Discrete element simulation of crushable rockfill materials

A discrete element method was used to study the evolution of particle crushing in a rockfill sample subjected to triaxial shear. A simple procedure was developed to generate clusters with arbitrary shapes, which resembled real rockfill particles. A theoretical method was developed to define the failure criterion for an individual particle subjected to an arbitrary set of contact forces. Then, a series of numerical tests of large-scale drained triaxial tests were conducted to simulate the behaviors of the rockfill sample. Finally, we examined the development of micro-characteristics such as particle crushing, contact characteristics, porosity, deformation, movement, and energy dissipation. The simulation results were partially compared with the laboratory experiments, and good agreement was achieved, demonstrating that the particle crushing model proposed can be used to simulate the drained triaxial test ofrockfill materials. Based on a comparison of macro behaviors of the roekfill sample and micro structures of the particles, the microscopic mechanism of the rockfill materials subjected to triaxial shear was determined qualitatively. It is shown that the crushing rate, rather than the number of crushed particles, can be used to reflect the relationship between macro- and micro-mechanical characteristics of rockfill materials. These research results further develop our understanding of the deformation mechanism of rockfill materials.

Generalized elastic curves in the Lorentz flat space L^4

In this paper, we study the extremals of the curvature energy actions on non-null curves in the four-dimensional Lorentz-Minkowski space. We derive the motion equations and find three Killing fields along the generalized elastic curves. We also construct a cylindrical coordinate system using these Killing fields and express the generalized elastic curves by means of quadratures.

Tracking and grasping of moving target based on accelerated geometric particle filter on colored image

Visual tracking and grasping of moving object is a challenging task in the field of robotic manipulation,which also has great potential in applications such as human-robot collaboration.Based on the particle filtering framework and position-based visual servoing,this paper proposes a new method for visual tracking and grasping of randomly moving objects.A geometric particle filter tracker is established for visual tracking.In order to deal with the tracking efficiency issue for particle filter,edge detection and morphological dilation are employed to reduce the computation burden of geometric particle filtering.Meanwhile,the HSV image feature is employed instead of the grayscale feature to improve the tracking algorithm’s robustness to illumination change.A grasping strategy combining tracking and interception is adopted along with the position-based visual servoing(PBVS)method to achieve stable grasp of the target.Comprehensive comparisons on open source dataset and a large number of experiments on real robot system are conducted,which demonstrate the proposed method has competitive performance in random moving object tracking and grasping.