Dynamic Behaviour of a Flexible Yacht Sail Plan

• Dynamic fluid structure interaction of a sail plan is modeled in harmonic pitching • Aerodynamic forces oscillations show hysteresis phenomena • Neglecting the structural deformation underestimates the forces oscillations • Both aerodynamic and structure inertia affect loads in the rig.A numerical investigation of the dynamic Fluid Structure Interaction (FSI) of a yacht sail plan submitted to harmonic pitching is presented to address both issues of aerodynamic unsteadiness and structural deformation. The FSI model | Vortex Lattice Method uid model and Finite Element structure model | has been validated with full-scale measurements. It is shown that the dynamic behaviour of a sail plan subject to yacht motion clearly deviates from the quasi-steady theory. The aerodynamic forces presented as a function of the instantaneous apparent wind angle show hysteresis loops, suggesting that some energy is exchanged by the system. The area included in the hysteresis loop increases with the motion reduced frequency and amplitude. Comparison of rigid versus soft structures shows that FSI increases the energy exchanged by the system and that the oscillations of aerodynamic forces are underestimated when the structure deformation is not considered. Dynamic loads in the fore and aft rigging wires are dominated by structural and inertial effects. This FSI model and the obtained results may be useful firstly for yacht design, and also in the field of auxiliary wind assisted ship propulsion, or to investigate other marine soft structures.This work was supported by the French Naval Academy

A Shallow Water Analogue of the Standing Accretion Shock Instability: Experimental Demonstration and Two-Dimensional Model

Despite the sphericity of the collapsing stellar core, the birth conditions of neutron stars can be highly non spherical due to a hydrodynamical instability of the shocked accretion flow. Here we report the first laboratory experiment of a shallow water analogue, based on the physics of hydraulic jumps. Both the experiment and its shallow water modeling demonstrate a robust linear instability and nonlinear properties of symmetry breaking, in a system which is one million times smaller and about hundred times slower than its astrophysical analogue.Comment: 4 pages, 4 figures, accepted for publication in Phys. Rev. Letters. Supplementary Material (6 movies) available at http://irfu.cea.fr/Projets/SN2NS/outreach.htm

Spatial integration in European cross-border metropolitan regions: A comparative approach

This article analyses the process of spatial integration in ten European cross-border metropolitan regions. On the basis of three indicators, relating to flows of cross-border commuters, gross domestic product and the housing market, it suggests that spatial integration can be viewed as a process of convergence between distinct territories, resulting from the intensification of interaction between social, political and economic actors. Our results allow, firstly, confirmation of the hypothesis that the greater the economic disparities, the greater the level of interactions measured by cross-border commuting. Our work also shows that strong economic interactions have an impact on the cross-border integration of communities, measured by the proportion of residents based on the other side of the border. Finally, this article leads to three models of cross-border integration being proposed: by specialisation, by polarisation and by osmosis.cross-border; metropilitan regions; spatial integration; commuters; gross domestic product; housing market; Europe

Challenges and obstacles in the production of cross-border territorial strategies: The example of the greater region

Cross-border strategies have been flourishing over the last few decades in Europe, mostly in a favourable context where European funding is available and legal instruments are well-developed. However, one may wonder which objectives are really targeted within this very broad and imprecise notion of cross-border strategy. The purpose of this paper is, first, to provide a theoretical framework in order to better understand the different meanings of the notion of cross-border integration and to provide a more critical perspective on its effects. Secondly, it analyses the policy content of the cross-border territorial strategy developed within the Greater Region before, in the final section, pointing out the difficulties faced by policy-makers during its elaboration. This final section is based on the insights brought both by the regional stakeholders interviewed and by our expertise as moderators and scientific advisors within the working group in charge of the realisation of the cross-border territorial strategy. The main finding of our analysis is that the consensus that has been reached by all the stakeholders is the “smallest common denominator”; that is to say, the least constraining

Christopher J. Shepherd, Haunted Houses and Ghostly Encounters. Ethnography and Animism in East Timor, 1860-1975. Copenhagen: NIAS Press, Southeast Asia Publication Series, 2019, xxiii-326 p. ISBN: 978-8-776942-67-0.

