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SUMMARY:MechE Colloquium: Beyond classical linear instability analysis- no
 nnormality and nonlinearity
DTSTART:20251007T120000
DTEND:20251007T130000
DTSTAMP:20260410T063635Z
UID:f9b0b130bde9b20a4c2b3e6ae61506d1dd290400cb662145b069a25f
CATEGORIES:Conferences - Seminars
DESCRIPTION:Prof. François Gallaire\, Institute of Mechanical Engineeri
 ng\, School of Engineering\, EPFL\nAbstract: Hydrodynamic instabilities 
 are ubiquitous in natural flows and across engineering. They are classical
 ly analyzed by a linear instability analysis\, aiming at the determination
  of the dominant eigenvalues and eigenmodes\, deemed to capture the post-b
 ifurcation dynamics and the response to external disturbances. This approa
 ch remains insufficient in many flow situations\, either because the dynam
 ics is not correctly captured by a small subset of eigenmodes (nonnormalit
 y) or because the amplitude of external disturbances is determinant (nonli
 nearity). The lack of predictive power of classical linear instability ana
 lysis is evidenced by challenges in deriving reduced order models that fai
 thfully capture the observed behavior\, as well as - more generally - our 
 limited understanding of the physical processes mediating the transition f
 rom laminar to turbulent flows and the patterns that may emerge during tra
 nsition.\nI will illustrate our recently developed theoretical tools to mo
 del flow such situations\, where classical linear stability approaches are
  insufficient. I will specifically demonstrate the rigorous derivation of 
 amplitude equations in the presence of nonnormality\, nonlinearity and sto
 chastic forcing. These amplitude equations allow us to describe\, control 
 and physically understand mechanisms underlying the dynamics of many seemi
 ngly simple\, yet technologically relevant and often mundane flow configur
 ations. After illustrating the concepts in the context of intricate patter
 ns of cold water droplets dripping from the condensation film forming unde
 r a Turkish bath ceiling and the surprising nonlinear damping of sloshing 
 motions in a glass of liquid covered by foam\, I will demonstrate the powe
 r of these novel predictive theoretical tools to flow configurations of in
 terest in a broad range of engineering applications like shear layers\, je
 ts\, and wakes and characterize their nonlinear stochastic response. \nTh
 ese theoretical models complement simulation and modern data-driven ML app
 roaches\, providing mechanistic understanding of mechanisms underlying bot
 h important and also simply beautiful flow phenomena.\n\n\nBiography: Fra
 nçois Gallaire graduated from Ecole Polytechnique in 1998 and earned a Ma
 ster’s Degree in Liquids Physics from Université Pierre et Marie Curie 
 in 1999. He completed his Ph.D. in 2002 at LadHyX\, on swirling jet instab
 ilities and vortex breakdown. After six years at CNRS in the mathematics d
 epartment in Nice\, he joined EPFL in 2009\, founding the Fluid Mechanics 
 and Instabilities Lab (LFMI). He became an associate professor in 2016 and
  served as Mechanical Engineering Section director for 5 years. In 2019\, 
 he was named a fellow of the American Physical Society. His research focus
 es on the fundamental description of hydrodynamic instabilities\, free int
 erface phenomena\, and microfluidics. He is associate editor in Physics Re
 view Fluids. 
LOCATION:CM 1 4 https://plan.epfl.ch/?room==CM%201%204 https://epfl.zoom.u
 s/j/61360740951
STATUS:CONFIRMED
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