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Scientists Discover Why Sharks Can Swim So Fast

timothy posted more than 5 years ago | from the goosebumps-might-help-evade-them dept.

Science 103

MediaSight writes "Shortfin mako sharks can shoot through the ocean at up to 50 miles per hour (80 kilometres an hour). Now a trick that helps them to reach such speeds has been discovered — the sharks can raise their scales to create tiny wells across the surface of their skin, reducing drag like the dimples on a golf ball."

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new? (1, Redundant)

dmbasso (1052166) | more than 5 years ago | (#25719333)

Wasn't this already known?

Re:new? (3, Funny)

bigstrat2003 (1058574) | more than 5 years ago | (#25719365)

Indeed it was. We've known that the lasers make them go fast for years. I mean, come on guys, the lasers go at the speed of light, of course they make the sharks go fast!

Re:new? (4, Funny)

Notquitecajun (1073646) | more than 5 years ago | (#25719767)

Fail - you got first post on a sharks column and made no mention of frickin' lasers.

Re:new? (1)

dmbasso (1052166) | more than 5 years ago | (#25720539)

Actually I was just waiting for a reply like yours, so I can whole-heartedly say: GET OFF MY LAWN!!!

Thanx for being part of my Tao.

Re:new? (1)

drik00 (526104) | more than 5 years ago | (#25724765)

"Wasn't this already known?" is now modded as +1 Redundant.... ...~ Iiiirony ~

J

pew pew lazerz

Re:new? (1)

MrMr (219533) | more than 5 years ago | (#25720513)

Yes this was known before the 2000 Olympics.
here [findarticles.com]
But perhaps we had forgotten it since then.

Re:new? (2, Informative)

NeutronCowboy (896098) | more than 5 years ago | (#25722821)

Not the same thing. Sharkskin was indeed known for a while to present an extremely slippery surface. What these researchers found is an additional effect: that the sharkskin can raise the individual "teeth" so that a turbulent layer gets created. This turbulent water layer prevents flow dissociation, which in turn reduces drag.

There was a 2-man boat at the last Olympics that was using dimples in its coating rather than the fairly standard sharkskin approach - it didn't win, but it was noted due to its novely.

Re:new? (1)

cellocgw (617879) | more than 5 years ago | (#25723027)

Not the same thing. Sharkskin was indeed known for a while to present an extremely slippery surface. What these researchers found is an additional effect: that the sharkskin can raise the individual "teeth" so that a turbulent layer gets created. This turbulent water layer prevents flow dissociation, which in turn reduces drag.
I think it's a bit of both, i.e. previously known, and new info. IIRC, back when the USA won the America's Cup back down in Australian water, people knew that the rough surface on sharks' skin helped reduce drag. The new-er part seems to be the fact that sharks can raise or lower their scales/bumps as needed to adjust the turbulence factors.
Any fluid engineers out there?

Re:new? (1)

madprof (4723) | more than 5 years ago | (#25723433)

I thought FISA had banned that sort of surface? Clever, if not.

Re:new? (0)

Anonymous Coward | more than 5 years ago | (#25720735)

Of course it was known. All science is already settled.

So You're Saying ... (4, Funny)

Anonymous Coward | more than 5 years ago | (#25719363)

... that we need to figure out how to replicate this on the outside encasings of lasers so they don't slow down the frickin' sharks?

Re:So You're Saying ... (3, Funny)

crakbone (860662) | more than 5 years ago | (#25720791)

What is the average waterspeed velocity of a laser ladened shark?

Re:So You're Saying ... (0)

Anonymous Coward | more than 5 years ago | (#25720827)

What is the average waterspeed velocity of a laser ladened shark?

African or European shark?

Re:So You're Saying ... (1)

tmosley (996283) | more than 5 years ago | (#25720833)

Great White or Tiger?

Re:So You're Saying ... (0)

Anonymous Coward | more than 5 years ago | (#25725923)

Tiger or Snow Leopard?

Re: new? (4, Insightful)

Trubadidudei (1404187) | more than 5 years ago | (#25719407)

I think only the structure of the scales was actually known, sharks raising them to obtain a different skin texture is the new part here.
I bet all those athletes who paid handsomely for their "shark scale" suits are regretting that purchase just about, now.

Re: new? (-1, Troll)

Anonymous Coward | more than 5 years ago | (#25719523)

FAGGOT YOU'RE WRONG

Re: new? (1)

aproposofwhat (1019098) | more than 5 years ago | (#25720061)

The scale structure has been known for around 20 years - I first saw it in a product at 3M in around 1989 or so, and the guys responsible (it was a plastic film intended to reduce drag) were full of enthusiasm about it.

