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Scientists Discover Why Sharks Can Swim So Fast
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."
Wasn't this already known?
`echo $[0x853204FA81]|tr 0-9 ionbsdeaml`@gmail.com
... 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?
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.
Catapultam habeo. Nisi pecuniam omnem mihi dabis, ad caput tuum saxum immane mittam.
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.
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.
Warning: this article may contain humor, sarcasm, parody, and perhaps even irony. Read at your own risk.
I always knew fins had something to do with it....I just never actually thought someone would actually prove it...and waste our time!
you would get further with a shark chasing you.
liqbase
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?
Nothing complicated here. They move fast because they're hungry.
End of lesson. You may press the button.
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!
I only look human.
My mother is a halfling and my dad is an ogre, so that makes me an Ogreling
Can someone please convert this to metric time? I don't understand "hour".
I wonder how long before we start to see this applied to swimmers bodysuits?
Wasn't there a plan a few years back to use microelectromechanical systems to do the same thing on aircraft wings?
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.
This is at least a full order of magnitude larger than the scales on a shark's skin.
According to this source, the kolmogorov scale 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..
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.
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.
I was dubious about this science when I read the article, but I learned something in the end.
From the article:
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.
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?
No sig for you. YOU GET NO SIG!
Of course sharks raise their scales, it is called "goosebumps". That water is cold!
It is by the juice of the coffee bean that thoughts acquire speed, the teeth acquire stains. The stains become a warning
And I thought that sharks just swam faster because they were hungry.
"Who controls the past controls the future. Who controls the present controls the past." -- George Orwell
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
Want to learn about race cars? Read my Book
They're trying to get away from Michael Phelps.
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)
Sounds alot like Super-cavitation studied by US and USSR Navies for torpedoes that go stupid fast underwater.
Most interesting...
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
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.
I figured I'd break it out again and see if I could get a nibble....
We call this trolling.
"You're right," Fisheye says. "I should have set it on 'whip' or 'chop.'"