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.
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.
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.
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.
Vortex Oscillation Technology
email Dr Evgeny Sorokodum
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