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Underwater creatures go with the flow.

A mechanical engineering professor at Tufts University (Medford, Mass.) has parlayed his fascination with marine life into a new laboratory that studies how plants and animals take advantage of fluid flow phenomena.

The inspiration for the Comparative Biomechanics Laboratory at Tufts started three years ago when Ioannis N. Miaoulis, assistant professor of mechanical engineering, visited Sydney, Australia, to deliver a paper. On the trip, Miaoulis, an enthusiastic snorkeler, spent some time observing the marine creatures of the Great Barrier Reef. "I was fascinated by the way sea anemones, which do not move about much, take the food the current brings them," Miaoulis recalled. He realized that these flower-like polyps had solved a classic engineering challenge: they grew large enough to capture enough food, but stayed streamlined enough so the current would not carry them away.

"I wondered if the sea anemones were smart enough to regulate drag coefficient in order to control the force of the water flowing over them." Miaoulis said. When he returned to the United States, Miaoulis tackled the question in the same spirit of scientific enquiry he displays as director of the Thermal Analysis of Materials Processing Laboratory at Tufts.

Miaoulis and his undergraduate research assistant, Megan McArdle, wanted to create different wave conditions in an aquarium tank at a Tufts laboratory and measure the reaction of live sea anemones. But building a wave machine was beyond the budget allotted to Miaoulis, and even if the financing were available the force of the waves could damage the glass and steel tank. "We used typical fluid mechanics to solve the problem. Instead of moving the water, we decided to move the sea anemones," said Miaoulis.

The researchers built an 8-foot-long aquarium tank that held 150 gallons of water. They borrowed the wagon of a toy train and placed strain pages on top of it. A glass plate was set atop the strain gages and the sea anemones were put on the plate.

Using strings, Miaoulis and McArdle joined the toy wagon to an electric motor, which was controlled by a Macintosh IIci computer. By moving the wagon back and forth, the contraption would simulate waves acting upon the sea anemones. The strain gages measured the forces exerted on the sea anemones and fed that information into the computer. At the same time, a video camera captured images of the sea anemones and downloaded them into the computer.

Using digital image processing, the researchers were able to calculate the area of the sea anemone that faces the flow. This information, combined with the force of the water and its velocity, permitted them to calculate the drag coefficient. "By running the anemones through different waves, we can see how the drag coefficient varies and how the size and shape of the anemones adapt to those variations," explained Miaoulis.

Miaoulis and Tufts biology and engineering students are setting up the Comparative Biomechanics Laboratory so that students can explore how plants and animals use fluid dynamics.

Additionally, a new introductory course in comparative biomechanics will begin in the fall, said Miaoulis. The laboratory will be equipped with four aquaria, each simulating a different aqueous environment: Atlantic salt water, Pacific salt water, fresh water, and a hospital tank for sick fish. Other lab apparatus will include sophisticated video equipment, thermal anemometry, laser-doppler anemometry and particle image radiometry capabilities, video microscopes, Macintosh computers, and both liquid and air tunnels.

Besides continuing to experiment with the reaction of sea anemones, the Comparative Biomechanics Lab at Tufts will be used to explore several other animal and plant uses of fluid phenomena. "For example, the eyes of a fish are located at that point on its body where the pressure of the water fluctuates the least as the fish swims around," said Mioulis. This could mean, he said, that the optic system of fish developed specifically so that fluid pressure would not interfere with their vision.

Another piscine use of fluid dynamics that will be researched at the Tufts lab involves finding the reason smaller fish swim nearer to the surface of the water. Miaoulis suggested that the small fry use fluid principles to escape larger predators. "The bigger fish have a greater effective drag coefficient near the surface, which slows them down when they are trying to catch smaller fish," he said.

No creature is too humble for the researchers at the Comparative Biomechanics Lab. Even that shipwright's pest, the barnacle, will come under scrutiny. Students will be studying how the flow induced by the feeding of large barnacles affects smaller neighboring barnacles.

Another project slated for the new laboratory, according to Miaoulis, will explore how prairie dogs build their nests to take advantage of the Bernoulli effect to ventilate them.
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Title Annotation:Tufts University's Comparative Biomechanics Laboratory
Author:Valenti, Michael
Publication:Mechanical Engineering-CIME
Date:May 1, 1993
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