Engineers at Virginia Polytechnic¹（工业学院） Institute and State University (VirginiaTech) have developed a robot that mimics² the graceful⁴ motions of jellyfish（水母，海蜇） so precisely⁵ that it has been named Robojelly. Developed for the U.S. Office of Naval⁶ Research in 2009, this vehicle was designed to conduct ocean underwater surveillance, enabling it potentially to detect chemical spills, monitor the presence of ships and submarines, and observe the migration⁷ of schools of fish. Recently, a team at VirginiaTech has improved the performance of this silicone（硅树脂） swimmer, enabling it to better overcome the limitations of its artificial skin and better mimic³ the true motion of a jellyfish. Details on this new design and how it might provide new insights into jellyfish propulsion（推进） mechanisms⁹ are being presented at the 2011 meeting of the American Physical Society's Division of Fluid Dynamics¹⁰ in Baltimore, Md., Nov. 20-22.

According to VirginiaTech mechanical engineer Alex Villanueva, Robojelly looks very similar to an actual jellyfish. "Its geometry is copied almost exactly from a moon jellyfish [Aurelia aurita]," he said. The robot is built out of silicone and uses shape memory alloy¹¹ (SMA) actuators to swim.

To move through the water, the natural animal uses the bell section of its body, which deforms¹² and contracts to provide thrust. The lower, or lagging, section of the bell is known as the flexible margin¹³, and it deforms slightly later in the swimming process than the rest of the bell. Until recently, however, Robojelly lacked this crucial piece of anatomy¹⁴（解剖学） in its design.

Villanueva and his colleagues tested a number of different designs for their robot, some with and without an analog¹⁵ to a flexible margin. Initially¹⁶, the artificial materials used in construction presented a problem. Unlike their natural counterparts, the artificial materials tended to fold as they deformed¹⁷, reducing Robojelly's performance. After testing a number of designs and lengths for the folding margin, the engineers discovered that cutting slots into the bell reduced this unwanted folding effect.

This gave Robojelly a truer swimming stroke, as well as a big boost in speed.

"These results clearly demonstrate that the flap plays an important role in the propulsion mechanism⁸ of Robojelly and provides an anatomical understanding of natural jellyfish," said Villanuerva.