Being able to change the texture is pretty cool - to replicate that capability would be even cooler.

Re: new? (3, Insightful)

amorsen (7485) | more than 5 years ago | (#25720929)

I bet all those athletes who paid handsomely for their "shark scale" suits are regretting that purchase just about, now.

Considering how many swimming records have been set in the last year, I'd say that the suits work great.

Re: new? (0, Flamebait)

Grishnakh (216268) | more than 5 years ago | (#25721923)

That's not from any fancy suits, it's probably from steroids, the same reason athletic records of all kinds have been broken in recent years.

It's pretty much pointless to compare modern-day athletics to any historical records because of the extreme use of steroids now.

Re: new? (2, Insightful)

Paradise Pete (33184) | more than 5 years ago | (#25722467)

it's probably from steroids, the same reason athletic records of all kinds have been broken in recent years.

It's not a new phenomenon. Athletic records have been consistently being bettered for as long as they have been keeping them. I'm not denying enhancements, I'm just saying that the facts that records are falling is not by itself proof.

Re: new? (1)

Chris Burke (6130) | more than 5 years ago | (#25722689)

That's not from any fancy suits, it's probably from steroids, the same reason athletic records of all kinds have been broken in recent years.

It's pretty much pointless to compare modern-day athletics to any historical records because of the extreme use of steroids now.

Yes, it's from fancy suits. They didn't just invent steroids for swimmers. They did just invent a new type of suit, and since it's invention records have been falling far faster than before. Before, some potentially-juiced-up swimmer would cream an old record. But in this past Olympics, we had races where half the field was well ahead of the world record that had been set only a year or two before. How often does the 4th place finisher beat the old world record? Nearly every short distance record was broken by someone wearing the new suit. Neither drugs nor swimming techniques got that much better in that time period. Suits did.

That said, nothing about the suits seems to have come from studying shark skin in particular. They're about reducing drag via shape and ultrasonically welded seams, and increasing buoyancy with water repellent fabric. Shark scales don't enter the picture.

Re: new? (1)

SmokeyTheBalrog (996551) | more than 5 years ago | (#25729065)

Shark scales don't enter the picture.

But they should!

Re: new? (1)

drinkypoo (153816) | more than 5 years ago | (#25733051)

I'd bet good money that the particular effect we're talking about, while it is likely slightly relevant at human speeds, doesn't really make a big difference until you get up to shark speeds.

Is it just me (-1, Offtopic)

zygotic mitosis (833691) | more than 5 years ago | (#25719413)

Is it just me, or do the editors seem to look for any excuse to post a shark story? I mean, memes can only go so far.

Re:Is it just me (1)

LiquidCoooled (634315) | more than 5 years ago | (#25719743)

you would get further with a shark chasing you.

I have mod points but... (0, Offtopic)

Dareth (47614) | more than 5 years ago | (#25719763)

I see that some of the other sharks/moderators have already bit you in the ass.

"memes can only go so far"...

Next you will say we should give up on Natalie in hot grits! Heresy!

No walking on the submarines of tomorrow! (1)

K3ba (1012075) | more than 5 years ago | (#25719529)

If it works out that the drag is reduced significantly, I can see new submarines being coated with a shell of something that gives the same properties. No more crew on deck entrances to port though!

Underwater planes sound more fun of course.

Re:No walking on the submarines of tomorrow! (1)

K. S. Kyosuke (729550) | more than 5 years ago | (#25719949)

How about squeezing into one of those shiny new supercavitating torpedoes (after enlarging them a bit, of course)? Sounds like even more fun to me. ;-)

Re:No walking on the submarines of tomorrow! (1)

jandrese (485) | more than 5 years ago | (#25720993)

Isn't supercatavation basically an extreme form of the same basic principal?

Re:No walking on the submarines of tomorrow! (1, Informative)

Anonymous Coward | more than 5 years ago | (#25723511)

No, the principal is still in your school. He's asking you to take your grammar and spelling more seriously.

Re:No walking on the submarines of tomorrow! (1)

jandrese (485) | more than 5 years ago | (#25724097)

And I'm asking you not to be an ass. It appears that neither of us will go home happy.

Re:No walking on the submarines of tomorrow! (1)

idontgno (624372) | more than 5 years ago | (#25724545)

There is an upside, though. You can learn to spell. AC will still be an ass, now and forever.

