Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Fast parallel algorithms for short-range molecular dynamics

Mesoscale modelling of concrete – A review of geometry generation, placing algorithms, constitutive relations and applications

We investigate the dynamic behavior of concrete in relation to its composition within a computational framework (FEM). Concrete is modeled using a meso-mechanical approach in which aggregates and mortar are represented explicitly. Both continuum phases are considered to behave elastically, while nucleation, coalescence and propagation of cracks are modeled using the cohesive-element approach. In order to understand the loading-rate sensitivity of concrete, we simulate direct tensile-tests for strain rates ranging 1–1000 s−1. We investigate the influence of aggregate properties (internal ordering, size distribution and toughness) on peak strength and dissipated fracture energy. We show that a rate independent constitutive law captures the general increase of peak strength with strain rate. However, a phenomenological rate-dependent cohesive law is needed to obtain a better agreement with experiments. Furthermore, at low rates, peak strength is sensitive to the inclusions' toughness, while the matrix dominates the mechanical behavior at high rates.

Influence of Meso-structure on the Dynamic Fracture Simulation of Concrete Under Tensile Loading

Modeling the fragmentation of rock grains using computed tomography and combined FDEM

Discrete element modeling of crushable sands considering realistic particle shape effect

It is well known that particle breakage plays a critical role in the mechanical behavior of granular materials and has been a topic subject to intensive studies. This paper presents a three dimensional fracture model in the context of combined finite-discrete element method (FDEM) to simulate the breakage of irregular shaped granular materials, e.g., sands, gravels, and rockfills. In this method, each particle is discretized into a finite element mesh. The potential fracture paths are represented by pre-inserted non-thickness cohesive interface elements with a progressive damage model. The Mohr–Coulomb model with tension cut-off is employed as the damage initiation criterion to rupture the predominant failure mode at the particle scale. The particle breakage modeling using combined FDEM is validated by the qualitative agreement between the results of simulated single particle crushing tests and those obtained from laboratory tests and prior DEM simulations. A comprehensive numerical triaxial tests are carried out on both the unbreakable and breakable particle assemblies with varied confining pressure and particle crushability. The simulated stress–strain–dilation responses of breakable granular assembly are qualitatively in good agreement with the experimental observations. The effects of particle breakage on the compressibility, shear strength, volumetric response of the fairly dense breakable granular assembly are thoroughly investigated through a variety of mechanism demonstrations and micromechanical analysis. This paper also reports the energy input and dissipation behavior and its relation to the mechanical response.

A hybrid approach for modeling of breakable granular materials using combined finite-discrete element method

Mesoscopic simulation of the dynamic tensile behaviour of concrete based on a rate-dependent cohesive model

Three-dimensional mesoscopic simulation of the dynamic tensile fracture of concrete

Molecular dynamics study of fatigue mechanical properties and microstructural evolution of Ni-based single crystal superalloys under cyclic loading

Orientation-Dependent Morphology and Evolution of Interfacial Dislocation Networks in Ni-Based Single-Crystal Superalloys: A Molecular Dynamics Simulation

Ming-Xiang Chen

Papers

A hybrid approach for modeling of breakable granular materials using combined finite-discrete element method

Mesoscopic simulation of the dynamic tensile behaviour of concrete based on a rate-dependent cohesive model

Three-dimensional mesoscopic simulation of the dynamic tensile fracture of concrete

Molecular dynamics study of fatigue mechanical properties and microstructural evolution of Ni-based single crystal superalloys under cyclic loading

Orientation-Dependent Morphology and Evolution of Interfacial Dislocation Networks in Ni-Based Single-Crystal Superalloys: A Molecular Dynamics Simulation