Submitted as: model description paper 07 Dec 2020

Submitted as: model description paper | 07 Dec 2020

Review status: this preprint is currently under review for the journal GMD.

SCARLET-1.0: SpheriCal Approximation for viRtuaL aggrEgaTes

Eduardo Rossi and Costanza Bonadonna Eduardo Rossi and Costanza Bonadonna
  • Department of Earth Sciences, University of Geneva, Geneva, 1203, Switzerland

Abstract. Aggregation of particles occurs in a large variety of settings, and, therefore, it is the focus of many disciplines, e.g. Earth and environmental sciences, astronomy, meteorology, pharmacy, food industry. It is thus very important to provide a full description of the outcome of an aggregation process, starting from its basic features such as the position in space of its components and the overall porosity of the final object. We present SCARLET-1.0, a Matlab package specifically created to provide a 3D virtual reconstruction of aggregates in central oriented collisions that can be later 3D printed. With aggregates in central oriented collisions we refer to aggregates that build up their own structure around the first particle (the core) acting as a seed. SCARLET-1.0 belongs to the class of sphere-composite algorithms, a family of algorithms that approximate 3D complex shapes in terms of not-overlapping spheres. The conversion of a 3D surface in its equivalent spherical approximation allows an analytical computation of their intersections. Thus, provided a vector of sizes and shapes, SCARLET-1.0 places each element in the vector around the core minimizing the distances between their centers of mass. The user can play with three main parameters that are in charge of controlling the minimization process, namely the solid angle of the cone of investigation (Ω), the number of rays per cone (Nr), and the number of orientations of the object (No). All the 3D shapes are described using the STL format, the nowadays standard for 3D printing. This is one of the key features of SCARLET-1.0, which results in an unlimited range of application of the package. The main outcome of the code is the virtual representation of the object, its size, porosity, density and the associated STL file. As an example, here SCARLET-1.0 has been applied to the investigation of ellipsoid-ellipsoid collisions and to a more specific analysis of volcanic ash aggregation. In the first application we show that the final porosity of two colliding ellipsoids is less than 20 % if flatness and elongation are greater than or equal to 0.5. Higher values of porosities (up to 40–50 %) can be, instead, found for ellipsoids with needle-like or extremely flat shapes. In the second application, we reconstruct the evolution in time of the porosity of two different aggregates characterized by different inner structures. We find that aggregates whose population of particles is characterized by a narrow distribution of sizes tend to rapidly reach a plateau in the porosity. In addition, to reproduce the observed densities, almost no minimization is necessary in SCARLET-1.0; a result that suggests how these objects are quite far from the maximum packing condition often investigated in literature.

Eduardo Rossi and Costanza Bonadonna

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Eduardo Rossi and Costanza Bonadonna

Eduardo Rossi and Costanza Bonadonna


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Short summary
SCARLET-1.0 is a Matlab package that creates virtual aggregates starting from a population of irregular shapes. Shapes are described in terms of the STL format and this allows importing a great variety of shapes, such as the one from 3D scanning. The package produces a new STL file as an output and different analytical information about the packing, such as the porosity. It has been thought for an use in volcanology, planetary formation and for scientific education.