Analysis of Fluids Seminars
Speaker: Gautam Iyer, Carnegie Mellon University Date: Dec 7 2017  4:30pm Event type: Analysis of Fluids and Related Topics Room: Fine Hall 322 
Analysis of Fluids and Related Topics: TBASpeaker: Serguei Denissov, University of Wisconsin Date: Nov 30 2017  4:30pm Event type: Analysis of Fluids and Related Topics Room: Fine Hall 322 
Analysis of Fluids and Related Topics: TBASpeaker: Mimi Dai, University of Illinois at Chicago Date: Nov 16 2017  4:30pm Event type: Analysis of Fluids and Related Topics Room: Fine Hall 322 
PrincetonTokyo Fluid Mechanics WorkshopSpeaker: Various, see below Date: Nov 7 2017  9:30am Event type: Analysis of Fluids and Related Topics Room: Location TBD Abstract: Confirmed Speakers From Princeton:
From Tokyo:

Analysis of Fluids and Related Topics: TBASpeaker: Jens Eggers, University of Bristol Date: Oct 26 2017  4:30pm Event type: Analysis of Fluids and Related Topics Room: Fine Hall 322 
Analysis of Fluids and Related Topics: TBASpeaker: Alexei Mailybaev, Nacional de Matemática Pura e Aplicada (IMPA) Date: Oct 19 2017  4:30pm Event type: Analysis of Fluids and Related Topics Room: Fine Hall 322 
Analysis of Fluids and Related Topics: The optimal design of wallbounded heat transportSpeaker: Ian Tobasco, University of Michigan Date: Oct 12 2017  4:30pm Event type: Analysis of Fluids and Related Topics Room: Fine Hall 322 Abstract: Flowing a fluid is a familiar and efficient way to cool: fans cool electronics, water cools nuclear reactors, and the atmosphere cools the Earth. In this talk, we discuss a class of problems from fluid dynamics concerning the design of incompressible wallbounded flows achieving optimal rates of heat transport for a given flow intensity budget. Guided by a perhaps unexpected connection between this optimal design problem and various “energydriven pattern formation” problems from materials science, we construct flows achieving nearly optimal rates of heat transport in their scaling with respect to the intensity budget. The resulting flows share striking similarities with selfsimilar elastic wrinkling patterns, such as can be seen in the shape of a hanging drape or nearby the edge of a torn plastic sheet. They also remind of (carefully designed versions) of the complex multiscale patterns seen in turbulent fluids. Nevertheless, we prove that in certain cases natural buoyancydriven convection is not capable of achieving optimal rates of cooling. This is joint work with Charlie Doering. 
Analysis of Fluids and Related Topics: TBASpeaker: Sam PunshonSmith, University of Maryland Date: Oct 5 2017  4:30pm Event type: Analysis of Fluids and Related Topics Room: Fine Hall 322 
Analysis of Fluids and Related Topics: TBASpeaker: Minh Binh Tran, University of Wisconsin Date: Sep 28 2017  4:30pm Event type: Analysis of Fluids and Related Topics Room: Fine Hall 322 
Analysis of Fluids and Related Topics: Global wellposedness for the 2D Muskat problemSpeaker: Stephen Cameron, University of Chicago Date: Sep 21 2017  4:30pm Event type: Analysis of Fluids and Related Topics Room: Fine Hall 322 Abstract: The Muskat problem was originally introduced by Muskat in order to model the interface between water and oil in tar sands. In general, it describes the interface between two incompressible, immiscible fluids of different constant densities in a porous media. In this talk I will prove the existence of global, smooth solutions to the 2D Muskat problem in the stable regime whenever the initial data is monotonic or has slope strictly less than 1. The curvature of these solutions solutions decays to 0 as t goes to infinity, and they are unique when the initial data is C1,ϵ. We do this by constructing a modulus of continuity generated by the equation, just as Kiselev, Naverov, and Volberg did in their proof of the global wellposedness for the quasigeostraphic equation. 
