Sharkskin Paint

September 25, 2011 at 4:47 pm

The idea of shark attacks has terrorized humans for years, helped along by movies like Jaws. When we imagine them, we mostly think about the sharks’ vicious, powerful jaws, filled with hundreds of razor-sharp teeth that are so adept at killing. But what we don’t always think about is how they swim quickly, efficiently, and silently through the water towards their prey. What gives them this extra advantage?

Sharkskin isn’t smooth like many other fish, but instead made of many tiny, ridged scales called  dermal denticles (pictured below). These ridges are arranged very close together and parallel to the shark’s direction of motion. While the dermal denticles have many functions, one of them is clearly to reduce a shark’s drag while swimming.

Close-up of the dermal denticles.

Close-up of the dermal denticles.

Drag, as we learned in class, is a force that acts on objects opposite to their direction of motion, when in a fluid like air or water. Engineers try to achieve laminar flow of fluid around an object, because then drag is often proportional to velocity (Fd ∝ v). But when flow becomes turbulent, Fd ∝ v2, so the drag force shoots up.

A shark without ridges would feel a turbulent flow of the water layer just above its skin, resulting in a large drag force. But with the ridges, the boundary layer of water is directed so there is little turbulence. It may seem strange that a rough surface is better suited for smooth swimming, but idea is not unheard of. For example, without their dimpled surfaces, golf balls would not be as aerodynamic.

Aircraft engineers have recently been looking to mimic the ridges of sharkskin. Airplanes are subject to a very large drag force, and 40% of that comes from turbulence on the boundary layer. Scientists at the Fraunhofer Institute in Germany have developed paint for aircrafts that is inspired by sharkskin. The paint is made out of nanoparticles, and when applied using a special stencil, it forms grooves on the surface of airplanes, reducing the drag force.

This innovation has large environmental impacts. Engineers estimated that the paint reduces skin friction by 4-7%. This means that much less fuel is used up opposing the force of drag. If every airplane in the world used this paint, this could mean saving 4.48 million metric tons of fuel per year – good news for anyone cringing at the current gas prices.

So, next time you watch Jaws, keep an eye out for those energy-saving denticles – not just the terrifying teeth.

References

Anitei, Stefan. “The Shark Coating – Softpedia.” Latest News – Softpedia.

Reals, Kerry. “Aircraft Engineers Turn to Biomimicry for Greener Designs.” Aviation News and Aviation Jobs from Flightglobal.

“‘Sharkskin’ Paint Could Make Planes, Ships More Fuel-efficient.” Greenbang – Smart Technology Analysts.

“Skin of the Teeth.” ReefQuest Centre for Shark Research Home. Web. 25 Sept. 2011.

By Hersh Bendre | Posted in student post | Tagged , , | Comments (3)

Robots in Disguise

September 25, 2011 at 3:32 pm

robug

Cornell University has recently been working on perfecting the replication of insect flying techniques in robots.  While not a new idea, their approach uses new technology to make the process of creating the robot less time-consuming and faulty.  The wings of the rob-insect were created using a 3-D printer in order to achieve the optimal wing shape and consistent wing size. In total, the wings weigh 3.8 grams, allowing the robot to carry a payload of 1.5 grams, meaning it can barely carry its own batteries.  With these two small advancements though, not only can the robot hover for 85 seconds, it can also do an untethered and controlled descent.  In order to keep it stable during untethered flight, the researchers attached stabilizers to the top and bottom, as shown in the video.  Yet there is still much more work to be done, as batteries are still too heavy, and flapping flight is too unstable.  The technology is still far from perfect. One day, the Army hopes to use robo-insects as mini spy planes.  Just dont expect to be flying on a plane with flapping wings any time soon ...

References

By Matthew Farmer | Posted in student post | Tagged , , | Comments (1)

Bernoulli’s Principle Explained:

September 25, 2011 at 2:51 pm

Before we begin here's a few definitions to make following this post easier.

1. Kinetic energy - noun. the energy of a body or a system with respect to the motion of the body or of theparticles in the system.

2. Potential Energy - noun. the energy of a body or a system with respect to the position of the body or thearrangement of the particles of the system

Birds, planes, and everything else with wings are able to fly because of lift, the phenomenon explained by Bernoulli's Theorem and Equation.

They are as follows:

Bernoulli's Theorem: "...the total mechanical energy of the flowing fluid, comprising the energy associated with fluid pressure, the gravitational potential energy of elevation, and the kinetic energy of fluid motion, remains constant."1

Bernoulli's Equation:

\tfrac12\, \rho\, v^2\, +\, \rho\, g\, z\, +\, p\, =\, \text{constant}\,

This equation may look difficult and confusing but if we break it down its extremely manageable. Lets begin by looking at the underlying principle.

Essentially what Bernoulli found was that the sum of all of the energy in a system, from all sources ie. potential energy, kinetic energy, and the internal energy from fluid pressure, adds up to a constant. This can be seen in the equation above.

The formula for kinetic energy of a fluid is 1/2 times the density of the fluid times the velocity its moving squared. Velocity is given by V and density by the Greek letter rho ρ. This is the first part of Bernoulli's equation.

The formula for potential energy of a fluid is the density times the acceleration due to gravity times the height of the fluid above the source of the gravity (normally earth). Acceleration from gravity is given by g and the height is given by z.