Re:No walking on the submarines of tomorrow! (1)

drinkypoo (153816) | more than 5 years ago | (#25733067)

And I'm asking you not to be an ass. It appears that neither of us will go home happy.

Next time, use firefox and correct the spelling errors it underlines, then we can all go home happy. Or for that matter, stay home.

You ask him not to act like an ass, he expects you not to act like an idiot. I'd say that's a fair trade, and I'd suggest that you go first. After all, let peace begin with me.

Or put another way, instead of getting sand in your vagina, why don't you try to better yourself?

Re:No walking on the submarines of tomorrow! (0)

Anonymous Coward | more than 5 years ago | (#25733459)

A spelling checker can't correct usage of homophones, not even in Firefox. Such corrections require a grammar checker. In case there's any doubt, look up the words "principal" and "principle" and discover that they both exist.

Re:No walking on the submarines of tomorrow! (3, Informative)

wagnerrp (1305589) | more than 5 years ago | (#25725211)

Not at all. Supercavitation puts a small high frequency oscillator at the front of the submersible. While cavitation creates small air bubbles which form and collapse, supercavitation produces an entire cavity of air in the water which the submersible now flies through with reduced drag. It's reduction of drag through reduction of medium density.

This method energizes the flow, and induces a premature shift from laminar to turbulent flow. When a laminar flow encounters an adverse pressure gradient (large cross section to small cross section), it detaches from the surface creating large drag inducing vorticies. Think of the suction behind a semi, or other flat backed truck. By inducing turbulence in the flow, it has sufficient kinetic energy to remain attached to the surface, preventing drag. So called 'vortex generators' have been used for decades on aircraft to improve airflow over wings, allowing higher lift and lower drag.

I initially dismissed this, thinking the flow should have become turbulent, but at those speeds, water becomes turbulent after about 5 meters. However that means it would be of marginal benefit for anything but the control surfaces on a submarine.

Re:No walking on the submarines of tomorrow! (2, Interesting)

BlackSnake112 (912158) | more than 5 years ago | (#25720723)

Wouldn't the new shape be more likely to create noise? Subs want no noise at all. If the shape could change on the fly, smooth and slower to sneak up while rough and faster to get away.

Re:No walking on the submarines of tomorrow! (1)

m50d (797211) | more than 5 years ago | (#25725641)

No - reducing turbulence will reduce noise as well as allowing you to go faster. It really is a win on both fronts.

Re:No walking on the submarines of tomorrow! (2, Interesting)

fbjon (692006) | more than 5 years ago | (#25721135)

That raises the question: why don't airplanes have dimples like a golf ball?

Re:No walking on the submarines of tomorrow! (3, Insightful)

von_rick (944421) | more than 5 years ago | (#25721953)

My guess is it would require a thicker sheet of metal to achieve this. This would result in added weight and thus lower efficiency.

Re:No walking on the submarines of tomorrow! (4, Interesting)

pato101 (851725) | more than 5 years ago | (#25722863)

Because their Reynolds number is very big and their boundary layers are already turbulent.
The story is so oversimplified that raising questions from it is just pointless.
The facts are as follow:
1. Roughness tends to increase drag because makes boundary layers turbulent.
2. Turbulent boundary layers do stand higher adverse pressure gradients prior to separation
3. Separation increases drag much more than turbulent boundary layers.
Then, there are some applications where you would have a separated flow, and promoting turbulence through roughness would reduce the drag. This is not the case of aviation. It is not the case for sure of sharks when they are not moving their tails. It may be the case of sharks when they are moving their tails to obtain propulsion.

Re:No walking on the submarines of tomorrow! (1)

afidel (530433) | more than 5 years ago | (#25725491)

Actually Boeing was researching doing just that, both as a material change and using compressed air to create a virtual shape which could be controlled to allow a change in resistance for takeoff, landing, and cruise.

Re:No walking on the submarines of tomorrow! (1)

Sebilrazen (870600) | more than 5 years ago | (#25726495)

Actually, the booms on KC-135R do have these dimples and a raised chaotic surface. I used to repair them when boomers would raise them too quickly and smash them against the retaining hook. It was a bear fixing these surfaces due to the way the boom was shaped, adding in the weird surfaces? A repair that should take an hour took a whole afternoon.

