Instationary compaction wave propagation in highly porous cohesive granular media

et al. 2017

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Context. Dust impact into granular materials leads to crater formation and material ejection. Aims. The impact of dust aggregates, composed of a number Np of grains, into a granular bed consisting of the same grains is studied as a function of impact velocity v and projectile size Np. No gravitational effects are included. Methods. Granular-mechanics simulations are used to study the outcome of dust-aggregate impacts. The granular bed and the aggregates are composed of silica grains and have filling factor 0.36. Results. Both the crater volume and the ejection yield increase sublinearly with total impact energy. No crater rims are formed. Crater shapes change from hemispheric to elongated when increasing either projectile size or velocity. The crater walls are compacted by the impact within a zone of a size comparable to the crater radius. Ejecta are produced at the edges of the impact; only a small fraction of the ejecta stem from the projectile. The energy distribution of the ejecta follows at high energies a 1/E 2 decay reminiscent of sputtering from atomic targets. The maximum of the distribution is shifted to higher energies for larger projectiles; this is caused by the increasing depth from which ejected grains originate. Conclusions. Due to the dissipative nature of intergranular collisions and the porosity of the target, crater morphology and ejecta yield deviate characteristically from impacts into atomic materials.

Section: Analysis Of An Exemplary Casementioning

confidence: 99%

Dust-aggregate impact into granular matter: A systematic study of the influence of projectile velocity and size on crater formation and grain ejection

Planes

Millán

et al. 2017

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“…5 in Paper III, and Fig. 7 in Gunkelmann et al (2016b) we see that a 100 % increase seems to be approximately the maximum reached and then the compaction values decrease.…”

Section: Porosities Of the Resulting Fragmentsmentioning

confidence: 50%

“…We have limited data on compaction changes after a collision, but we found that it depends on µ (Paper III): If we consider a v 10 m/s (v rms value of our MB distributions of random initial velocities), for all the φ analyzed, when µ = 10 we observe an increase in compaction of 75 − 100 % and when µ = 60 of 50 − 75 %. Gunkelmann et al (2016b) find for µ = 1 (and 0.08 < φ < 0.201) an increase of 100%. So as µ increases the final compaction decreases.…”

Section: Porosities Of the Resulting Fragmentsmentioning

confidence: 86%

A Monte Carlo code for the collisional evolution of porous aggregates (CPA)

Millán

Planes

et al. 2023

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Context. The collisional evolution of submillimeter-sized porous dust aggregates is important in many astrophysical fields. Aims. We have developed a Monte Carlo code to study the processes of collision between mass-asymmetric, spherical, micron-sized porous silica aggregates that belong to a dust population. Methods. The Collision of Porous Aggregates (CPA) code simulates collision chains in a population of dust aggregates that have different sizes, masses, and porosities. We start from an initial distribution of granular aggregate sizes and assume some collision velocity distribution. In particular, for this study we used a random size distribution and a Maxwell-Boltzmann velocity distribution. A set of successive random collisions between pairs of aggregates form a single collision chain. The mass ratio, filling factor, and impact velocity influence the outcome of the collision between two aggregates. We averaged hundreds of thousands of independent collision chains to obtain the final, average distributions of aggregates. Results. We generated and studied four final distributions (F), for size (n), radius (R), porosity, and mass-porosity distributions, for a relatively low number of collisions. In general, there is a profuse generation of monomers and small clusters, with a distribution F (R) ∝ R−6 for small aggregates. Collisional growth of a few very large clusters is also observed. Collisions lead to a significant compaction of the dust population, as expected. Conclusions. The CPA code models the collisional evolution of a dust population and incorporates some novel features, such as the inclusion of mass-asymmetric aggregates (covering a wide range of aggregate radii), inter-granular friction, and the influence of porosity.

“…The model used here is based on the work of Dominik & Tielens (1997) and has been implemented (Ringl & Urbassek 2012;Gunkelmann et al 2016) in the molecular dynamics software LAMMPS (Plimpton 1995) and in the open-source code LIGGGHTS (Kloss et al 2012). It uses the effective radius,…”

Section: Granular Mechanics Modelmentioning

confidence: 99%

Granular mechanics simulations of collisions between chondritic aggregates

Umstätter

2021

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Context. Collisions of dust aggregates are relevant for the evolution of protoplanetary disks. Aims. While in the past interest focused on aggregates composed of monodisperse grains, here we study the collision of chondritic aggregates, in which – besides a majority of dust grains – larger chondrules are embedded. Methods. We use granular-mechanics simulations to study collisions of chondritic aggregates. Results. Low-velocity collisions lead to pancake-shaped deformations of the fused cluster accompanied by a compaction of the dust grains. Higher collision velocities fragment the aggregates. While some chondrules are almost laid bare after the collision, we find that the largest fragments typically contain chondrules; large fragments thus capture chondrules. Grain compaction is accompanied by an increase in grain – chondrule contacts and is maximum for intermediate velocities, just before aggregates start fragmenting. Conclusions. The presence of chondrules considerably influences the fragmentation behavior of dust aggregates.