2024-08-24 04:00:05
Researchers from the Fluids, Automation and Thermal Systems laboratory and UNICAMP (Brazil) have provided the first demonstration that the rotation of a projectile on itself promotes its penetration into the ground. Published in the journal Physical Reviewthis work provides a model that predicts the burial depth as a function of the vitesse of fall and rotation.
© Y. Bertho
Unlike fluids and solids, the mechanical behavior of granular media is not guided by large, well-established physical laws. However, many disciplines need to be able to predict how a projectile will sink into soils and materials composed of grains, such as sablegravel, powders or grains in silos. Applications range from the InSight space mission, tasked with studying the temperature you sun Martin up to five meters deep, to reforestation efforts by dropping seeds by plane or helicopter. There are two cases, depending on whether the projectile rotates on itself during its movement. Researchers from the Fluids, Automation and Thermal Systems laboratory (FASTCNRS/Paris-Saclay University) and theUniversité State University of Campinas (UNICAMP, Brazil) have shown that, at equal fall speed, the faster the rotation of the projectile, the deeper it sinks into a granular medium.
They quantified the effectiveness of the maneuver by a ratio between the rotation speed and the impact speed. In the speed ranges studied, the projectiles plunged up to 15% further in the case of rotation. This is the first real demonstration that rotation promotes penetration into the ground.
To do this, scientists have created an experimental device that allows a spherical projectile to be impacted at a controlled speed, by varying its release height, into millimeter-sized glass balls. These are contained in a rotating container, because it is much easier to control the rotation of the granular medium than that of the projectile, which would risk no longer going straight.
The researchers stayed within speed ranges that were limited enough to keep the balls in place, meaning that there were no differences in mechanical forces depending on whether the granular medium or the projectile was rotating. They found that during burial, rotation promotes fluidization of the granular medium around the projectile. This reduces the pressure under the projectile, which therefore sinks more easily.
The researchers derived a physical model capable of predicting the depth of burial of the projectile based on its fall speed and the rotation of the granular medium. They are now trying to model the morphology of the craters produced by such impacts and the ejection trajectory of the grains.
References:
Penetration of a spinning sphere impacting a granular medium.
DD Carvalho, Y. Bertho, EM Franklin, and A. Seguin.
Phys. Rev. E 109, 054902 (2024).
https://doi.org/10.1103/PhysRevE.109.054902.
Article available on the open archive database Arxiv.
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