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contact detection algorithm were developed, which enhances the overall calculation ef-
ficiency for particle interaction characteristics. In this work, the irregular particle shapes
and random sizes are represented as a pseudo-particle assembly having a scaled-up ge-
ometry, but based on variations of real powder particles. The simulation results show
that particle size, shapes, and material properties have a significant influence on the be-
havior of compaction and deformation. Gethin et al. (2006) utilized the combined finite-
discrete element method to simulate the flow and compaction of irregular randomly
packed particles to form a tabletted product. In this work, the techniques which have
been adopted to achieve computational efficiency are described, which include contact
detection, particle-level deformation analysis, and a homogenization strategy. The com-
putational scheme is validated using published data and is shown to be capable of simu-
lating effects of particle shape, size, and friction on the flow rate. The advantage of the
scheme is the flexibility that it offers to capture a mixture of material properties and par-
ticle shape and that no restrictions are necessary on the contact models since these are
integral in the calculation procedures. Mamaghani (2006) used the discrete finite element
method (DFEM) to model masonry bridges, which are composed of a finite number of
distinct interacting blocks that have a length scale relatively comparable to the structure
of interest. The developed DFEM is based on the principles of the FEM that incorporate
contact elements. DFEM considers blocks as sub-domains and represents them by solid
elements. Contact elements, which are superior to joint or interface elements, are used to
model the block interactions, such as sliding or separation. In this work, some typical
examples are illustrated in order to analyze the applicability of the DFEM. Based on their
conclusion, the DFEM could become a useful tool for researchers in designing, analyzing,
and studying the behavior of masonry bridges under static and dynamic loading.

9.8 Similarities between DEM and Molecular Dynamics
An analysis of the similarity between the DEM approach and the molecular dynamics
(MD) approach would be interesting in that these two techniques may be combined for
multiscale modeling. Both methods use the finite difference method to simulate the
multi-body interactions. MD uses potential and derives forces from potentials. It can
consider not only the nearest neighbor interactions, but also interactions with molecules
some distances away. However, the DEM approach can only consider the interactions
of particles in contact. A combination of the two methods may present potential for
multiscale modeling.

References
Abbas, A., Masad, E., Papagiannakis, T. and Shenoy, A. (2005). Modeling asphalt mastic stiffness
using discrete element analysis and micromechanics-based models. International Journal of
Pavement Engineering, Vol.6, No.2, pp.137–146.
Abbas, A., Masad, E., Paapagiannakis, T. and Harman, T. (2007). Micromechanical modeling of
the viscoelastic behavior of asphalt mixtures using the discrete-element method. Interna-
tional Journal of Geomechanics, Vol.7, No.2, pp.131–139.
Abbas, A. R., Papagiannakis, A. T. and Masad, E. A. (2006). Micromechanical simulation of
asphaltic materials using the discrete element method. Geotechnical Special Publication,
No.146, pp.1–11.
Bangash, T. and Munjiza, A. (2003). Experimental validation of a computationally effi cient beam

for combined finite-discrete element modeling of structures in distress. Computational Me-
chanics, Vol.30, No.5/6, pp.366–73.