Re:No walking on the submarines of tomorrow! (1)

pato101 (851725) | more than 5 years ago | (#25722779)

well, not necessary, since submarines Reynolds number (rho*V*L/mu) tends to be much bigger, and it may happen that the boundary layer is already turbulent.
I'm confused with the story itself, it is poorly written.
From my knowledge on fluid mechanics, turbulent boundary layers increase drag unless separation is avoided (turbulent boundary layers stand higher adverse pressure gradients prior to separation). I guess that what happens with sharks is that they can twist their tails with higher energy providing higher propulsion because the boundary layer withstands such pressure gradients generated thanks to the triggering to turbulent (which should not be the case because their low Reynolds number).
Of course, higher roughness would induce higher drag, so the evolution has found a right equilibrium for them.

This has been known for many years (5, Interesting)

Anonymous Coward | more than 5 years ago | (#25719591)

Back in the 80s we switched from polishing the bottom of our race boat to a glass like finish to spraying it with a gel mixture (as in gel coat, not jello) full of small oblong granules. We found that by spraying it a certain way we could get the particles to more or less line up in the orientation we needed. Careful polishing after the fact gave us the finish we were looking for without destroying this new, textured surface. We did this directly in response to an article I had read about how a sharks skin allows it to move quickly through the water. The article went further to say that this also applied to most all scaled fish.

This modification allowed the boat to break the surface tension of the water more easily when launching from a standing start and added several miles an hour to our top end speed. In a game where every mile an hour might cost 1000s or 10s of thousands of dollars this was *the* most effective modification we had ever done to the boat and one that to this day we joke about because it took our competition many years to figure out.

Re:This has been known for many years (2, Interesting)

n1ckml007 (683046) | more than 5 years ago | (#25720743)

Interesting AC. In Alpine ski racing a "pattern" is needed on the base of the ski for increased speed:

http://www.californiaskicompany.com/Ski_tune.html [californiaskicompany.com] (step 7)

Step Seven- New Structure on the base Much like a car tire, your ski has a tread pattern we call the structure. What type of structure works best depends on what kind of snow you typically ski in. Utah shops will run a different pattern on their skis than we do here in California. In any case this is the part that puts the pattern into the base. A very big stone is actually used for this process. This is the stone that makes us call the machine a stone grinder. We use a diamond to score a pattern into the stone. The stone is then used to cut this pattern into the ski. In addition, the stone is very precise and ensures that the ski base is perfectly flat and even.

Re:This has been known for many years (0)

Anonymous Coward | more than 5 years ago | (#25724279)

That sounds like it is done more for traction then speed. Interesting read though.

Re:This has been known for many years (1, Interesting)

Anonymous Coward | more than 5 years ago | (#25721925)

The placebo effect is powerful, yes?

In all honesty, without knowing the flow conditions existing on the hull surface, there is just as good a chance that you increased drag (increased skin friction with a fully attached flow) as decreased it (tripped the laminar boundary layer into turbulence and delayed flow separation). Without a carefully controlled experiment, you probably just attributed speed increases from outside sources to your new, expensive hull finish.

You probably would've done better with keel winglets, but again, that's something that must be designed with knowledge of the existing flow conditions.

Re:This has been known for many years (1)

RedBear (207369) | more than 5 years ago | (#25727559)

It's just like my father has always said to me. Every 20-30 years any particular bit of knowledge is "discovered" and it's almost never the first time. Many examples can be found of knowledge being repeatedly discovered and forgotten periodically sometimes dozens of times over decades or centuries. The only reason we've gotten this far now is because we've learned to record and reference information accurately.

I would also venture to point out that scientists did not just "discover" why the mako shark can swim so fast. They discovered that mako sharks can raise their scales to create the surface divots that _explain_ why they can swim so fast. We already knew decades ago why the pitted surface of a golf ball allows it to go so much further than a smooth surfaced ball of the same size and mass.

What gets me is how many boats today are still made with smooth hulls when we've technically known for so long that it isn't the ideal surface to minimize drag. A guy I know locally used to teach a class at the community college on how to make a kayak out of a light wooden frame covered by a rough linen/cotton cloth sealed with boiled linseed oil or something. He said those boats were faster in the water than any commercial plastic or fiberglass kayak. There had to be a reason for that.

Billions of gallons of fuel has been and is being wasted just battling surface tension. The same goes for airplanes and cars. It will take them another 20 years to "discover" that a bumpy-surface airplane or car is faster and/or more fuel efficient and actually start putting it into practical use.

Re:This has been known for many years (0)

Anonymous Coward | more than 5 years ago | (#25727625)

Doesn't Lexus now put dimples in the underside of their cars to reduce drag and noise?

