for long times. The algorithm can be easily implemented on
systems of a few qubits.Comment: revtex, 4 pages, 4 figure
Exponential Gain in Quantum Computing of Quantum Chaos and Localization
We present a quantum algorithm which simulates the quantum kicked rotator
model exponentially faster than classical algorithms. This shows that important
physical problems of quantum chaos, localization and Anderson transition can be
modelled efficiently on a quantum computer. We also show that a similar
algorithm simulates efficiently classical chaos in certain area-preserving
maps.Comment: final published versio
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