1. Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
2. MIT Sea Grant College Program, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
3. Laboratory of Systems & Applications of Information & Energy Technologies, École Normale Supérieure de Rennes, 35170 Bruz, France.
4. Division of Applied Mathematics, Brown University, Providence, RI 02912, USA.