Re:This has been known for many years (1)

Michael Snoswell (3461) | more than 5 years ago | (#25730651)

You can buy sheets of roughened film to still to the hull of your boat to provide the same effect. Not sure what it's called, but no doubt someone like 3M sell it.

No Discovery About Sharks (4, Insightful)

John Hasler (414242) | more than 5 years ago | (#25719631)

From the article I conclude that the researchers have performed an experiment that indicates that if sharks do raise their scales while swimming it might allow them to go faster. They've discovered nothing about what sharks actually do.

I always knew... (0, Troll)

hesaigo999ca (786966) | more than 5 years ago | (#25719719)

I always knew fins had something to do with it....I just never actually thought someone would actually prove it...and waste our time!

WRONG (0)

Anonymous Coward | more than 5 years ago | (#25719745)

The REAL reason they swim so fast is that the lasers heat the water before they swim through it, thereby reducing the polametric drag on the dorsal fins. Or something. Right?

Hydrodynamics? Bah. (4, Funny)

Verteiron (224042) | more than 5 years ago | (#25719749)

Nothing complicated here. They move fast because they're hungry.

Re:Hydrodynamics? Bah. (4, Funny)

jollyreaper (513215) | more than 5 years ago | (#25719893)

Nothing complicated here. They move fast because they're hungry.

And people taste like snausages.

80 kilometres an hour? (0)

Anonymous Coward | more than 5 years ago | (#25719855)

Can someone please convert this to metric time? I don't understand "hour".

Re:80 kilometres an hour? (1)

Sique (173459) | more than 5 years ago | (#25720403)

About 22 m/s ;)

Re:80 kilometres an hour? (1)

colinrichardday (768814) | more than 5 years ago | (#25729057)

1 hour = 3.6 kiloseconds (exact)

Elite swimming (1)

aussiedood (577993) | more than 5 years ago | (#25719881)

I wonder how long before we start to see this applied to swimmers bodysuits?

aircraft wings and MEMS (1)

BenJaminus (472372) | more than 5 years ago | (#25719905)

Wasn't there a plan a few years back to use microelectromechanical systems to do the same thing on aircraft wings?

Re:aircraft wings and MEMS (1)

vbraga (228124) | more than 5 years ago | (#25720719)

You're probabily talking about boundary layer suction [wikipedia.org] . It looks similar to me, but I don't enough fluid dynamics to be sure.

Re:aircraft wings and MEMS (1)

wagnerrp (1305589) | more than 5 years ago | (#25725367)

On the back half of a wing, the boundary layer needs sufficient kinetic energy to remain attached to the surface. By sucking off the static air, moving air would take its place and keep the flow laminar out to the trailing edge. The MEMS devices were small diaphragms inserted into cavities in the wing surface. Rather than remove the static boundary layer, they would oscillate and energize the existing boundary layer, achieving the same effect with considerably less power and substructure.

Re:aircraft wings and MEMS (1)

CarbonShell (1313583) | more than 5 years ago | (#25730255)

Yes and iirc the fuel savings for commercial airliners were about 6%.

Nitpicking (5, Informative)

Anonymous Coward | more than 5 years ago | (#25720129)

The article mistates several things

First, the turbulent layer formed by the raised scales does not act as a buffer and will actually cause more surface drag on the shark than a smoother layer (if the scales were flat, for example).

Second, the scales do not prevent a turbulent wake, they create it.

The way this reduces drag is reasonably straightforward and has to do with the boundary layer.

In an idealized model (no friction) you would calculate that any object has zero drag, or net force from the air acting on it. You would integrate the force of the air pressure acting on all sides of the object and get zero. If you are looking at a circular cross section object, you have high pressure at the leading point, very low pressures at the top and bottom, and high pressure again at the trailing point, for a net of zero drag.

However, what happens (aside from the usually small effect of friction) is that the boundary layer "seperates" from the object, so (back to our circle) you have high pressure in front, low pressure on the sides, and then the boundary layer seperates from the object and you wind up with low pressure in the back, too. So, high pressure in front, low pressure everywhere else, you have drag.

The way that golf balls (and sharks, apparently) attack this problen is to screw with the boundary layer flow. They "trip" the flow (using dimples or raised scales) into a turbulent boundary layer. This boundary layer creates more friction drag than a viscous (smooth) boundary layer, but because the particles in the boundary layer are moving every which way (it's a higher energy boundary layer) it will remain attached to more varying geometries than a viscous boundary layer will, so it won't seperate (or at least it won't seperate as early) from a shape like a golf ball or a shark, so you've reduced pressure drag by increasing viscous drag.

