# Seminars

# Atmosphere Ocean Science Colloquium

#### The Material Skeleton of Fluid Flows

**Speaker:**
Mattia Serra, ETH Zurich

**Location:**
Warren Weaver Hall 1302

**Date:**
Wednesday, May 17, 2017, 3:30 p.m.

**Synopsis:**

Lagrangian Coherent Structures (LCSs) and Objective Eulerian Coherent Structures (OECSs) are distinguished features in a dynamical system that create coherent trajectory patterns over a finite-time or infinitesimally-short-time interval. LCSs and OECSs are defined as stationary solution of frame-invariant functionals describing the material deformation in the phase space. LCSs are suitable for quantifying finite-time transport and mixing in fluid flows, intrinsically tied to a preselected time interval. OECSs, by contrast, can be computed at any time instant, are free from any assumptions on time scales, and hence are promising tools for flow-control and real-time decision-making problems. Using model-based and experimental velocity fields, we compute LCSs and OECSs in several complex dynamical systems as multi-scale Oceanic and Atmospheric Flows. Remarkably, we find that LCSs and OECSs uncover the material skeleton of fluid flows, which, in contrast, remains hidden to common diagnostics for coherent structures detection.