Cet ouvrage sur l’animisme au Timor Oriental assume d’emblée la notion de subjectivité, dans la mesure où l’auteur a pris le parti de présenter dix visions liées à ce sujet, à travers dix témoignages écrits couvrant la période de l’amorce de l’emprise coloniale en 1860 à la veille de l’invasion indonésienne en 1975. On en profitera à ce titre pour souligner une erreur encore trop fréquente dans nombre d’ouvrages sur Timor-Est, avec l’affirmation en introduction selon laquelle « No sooner had ..

Neural Nets trained by genetic algorithms for collision avoidance

As air traffic keeps increasing, many research programs focus on collision avoidance techniques. For short or medium term avoidance, new headings have to be computed almost on the spot, and feed forward neural nets are susceptible to find solutions in a much shorter amount of time than classical avoidance algorithms (A_, stochastic optimization, etc.) In this article, we show that a neural network can be built with unsupervised learning to compute nearly optimal trajectories to solve two aircraft conflicts with the highest reliability, while computing headings in a few milliseconds

José Mattoso, A dignidade, Konis Santan e a resistência timorense

Les compétences historiques du professeur José Mattoso ne sont plus à prouver, mais il était essentiellement connu pour son érudition en matière d’histoire médiévale du Portugal ; aussi cela pouvait paraître ambitieux, voire périlleux, de le voir entreprendre un ouvrage en histoire contemporaine sur la résistance est-timoraise dans le dernier quart du xxe siècle. En fait, il nous donne ici un ouvrage non seulement convaincant, mais surtout sans équivalent sur la période 1975-1999, en dépit d’..

Timor-Leste face à la récurrence des crises

Après presque vingt-cinq ans d’occupation indonésienne, le référendum du 30 août 1999 a montré que la très grande majorité de la population ne souhaitait pas vivre sous contrôle étranger. Dix ans plus tard, la série de crises qui a troublé le territoire interroge ceux qui avaient considéré le processus d’accession à l’indépendance comme un succès.Dès novembre-décembre 2002, des manifestations ont amené la destruction de bâtiments administratifs et de résidences de proches du Premier ministre, soupçonnés de corruption. Entre avril et mai 2005, des manifestants ont défilé massivement à Dili pour protester contre un projet de loi visant à réduire l’influence de la religion dans l’enseignement. En février 2006, près de six cents militaires entraient en sédition en arguant de discriminations sur des bases régionales. Les troubles ont amené le déplacement de plus de 150 000 personnes et ont perturbé les élections législatives de 2007. L’instabilité n’a pris fin qu’après la double tentative d’assassinat manqué du Président de la République et du Premier ministre en février 2008. Pourtant, le concept de failed state ne paraît pas opératoire pour Timor oriental (ou Leste).After almost twenty-five years of Indonesian occupation, the referendum of 30 August 1999 showed that the very great majority of the population did not wish to live under foreign control. Ten years on, the series of crises that has troubled the territory raises questions for those who considered the independence process to have been a success.Back in November-December 2002, demonstrations destroyed administrative buildings and the residences of figures close to the Prime Minister who were suspected of corruption. In April and May 2005, demonstrators turned out in mass in Dili to protest against a government bill aiming to reduce the influence of religion in teaching. In February 2006, almost six hundred members of the military rebelled in protest at discrimination along regional lines. The unrest led to over 150,000 people being displaced and disrupted the 2007 general elections. The instability only came to an end after the failed double assassination attempt on the President of the Republic and Prime Minister in February. And yet the concept of failed state does not seem to apply to Timor-Leste.Depois de quase vinte e cinco anos de ocupação indonésia, o referendo de 30 de Agosto de 1999 revelou que a grande maioria da população não desejava viver sob controlo estrangeiro. Dez anos mais tarde, a série de crises que abalou o território levou a que aqueles que tinham considerado o processo de acesso à independência como um sucesso se questionassem.As manifestações provocaram, desde Novembro-Dezembro de 2002, a destruição de prédios administrativos e de residências de pessoas próximas do Primeiro-Ministro, tidas como corruptas. Entre Abril e Maio de 2005, os manifestantes desfilaram em massa, em Díli, para protestar contra um projecto de lei, que visava reduzir a influência da religião no ensino. Em Fevereiro de 2006, perto de seiscentos militares iniciavam uma sedição, denunciando problemas de discriminação baseados nas diferentes origens regionais. Estes problemas levaram à deslocação de mais de 150 000 pessoas, tendo ainda perturbado as eleições legislativas de 2007. A instabilidade apenas viu o seu fim depois da tentativa, falhada, de assassinato do Presidente da República e do Primeiro-Ministro, em Fevereiro de 2008. E no entanto, o conceito failed state parece não se aplicar a Timor-Leste

