A new way to harness the power of moving water comes from something we've known about for hundreds of years: Vortex Induced Vibrations (VIVs).
Read about the new technology at ENN
First observed by Leonardo DaVinci, these vibrations result from spinning water flows forming and breaking up ("shedding") on the downstream side of a rounded ("bluff") mass that sits passively in a current of moving water.
A vortex is a spinning flow of liquid or air. We all see vortices (vortexes? vorteci?) each day as the water in the commode spins away. Other examples include tornados, hurricanes and black holes in space. A wind vortex creates the drag that moves sailboats. Anyone who has seen eddies (little cyclones of spinning water) form around rocks in a river or stream knows about this phenomenon, and has observed that water in the eddy spins on itself faster than the current is moving.
Scientists at the University of Michigan observed the way fish swim through the vortex created by the fish swimming in front of them (similar to drafting or slipstreaming in car or bicycle racing), and have figured out how to harness the power of slowly moving water by mimicking that process. Fish aren't the only animals to do this. We see geese and other birds flying in a "V" formation for the same reason. Lift force from the vortex created by the leader bird helps the trailing birds move along using less energy.
The U Michigan folks found that by placing a passive rounded cylinder in the water such that two vortices are created (above and below the cylinder), slowly moving water creates vortices that cause the cylinder to move like a piston. Presto! A renewable power source.
The thing that comes to mind for me is seeing a crab trap buoy move back-and-forth in a quickly moving tide, just like a piston. Why didn't anyone think of this before?