Hydroenergy Revolution LLC (
http://hydroenergyrevolution.com/) claims a free energy machine. The underlying principle called "Travis effect" is given in this video:
http://www.youtube.com/watch?v=0JUj42h6j7YSee particularly the time range: 1:00 - 1:50.
A cylindrical bucket is inverted and immersed in water, partially filled with air. A weight placed above sinks it down to the aquarium bottom. We deduce that the weight is more than the Archimede's thrust.
An identical bucket, filled with less air and provided with the same weight, is immersed in the same way, but it can slide around a concrete cylinder. We observe that air redistributes itself around the cylinder, that the thrust depends on this redistribution, and that there is a balance position. If the Archimede's thrust of the first case is equal to the weight of the volume of displaced water, in the second one it is (apparently) higher.
Did we gain energy?
The important thing to retain is that the pressure depends on the depth. The air pressure is equal the water pressure existing at the air/water interface. When the air redistributes itself around the concrete, the air/water interface is lowered, and consequently the air pressure is increased. It becomes more than when there is no concrete. Therefore the Archimede's thrust is stronger and balances the weight. The difference between the two cases comes from the reshaping of the volume of the immersed object, due to the air redistribution. This is as if we had two objets of different shapes: the two cases can't be directly compared.
Now the question is: can this reshaping be the source of free energy?
We would have free energy if the raising of the bucket of the second case could be done at a less price than that of the first case, which is the normal case.
To raise the bucket with its weight, we need to inject compressed air. For the bucket to rise a heigh h, we need to inject an air volume h*S where S is the inside section of the bucket. This is true for the two cases: if the bucket rises, the added air will have to fill the space between the top of the concrete and the top of the bucket, i.e. an identical volume as for the raising of the bucket without concrete! So the work to provide compressed air (which is dW=P*dV), will be the same in the two cases.
I came to this conclusion with the help of 2 independant physicists who gave the same verdict, seeing the flaw very rapidly.
Obviously the video is presenting a conventional effect in a fallacious way. I can't believe that the authors would be unaware of the real principle of the effect. And so I recommend to not invest in this company.