The final part is simply the pressure of the fluid given by p.

Now, why is this important at all? Who really cares if they add up to some constant that seems to mean nothing? Well its important because the identical fluids will always have the same constant. So if you can calculate how changing one variable effects the others. For example, we can change the velocity at which a fluid flows, and calculate from the expression what the change in pressure would be if we kept the other variables constant.

This allows us to get back to flight, and the applications of the Bernoulli Equation. Airfoils (wings are essentially big airfoils), cause the air above the wing to be at a lower pressure than below the wing because of their shape. Lower pressure means the air above the wing moves faster. Recall that as you decrease pressure you need to increase one of the other variables to still equal the constant. If the fluid is moving horizontally (or the wing is moving through the fluid horizontally) the height and acceleration due to gravity wont change. The fluids density wont change either so the only way for it to equal the same value is if the velocity of the fluid increases. This continues to keep the pressure low and air speed fast on the top of the wing. On the bottom it is the exact opposite, higher pressure means lower fluid velocity.

Now, Bernoulli's equation only shows that there will be a difference of pressure between the top and the bottom of a wing. The fact that this generates an upward force is an other topic all together, but the point is that it does. The pressure difference leads to a force that counters the weight of the object enabling it to stay in the air with out falling.

Here is a video that explains how Bernoulli's Principle works with examples other than wings and flight.

And that is how Bernoulli's theorem works and why it is important.

References:

1. "Bernoulli's Theorem (physics)." Encyclopedia - Britannica Online Encyclopedia. Britannica Online Encyclopedia. 25 Sept. 2011.

2. "Bernoulli's Principle." Wikipedia, the Free Encyclopedia. Wikipedia. 25 Sept. 2011.

3. Fishbane, Paul M., Stephen Gasiorowicz, and Stephen T. Thornton. "16-7 Bernoulli's Equation." Physics for Scientists and Engineers. Upper Saddle River, NJ: Pearson/Prentice Hall, 2005. Print.

By Ryan Erf | Posted in student post | Tagged | Comments (3)

Robotic Flies at Harvard

September 24, 2011 at 4:31 pm

Researchers from Harvard and UC Berkeley have collaborated to build a 60-milligram robotic fly, the smallest scale biomimetic device ever created. Although the robot is currently only capable of tethered vertical flight, the technology could one day lead to miniature drones with military or rescue functions.

Houseflies, and all insects capable of flight, are extremely efficient in their movement. “Developed” over millions of years, it’s extremely difficult to reproduce a fly’s ability with out current technology. Trying to reproduce it on such a small scale is even harder. "Simply scaling down existing macro-scale techniques [would] not come close to the performance that we need," says Robert Wood, an engineering professor at Harvard and the researcher leading the robotic-fly project.

Wood’s team was thus forced to fabricate all of their parts in-house with laser micromachining. Small carbon-polymer joints were able to twist and rotate in almost the same manner as an actual fly. The carbon-fiber wings are required to create two to three times more lift than a fixed-wing aircraft, but the team’s robot is able to perfectly mimic a real fly’s takeoff.

The robotic fly has 15-millimeter wings that beat 110 times per second.

From here, the team is looking to integrate flight controllers, so that the fly could maneuver in all directions, and an onboard power supply. Sensors and flight software so that the robot can avoid obstacles is likely a ways away, but is the logical next step towards functional drones. In the near future, drones developed from Wood’s robotic fly could be spying for the CIA or locating earthquake victims in a collapsed building.

References:

1 "Robotic Insect Takes off", R Ross, Technology Review. MIT. (2007)

2 "An Insect's Role in the Development of Micro Air Vehicles", M Camper [pdf]

Links:

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The Flying Fish!

September 23, 2011 at 5:05 pm

Resident of both sea an sky, the Flying Fish is often seen gliding above the water and maneuvering away from predators with ease.

The term "Flying Fish" is a broad nickname for the Exocoetidae family which contains over 40 different species of flying fish. These species can be seperated, roughly, into two different groups - a two wing and a four wing flying fish. Both groups have unevenly forked tails which help them taxi when preparing to fly, but the four-winged fish has a higher clearence capacity because of its increased wing area.

These fish have evolved to deal with both the water and air, in an attempt to escape the many predators they have beneath the surface. They can hold their breath for minutes at a time and can use their forked tail to break the water and gain speeds of about 37 mph underwater. They use this initial velocity to gain lift while taxing on the surface. As they begin to angle upward, they maintain open wings to take in maximum wind power and can, at times, gain four feet of clearance above the water. The fish can maintain a gliding angle for over 650 ft, but can quickly come down and taxi again to maintain consecutive "leaps" for over 1300 ft.

A video displays the flight and angling of a fish as it gains and regains flight:

Ranging between 14 and 46 cm, the flying fish has been astounding sailors and scientists for years. Its ability to hold its breath and use gliding powers is an amazing representation of arial locomotion.

References:

1-"Flying Fish" Animals: National Geographic Wild. National Geographics, n.d. Web. 18 Sep 2011.

2-"Flying Fish" Yahoo Education. Youtube, n.d. Web. 19 Sep 2011.

3- Aquatic Life of the World. Tarrytown: Marshall Cavendesh Corporation, page 211 (link to Google books), 2001.

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