DEM: Discrete Element Modeling

Beside the already large need of simulating continuum phenomena (e.g. by means of CFD, FEM, …), requests for simulating phenomena belonging to the discrete domain are quickly growing up, mainly for the granular mechanics and/or its interaction with continuum fields like fluids. DEM is the technique devoted to this aim. Every single particle, even with shapes and properties different one from each others, is tracked alongside its dynamic behavior in time. Newton’s second law and Euler law are integrated in time in order to compute forces and moments acting on solid particles, thus infering their velocity vectors. Standard numerical techniques scale well among several parallel CPUs, but industrial applications would need hundreds of CPUs for studying complex systems made by several millions of particles in order to meet the time constraints of the Customers. GPU technology solves this kind of problems. DOFWARE takes advantage of this technique, reducing the computational time by some orders of magnitude.

Among the main codes DOFWARE is using for performing DEM simulations, we cite LIGGGHTS®, an open-source tool based on the well known LAMMPS® code, applied to molecular dynamic simulations. LIGGGHTS® is the solution both as standalone code and coupled with OpenFOAM® (ref. CFDEM® project): a 2-way coupling describes the interaction between solid particles and fluid domains.

SPH: Smoothed Particle Hydrodynamics

SPH adopts a qualitatively similar approach, in the sense that, as DEM, solves the dynamics of discrete particles. However the aims and the physical approach are completely different. The SPH is a so-called CFD meshless technique, since it allows to reproduce fluid dynamic fields behavior without adopting static Eulerian meshes as the standard FVM. The SPH solves the Navier-Stokes equations over several discrete points which move according to the flow field (Lagrangian point of view). 

SPH is growing up very quickly in the last years: its appeal is outdoing that of standard CFD, mainly for what concerns multiphase flows where a sharp interface separates different kinds of fluids (e.g. wave phenomena, hydrodynamics, hydraulics, aquaplaning). The main advantages of SPH concern the simulation effort:

  • quick pre-processing stage, as no volume mesh is needed;
  • discretization focused only on important fluids;
  • great ability to deal with moving boundaries without reducing stability;
  • great ability to run not only on standard CPU architectures, but also on GPUs, with a drastic computational time reduction.

DOFWARE adopts the SPH mainly for multiphase flow analysis: open-source codes are used, which enable customizations tailored to the Customer needs.