This usually works out in your favor, viscous drag is usually nearly negligible next to pressure drag.

I think the whole thing is very cool.

Re:Nitpicking (1)

mapsjanhere (1130359) | more than 5 years ago | (#25721523)

It's also important to mention that it's a speed dependent phenomenon. I remember a discussion about this when they started with dimpled motorcycle helmets that, in air, the effect only works around 100 mph and up, and was useless for the average motorcycle driver. In water, with it's higher density, this regime seems to be effective at much lower speeds, so I haven't seen any dimpled submarines, yet.

Re:Nitpicking (0)

Anonymous Coward | more than 5 years ago | (#25721725)

Not quite, it's Reynolds number dependent, where

Re = (density*velocity*length scale)/viscosity

Re:Nitpicking (1)

mapsjanhere (1130359) | more than 5 years ago | (#25722147)

As I said, higher density means lower required velocity to transition from laminar to turbulent flow. The change in density is about a factor of 20 higher than the corresponding change in viscosity.
And Reynolds numbers aren't really applicable in transition regimes, but I'm not digging out my BSL.

Re:Nitpicking (1)

quacking duck (607555) | more than 5 years ago | (#25726545)

In water, with it's higher density, this regime seems to be effective at much lower speeds, so I haven't seen any dimpled submarines, yet.

Since most submarines in the world are the military type, would not a dimpled/scaled hull, which would cause turbulence even while allowing the sub to go faster, defeat the whole purpose of having a sub--to go places undetected?

Re:Nitpicking (1)

mapsjanhere (1130359) | more than 5 years ago | (#25726689)

I'm afraid the answer to that question is one of those that gets black helicopters flying over your house ;)
My guess is that the hydrodynamic flow around the stern of advanced submarines is so optimized that you don't get a loss of laminar flow along the surface - in that case the dimples would actually make things worse.

Re:Nitpicking (1)

quacking duck (607555) | more than 5 years ago | (#25727189)

I'm afraid the answer to that question is one of those that gets black helicopters flying over your house ;)

Don't worry, I'm in Canada, we can't afford black helicopters ;-)

Re:Nitpicking (0)

Anonymous Coward | more than 5 years ago | (#25722455)

so how does this give better gas mileage?

Re:Nitpicking (1)

wagnerrp (1305589) | more than 5 years ago | (#25725409)

Take out your pick axe and put some speed holes in your car.

Re:Nitpicking (1)

nacturation (646836) | more than 5 years ago | (#25726341)

Thank you for the clear explanation, AC. This is exactly the reason why I like reading about this kind of news on Slashdot -- the real story is in the comments.

Re:Nitpicking (0)

Anonymous Coward | more than 5 years ago | (#25729837)

some wonderful movies demonstrating the Fluid Dynamics of Drag can be found here:
http://web.mit.edu/hml/ncfmf.html [mit.edu]

What about Kolmogorov? (2, Interesting)

tick-tock-atona (1145909) | more than 5 years ago | (#25720187)

The team created artificial shark skin with a 16 x 24 array of synthetic scales, each 2 centimetres in length and angled at 90Â to the surface of the "skin".

This is at least a full order of magnitude larger than the scales on a shark's skin.

According to this source [google.com.au] , the kolmogorov scale [wikipedia.org] in the ocean is in the order of 1mm. Therefore, is the effect described in TFA going to actually be present for shark's skin? It seems to me that the effect will be minimal, if it is present at all..

I'm such a nerd (1)

jonaskoelker (922170) | more than 5 years ago | (#25725351)

I'm such a nerd.

I read "What about Kolmogorov" and instantly thought about how I could write a shortest possible program that outputs your post.

(http://en.wikipedia.org/wiki/Kolmogorov_complexity)

will this work on cars? (0)

Anonymous Coward | more than 5 years ago | (#25720319)

Maybe the answer to 50+ mpg is to NOT have a super smooth surface which creates a pulling wake behind the vehicle but a dimpled surface.

Ever have a Landau top? (1)

DG (989) | more than 5 years ago | (#25721831)

Don't you remember all the cars back in the 80's that had textured vinyl (Landau) tops?

That was a direct response to the fuel crisis of the mid 70's. The pebbled texture of the vinyl roof allowed the boundary layer to remain attached longer and directly reduced the amount of drag on the vehicle, increasing fuel economy my a couple of MPG.

A couple of clued-in NASCAR teams adopted it for their race cars.

