Thursday, 2 October 2014

Back To Nature

It is not uncommon to come across technology borrowing inspiration from mother nature and the shipping industry has not been late in adapting to the trends. Natural systems are often quite efficient. Sometimes when faced with complex challenges in design and construction, it is often fruitful for us us to take clues from the billions of years of the process of evolution which has selected only 'fit' designs.

Today, the technologies which you are about to get introduced to are all potential breakthrough technologies which may one day become reality. We shall talk of bio-mimicry and the use of live organisms for various purposes in marine systems. 


Biofouling


Bioflouling is the build-up of both micro/macroscopic organisms on surfaces of the ship exposed to the sea i.e. primarily the hull and adds to the fuel consumption of a vessel from years of accumulation as a result of which there is an increase in the environmental effects like release of oxides of sulphur and carbon. All of these are caused due to the increase in the hydrodynamic drag from the increased mass and it's resulting interactions with flowing water, both slow and fast.

As in other cases, the technologies which we have come up with for reducing biofouling which are nature inspired have significantly reduced costs, wastage of resources.In this case, the skin of sharks seems of interest to researchers.
Fig. 1: A close up of shark skin 
(Image Courtsey: biomimicryinstitute.org)


The microscopically small individual scales of shark skin, called dermal denticles or “little skin teeth”, are ribbed with longitudinal grooves which result in water moving more efficiently over their surface.
Over smooth surfaces, fast-moving fluids begin to break up into circulating currents, or eddies, due to the velocity gradient which exists across layers. These eddies are reduced in number by this kind of surface venation.Some of the features are:

(1) The grooves channelize the flow as evident from the figure.They also reduce the sizes of vortices by dividing the water 
sheets areas into smaller ones, an approach somewhat analogous  to reducing eddy currents in transformers by dividing the area into smaller compartments.

(2) They speed up the slower water at the surface by reducing the area of outflow which means same volume flow happens through a smaller volume (consistent with mass conservation), reducing the surface flow velocity gradient with respect to the shark skin.

Think about it, who knows someday we might even come up with latest improvements like biomorphic mineralization applicable to creation of marine materials.


Hydrophobic Hulls


The water fern, by nature is super hydrophobic, which means it does not get wet even when immersed because of small, fibrous hair that keep a thin layer of air close to the plant's body. 


Fig. 2: Hydrophobic hulls may be next 
big innovation in Hull Engineering 
(Image Courtsey:Google Images)
Ships consume more fuel with increasing drag on the hull. Bio-mimicry research has been looking looking forward to water fern for to help ships move faster and save energy resources.It is said that the researchers can design container ships having hulls with similar super-hydrophobic properties, keeping a layer of air between water and vessel hull.

If researchers could design container ships that have hydrophobic hulls, fuel costs and emissions could be reduced by as much as a valuable ten percent.


Considering that global shipping emission estimates stood at around 850 million tons of CO2 in 2007 which is nearly 3 percent of man-made emissions that year, this is definitely no minor reduction. The researchers estimate such technology could trim a full percent off global fuel consumption.


Submarine Designs


"Most fish wag their tails to swim. A stingray's swimming is much more unique, like a flag in the wind," Richard Bottom, a mechanical engineering graduate student at the University at Buffalo, said in a statement.


Fig. 3: 3D Maps of the way vortices flow around swimming Stingrays 
(Image Courtsey: www.livescience.com & Richard Bottom)


A study by the students at Harvard University and University at Buffalo focused on motion of Stingrays, which are cartilaginous fishes.They studied the dynamics of motion of their round and flattened bodies and how they appear to 'ripple' through water. The ''Leading Edge Vortex'', as it is so called because of it being at the front of a body in motion, creates the low pressure at the front and high at the end.

Although a common phenomenon in birds and insects, this seems to be the first case of the phenomenon being observed in underwater motion.


Strait Power Turbines


The inspiration for designs from sharks are not only limited to anti fouling materials. It is seen that a shark, which in this case is the basking shark, spends a larger part of the day open mouthed, in the process it allows water to enter through its mouth and out through the gills while aiding in swimming.

Fig. 4: Concept rendition of the the principles of fluid movement 
in a basking shark
(Image Courtsey: www.designboom.com/)

Industrial Designer Anthony Reale’s Strait Power provides a highly efficient redesign 
of water-powered turbine generators. Given below is a 3-D rendered model of the pressure differential and water movement that is responsible for the high energy efficiency of ‘strait power'.


Fig. 5: Artistic rendering of the pressure differential and water movement that is responsible for the high energy efficiency of ‘strait power'
(Image Courtesy: www.designboom.com)

Fig.6: Rendered structural images of ''Strait Power'' prototype 
(Image Courtesy: www.designboom.com)

The team calculated that this prototype already improves power output of a single turbine blade by 40%, a figure Reale expects to improve in later versions.



Air bubbles against drag

The next source of inspiration from Mother Nature comes from these lovely creatures inhabiting the Polar Regions. Penguins use air bubbles for lubricating their passage in water. This concept is being applied to vessels for improving their performance by increasing their efficiency and lowering the drag. Sounds pretty routine? Here's something to note however, the penguins release the bubbles from the air trapped in their feathers.

Ships however use a air bladder to exploit this effect. At the stem of the ship, a combination of compressors and shell cavities release the stream of pressurised air bubbles which form a carpet along the hull of flat bottomed vessels. This technology has been used for trials onbaord oil tanker vessels with increase in efficiencies averaging around 4%.

Fig.7: Penguins surging through water. Note the air bubble stream behind them.
(Image Courtesy: www.bbc.com)

The first commercial installation of the technology, (now known as) Silverstream® system is expected to be fitted on a Norwegian cruise liner. This technology could improve ship energy efficiency by more than 5%.



Fig.7: Schematic representation of the Silverstream® Technology
(Image Courtesy: www.shell.com)

What Else


We often think of how to implement intelligent control and automation of tasks which have been traditionally solved by humans.One school of thought often suggests-''Why not use humans to carry out automated tasks?'', on similar lines, another school suggests- ''Why not use biological organisms to do the same? ''.How far can this idea go?

Something you might however point out against the first school of thought is that there is a desire to remove the need for humans to perform simple and boring repetitive tasks so that they can pursue more enjoyable and involving tasks.LSD



Article By: Sudripto Khasnabis

Recommended Readings: 

3. Bio-mimicry for Optimization, Control, and Automation (Book) By Kevin M. Passino


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