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Blur the dream of ideal "Invisibility" coats for stress waves



  The dream of ideals
In many earthquake-prone regions, Roman arenas have survived. Did the Romans inadvertently build seismic wave coats when designing Colisees? Some researchers believe this because of the similarity of the arenes with modern experimental elastodynamic cloaking devices. Picture credits: David Iliff, License: CC BY-SA 3.0

It remains to be seen whether Harry Potter's invisibility cloak, which directs light waves perfectly around objects to make them invisible, will ever become reality, but it is impossible to perfect a more crucial mantle, a new study says. It would have directed stress waves in the ground, as they go out of an explosion, perfectly around objects like buildings, to make them "untouchable".

Although dozens of theoretical papers on "elastodynamic" camouflage have been called into question, the authors of the new study from the Georgia Institute of Technology do not believe that civil engineers should abandon it altogether, just on the idea of ​​ideal camouflage. Limited cloaking can still give the structures some protection, especially against some stress waves that often occur in earthquakes.

"When cloaking, there is the expectation that if you get some kind of stress wave from any direction, a cloak should do that. We now see that it is not possible," said lead investigator Arash Yavari, a professor at Georgia Tech School of Civil and Environmental Engineering and George W. Woodruff School of Mechanical Engineering. "But for a large class of disturbances, the in-plane perturbations, you could probably design a good mantle."

In an earthquake, in-plane disturbances are seismic waves that run on flat and wide or flat paths through the Earth's surface.

Yavari and co-author Ashkan Golgoon, a research associate who studied at Yavari, published their study in the journal Archive for Rational Mechanics and Analysis a leading journal of theoretical solid mechanics, on May 1

6, 2019 The research was funded by the Army Research Office.

The Dream Cloak

The dream of enveloping to pass stress waves past a building as if there were not even there. Much has to do with the dream of an invisible mantle, the light – electromagnetic waves – around bends an object and then points to the other side.

The waves of light that strike the eye of the beholder reveal what is behind the object, but not the object itse lf. In the case of elastodynamic camouflage, the waves are not electromagnetic but mechanical and move through the ground. Hypothetically, camouflaging the object would completely isolate it from the waves.

  The Dream of Ideal
invisibility camouflage illustrates how camouflage works with electromagnetic camouflage. Electromagnetic waves scatter on the left, which can be light when they hit the cylinder in the middle. On the right, the cylinder is covered; The waves do not scatter, and for a viewer standing in the field, it appears invisible. Photo credits: Creative Commons, upload.wikimedia.org/wikipedia/commons/thumb/7/73/Circular_EM_cloak_using_transformation_optics.svg/2000px-Circular_EM_cloak_using_transformation_optics.svg.png (2)

In a scenario where, for example, a nuclear reactor is protected from voltage waves flowing through the ground, whether due to a natural or man-made disaster, civil engineers could ideally lower the bottom of the reactor to a hole below the surface from the ground. They built a protective cylinder or hemispherical subterranean shell with special materials to direct the voltage waves around the circle.

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

"We have proved that the shape of the mantle does not matter, whether spherical or cylindrical, you can not completely disguise it," said Yavari.

The False Analogy

Much of the theory and mathematics of electromagnetic (light) camouflage has been applied to elastodynamic camouflage research, and some of the former seem to have thrown a wrench into the latter.

"Often, analogies from other fields are useful, but elasticity adds several physical factors that you do not consider electromagnetism," said Yavari. "For example, the angular momentum balance is violated in much of the research literature."

The angular momentum is a property of mass in rotational motion and resistant to change Many people experience angular momentum by tilting a rotary motion Gyroscope and observation stubbornly move on an unexpected Path.

Although it is a wave, photons are massless photons, whereas voltage waves move through matter, especially solid matter, as opposed to liquid or gas – and that adds crucial momentum to the equation

  The dream of ideal
parts of Italy and other parts of the former Roman Empire along the Mediterranean Sea lie in earthquake areas Nevertheless, Roman arenas have been proven to be robust for some 2,000 years, some researchers believe the ancient Romans they had accidentally as a partial mech Anic wave coats designed. Credit: Wikimedia Commons commons.wikimedia.org/wiki/File:2016_Amage_earthquake.jpg

This dynamic also affects the hole that hides the object. Without them, the stress waves travel fairly evenly through a medium, but with it the stresses concentrate around the hole and destroy the clean geometry of the wave patterns.

The Roman coat?

What to do? Cape anyway. If the ideal solution does not exist, make an imperfect one.

"Mathematics says it's not possible to obfuscate in the narrower sense, and if you understand that, do not waste time," Yavari said. "They formulate problems that will improve with your knowledge of specific stresses or stresses that you want to protect against."

Engineers could protect themselves against major earthquake stresses by using materials that are specially toughened, have certain elastic properties, and distribution of densities, which are detailed in the study. A real coat can lag behind an ideal and still be great.

"If I feel only 10 or 20 percent instead of 100 percent of the wave energy, that's a big deal, because engineering is not a pursuit of absolute ideals," Yavari said.

Even the ancient Romans, who are known to be mathematic, seem to have inadvertently incorporated seismic coats into their amphitheater designs, according to a MIT Technology Review report. Their similarity to modern experimental cloaking devices may have contributed to maintaining them in seismically active regions for 2000 years.

The new study also looked at a popular idea in civil engineering that built with a family of materials whose microstructure turned them into Cosserate solids "could enable perfect camouflage, and the authors concluded that this could not work. The study did not consider so-called metamaterials that received attention for redirection in certain light waves.


New invisibility cloak hides objects from a human perspective


Further information:
Arash Yavari et al., Nonlinear and Linear Elastodynamic Transformation Cloaking, Archive for Rational Mechanics and Analysis (2019). DOI: 10.1007 / s00205-019-01389-2

Provided by
Georgia Institute of Technology




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Blur the Dream of Ideal "Invisibility" Mantles for Stress Waves (2019, June 7)
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