Sadly, the vinyl roof was subject to the whims of fashion and styling and died out in the 90's - just in time for electronic fuel injection and real-time O2 sensor feedback to make milage gains on the powertrain side.

With the current fuel crisis, I imagine we might see the return of the vinyl roof.

DG

Re:Ever have a Landau top? (1)

bzipitidoo (647217) | more than 5 years ago | (#25725865)

Never thought a vinyl roof had anything to do with fuel economy. Not sure I believe it either. Surely a much easier way to achieve a textured top is texture the metal, or possibly the paint?

Every time we got stuck with a car with a vinyl cover over a metal roof, we'd rip the thing off and paint the metal underneath. Exterior vinyl roofs on cars that already have metal roofs are stupid. I always thought of them as particularly obnoxious fashion whims. High maintenance, adds weight, traps water and rusts the roof out faster, and for all that you're suppose to pay more?!

Re:Ever have a Landau top? (1)

drinkypoo (153816) | more than 5 years ago | (#25733093)

You're hilarious. There's no need to do that with vinyl. And the bullshit vinyl roof was just one more thing that had to be thrown away. And that assumes I believe you, anyway. If they really wanted to reduce drag, they would have redesigned the cars of the day not to look like a concrete bunker.

Re:Ever have a Landau top? (1)

DG (989) | more than 5 years ago | (#25733349)

Heh.

My parent post is actually an obscure reference to a running gag perpetrated during the early 90's by Circle Track magazine - back when it was a technical mag and not "NASCAR People"

One of their readers wrote a letter to their tech column asking about the Landau tops he had seen on a couple of NASCAR Winston Cup cars (this was back in the days when Stock Cars really started life as factory-floor "stock" cars) and if said Landau tops had conferred any sort of racing advantage.

The Circle Track tech staff - who at the time included one Smokey Yunick - jumped on it, provided the "golf ball boundary layer" explanation, and a legend was born.

I figured I'd break it out again and see if I could get a nibble....

DG

Dimples on golf balls don't reduce drag (1, Informative)

Anonymous Coward | more than 5 years ago | (#25720543)

They actually increase it! What they do is exploit the Bernoulli effect and create lift so the ball goes further away before coming down again.

While I don't question the conclusions of the researchers, I do doubt that comparing sharks to golf balls is a good analogy. I haven't read TFA so I don't know if the golf ball analogy is by the submitter or the scientists but at any rate, it seems wrong.

Re:Dimples on golf balls don't reduce drag (3, Informative)

butalearner (1235200) | more than 5 years ago | (#25721009)

Dimples increase surface drag, yes, but they greatly reduce what is almost always the most significant drag force, the drag caused by the flow separating from the ball.

The reason we don't use dimples on cars or planes is because the situation is reversed - the surface drag is the most significant factor, so it's better to have a mostly smooth surface.

This link [aerospaceweb.org] explains it well.

Re:Dimples on golf balls don't reduce drag (1)

wagnerrp (1305589) | more than 5 years ago | (#25725465)

Actually, its the spin that exploits the Bernoulli effect, and specifically backspin that gives it lift. Spin sideways and you end up with a slice.

WTF?? - Ah! (5, Interesting)

IcyHando'Death (239387) | more than 5 years ago | (#25720583)

I was dubious about this science when I read the article, but I learned something in the end.
From the article:

The team created artificial shark skin with a 16 x 24 array of synthetic scales, each 2 centimetres in length and angled at 90 to the surface of the "skin".
They then placed the arrangement in a stream of water travelling at a steady 20 centimetres per second.

Shark scales are tiny - the crown is barely visible to the naked eye. So these scientists have scaled them up (so to speak) at least 2 orders of magnitude. With fluid dynamics the scale of a model can change everything, especially in the range of sizes they are working with here. I thought they should have substituted a more viscous fluid for the water in order to get a useful model. I thought maybe this was just preliminary work and they'd do a better study if their results suggested that it could be valuable."

But before flaming the Slashdot editors for trumpeting this study as a "discovery", I did a little Googling and quickly wound up at Wikepedia learning about Reynolds numbers. Turns out you can model turbulence pretty accurately as long as the Reynolds number stays the same. In this case the Reynolds number is proportional to both the size of the shark scales and the velocity of the water flow, so it can be preserved while the scales are made larger if the velocity is reduced proportionally.

Which is exactly what they did. They're studying sharks swimming at 80 km/hr.

80km/hr = 8,000,000 / 3600 cm/sec = 2200 cm/sec

Or, about 100 times faster than the flow rate they used in their model. Neat.

