The science behind swimming: From whales to larvae, common principles at work in swimming

Whale and diver (stock illustration). Using simple hydrodynamics, researchers were able to show that a handful of principles govern how virtually every animal -- from the tiniest fish to birds to gigantic whales propel themselves though the water. Credit: © James Thew / Fotolia

At nearly 100 feet long and weighing as much as 170 tons, the blue whale is the largest creature on the planet, and by far the heaviest living thing ever seen on Earth. So there's no way it could have anything in common with the tiniest fish larvae, which measure millimeters in length and tip the scales at a fraction of a gram, right?

Not so fast, says L. Mahadevan, the Lola England de Valpine Professor of Applied Mathematics, of Organismic and Evolutionary Biology, and of Physics.

Using simple hydrodynamics, a team of researchers led by Mahadevan was able to show that a handful of principles govern how virtually every animal -- from the tiniest fish to birds to gigantic whales propel themselves though the water. The study is described in a September 14 paper in Nature Physics.

"What we wanted to investigate was how the speed of an organism changes as a function of how large it is, how quickly it moves and how much it moves," Mahadevan said. "To resolve that in detail, however, is very complex, because there is a great deal of differences in morphology and what parts of the body different creatures use to swim. The question is: Is there anything in common across all these organisms? The answer, we found, is yes."

In an effort to uncover those common principles, Mahadevan working with a postdoctoral fellow in his group , Mattia Gazzola, and a colleague Mederic Argentina from the University of Nice, began by trying to unpack the physics of how different creatures swim.

"The traditional approach to swimming phenomena is to take a certain specimen and accurately characterize it via experiments and/or simulations, and try to generalize from there, but it is very hard to strip out specific biological effects from general principles," Gazzola said. "We instead thought that while swimmers exhibit a huge diversity in shapes and kinematics, at the end of the day they all live in the same media, water.

"Therefore we thought that if a unifying mechanistic principle existed, it had to lie in the constraints that the flow environment poses to all its inhabitants," he continued. "And this is a purely physical problem, much easier to solve since it is not affected by biological vagaries. What I like about this paper is that in one line of algebra we derived a compact formula that accounts for 50 years of experiments. This is an example of how powerful minimal modeling can be."

"The basic relationship we wanted to understand was how the input variables -- namely the size of the organism, the amount an organism moves and how quickly it moves -- control the output variable, which is effectively the speed at which it moves," Mahadevan explained. "What we found is that there is a specific relationship, which can be described by in terms of a simple scaling law with two limits."

The first, which corresponds to creatures moving at intermediate speeds, describes situations where the bulk of the resistance is caused by skin friction, because water "sticks" to the organism's body. At faster speeds, Mahadevan said, the resistance organisms face largely comes from pressure that builds up in front of and around them, which is described by the second limit.

"While it wasn't a surprise that the resistance changed at organisms moved faster, the fact that those challenges could be so simply described was interesting and provocative, because we are talking about organisms that range in size from a few millimeters to the size of a blue whale," Mahadevan said.

Armed with those observations, Mahadevan and colleagues turned to a host of empirical observations that had been made over the past 50-plus years. When those data were plotted on a graph, the researchers found that the swimming speed of virtually every organism, from fish larvae to frogs to birds, amphibians and even whales, could be described by one of the two equations.

The same also held true, Mahadevan said, when Gazzola created complex computer models to solve the governing equations of fluid dynamics to describe how different organisms swim.

"What is particularly interesting is that all the organisms essentially reach the hydrodynamic limits of performance," he said. "Our simple theory, which doesn't distinguish in any detailed way between something like a blue whale and fish larvae, except in the parameters of how large you are, much you move and how quickly you move, can describe all this diversity. That suggests there are general principles at work here."


Source: Harvard University

Tailor-made for the aquaculture sector

Details are important. The hood is specially adapted for personnel wearing helmets – without compromising vision. Credit: SINTEF Health Research

Fish husbandry workers have played an active part in developing work clothing tailor-made for their wet, windy and messy working conditions.

