Hands-on Meeting

Computing Lagrangian Coherent Structures in Time-dependent Flows
Philip Du Toit

Friday June 13, 2008
114 Steele --- CDS Library
2:00--4:00pm

This will be a hands-on meeting in which participants will learn the LCS software and what it all means. For further information, contact:  Philip DuToit

Participants in the workshop will be introduced to software for computing Finite Time Liapunov Exponents (FTLE). Computation of the FTLE has proven fruitful in revealing and analyzing structures that govern transport in time-dependent flows and has been used in a wide range of applications including oceanic and atmospheric flows, hurricanes, empirically-produced vortices, bio-locomotion of jelly-fish, and transport in the solar system. The flow structures extracted using the FTLE are called Lagrangian Coherent Structures (LCS).

Software for the efficient computation of FTLE called Newman will be introduced. Newman allows for computation of the FTLE at high resolution in arbitrary dimension using parallel computing. Newman can also be used to compute and visualize trajectories of passive drifters in a flow.

The workshop is intended to be very practical in nature, and all students are encouraged to bring their laptop computers so that the software can be installed and example computations can be executed. A specific goal of the workshop is to ensure that all summer SURF students who are interested in computing LCS learn how to install and use the software. In brief, we will discuss code installation; data formats; parameter settings; code capabilities; output formats; visualization of LCS, trajectories, and velocity fields; and parallelization. The format will be informal and consist primarily of group discussion as we work through example computations together.

What can I do to prepare for the Workshop?

• 1. Helpful background for FTLE and LCS is provided in an online tutorial written by Shawn Shadden:

http://www.cds.caltech.edu/~shawn/LCS-tutorial/contents.html

• 2. If you would like to bring your laptop to install the software, you will need a C/C++ compiler. The code is written to run in a UNIX-like environment.

Also, you will need to install two libraries:

• a. GNU Scientific Library: http://www.gnu.org/software/gsl/
  
• b. Open MPI Library: http://www.open-mpi.org/

(If you have questions, we can install these during the workshop as well.)