"Ships expend a great deal of energy pushing the water around them out of the way as they move forward," said Yaroslav Urzhumov, assistant research professor in electrical and computer engineering at Duke's Pratt School of Engineering. "What our cloak accomplishes is that it reduces the mass of fluid that has to be displaced to a bare minimum.
"We accomplish this by tricking the water into being perfectly still everywhere outside the cloak," Urzhumov said. "Since the water is still, there is no shear force, and you don't have to drag anything extra with your object. So, comparing a regular vessel and a cloak of the same size, the latter needs to push a much smaller volume of water, and that's where the hypothesized energy efficiency comes from."
The results of Urzhumov's analysis were published online in the journal Physical Review Letters. The research was supported by the U.S. Office of Naval Research and a Multidisciplinary University Research Initiative (MURI) grant through the U.S. Army Research Office. Urzhumov works in the laboratory of David R. Smith, William Bevan Professor of electrical and computer engineering at Duke.
While the cloak postulated by Urzhumov differs from other cloaks designed to make objects seem invisible to light and sound, it follows the same basic principles – the use of a man-made material that can alter the normal forces of nature in new ways.
In Urzhumov's fluid flow cloak, he envisions the hull of a vessel covered with porous materials – analogous to a rigid sponge-like material – which would be riddled with holes and passages. Strategically placed within this material would be tiny pumps, which would have the ability to push the flowing water along at various forces.
"The goal is make it so the water passing through the porous material leaves the cloak at the same speed as the water surrounding by the vessel," Urzhumov said. "In this way, the water outside the hull would appear to be still relative to the vessel, thereby greatly reducing the amount of energy needed by the vessel to push vast quantities of water out of the way as it progresses."
While the Duke invisibility cloak involved a man-made structure – or metamaterial – based on parallel rows of fiberglass slats etched with copper, Urzhumov envisions a different sort of metamaterial for his fluid flow cloak.
"In our case, I see this porous medium as a three-dimensional lattice, or array, of metallic plates," he said. "You can imagine a cubic lattice of wire-supported blades, which would have to be oriented properly to create drag and lift forces that depend on the flow direction. In addition, some of the cells of this array would be equipped with fluid-accelerating micro-pumps."
Urzhumov explained that when a regular vessel moves through fluid, it also pushes and displaces a volume of water that greatly exceeds the volume of the vessel itself. That is because in a viscous fluid like water, an object cannot just move a single layer of water without all others; the shear force effectively attaches an additional mass of water to the object.
"When you try to drag an object on a fishing line through water, it feels much heavier than the object itself, right?" he said. "That's because you are dragging an additional volume of water with it."
Based on this understanding of the flow cloaking phenomenon, Urzhumov believes that the energy expended by the micropumps could be significantly less than that needed to push an uncloaked vessel through the water, leading to the greatly improved efficiency.
Richard Merritt | EurekAlert!
Astronomers find unexpected, dust-obscured star formation in distant galaxy
24.03.2017 | University of Massachusetts at Amherst
Gravitational wave kicks monster black hole out of galactic core
24.03.2017 | NASA/Goddard Space Flight Center
Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.
The results will be published on March 22 in the journal „Astronomy & Astrophysics“.
Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...
Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.
Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...
In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...
Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to simulate these confined natural conditions in artificial vesicles for the first time. As reported in the academic journal Small, the results are offering better insight into the development of nanoreactors and artificial organelles.
Enzymes behave differently in a test tube compared with the molecular scrum of a living cell. Chemists from the University of Basel have now been able to...
20.03.2017 | Event News
14.03.2017 | Event News
07.03.2017 | Event News
24.03.2017 | Materials Sciences
24.03.2017 | Physics and Astronomy
24.03.2017 | Physics and Astronomy