James A. Elliott^a, Dingeman L.H. van der Haven^a, Ioannis S. Fragkopoulos^b

^a Department of Materials Science & Metallurgy, University of Cambridge, 27 Charles Babbage Road, Cambridge, CB3 0FS, United Kingdom

^b Oral Drug Product Process Development, Novo Nordisk A/S, Måløv, Denmark

Purpose. Describing particle shape in discrete element models of pharmaceutical powder compaction or flow is constrained by the lack of a simple way to map the diverse range of complex contours onto a set of parameters which are easily characterizable experimentally. I will describe a recently developed technique for describing particles of arbitrary shape based on mathematical objects called level sets and show how these can be used to predict the porosity and angle of repose for particles with differing convexity and angularity. I will also show in principle how they can be parameterized experimentally, which will be enlarged upon in a related contributed talk.

Methods. The level set discrete element method (Andrade et al. 2016) uses a signed distance function to represent particle shape as a continuous contour where the function is zero. Although this allows greater flexibility in describing shape than using spheres or polygons, it makes it much more difficult to describe particle interactions correctly. Here, I explain how elastic forces between particles of arbitrary shape can be calculated from the volume overlap of particles at a computational cost not greatly exceeding the original method, and much less than clumped spheres with a comparable level of spatial resolution.

Results. Validation tests for spheres and concave particles will be presented, together with predictions of angle of repose and porosity for hyperbolized Platonic solids with differing convexity and angularity.

Conclusions. The VLS-DEM method is a versatile and powerful new method for pharmaceutical powder simulations implemented in open-source software (YADE).