Durham, North Carolina—A plane must fly very fast to break the raindrops and thus the windshield, but it can happen. Now, the new physical model behind this impossible feat may just help doctors break kidney calculi.
In the 1960' s, when supersonic jets were first put into commercial development, researchers found a strange phenomenon, which sometimes occurred in the test flight through the rainforest. Even though raindrops are hardly heavy, they can still form annular cracks on the windshield of a jet plane.
Although it was difficult for scientists to explain this curiosity at first, Professor Frank Philip Bowden and Professor john field of Cambridge University finally thought that surface waves were the culprit. Because surface waves only propagate in two-dimensional space, they have more powerful impact than three-dimensional waves. However, due to the lack of mathematical methods and experimental devices to describe this phenomenon to verify the proposed model, some details of this phenomenon are still unknown.
Pei Zhong, a professor of mechanical engineering and materials science at Duke University, and Zhang Ying, a former graduate student and now employed as a Bose Acoustics Engineer, published a new paper in Physical Review Research on June 5438+065438+ 10/day, which filled the gap in scientific knowledge.
They created an experimental system to visualize the stress caused by this surface wave. They placed a gravel device, which was designed to crush kidney calculi with a wave of sound waves in a bucket of glass-covered water, and then caused a point source explosion in the form of a spherical shock wave. According to the angle of the shock wave hitting the glass, surface waves propagating at the boundary of water glass can be generated.
Using a high-speed camera, the research team only measured the speed of each element at the moment when the shock wave passed through the glass. Zhang used these measured data to verify the finite element model established by the multi-physical field software COMSOL. These models successfully reproduce a series of features of body waves and surface waves that are often observed in this situation, including features that can avoid surgical removal of kidney calculi.
Researchers have found that the wave that causes most stresses and faults is mainly leakage Rayleigh wave, which propagates faster than the second wave, van evanescent wave. Although they are generated at the boundary of sodium silicate at the same time, the leaked Rayleigh wave is finally pulled away from the evanescent wave, and the E evanescent wave is the moment and position of the maximum tensile stress caused by this phenomenon.
They also found that the circular cracks first observed on the windshield of supersonic jet did not necessarily form at this time-they needed defects in the glass to start using it. But once it starts, the crack will propagate along a circular trajectory, followed by the first principal stress in the solid caused by the advancing leaked Rayleigh wave.
Zhong said: The challenge in treating kidney calculi is to cut the stone into very small pieces, so that doctors don't have to perform any auxiliary surgery. Based on the knowledge gained from this model, we can optimize the shape of shock wave and the design of stone crusher, so as to generate greater tension on the surface of kidney calculi, thus opening the defect more effectively.
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