Analysis of Fluids and Related Topics: Vortex sheets in domains with boundarySpeaker: Helena Nussenzveig Lopes IMUFRJ Date: May 11 2017  4:30pm Event type: Analysis of Fluids and Related Topics Room: Fine Hall 322 Abstract: In this talk we consider the vanishing viscosity problem for incompressible fluid flow in a smooth, bounded domain. We are particularly concerned with the shear layer occurring near the boundary, a phenomenon which we explore in a few examples of flows with symmetry. We use this discussion as motivation for a framework for weak solutions of the inviscid equations which allow for exchange between circulation around the boundary and vorticity in the bulk of the fluid. 
Analysis of Fluids and Related Topics: Travelingstanding water waves and their stabilitySpeaker: Jon Wilkening , UC Berkeley Date: May 4 2017  4:30pm Event type: Analysis of Fluids and Related Topics Room: Fine Hall 322 Abstract: We describe a computational framework for computing hybrid travelingstanding waves that return to a spatial translation of their initial conditions at a later time. We introduce two parameters to describe these waves, and explore bifurcations from pure traveling or pure standing waves to these more general solutions of the freesurface Euler equations. Next, we combine Floquet theory in time and Bloch theory in space to study the stability of travelingstanding waves to harmonic and subharmonic perturbations. For the latter, we have developed new boundary integral methods for the spatially quasiperiodic DirichletNeumann operator. While much is known about the spectral stability of pure traveling waves, this is the first study of general subharmonic perturbations of pure standing waves. Our unified approach for travelingstanding waves simplifies the eigenvalue problem that arises in the pure traveling case as well. We conclude with a discussion of general quasiperiodic solutions of the freesurface Euler equations and present preliminary calculations of some simple cases. 
Analysis of Fluids and Related Topics: Investigating stability and finding new steady vortex flows through numerical bifurcation approachesSpeaker: Paolo LuzzattoFegiz , UC Santa Barbara Date: Apr 27 2017  4:30pm Event type: Analysis of Fluids and Related Topics Room: Fine Hall 322 Abstract: In 1875, Lord Kelvin stated an energybased argument for determining equilibrium and stability in vortex flows. The possibility of implementing Kelvin’s argument, in the form of a simple bifurcation approach, had been the subject of debate. In this talk, we build on results from dynamical systems theory to show that, by constructing solution families through isovortical rearrangements, one obtains a bifurcation diagram that contains stability information. To detect bifurcations to new equilibrium families, we propose calculating vortices that have been made “imperfect” through the introduction of asymmetries in the vorticity field. The resulting approach can in principle be used to determine the number of positiveenergy (likely unstable) modes for each solution belonging to a family of steady vortices. However, to compute full bifurcation diagrams, we must numerically solve the Euler equations in an unbounded domain, without prescribing any symmetry. These requirements pose challenges in achieving convergence (due to degeneracies in the Euler equations) and accuracy (as smallscale features develop). We introduce a numerical method that overcomes these limitations. We apply the overall numerical bifurcation methodology to several families of flow equilibria, including elliptical vortices, oppositesigned vortex pairs (of both rotating and translating type), single and double vortex rows, as well as gravity waves. For all flows, we discover new families of equilibria, which exhibit lower symmetry, and obtain stability properties in agreement with detailed linear stability analyses. We conclude by highlighting general solution features that still require explanation. 
Analysis of Fluids and Related Topics: Culmination of the inverse cascade  mean flow and fluctuationsSpeaker: Anna Frishman , Princeton PCTS Date: Apr 13 2017  4:30pm Event type: Analysis of Fluids and Related Topics Room: Fine Hall 322 Abstract: An inverse cascade, energy transfer to progressively larger scales, is a salient feature of twodimensional turbulence. If the cascade reaches the system scale, it creates a coherent flow expected to have the largest available scale and conform with the symmetries of the domain. In a square doubly periodic domain, the mean flow is expected to take the form of a vortex dipole. The velocity profile of a corresponding single vortex was recently obtained analytically and subsequently confirmed numerically. I will describe the next step in the derivation: using the mean velocity profile to predict features of the turbulent fluctuations. I will also address the mean flow in a doubly periodic (nonsquare) rectangle. For a rectangle, the mean flow with zero total momentum was believed to be unidirectional, with two jets along the short side. I will describe how direct numerical simulations reveal that neither the box symmetry is respected nor the largest scale is realized: the flow is never purely unidirectional since the inverse cascade produces coherent vortices, whose number and relative motion are determined by the aspect ratio. This spontaneous symmetry breaking is closely related to the hierarchy of averaging times. Longtime averaging restores translational invariance due to vortex wandering along one direction, and gives jets whose profile, however, can be deduced neither from the largestavailablescale argument, nor from the often employed maximumentropy principle or quasilinear approximation. 