Re:WTF?? - Ah! (4, Informative)

tick-tock-atona (1145909) | more than 5 years ago | (#25721425)

There's still a problem with this - The Kolmogorov scale [wikipedia.org] is all about the smallest scales at which turbulence can occur in a fluid. It is effectively a fundamental constant in a fluid (can fluctuate in time/space, but usually treated as a field constant). Now, according to this source [google.com.au] , the K-scale in the ocean is in the order of 1 mm. This means that while vortices may form easily behind 2cm high "scales", they probably do not form so easily behind real shark scales which are an order of magnitude or two below 2cm in length. I believe this is what TFA meant in this part at the end:

Sergei Chernyshenko, an aeronautical engineer from Imperial College London, UK, describes the research as fascinating. However, he points out that while the team have shown the existence of vortices, they haven't yet quantified the extent of the effect on the shark's drag, which he thinks could be minimal.

Evolution wins (0)

Anonymous Coward | more than 5 years ago | (#25726057)

Dunno about the fluid dynamics, but sharks have been evolutionary stable for a *long* time - if it's there, you can bet it gets used and it works. Nature is the ultimate empiricist.

Dimpling on race cars? (1)

LoudMusic (199347) | more than 5 years ago | (#25720673)

We've been dimpling golf balls for a long time. I've often wondered why they haven't done dimpling on race cars. Does it also create lift or something?

Re:Dimpling on race cars? (2, Interesting)

iksbob (947407) | more than 5 years ago | (#25721557)

Well, if you're talking about devices that cause turbulence for the sake of boundary-layer adhesion, vortex generators have been in use on aircraft for years. More recently, they have been adapted to automotive use. Take a look at the trailing edge of the Lancer Evolution IX's roof... It has a line of 8-9 (if you count the antenna) vortex generators.

Re:Dimpling on race cars? (1)

bzipitidoo (647217) | more than 5 years ago | (#25726003)

I saw just one model that uses dimples. The trailing edges of the sides of the Corbin Sparrow [corbinsparrow.com] have dimples, and you can see the dimples in those pics. Anyone know of any others?

Re:Dimpling on race cars? (2, Funny)

John Hasler (414242) | more than 5 years ago | (#25727541)

Does a Mustang that went through a hailstorm count?

Re:Dimpling on race cars? (1)

drinkypoo (153816) | more than 5 years ago | (#25733131)

The dimples on a golf ball not only increase its travel but also its controllability. They're what make a spinning golf ball hook significantly one way or the other.

Brrr! (3, Funny)

Hoi Polloi (522990) | more than 5 years ago | (#25720769)

Of course sharks raise their scales, it is called "goosebumps". That water is cold!

Re:Brrr! (1)

weirdcrashingnoises (1151951) | more than 5 years ago | (#25724611)

human is to goose
as shark is to _____?

a) goose
b) human
c) squirrel
d) cowboy (you know the one)

i think i'll go with C.

therefor sharks have Squirrelbumps.

Gee! (1)

OhHellWithIt (756826) | more than 5 years ago | (#25721535)

And I thought that sharks just swam faster because they were hungry.

Why do sharks swim so fast? (0)

Anonymous Coward | more than 5 years ago | (#25722285)

They're trying to get away from Michael Phelps.

Sounds like super-cavitation (0)

Anonymous Coward | more than 5 years ago | (#25725563)

Sounds alot like Super-cavitation studied by US and USSR Navies for torpedoes that go stupid fast underwater.

Most interesting...

NASA discovered this years ago (2, Informative)

figleaf (672550) | more than 5 years ago | (#25725845)

In fact a sharkskin like surface was added to Stars and Stripes racing yacht. Stars and Stripes scored a 4-0 sweep in America Cup in 1987.
The technology provided such a tremendous advantage that it was banned in subsequent years of America Cup

http://www.nasa.gov/centers/langley/news/factsheets/Riblets.html [nasa.gov]

Re:NASA discovered this years ago (1)

drinkypoo (153816) | more than 5 years ago | (#25733155)

The technology provided such a tremendous advantage that it was banned in subsequent years of America Cup

That's something that's always chapped my hide. Instead of expecting other competitors in racing to improve, generally speaking we just ban the things that allowed them to win. This happens constantly in auto racing; SCCA moved the 240SX from E to D class where it had to compete with cars with vastly more power, because it was doing too much winning. They changed restrictions specifically to eliminate Ford's GT40 from LeMans because it won too much. Why not just set a maximum dollar value if you want to level the playing field?

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