Does the Reverse Brazil Nut Problem Exist?

Vibration-Induced Granular Segregation: A Phenomenon Driven by Three Mechanisms

“…The dilemma is not yet settled on the verge of even more recent findings [15]; being the most relevant the surprising result that decreasing the density of the intruder does not necessarily mean a monotonic increasing of the rise time, as might be previously suggested by studies in 3D [9] and 2D [16]. Furthermore, based on computer simulations Hong et al even dared to predict the reverse segregation effect in the BNP [17,19] (known now in the literature as the RBNP), which was immediately confronted by two groups [20,24], but nevertheless observed in the laboratory by Breu et al [25]. Finally, Yan et al [21] recently failed to confirm the experimental findings of Möbius et al [15].…”

“…However, when this phenomenon intensively investigated appeared to be well understood, new scientific puzzles came into scene [15,16,17,18,19,20,21,22]. Air-driven segregation, inertia, condensation, are now new words added to the already vast list of concepts important in the subject.…”

“…Many theoretical and experimental studies have been carried out in the last five decades aimed to reveal the physics of one of the most intriguing phenomena in granular matter: vibration-induced segregation [1,2,3,4,5,6,7,8,9,10,11,12,13,14]. However, when this phenomenon intensively investigated appeared to be well understood, new scientific puzzles came into scene [15,16,17,18,19,20,21,22]. Air-driven segregation, inertia, condensation, are now new words added to the already vast list of concepts important in the subject.…”

Dissipative Dynamics of Granular Materials

“…Techniques to determine the coefficients of restitution of colliding viscoelastic spheres can be found elsewhere [58]. This approach can be readily applied to densely packed granular medium with small movements or vibrations such as the Brazilian bean problem [59][60][61][62][63][64]. However, time integration per collision, consisting of compression and restoration, should be from 0 to t c , while t c is a negligibly short time in the collision-rule approach.…”

100 and 50 years ago

“…On the other hand, intruders of a fixed size rise with a speed that grows and then diminishes non-monotonically as the intruder density is increased. To complicate matters still further, there have been numerous commentaries on the RBN effect, some of which question whether the effect even exists, or whether it is actually a computational artefact 11 . Huerta and Ruiz-Suárez 3 have shown that there are actually two distinct regimes of segregation: one seen at higher frequencies of vibration (50 Hz), in which the bed becomes fluidized and ordinary buoyancy prevails…”