Cirkadijalni ritam, disanje i ponašanje hipogejskih i epigejskih repaša

Comparisons of circadian rhythmicity, behavior, and metabolism between surface and cavedwelling salamanders enable elucidation of evolutionary trends in these processes. The obligate cave-dwelling proteid Proteus anguinus did not show any apparent daily rhythm of activity or resting metabolic rate. In contrast, the surface-dwelling salamandrid Euproctus asper had a circadian SMR and activity cycle. These circadian rhythms possessed an endogenous component. The lives of both salamanders studied were characterized by long periods of inactivity punctuated by bouts of foraging or exploratory/predatory behavior. Proteus anguinus had reduced resting metabolic and spontaneous activity rates (considerably lower than most surface-dwelling amphibians), and therefore appears to be a good example of a vertebrate as a low-energy system. The low metabolic and activity rates of P. anguinus are interpreted as adaptations to a subterranean existence where poor and discontinuous food supplies and/or intermittent hypoxia may be present for long periods.Usporedbe cirkadijalnog ritma, ponašanja i metabolizma kod površinskih i špiljskih proteida omogućuju rasvjetljavanje evolucijskih trendova u tim procesima. Obligatorni stanovnik špilja, proteid Proteus anguinus, nije pokazivao nikakav vidljiv dnevni ritam aktivnosti ili posebni metabolizam prilikom odmora. Naprotiv, salamandrid Euproctus asper koji boravi na površini, imao je cirkadijalni SMR i ciklus aktivnosti. Ti cirkadijalni ritmovi imali su endogenu komponentu. Životi obaju proučavanih životinja bili su karakterizirani dugim periodima neaktivnosti, prekidanih hranjenjem ili izviđačkim/predatorskim ponašanjem. Proteus anguinus imala je smanjen metabolizam tijekom odmaranja i tijekom spontane aktivnosti (znatno niži od većine površinskih vodozemaca), pa se čini dobrim primjerom kralježnjaka kao niskoenergetskog sustava. Niske vrijednosti metabolizma i aktivnosti P. anguinus interpretiraju se kao prilagodbe na život u podzemlju, gdje je u duljim periodima prisutna slaba i nekontinuirana opskrba hranom i/ili hipoksija

Experimental validation of unsteady models for wind / sails / rigging fluid structure interaction

The aim of this paper is to present the work of experimental validation elements of the aero elastic and unsteady model ARAVANTI. Numerical and Experimental results comparison is made on the rigging and sails of a J80 sail boat. Yacht modelling demands to consider unsteady phenomena resulting from the sea state, variations of wind speed and direction, yacht motion or trimming by the crew. A dedicated instrumentation is developed to measure the loads in shrouds and tension points of the sail, the apparent wind, the yacht motion, the sails flying shape and the navigation data. A special effort is made on sensors calibration, physical measurement comprehension and data synchronisation. Comparison with numerical results shows that the loads and flying shapes are well predicted by the model