A TWO-DIMENSIONAL PARTICLE MODELING METHOD FOR COMPLEX REGIONS BASED ON EXPANDING PARTICLE DDA

This paper proposes a novel modeling method for disk-based models of materials with complex geometries containing holes and fractures. This method innovatively adopts the Discontinuous Deformation Analysis (DDA) method as the mechanical framework and achieves a uniformly dense packing state through three steps: initial particle placement, particle expansion and self-coordinated equilibrium, and acquisition of a uniformly dense packing. In the modeling process, the filling region is first defined, and the packing density and particle size distribution are specified. Particles are then gradually reduced in size and placed into the filling region without overlap. Subsequently, while progressively enlarging the particles, the disk DDA is employed to drive the particles toward equilibrium positions. Finally, when the displacement increments of the particles satisfy the preset convergence criteria, the final circular element model is obtained. A series of systematic case studies were carried out, and the results showed that the proposed method exhibits high computational stability and strong adaptability to complex internal and external contours as well as fractures of the filling region. Owing to the advantages of the implicit solution used in DDA method, this modeling approach can simultaneously precisely control both the particle size distribution and packing density while ensuring the uniformity and randomness of the final model. The modeling method also maintains reasonable computational efficiency; when running the modeling program serially on an ordinary PC, models containing tens of thousands of particles can be generated within several minutes, yielding a modeling efficiency slightly higher than that of the PFC (Particle Flow Code) software. The complexity of model contours and fractures does not affect the computation time per time step, but does influence the number of steps required to achieve convergence. This modeling method can further promote the development and application of discontinuous numerical methods that use circular elements as fundamental elements.