Chong Peng

Dilatancy and compaction effects on the submerged granular column collapse

The effects of dilatancy on the collapse dynamics of granular materials in air or in a liquid are studied experimentally and numerically. Experiments show that dilatancy has a critical effect on the collapse of granular columns in the presence of an ambient fluid. Two regimes of the collapse, one being quick and the other being slow, are observed from the experiments and the underlying reasons are analyzed. A two-fluid smoothed particle hydrodynamics model, based on the granular-fluid mixture theory and the critical state theory, is employed to investigate the complex interactions between the solid particles and the ambient water. It is found that dilatancy, resulting in large effective stress and large frictional coefficient between solid particles, helps form the slow regime. Small permeability, representing large inter-phase drag force, also retards the collapse significantly. The proposed numerical model is capable of reproducing these effects qualitatively.

Modelling of a Free Surface Flow at Variable Gravity Conditions with SPH

Smoothed Particle Hydrodynamics (SPH) are adapted to model a free surface flow at variable gravity conditions. Implementation of SPH related to high gravity fields are discussed. The analysis shows that the original formulation of SPH needs no modification for the variation of gravity, though a smaller time step must be used. Numerical simulations of a water flow problem show that SPH is consistent at different gravity fields, and produce reasonable results. The scaling principle of the velocity and time of a flowing mass down an incline is discussed.

Large Deformation Modeling of Soil-Machine Interaction in Clay

The evaluation of soil reaction force on tillage tool is important for design and management optimization. The large deformation, dynamic nature and complex soil-tool contact in the problem make it a challenge in numerical modeling. The popular finite element method (FEM) has distorted mesh in large deformation, and complex adaptive remeshing techniques need to be used in soil-tool interaction simulation. On the other hand, numerical approaches based on computational fluid mechanics (CFD) and discrete element method (DEM), although avoid mesh distortion, have difficulties in capturing the true mechanical properties of soils. In this study, we develop a total Lagrangian SPH (TL-SPH) approach for simulating the large deformation soil-machine interaction in clay. The TL-SPH is simple in formulation and computationally efficient. The accuracy and stability of the method is improved by employing an hourglass control technique. Soil-tool contact is modeled using a node-to-segment (NTS) contact algorithm. Preliminary numerical studies are carried out, it is demonstrated that the presented approach is capable of capturing salient soil-tool interaction properties.

Model Tensile Cracking in Soil with Coupled Meshless-FEM Method

An adaptive, coupled method based on radial point interpolation meshless method (RPIM) and finite element method (FEM) is proposed for the simulation of tensile cracking in soil structure. Potential crack area in the initial FEM mesh is converted to RPIM nodes and refined for crack analysis. A crack tracking approach is adapted to model complex crack surface and eliminate node distribution bias. Numerical example is presented to verify the proposed method.