Which has a more efficient 'engine': A tuna or a whale?

May 12, 2014

A large gray whale and a much smaller skipjack tuna each propels itself through water. Which is the more efficient swimmer? It has been difficult to compare propulsion efficiencies of animals of different sizes, like comparing apples and oranges, but now Northwestern University researchers have developed a new metric, or standard, to measure individual energy consumption efficiency and make such a comparison possible.

Contrary to what one might expect, the Northwestern researchers found that, despite the great difference in mass, the whale and the tuna are almost equally efficient.

Much like a semi-trailer truck needs more fuel to go the same distance compared to a small car, one might think the much heavier whale would consume more energy compared to the tuna. While this is true, does it mean that the muscular "engine" propelling the whale is less efficient compared to the tuna or is the higher fuel consumption of the whale an unavoidable consequence of the laws of physics?

The whale's higher fuel consumption is unavoidable, the researchers report, and the engine efficiencies of the whale and tuna are similar. The new Northwestern metric for efficiency that enabled this comparison could be extremely useful in designing underwater vehicles -- such as those used to study fragile coral reefs, repair damaged deep-sea oil rigs or investigate sunken ships -- to be as efficient and agile as a real fish.

"Our study is about how energy flow changes with size or mass," said Neelesh Patankar, who led the research. "This is good insight to have in the transportation field, whether you are working with cars, ships or planes. What are the limits of how good you can become? Our metric can be used to determine the point where an animal or a vehicle would function most efficiently. We want to know the sweet spot."

Patankar is a professor of mechanical engineering in Northwestern's McCormick School of Engineering and Applied Science. He currently is doing a mini-sabbatical at Argonne National Laboratory's Advanced Vehicle Technology Center investigating efficiency metrics for automotive vehicles.

The metric, called the energy consumption coefficient, is a non-dimensional measure of fuel consumption. Now, for the first time, scientists and engineers can compare apples to apples, no matter what the size of the animals or vehicles, to understand the energy efficiency of a self-propelled body or machine. This metric is as useful to quantify efficiency of self-propelled bodies as the drag coefficient metric is to quantify aerodynamic shapes of vehicles.

While the Northwestern study focused on swimming and flying animals, the concept potentially could be applied to define efficiencies of cars, too -- something the researchers are now pursuing.

"The study helps quench my curiosity about how nature works, but, as an engineer, I also want to see utility," Patankar said. "The energy consumption coefficient can be an important tool in designing self-propelled underwater vehicles as well as aerial vehicles. And, as a driver, I also would like to know how efficient my car is, information currently not available to me."

The study will be published the week of May 12 by the Proceedings of the National Academy of Sciences (PNAS).

The energy consumption coefficient takes into consideration metabolic rate, muscle mass and, of course, physics. After developing the metric, first author Rahul Bale and Patankar applied it to data for energy consumption by animals available from biologists. The data represented thousands of species of swimming and flying animals. Swimming animals ranged from tiny larval zebrafish to massive mammalian swimmers such as dolphins and whales. Flying animals ranged from tiny insects to the largest flying birds.

The new metric successfully collapsed energy consumption data on to a single trend with respect to mass -- mass that varied almost a trillion times from the smallest to the largest animal. The key idea was not to plot the energy consumption itself versus mass but instead to plot energy consumption normalized by an appropriate scale that accounts for the size of the animal.

This is conceptually analogous to how aerodynamic shapes of vehicles are assessed not by comparing drag but by comparing drag that is suitably normalized -- the normalized drag being the drag coefficient.

The new metric, the researchers said, is a step in the direction of eventually providing efficiency information to consumers about their cars.
The title of the paper is "Energy efficiency and allometry of movement of swimming and flying animals." In addition to Patankar and Bale, other authors of the paper are Max Hao and Amneet Pal Singh Bhalla, both from Northwestern.

Northwestern University

Related Energy Consumption Articles from Brightsurf:

Optimizing of VCSEL photon lifetime for minimum energy consumption at varying bit rates
Prof. Bimberg's group at Bimberg Chinese-German Center for Green Photonics Changchun at Institute of Optics, Fine Mechanics, and Physics, Chinese Academy of Sciences has developed VCSELs emitting at 850 nm, 880 nm, 910 nm, 940 nm, which were optimized to achieve 50+ Gb/s, enabling 200+ Gb/s data transmission across a multimode fiber.

Solar assisted heating networks reduce environmental impact and energy consumption
More than 40% of energy consumption in the European Union is by buildings and 63% of this figure is due to residential dwellings.

First measurement of electron energy distributions, could enable sustainable energy technologies
To answer a question crucial to technologies such as energy conversion, a team of researchers at the University of Michigan, Purdue University and the University of Liverpool in the UK have figured out a way to measure how many 'hot charge carriers' -- for example, electrons with extra energy -- are present in a metal nanostructure.

Long-term developments of energy pricing and consumption in industry
Researchers at the Paul Scherrer Institute PSI have collaborated with British economists to study how energy consumption by Swiss industry develops depending on energy pricing.

Mandatory building energy audits alone do not overcome barriers to energy efficiency
A pioneering law may be insufficient to incentivize significant energy use reductions in residential and office buildings, a new study finds.

A smart way to predict building energy consumption
In a time of aging infrastructure and increasingly smart control of buildings, the ability to predict how buildings use energy -- and how much energy they use -- has remained elusive, until now.

Mapping the energy transport mechanism of chalcogenide perovskite for solar energy use
Researchers from Lehigh University have, for the first time, revealed first-hand knowledge about the fundamental energy carrier properties of chalcogenide perovskite CaZrSe3, important for potential solar energy use.

Space dragons: Researchers observe energy consumption in quasars
Researchers, for the first time, have observed the accelerated rate at which eight quasars consume interstellar fuel to feed their black holes.

New discipline proposed: Macro-energy systems -- the science of the energy transition
In a perspective published in Joule on Aug. 14, a group of researchers led by Stanford University propose a new academic discipline, 'macro-energy systems,' as the science of the energy transition.

How much energy storage costs must fall to reach renewable energy's full potential
The cost of energy storage will be critical in determining how much renewable energy can contribute to the decarbonization of electricity.

Read More: Energy Consumption News and Energy Consumption Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.