#### Filter Results:

- Full text PDF available (33)

#### Publication Year

1970

2017

- This year (2)
- Last five years (25)

#### Publication Type

#### Co-author

#### Publication Venue

#### Key Phrases

#### Organism

Learn More

- G. Haller
- 2001

We prove analytic criteria for the existence of finite-time attracting and repelling material surfaces and lines in three-dimensional unsteady flows. The longest lived such structures define coherent structures in a Lagrangian sense. Our existence criteria involve the invariants of the velocity gradient tensor along fluid trajectories. An alternative… (More)

We introduce a Lagrangian definition for the boundaries of coherent structures in two-dimensional turbulence. The boundaries are defined as material lines that are linearly stable or unstable for longer times than any of their neighbors. Such material lines are responsible for stretching and folding in the mixing of passive tracers. We derive an analytic… (More)

The relationship between the statistical and geometric properties of particle motion in aperiodic, two-dimensional ows is examined. Finite-time invariant manifolds associated with transient hyperbolic trajectories are shown to divide the ow into distinct regions with similar statistical behavior. In particular, numerical simulations of simple, eddy… (More)

The motion of inertial (i.e., finite-size) particles is analyzed in a three-dimensional unsteady simulation of Hurricane Isabel. As established recently, the long-term dynamics of inertial particles in a fluid is governed by a reduced-order inertial equation, obtained as a small perturbation of passive fluid advection on a globally attracting slow manifold… (More)

- A A Abdo, M Ackermann, +249 authors M Ziegler
- Science
- 2009

Gamma-ray bursts (GRBs) are highly energetic explosions signaling the death of massive stars in distant galaxies. The Gamma-ray Burst Monitor and Large Area Telescope onboard the Fermi Observatory together record GRBs over a broad energy range spanning about 7 decades of gammaray energy. In September 2008, Fermi observed the exceptionally luminous GRB… (More)

- M. J. Olascoaga, F. J. Beron-Vera, +11 authors A. Valle-Levinson
- 2013

[1] Application of recent geometric tools for Lagrangian coherent structures (LCS) shows that material attraction in geostrophic velocities derived from altimetry data imposed an important constraint to the motion of drifters from the Grand Lagrangian Deployment (GLAD) in the Gulf of Mexico. This material attraction is largely transparent to traditional… (More)

- M.-R. Alam, W. Liu, G. Haller
- 2006

We develop an analytic approach to two-dimensional flow separation control by feedback. With two wall-based actuators enclosing an array of distributed wall-shear sensors, we control the wall-shear evolution equation through its boundary values at the actuators. Using this approach, we induce separation at prescribed locations in steady and unsteady channel… (More)

- Alireza Hadjighasem, Daniel Karrasch, Hiroshi Teramoto, George Haller
- Physical review. E
- 2016

One of the ubiquitous features of real-life turbulent flows is the existence and persistence of coherent vortices. Here we show that such coherent vortices can be extracted as clusters of Lagrangian trajectories. We carry out the clustering on a weighted graph, with the weights measuring pairwise distances of fluid trajectories in the extended phase space… (More)

Recent developments in identifying Lagrangian coherent structures from finite time velocity data have provided a theoretical basis for understanding chaotic transport in general flows with aperiodic dependence on time. As these theoretical developments are extended and applied to more complex flows, an accurate and general numerical method for computing… (More)

We derive criteria that locate intense material stretching and shear in two-dimensional flows with slow time dependence. Our derivation makes use of the near integrability of the equation of variations along trajectories of the slowly varying flow. The criteria yield two diagnostic scalar fields for use in real-time Lagrangian predictions in geophysical… (More)