Analysis of Fluids and Related Topics: Determining the Global Dynamics of the 2D NavierStokes Equations by 1D ODESpeaker: Edriss Titi, Texas A&M and Weizmann Institute Date: Apr 7 2017  2:00pm Event type: Analysis of Fluids and Related Topics Room: Fine Hall 224 Abstract: One of the main characteristics of infinitedimensional dissipative evolution equations, such as the NavierStokes equations and reactiondiffusion systems, is that their longtime dynamics is determined by finitely many parameters  finite number of determining modes, nodes, volume elements and other determining interpolants. In this talk I will show how to explore this finitedimensional feature of the longtime behavior of infinitedimensional dissipative systems to design finitedimensional feedback control for stabilizing their solutions. Notably, it is observed that this very same approach can be implemented for designing data assimilation algorithms of weather prediction based on discrete measurements. In addition, I will also show that the longtime dynamics of the NavierStokes equations can be imbedded in an infinitedimensional dynamical system that is induced by an ordinary differential equations, named {\it determining form}, which is governed by a globally Lipschitz vector field. Remarkably, as a result of this machinery I will eventually show that the global dynamics of the NavierStokes equations is be determining by only one parameter that is governed by an ODE. The NavierStokes equations are used as an illustrative example, and all the above mentioned results equally hold to other dissipative evolution PDEs, in particular to various dissipative reactiondiffusion systems and geophysical models. 
Analysis of Fluids and Related Topics: Incompressible flow around small obstacles *Please note this is an additional seminar (5:30)Speaker: Milton Lopes , Instituto de Matemática, UFRJ Date: Apr 6 2017  5:30pm Event type: Analysis of Fluids and Related Topics Room: Fine Hall 322 Abstract: In this talk we examine several results concerning the asymptotic behavior of incompressible flow outside small obstacles, including a single obstacle in two and three space dimensions, several small obstacles, viscous and inviscid flows and moving obstacles. 
Analysis of Fluids and Related Topics: Stochastic homogenization for reactiondiffusion equationsSpeaker: Andrej Zlatos, UC San Diego Date: Apr 6 2017  4:30pm Event type: Analysis of Fluids and Related Topics Room: Fine Hall 322 Abstract: We study spreading of reactions in random media and prove that homogenization takes place under suitable hypotheses. That is, the medium becomes effectively homogeneous in the largescale limit of the dynamics of solutions to the PDE. Hypotheses that guarantee this include fairly general stationary ergodic KPP reactions, as well as homogeneous ignition reactions in up to three dimensions perturbed by radially symmetric impurities distributed according to a Poisson point process. In contrast to the original (secondorder) reactiondiffusion equations, the limiting "homogenized" PDE for this model are (firstorder) HamiltonJacobi equations, and the limiting solutions are discontinuous functions that solve these in a weak sense. A key ingredient is a novel relationship between spreading speeds and front speeds for these models (as well as a proof of existence of these speeds), which can be thought of as the inverse of a wellknown formula in the case of periodic media, but we are able to establish it even for more general stationary ergodic media. 
