Mechanics Colloquium

 

PROGRAM

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MATEMATIČKI INSTITUT SANU
ODELJENJE ZA MEHANIKU

PROGRAM ZA MAJ 2017.

Pozivamo Vas da učestvujete u radu sednica Odeljenja i to:

SREDA, 03.05.2017. u 18:00, Sala 301f, MI SANU, Kneza Mihaila 36
Djordje Cantrak, Masinski fakultet Univerziteta u Beogradu
EKSPERIMENTALNO ISTRAZIVANJE KOHERENTNIH VRTLOZNIH STRUKTURA
Rezime: Razmatraju se koherentne vrtlozne strukture na potisu aksijalnog ventilatora u pravoj cevi, kao i iza avionskog krila modela aviona CRM (common research model). CRM je projektovan u saradnji NASA-e i Boeing-a. Prikazana je analiza generisanih vrtloznih struktura i njihovih statistickih svojstava. Eksperimentalna istrazivanja su obavljena primenom metoda vizualizacije i optickih mernih tehnika i to laser Dopler anemometrije (LDA) i PIV (PIV, particle image velocimetry). Na osnovu originalnih rezultata merenja detaljno se istrazuje uticaj rezima rada aksijalnog ventilatora na strukturu turbulencije i precesiju vrtloznog jezgra, kao i ugla aeroprofila na formiranu vrtloznu strukturu. Izmerene raspodele turbulentnih napona omogucile su formiranje invarijantnih mapa anizotropnosti za razlicite uglove lopatica kola, kao i napadne uglove modela CRM. Dobijeni su znacajni zaključci o uticaju rezima rada ventilatora na anizotropnost i strukturu turbulencije u jezgru, smicajnom sloju i osnovnom strujanju, kao i uticaja napadnog ugla aviona na vrtlozne strukture iza krila aviona.


PONEDELJAK, 08.05.2017. u 14:15, Sala 301f, MI SANU, Kneza Mihaila 36
Theodore Popelensky, Lomonosov State University, Moscow
ON COMBINATORIAL RICCI FLOW ON SURFACES
After R. Hamilton's paper "Three-manifolds with positive Ricci curvature" (1982), a natural question about properties of the Ricci flow on surfaces arose. In this dimension the long-time existence and convergence were proved more or less easy: in 1986, R. Hamilton announced and in 1988 published the proof of convergence of the Ricci flow to the metric of constant curvature for arbitrary initial metric for any closed surface different form the sphere; in 1991, B. Chow closed the question by proving the same statement for two-dimensional sphere.
In 2003 B. Chow and F. Luo investigated on of possible "discretization" of the Ricce flow. Fixed data consists of a closed surface, its triangulation, and weights on the edges of the triangulations. For this object one has so called "circle packing metrics", corresponding curvatures, and Ricci flow. This version of discretization is important due to the circle packings which were investigated by Thurston in his unpublished book "Geometry and topology of 3-manifolds".
Chow and Luo showed that under certain conditions on the weight function the Ricci flow converges exponentially fast to the metric of constant curvature. One of the important conditions consists in non-negativity of the weights.
Recently R. Pepa and me were able to weaken some of the Clow-Luo conditions. Namely some weights can be negative but still should satisfy some conditions. Also we show that the weakening the conditions cannot be unlimited. We found examples of triangulation of surfaces and weights on the edges of the triangulation such that there exists saddle points of the Ricci flow.
In the talk I give the exposition of old results and present some new ones.
* zajednicka sednica sa Odeljenjem za matematiku, Matematickog instituta SANU


SREDA, 17.5.2017. u 18:00, Sala 301f, MI SANU, Kneza Mihaila 36
Milovan Suvakov, Institut za fiziku u Zemunu
PERIODICNA RESENJA RAVANSKOG PROBLEMA TRI TELA KOJA INTERAGUJU JAKIM POTENCIJALOM
Rezime: U predavanju ce biti prikazani rezultati numericke potrage za periodicnim resenjima ravanskog problema tri tela iste mase sa nultim momentom impulsa koja interaguju tzv. jakim potencijalom (1/r^2). Fazni prostor u kom moze da se definise ovaj dinamicki sistem je sestodimenzioni. Dodatni uslovi koje zadovoljavaju periodicna resenja definisu trodimenzionalni podprostor faznog prostora u kome se do na skaliranje nalaze sva periodicna resenja. Mi koristimo dinamicki sistem definisan u ovom podprostoru kao okvir za numericku potragu za periodicnim resenjima. Bice prikazana ova procedura, kao i neka nadjena resenja.


SREDA, 24.05.2017. u 14:15, Sala 301f, MI SANU, Kneza Mihaila 36
Vladimir Dragovic, Matematicki institut SANU, The University of Texas at Dallas, USA
SLUCAJ KOVALJEVSKE DINAMIKE KRUTOG TELA I DISKRIMINANTNO SEPARABILNI POLINOMI
* zajednicka sednica sa seminarom Matematicke metode mehanike

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Predavanja su namenjena sirokom krugu slusalaca, ukljucujuci studente redovnih i doktorskih studija. Odrzavaju se sredom sa pocetkom u 18 casova u sali 301f na trecem spratu zgrade Matematickog instituta SANU, Knez Mihailova 36.

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