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EUREKA MAY COVER FEATURE STORY





EUREKA MAY COVER FEATURE STORY
EUREKA MAY COVER FEATURE STORY


Dolphin's tail wags way to fluid power efficiencies

Novel marine propulsion, low head water power generation, mixing and other fluid operations can be made much more efficient by non linear oscillatory control. Tom Shelley reports

Inspired by an English researcher's long forgotten study of how dolphins swim, research in Russia doubtless originally aimed at Cold War goals, but now being commercialised in America, shows practical ways of greatly improving a wide range of fluid power based processes.

All involve some kind of non-linear oscillation of a mechanical element to control a fluid power operation, with adaptive control to deliver optimum performance under different conditions.

Identified applications include silent and efficient marine propulsion, stream and tidal flow power generation, more efficient process mixers, heat pumps and mixers with no internal moving parts, and a possible spin on an improved design of hovercraft.

While the basic ideas have been around for quite some time, it is only now, with the advent of high speed computation in today's microcontrollers, that these schemes have become practicable.

According to Dr Evgeny Sorokodum, general director of Vortex Oscillation Technology, based in Moscow, the original ideas came out of research undertaken by Cambridge biologist Professor Sir James Gray in 1936. Following tests with rigid models of dolphins, he came to the conclusion that dolphins needed about ten times the energy they were able to develop with their muscles to be able to swim as fast as they do. In 1955, German researcher Max Kramer concluded that the dolphin's secret lay in the construction of their skin. Russian researchers, however, were more interested in the complex manner in which they move their tails in response to encountered requirements and conditions, and this led onto a Russian and American projects to devise silent submarines propelled by oscillating horizontal wing thrusters.

In a demonstration model tested in a water tank in Russia, the movements of the propulsion vane are controlled by a "Black box" algorithm run on a Pentium based PC. Dr Sorokodum told Eureka that no software model of the system is involved and that control feedback comes from two sensors. One measures speed through the water and the other, force applied to the actuator. Actuator speed (he said, "Frequency) and angle of attack are controlled throughout each stroke cycle. Dolphins and fish do all this, of course, without having to think about it. He said that a "Large number" of researchers had been involved in developing the various technologies, working at a research institute in Taganrog over a period of several decades.

 
The force diagram at wave flow of an underwater vehicle.

One immediate and obvious spinoff is to run the system in reverse and use it to extract energy from water flow. More than a few engineers have looked at the possibilities of recovering energy from oscillating vanes in the past. These include that described in an article published in Eureka in October 2000, "Turbulence offers easier power" (see article in the Reference Library on the www.eurekamagazine.co.uk web site). This included schemes conceived by Spain based semi-retired engineer Ken Upton with aerofoil and hydrofoil wings at high angle of attack on the end of swinging, trailing arms. His systems were designed to oscillate by having the wing go into stall after which it recovered and stalled again. However, the efficiency of a simple system based on quasi-static hydrodynamics tends to be low. Dr Sorokodum showed Eureka graphs that showed an approximate doubling of efficiency that could be obtained by forcing a oscillating hydrofoil wing to reciprocate in a non linear manner. Energy recovery, would, in his opinion, be best achieved by making it drive a pneumatic or hydraulic pump.

 
Relative velocity

The initiation of stall involves the generation of vortices and this leads onto another line of research to which much effort has been devoted in Russia, as reported in our November 2003 cover story, "Harnessing the tornado's energy" also accessible via our web site.

The simplest device proposed by Dr Sorokodum is a mixer. Many of our readers will recall moments spent swilling the contents of a glass by moving it in a circulatory motion. It will soon be noted that it is quite difficult to find the right motion of the glass to achieve maximum motion and mixing of the contents. However, with suitable feedback and adaptive control, it is possible to use this technique to produce and maintain a sufficiently strong vortex to not only achieve efficient mixing, but to achieve temperature separation effects as produced by vortex tubes.

 
The sheme of energy

Dr Sorokodum reckons he has the technology to build externally excited vortex mixers with capacities from 0.5 litres to 10 cu m. He claims that they require much less energy to achieve a the same degree of mixing as compared with use of internal motor driven agitators. He says they also run quieter and containers can be kept hermetically sealed and then opened when required.

A further development builds on effects found in Ranque-Hilsch vortex tubes. These use a vortex to produce a temperature difference between issuing streams of gas issuing from the tube. Hot gas issues from regions near the outer wall and cold gas from the centre. The effect is believed to be caused by loss of angular momentum and its associated energy from gas molecules at the centre of the vortex. If angular momentum were conserved, these molecules would move around the centre line faster than those near the wall but are constrained by friction. The vortex is usually induced by tengentially admitting compressed air or gas at 4 to 6 bar pressure. Sorokodum's version induces it by external motion of the tube. In this way, he believes he has an efficient technology for condensing water from the atmosphere in arid regions, working refrigeration and air conditioning systems, and liquefying natural gas.

His last idea, is to make a hovercraft which rides on a cushion of air held in by vortices generated by the movement of an oscillating skirt, instead of pumping air in from above via a ducted fan. He believes that such a machine would be quieter and more efficient and points out that ideas in this direction were first put forward by English designer named Kokerelli. Dr Sorokodum says he is in the process of organising a business to exploit his technologies in the UK to be named Vortex Oscillation Energy Ltd.


Pointers

* It is now possible to reproduce the complex movements that fish and dolphins use to propel themselves with such ease and efficiency

* Using the same technology in reverse allows energy to be extracted from water and tidal flows

* By externally moving a tube so as to generate an internal vortex, it is possible to devise more efficient mixers, coolers and heat pump based devices

For more technical developments see www.eurekamagazine.co.uk









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Опубликовано на: 2004-08-22 (4280 Прочтено)

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