Analysis of Fluids and Related Topics: Brief survey of computer assisted proofs for partial differential equationsSpeaker: Jacek Cyranka, Rutgers University Date: Mar 30 2017  4:30pm Event type: Analysis of Fluids and Related Topics Room: Fine Hall 322 Abstract: I will present a brief survey of computer assisted methods of studying partial differential equations that I have worked on. The methods I am going to discuss allow for obtaining proofs of the existence of particular solutions of a certain class of PDEs in a prescribed range of parameters. I will discuss opportunities and limitations of the presented approach. In particular most of the presented results have not been obtained using known techniques of 'classical analysis'. I will focus on two particular examples from my research, namely 1) a proof of the existence of globally attracting solutions for the 1d viscous Burgers equation (with nonautonomous forcing) https://arxiv.org/abs/1403.7170, and 2) recent proof of the heteroclinic connections in the 1d OhtaKawasaki (diblock copolymers) model https://arxiv.org/abs/1703.01022 
Analysis of Fluids and Related Topics: Mixing in Compressible Hydrodynamics as Diffusivities Approach ZeroSpeaker: Daniel Lecoanet , Princeton University Date: Mar 16 2017  4:30pm Event type: Analysis of Fluids and Related Topics Room: Fine Hall 322 Abstract: The KelvinHelmholtz (KH) instability is a prototypical hydrodynamic mixing process driven by velocity shear. I will present simulations of the KH instability in compressible hydrodynamics. Compressibility introduces baroclinic instabilities which can further enhance mixing. I compare simulations run at specific Reynolds numbers to "implicit large eddy simulations'' (ILES) in which numerical errors play the role of a subgrid scale diffusivity parameterization. Many of the simulations were run using Dedalus, an opensource spectral code which can solve nearly arbitrary PDEs. I will then discuss extrapolating our simulations to the limit of Re>infinity, extrapolating the ILES to the limit of resolution approaching infinity, and whether or not these two limits are the same. 
An algebraic reduction of the `scaling gap' in the NavierStokes regularity problemSpeaker: Analysis of Fluids and Related Topics: Zoran Grujic, University of Virginia Date: Mar 9 2017  5:30pm Event type: Analysis of Fluids and Related Topics Room: Fine Hall 322 Abstract: Please note special time (5:30). It is shownwithin a mathematical framework based on the suitably defined scale of sparseness of the superlevel sets of the positive and negative parts of the vorticity componentsthat the everresisting `scaling gap' in the 3D NavierStokes regularity problem can be reduced by an algebraic factor; all preexisting improvements have been logarithmic in nature, regardless of the functional set up utilized. The mathematics was inspired by morphology of the regions of intense vorticity/velocity gradients observed in computational simulations of turbulent flows. This is a joint work with A. Farhat and Z. Bradshaw. 
Recent results on 2D density patches for inhomogeneous NavierStokesSpeaker: Analysis of Fluids and Related Topics: Francisco Gancedo, Universidad de Sevilla Date: Mar 9 2017  4:30pm Event type: Analysis of Fluids and Related Topics Room: Fine Hall 322 Abstract: This talk is about the dynamics of a patch given by two fluids of different constant densities, evolving by the inhomogeneous NavierStokes equations. The main question to address is whether the regularity of the boundary of the initial patch is preserved in time. Using classical Sobolev spaces for the velocity, we establish the propagation of C1+γ, W2,∞and C^{2+\gamma}regularities with0<\gamma<1$. The results are based on new cancelations found for time dependent singular integrals given by the linear nonhomogeneous heat kernel acting on quadratic terms.

Analysis of Fluids and Related Topics: On a Slightly Compressible Water WaveSpeaker: Chenyun Luo, Johns Hopkins University Date: Mar 2 2017  4:30pm Event type: Analysis of Fluids and Related Topics Room: Fine Hall 322 Abstract: In this talk, I would like to go over some recent results on a compressible water wave. We generalize the apriori energy estimates for the compressible Euler equations established in LindbladLuo to when the fluid domain is unbounded. 
Analysis of Fluids and Related Topics: Scattering of the GrossPitaevskii equation in the 3D radial energy spaceSpeaker: Zaher Hani, Georgia Tech Date: Feb 23 2017  4:30pm Event type: Analysis of Fluids and Related Topics Room: Fine Hall 322 Abstract: We consider the 3D GrossPitaevskii (GP) equation, or the nonlinear Schrodinger (NLS) equation with nonvanishing constant amplitude at spatial infinity. We are interested in the asymptotic stability of the plane wave solutions. 
Analysis of Fluids and Related Topics: "Selfsimilar vortex spirals"Speaker: Volker Elling , University of Michigan Date: Feb 9 2017  4:30pm Event type: Analysis of Fluids and Related Topics Room: 322 Fine Hall Abstract: We construct a class of selfsimilar 2d incompressible Euler solutions that have initial vorticity of mixed sign. The regions of positive and negative vorticity form algebraic spirals. Connections to the problem of nonuniqueness for the Euler equations will be discussed. 
TBASpeaker: Edriss Titi, Texas A&M University Date: May 7 2015  4:30pm Event type: Analysis of Fluids and Related Topics Room: Fine 322 