In English

A software toolkit for generating ice and snow particle sharp data

Torbjörn Rathsman
Göteborg : Chalmers tekniska högskola, 2016. 124 s.
[Examensarbete på avancerad nivå]

Abstract Ice and snow particle shape data are important for understanding the scattering of microwave radiation from a cloud. This thesis presents a software toolkit that can be used to generate such data, for use with Discrete Dipole Approximation calculations. The toolkit has been used to implement a Gillespie-based algorithm with overlap rejection. This algorithm, when used with hexagonal columns, has reproduced some of the properties of real snowflakes, namely their fractal dimension, and their size distribution. The toolkit uses ice crystal prototypes to construct aggregates. Ice crystal prototypes can be modeled in 3D modelling software. This makes it is easy to construct exotic shapes, as opposed to a system based on different classes for different prototypes. In order to keep the possibility of arbitrary parameterisation, the ice crystal prototypes specifies transformation rules that are used if the ice crystal prototype should be deformed. Aggregates and ice crystal prototypes can be merged in different ways to form larger aggregates. To feed a DDA calculation program, the toolkit also provides a rasterisation system, which fills geometry with voxels by using a 6-directional floodfill algorithm. A large part of the thesis discusses various ways of measuring particles. This has lead to a unit neutral way of testing whether or not a model simulates reality. The idea is to compare an averaged spherical volume fill ratio, which according to measurements should follow a particular equation, derived within this thesis. Besides giving an overview of the toolkit, and presenting simulation results, this thesis also serves as a reference manual on how to use the toolkit.

Nyckelord: software toolkit for ice and snow particle shape data



Publikationen registrerades 2016-04-11. Den ändrades senast 2016-04-11

CPL ID: 234473

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