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

Review: Calibration of the discrete element method

The contribution of DEM to the science of comminution

Clayey soils are usually stiff when they are dry and give up their stiffness as they become saturated. Soft clays are associated with low compressive strength and excessive settlement. This reduction in strength due to moisture leads to severe damages to buildings and foundations. The soil behavior can be a challenge to the designer build infrastructure plans to on clay deposits. The damage due to the expansive soils every year is expected to be $1 billion in the USA, £150 million in the UK, and many billions of pounds worldwide. The damages associated with expansive soils are not because of the lack of inadequate engineering solutions but to the failure to identify the existence and magnitude of expansion of these soils in the early stage of project planning. One of the methods for soil improvement is that the problematic soil is replaced by suitable soil. The high cost involved in this method has led researchers to identify alternative methods, and soil stabilization with different additives is one of those methods. Recently, modern scientific techniques of soil stabilization are on offer for this purpose. Stabilized soil is a composite material that is obtained from the combination and optimization of properties of constituent materials. Adding cementing agents such as lime, cement and industrial byproducts like fly ash and slag, with soil results in improved geotechnical properties. However, during the past few decades, a number of cases have been reported where sulfate-rich soils stabilized by cement or lime underwent a significant amount of heave leading to pavement failure. This research paper addressed the some fundamental and success soil improvement that used in civil engineering field.

/pdf/fundamentals-of-soil-stabilization-4djewn9bar.pdf

Fundamentals of soil stabilization

Calibration of the discrete element method and the effect of particle shape

Characterization of artificial spherical particles for DEM validation studies

In this study experimental data on a model soil in a cubical cell are compared with both discrete element (DEM) simulations and continuum analyses. The experiments and simulations used point source transmitters and receivers to evaluate the shear and compression wave velocities of the samples, from which some of the elastic moduli can be deduced. Complex responses to perturbations generated by the bender/extender piezoceramic elements in the experiments were compared to those found by the controlled movement of the particles in the DEM simulations. The generally satisfactory agreement between experimental observations and DEM simulations can be seen as a validation and support the use of DEM to investigate the influence of grain interaction on wave propagation. Frequency domain analyses that considered filtering of the higher frequency components of the inserted signal, the ratio of the input and received signals in the frequency domain and sample resonance provided useful insight into the system response. Frequency domain analysis and analytical continuum solutions for cube vibration show that the testing configuration excited some, but not all, of the system’s resonant frequencies. The particle scale data available from DEM enabled analysis of the energy dissipation during propagation of the wave. Frequency domain analysis at the particle scale revealed that the higher frequency content reduces with increasing distance from the point of excitation.

https://link.springer.com/content/pdf/10.1007%2Fs10035-015-0599-4.pdf

Micromechanics of seismic wave propagation in granular materials

A pluviation device for the fabrication of cubical samples of granular materials has been recently developed. The granular material is pluviated under gravitational loading through a rectangular Pe...

Experimental and numerical assessment of a cubical sample produced by pluviation

Understanding wave propagation through soils is essential for site response analysis in earthquake engineering, interpretation of geophysical surveys and SASW (Spectral Analysis of Surface Waves), interpretation of laboratory bender element tests, etc. Analysis of wave propagation has largely been based on continuum descriptions and two dimensional analyses. This study presents recent developments in multiaxial testing that permit the combination of laboratory seismic testing with exploration of three-dimensional principal stress space. A Cubical Cell Apparatus with bender-extender piezoceramic elements fitted in all six faces are used so that wave propagation velocities of an analogue granular material can be determined. The results of a first series of wave propagation tests for a sample under isotropic confinement are presented.

S. Hamlin

Papers

Characterization of artificial spherical particles for DEM validation studies

Micromechanics of seismic wave propagation in granular materials

Micromechanics of seismic wave propagation in granular materials

Experimental and numerical assessment of a cubical sample produced by pluviation

Experimental investigation of wave propagation in three dimensions in unbounded particulate assemblies