ESyS-Particle: Virtual Rock Laboratory
A proposal for infrastructure construction within AuScope NCRIS
D. Weatherley(1), A. Ord(2) and R. Woodcock(2)
(1) Earth Systems Science Computational Centre (ESSCC), University of Queensland, Brisbane, Qld.
(2) Australian Resources Research Centre (ARRC), CSIRO, Bentley, WA.
Background and Aims
The Discrete Element Method (DEM) is a powerful and oft utilised numerical tool for rock mechanics
research, particularly for fundamental studies of rock breakage and laboratory-scale simulations of
comminution processes. Its power stems from the discretisation of rock into a large number of
constituent particles interacting via simplified laws for elasticity, friction, breakage and other
phenomena. DEMs capture naturally the self-organisation associated with damage evolution and
fragmentation, without the burden of dynamic re-meshing required by continuum-based breakage
models.
DEM permits investigation of the internal dynamics leading to damage and final failure of rocks –
features often beyond direct observation. However DEM research is generally stifled by the
computational demand imposed by the method. One example is the research by Ord et al. (REF) on the
self-organisation of micro-cracks preceding macroscopic failure of rock samples. A long-term goal of
this research has been to understand the observed reduction in compressive strength of rocks larger
than 20cm diameter, as compared with their smaller counterparts. A significant fraction of the world's
energy usage is expended on comminution in the mining industry, where the goal is to crush rocks to
powder for separation and processing of ores. The marked increase in the competency of small rocks is
a major factor contributing to comminution energy usage. Ord (REF) has demonstrated that DEM
models reproduce the stress-strain behaviour of small rock samples under compressive loads however
the computational demand of DEM has long prevented scaling these models for studies of larger rocks.
The ESyS-Particle DEM simulation software was developed by the Australian Computational Earth
Systems Simulator AccESS) MNRF specifically to address the computational limitations of existing
DEM software. EsyS-Particle provides a parallel DEM simulation engine optimised for high-end
supercomputers such as the Aust. Solid Earth Simulator (Univ. of Qld) and the iVEC supercomputer
(CSIRO, WA). The software implements a novel law for bonded particle interactions designed to
accurately model rock breakage, specifically the formation of wing-cracks emanating from pre-existing
cracks within a rock sample (Wang and Mora, 2006). Research on fault gouge formation demonstrates
the capacity of this software to accurately reproduce the results of laboratory shear cell experiments,
utilising models consisting of up to 1 million particles (Abe and Mair, REF).
A python scripting interface has been developed to permit rapid construction of new model setups
without changes to the core DEM engine of ESyS-Particle. The scripting interface provides a powerful
mechanism for users with computer programming skills, however the lack of a GUI detracts a broad
community of end-users familiar with the use of commercial DEM software. Coupled with a perception
that supercomputers are difficult to use or inaccessible by end-users, EsyS-Particle faces significant
challenges to broader its userbase, particularly in the comminution and geomechanics communities.
Whilst DEMs naturally model breakage, the parameters employed in the simplified interaction laws
typically have no known mathematical relationship with the macroscopic material properties typically
utilised to characterise rock masses (Young's modulus, poissons ratio, unconfined compressive strength
etc.). Consequently it is necessary to undertake a calibration process whenever DEMs are used to
model the dynamics of specific rock types. The calibration consists of a series of numerical simulations
(analogous to standard rock laboratory tests) to measure the macroscopic properties of DEM rock
samples and, in an inversion process, tune the microphysical parameters to achieve the desired
macroscopic properties. This procedure is currently laborious and time-consuming. Calibration is
performed on a needs basis by individual modellers and often the results of the calibration are
unpublished, despite being valuable for future studies.
We propose to address the accessibility and calibration issues of EsyS-Particle by constructing a virtual
rock laboratory. The laboratory will consist of a grid portal to construct and execute simulations on the
AuScope Grid, and an online simulation data repository providing an extensible, searchable database of
pre-calibrated DEM rock samples. The grid portal will be designed for easy use by end-users without
programming experience, providing a seamless interface to supercomputers on the AuScope Grid by
non-technical DEM modellers. The inversion component of the calibration process will be automated
so that users simply specify the target macroscopic properties and a series of simulations are initiated to
tune the DEM rock sample without further user interaction. The final calibrated rock sample will be
stored in the simulation data repository for use in future DEM studies on rock mechanics, thus
accelerating future research utilising DEM simulations.
Construction Plans
Grid Portal
1. Installation of EsyS-Particle on AuScope supercomputers
2. Meta-data schema for simulation setup, data and results
3. GUI Grid portal or desktop client for setup, execution and monitoring of simulations (based on
GGC?)
Automated Calibration Workflow
1. Development and testing of the rock laboratory simulation suite (Brazilian test, UCS/UTS tests,
friction angle etc.)
2. Nimrod implementation of inversion for macroscopic properties
Simulation Data Repository
1. Grid repository query service for searches
2. Import rock samples from repository directly into new simulations (staging etc.)
National Benefit and Technology Transfer
Benefits:
 targeted portal for users with moderate experience with applied DEM modelling but limited
computer programming skills -> greatly increase user-base for ESyS-Particle
 provision of HPC DEM simulation capability to user-base traditionally restricted to serial
computations and small model sizes
 rigorous framework for inversion-based calibration/validation studies
 comprehensive collation of simulation meta-data
 provision of virtual petrology database permitting future simulation studies to leap-frog the time-
consuming calibration procedures and jump straight to new simulations of R&D benefit
Collaborations:
 Australian Minerals Science Research Institute (AMSRI) Programme 1: Energy Efficient
Comminution (in collaboration with JKMRC/UQ) – calibrated virtual rock mass for studies on
fundamentals of rock breakage and optimisation of comminution devices
 Mass-Mining Technologies (MMT) Initiative – fundamentals of caving fragmentation
 Rio Tinto: fines migration in block-caving
 International Collaboration: University of Aachen, Germany – 3D HPC simulations of fault gouge
evolution and comminution in shear cells
Personnel

Chief Investigators:
 D. Weatherley, Project Leader, Auscope M&S Project 4.4
 A. Ord, ARRC Senior Research Scientist
 R. Woodcock, Working Group Leader, Auscope Grid WG

Project Personnel:
 D. Weatherley (25%) EsyS-Particle lead developer, strategic software development (ESSCC inkind) Supervision of embedded software engineer, installation of EsyS-Particle on VPAC,
APAC NF, iVEC, ESSCC, QCIF, (other PACs?)
 Embedded software engineer (100% 6-12months funded by Auscope Grid) grid portal
development – distributed simulation execution on Auscope Grid, Nimrod control of inversion
studies, construction of Grid Repository for simulation journal and virtual petrology database
 A. Ord (X%) Scientific oversight and high-level design of virtual petrology database
 R. Woodcock (or similar person X%) Grid development oversight
References