1,844 research outputs found
"Audacity or Precision": The Paradoxes of Henri Villat's Fluid Mechanics in Interwar France
In Interwar France, Henri Villat became the true leader of theoretical
researches on fluid mechanics. Most of his original work was done before the
First World War; it was highly theoretical and its applicability was
questioned. After having organized the first post-WWI International Congress of
Mathematicians in 1920, Villat became the editor of the famous Journal de
math\'ematiques pure et appliqu\'es and the director of the influential book
series "M\'emorial des sciences math\'ematiques." From 1929 on, he held the
fluid mechanics chair established by the Air Ministry at the Sorbonne in Paris
and was heading the government's critical effort invested in fluid mechanics.
However, while both his wake theory and his turbulence theory seemingly had
little success outside France or in the aeronautical industry (except in the
eyes of his students), applied mathematics was despised by the loud generation
of Bourbaki mathematicians coming of age in the mid 1930s. How are we to
understand the contrasted assessments one can make of Villat's place in the
history of fluid mechanics
Modeling Turbulent Flow in Stirred Tanks with CFD: The Influence of the Modeling Approach, Turbulence Model and Numerical Scheme
Single phase turbulent flow in a tank stirred by a down- and an up-pumping pitched blade turbine has been
simulated using CFD. The effect of the modeling approach, discretization scheme and turbulence model on mean
velocities, turbulent kinetic energy and global quantities, such as the power and circulation numbers, has been
investigated. The results have been validated by LDV data. The stationary and time-dependent modeling
approaches were found to have little effect on the turbulent flow, however the choice of the numerical scheme
was found to be important, especially for the predicted turbulent kinetic energy. A first order method was found
to highly underestimate LDV data compared with higher order methods. The type of the turbulence model was
limited to the k-e and RNG models due to convergence difficulties encountered with a Reynolds Stress Model
(RSM) and there was found to be little effect of these models on the mean flow and turbulent kinetic energy.
This latter quantity was found to be largely under predicted in the discharge region of the down-pumping
impeller in comparison with LDV data. Better agreement was found for the up-pumping pitched blade turbine.
Estimated power numbers were found generally to be in good agreement for the down- and up-pumping data.
However, the circulation number tended to be over predicted by about 30% and 40% for the down- and uppumping
agitators, respectively
Rescue, rehabilitation, and release of marine mammals: An analysis of current views and practices.
Stranded marine mammals have long attracted public attention. Those that wash up dead are, for all their value to science, seldom seen by the public as more than curiosities. Animals that are sick, injured, orphaned or
abandoned ignite a different response. Generally, public sentiment supports any effort to rescue, treat and return them to sea.
Institutions displaying marine mammals showed an early interest in live-stranded animals as a source of specimens -- in 1948, Marine Studios in St. Augustine, Florida, rescued a young short-finned pilot whale (Globicephala
macrorhynchus), the first ever in captivity (Kritzler 1952). Eventually, the public as well as government agencies looked to these institutions for their recognized expertise in marine mammal care and medicine. More recently,
facilities have been established for the sole purpose of rehabilitating marine mammals and preparing them for return to the wild. Four such institutions are the Marine Mammal Center (Sausalito, CA), the Research Institute for
Nature Management (Pieterburen, The Netherlands), the RSPCA, Norfolk Wildlife Hospital (Norfolk, United Kingdom) and the Institute for Wildlife Biology of Christian-Albrects University (Kiel, Germany).(PDF contains 68 pages.
La politique aéroportuaire wallonne depuis la régionalisation (1988-2010)
L’objectif de cette étude est de retracer l’évolution de la politique aéroportuaire wallonne depuis la régionalisation complète de cette compétence en 1988. Ce travail s’inscrit dans un projet de recherche plus large qui a été mené au sein de l’Institut de science politique Louvain-Europe de l’Université catholique de Louvain, intitulé : « Impacts de la libéralisation sur les secteurs d’industrie de réseaux : analyse comparée des secteurs du rail et de l’aviation civile en Belgique (DUREBEL) »
Structure and evolution of strange attractors in non-elastic triangular billiards
We study pinball billiard dynamics in an equilateral triangular table. In
such dynamics, collisions with the walls are non-elastic: the outgoing angle
with the normal vector to the boundary is a uniform factor
smaller than the incoming angle. This leads to contraction in phase space for
the discrete-time dynamics between consecutive collisions, and hence to
attractors of zero Lebesgue measure, which are almost always fractal strange
attractors with chaotic dynamics, due to the presence of an expansion
mechanism. We study the structure of these strange attractors and their
evolution as the contraction parameter is varied. For in
the interval (0, 1/3), we prove rigorously that the attractor has the structure
of a Cantor set times an interval, whereas for larger values of the
billiard dynamics gives rise to nonaccessible regions in phase space. For
close to 1, the attractor splits into three transitive components,
the basins of attraction of which have fractal basin boundaries.Comment: 12 pages, 10 figures; submitted for publication. One video file
available at http://sistemas.fciencias.unam.mx/~dsanders
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