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Rattles dreams for ideal "invisible" stress waves



Is Harry Potter's invisible cloak that perfectly directs light waves around objects to make them invisible will ever become a reality, remains to be seen, but the improvement of the more essential cloak is impossible, according to a new study. You would be perfectly managing the stress waves in the country, like those that came out of the blast, around objects like buildings to make them "untouchable".

Although deeply suspicious of dozens of theoretical papers for "elastodynamic" masking, the authors of a new study from the Georgian Institute of Technology do not think that construction engineers should completely give up on this, only the idea of ​​an ideal gown. Restricted masking can still add some degree of protection to structures, especially against some stressful waves that are common in earthquakes.

"With poetry, there is an expectation that if you have any stress wave in any direction, the gown should be able to hide the object from it. Now we see that this is not possible," said chief researcher Arash Jawari, professor at the Faculty of civil engineering and engineering sciences in Georgia, and the George C. Wilson Faculty of Mechanical Engineering. Woodruff. "But for a large class of disturbances, namely in aircraft hurdles, you can probably design a good gown."

In an earthquake, aviation disruptions are seismic waves that follow flat and wide or flat paths across the surface of the Earth.

Jawari and co-author Ashkan Golgon, a graduate research assistant who studied with Jawari, published his study in the journal Archive for Rational Mechanics and Analysis, a leading magazine on theoretical solid mechanics, on May 16, 2019. The research was funded by the Army Research Office.

The dream gown

The dream of poetry is managed by the stress waves of the past structure as it is not even has much in common with the dream of invisibility cloak, which will bend the light – electromagnetic waves – around an object, then point the other side.

The light waves that hit the viewer's eye will reveal what lies behind the object, but not the object itself. In elastodynamic masking, waves are not electromagnetic but mechanical, they move around the earth. Hypothetically, the concealment of the object will completely isolate it from the waves.

In a scenario to protect, for example, a nuclear reactor from any stressful waves traveling across the country, whether from a natural or human catastrophe, ideally, civil engineers can lower the base of the reactor into a hole beneath the surface of the earth. They will build protective cylinders or hemispherical underground vessels around it with special materials to guide the stress waves around the circle.

There are dreams, then there are findings of the study.

"We have proven that the shape of the cloak is not important, whether it is spherical or cylindrical, you can not completely impose," Jawari said.

The wrong analogy

Many theory and mathematics of electromagnetic (lightweight) poetry is transmitted on elastodynamically masked research, and some of the first appear to have thrown a key in the latter.

"Many times, analogies in other fields are useful, but elasticity adds more physical factors that you do not have in electromagnetism," Jawari said. "For example, the balance of the angular momentum is broken in most of the research literature.

Angular momentum is a mass property in rotational motion and is resistant to change. Many people experienced angular dynamics by moving the rotating gyroscope and watching it persistently move along an unexpected path.

Although wave, light is photons that do not have a mass. The stress waves, on the other hand, travel through matter – specifically, solid matter in contrast to fluid or gas – and which adds crucial dynamics to the real world of the equation.

Those dynamics also affect that hole that hides the object. Without it, stress waves travel fairly evenly through a medium, but with this, the emphasis concentrates around the hole and mess with the neat geometry of the wave patterns.

Roman cloak?

What to do? Anyway. If the ideal solution does not exist, make it imperfect.

"Mathematics says that poetry is not possible in the strict sense. When you understand this, you do not waste time," Jawari said. "You formulate problems that are optimized with what you know about the target stresses or loads you want to protect."

Engineers could be protected from important stressful earthquakes, if they use materials that are specifically tired, have certain elastic properties and density distribution that are explained in detail in the study. And the real gown can fall short of the ideal and still be great.

"If instead of 100 percent of the energy of the wave, I feel only 10 or 20 percent, it's a huge thing because engineering is not a quest for absolute ideals," Jawari said.

Even the ancient Romans, known mathematical phobias, seem to have unintentionally constructed seismic cloaks in their design of amphitheatres, according to a report in MIT Technology Review. Their resemblance to modern experimental contraceptive devices may have helped to preserve 2000 years in seismically active regions.

The new study also examined a popular idea in the construction that a building with a family of materials that have a microstructure that makes "Cosserat solids" can provide perfect poetry. The authors concluded that this also can not work. The study did not take into account the so-called. metamaterials that have received attention for redirection of certain light waves.

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This research was supported by the Army Research Office (grants ARO W911NF-16-1-0064 and ARO W911NF-18-1-0003). All findings, conclusions or recommendations are those of the authors, and not necessarily from the Army Research Office.


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