They're standing in a small circle around a net pen out in the ocean. Their job is to maintain the net pens, de-louse the salmon, and carry out the many other tasks essential to the running of a fish farm facility. The wind is bitter and the rain is lashing in from all directions. Sea water is splashing around their feet. Everything they handle is wet. Cold water creeps relentlessly up to their knees and along to their elbows inside their coveralls, which are only waterproof up until the second wash.

This is a normal working day for a couple of thousand workers in fish farms all along the Norwegian coast. In spite of this no work clothing exists that is specifically adapted to their very special working conditions. Yet.

Industrial designers Tore Christian Bjørsvik Storholmen and Ole Petter Næsgaard at SINTEF Health Research have developed work clothing which they hope will make conditions both safer and more comfortable for husbandry workers out on the fish farms. Their project has been carried out in close collaboration with the workers who will be wearing the clothing.

Better together

"We've spent a lot of time getting to know the business and the needs of the husbandry workers," says Næsgaard. "We've taken part in many tasks, observed what goes on, and have obtained input and feedback in response to our suggestions," he says. "We've met with a thoroughly honest group of people. They don't hold back when they're not satisfied," he says.

They visited three different facilities close to Hitra and Frøya as part of a pilot project. Ideas and sketches made during one visit were taken to the next so that they could encourage reactions and get feedback. It has been an iterative process involving an ongoing series of corrections and improvements.

"This has served as a quality control on our work to develop relevant and attractive solutions," says Storholmen. "We could never have put the first prototype on the market," he says. "But our dialogue with the users has enabled continuous refinement. New details are always being developed and incorporated. "We're now getting close to a product that can be introduced to the market," he says.

Inspired by climbers and skiers

"When we were studying the husbandry workers, we saw that they do a lot of climbing from boat to boat through ropes and cables and across a variety of different barriers. This led us to obtain inspiration from clothes developed for climbers. The result is that the clothing now offers a very good fit - combined with excellent freedom of movement," explains Storholmen.

When it comes to choosing fabrics, the researchers have obtained greater inspiration from sports clothes than from other types of work clothing. Instead of thick, insulated suits, the new clothing concept has much more in common with kit worn by skiers.

"We've exploited the shell principle," says Storholmen. "The fabric of the outermost layer is water- and wind-proof and very light and durable," he says. "We've also developed intermediate layers and underwear, so users can select the clothing they need based on weather conditions and their own level of activity," he explains.

The clothing is also specifically adapted to allow good freedom of movement in the neck area - even when wearing a life vest. The same applies to the hood which has plenty of room for the mandatory helmet. What about reflective patches? These are placed strategically on the arms, hood and shoulders, and not across the shoulders and legs which is standard for the majority of existing work clothing.

"Actually, we saw that workers testing the clothing were at first sorry to have to return it following the tests," says Storholmen. "This has to be a good sign," he says.

However, the developers are not satisfied simply with anatomical adjustments, new fabrics and good visibility. There has to be a place for modern technology in this type of clothing. So the suit is equipped with a waterproof pocket for a mobile phone, and will also be fitted with a separate pocket to accommodate a man-overboard alarm.

Comfort equals effective HSE

The fish farms visited by the researchers are in exposed coastal locations, often about a half-hour's boat trip from land. The husbandry workers are housed in floating pontoons, surrounded by net pens. They may have to stay here for as much as a week at a time. There have been situations where workers have fallen into the sea. It is essential that the new work clothing represents an improvement in safety. It must be easy for the wearer to get hold of important tools such as knives, tape and communications equipment.

"An Operations Manager told us that good work clothing is one of the most important aids to effective HSE," says Storholmen. "People standing around getting cold lose concentration on what they're doing, making accidents more likely. We believe that this is thoroughly addressed by the new clothing," he says.

A net pen is an enormous "warehouse," and if a major accident occurs, the consequences for the environment and the company's profitability may be very large.

"Aquaculture uniform"

The clothing currently worn by husbandry workers is essentially the same as the standard primarily developed for the building and construction industry, where competitive pricing is a major issue. The clothing being developed in this project will probably be more expensive.

"Current work clothing is a consumer item," say the researchers. "Our impression is that there is a willingness to pay for a better and more durable product specifically adapted to the needs of the aquaculture industry - a specially designed "aquaculture uniform" which can identify the workers and promote an increase in the pride they have in their profession," they say.

Source: SINTEF