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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."
... 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?
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!
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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.
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.
Nothing complicated here. They move fast because they're hungry.
End of lesson. You may press the button.
Fail - you got first post on a sharks column and made no mention of frickin' lasers.
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..
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.
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.
Of course sharks raise their scales, it is called "goosebumps". That water is cold!
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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.
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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 explains it well.
That raises the question: why don't airplanes have dimples like a golf ball?
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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.
My guess is it would require a thicker sheet of metal to achieve this. This would result in added weight and thus lower efficiency.
Face your daemons!
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.
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.
Those who can, do. Those who can't, sue.
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.
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.
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
Does a Mustang that went through a hailstorm count?
Warning: this article may contain humor, sarcasm, parody, and perhaps even irony. Read at your own risk.