Contact detection algorithms for DEM simulations of tablet-shaped particles Yongxin Song a,1 , Richard Turton a, * , Ferhan Kayihan b a Department of Chemical Engineering, West Virginia University, P.O. Box 6102, Morgantown, WV 26506, USA b IETek, Integrated Engineering Technologies, 5533 Beverly Ave. NE, Tacoma, WA 98422-1402, USA Received 17 May 2005; received in revised form 11 July 2005; accepted 12 July 2005 Available online 8 September 2005 Abstract The shape of standard round tablet was represented by using the intersection of three spherical surfaces. Using this model, the contact criteria for tablet – flat surface and tablet – tablet contact were developed and were applied for tablet – tablet contact using a DEM simulation implemented in Matlabi code. In addition, a high-speed digital imaging system was used to capture the images of one tablet hitting another fixed tablet anchored to a flat surface. Comparison of angular velocity showed good agreement between simulation and experimental results. The simulations were compared with alternative multi-sphere representations for the shape of the tablet and the results showed that the simulation times for 66- and 178-sphere representations were much larger than that for the tablet simulations. In addition, the simulation results for all the multi-sphere representations were significantly different from those of the tablet simulation. D 2005 Elsevier B.V. All rights reserved. Keywords: Tablets; DEM; Contact algorithm; Imaging 1. Introduction The Discrete Element Modeling (DEM) method is being used widely in particulate systems to simulate the dynamic behavior of particle assemblies. The factors affecting the accuracy of the DEM simulations include the particle shape representation and the contact force models for the interact- ing particles in the system [1–3]. Much simulation work has been done on circular and elliptical particles in two- dimensional coordinate systems and on spherical particles in three-dimensional systems [4–9]. For simplicity, spherical particles have been used to estimate the dynamic behavior of particle assemblies [10] in simulations of non-spherical particle-systems. However, the concern of using this approximation is the accuracy of the simulation results. It was shown in investigations of the effects of particle shape on the dynamic behavior in a rotating drum [11], that there were higher dynamic angles of repose for tablets and much higher average velocity for tablets in the cascading layer than for spheres. Therefore, using some form of equivalent spherical particle to represent non-spherical tablet-shaped solids in DEM simulations is probably not a good approximation. Accompanying the increase in CPU speed and distributed computing techniques, non-spherical particles such as ellip- soidal, polyhedral, superquadric, multi-sphere particles, and digitized representations have been modeled in three-dimen- sional systems [12–18]. However, due to the complex contact detection schemes for these non-spherical particles, it is extremely computationally expensive to implement the DEM simulations for systems with a large number of particles. Nevertheless, if accurate DEM simulations of real solids are to be achieved then more realistic particle shapes must be used. In the current work, the intersection of just three spheres is used to describe accurately the shape of a typical round tablet. This is illustrated in Fig. 1. From the figure, it can be 0032-5910/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.powtec.2005.07.004 * Corresponding author. Tel.: +1 304 293 2111x2415; fax: +1 304 293 4139. E-mail addresses: s _ yongxin@yahoo.com (Y. Song), richard.turton@mail.wvu.edu (R. Turton), fkayihan@ietek.net (F. Kayihan). 1 Tel.: +1 304 293 2111x2402; fax: +1 304 293 4139. Powder Technology 161 (2006) 32 – 40 www.elsevier.com/locate/powtec