Micromechanics of seismic wave propagation in granular materials
TL;DR: In this paper, experimental data on a model soil in a cubical cell are compared with both discrete element (DEM) simulations and continuum analyses and the results show that 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.
Abstract: 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.
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01 May 1993
TL;DR: 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.
Abstract: 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.
29,323 citations
TL;DR: This Topical Collection includes novel theories, innovative experimental tools and new numerical approaches focusing primarily on three subtopics governing important multiscale properties of granular media: the jamming transition from fluid- to solid-like behavior, critical state flow and wave propagation.
Abstract: We report the latest advances in understanding, characterization and modeling of key micro mechanisms and origins underpinning the interesting and complex macroscopic behavior of granular matter. Included in this Topical Collection are novel theories, innovative experimental tools and new numerical approaches, focusing primarily on three subtopics governing important multiscale properties of granular media: (a) the jamming transition from fluid- to solid-like behavior, critical state flow and wave propagation, (b) the signature of fabric and its evolution for granular media under general loading conditions, and (c) mechanisms like rotation, breakage, failure and aggregation. The significance of these contributions and exploratory future directions pertaining to cross-scale understanding of granular matter are discussed
51 citations
TL;DR: In this article, the sensitivity of the DEM simulation results to sample size, contact model and stiffness inputs, and ring wall boundary effects was examined by examining the radial and vertical void ratio distributions throughout the samples.
45 citations
TL;DR: In this paper, the authors perform static and dynamic probing to deduce elastic moduli/wave velocities from small-strain modulus degradation and time/frequency-domain signals.
29 citations
Cites methods from "Micromechanics of seismic wave prop..."
...The peak-to-peak method (O’Donovan et al., 2015) is employed to determine the travel time in the time domain....
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TL;DR: In this article, discrete element method (DEM) simulations of planar compression wave propagation were performed to generate the data for the study, and the assembly stiffness and mass matrices were extracted from the DEM model and these data were used in an eigenmode analysis that provided significant insight into the observed overall dynamic response.
Abstract: Laboratory geophysics tests including bender elements and acoustic emission measure the speed of propagation of stress or sound waves in granular materials to derive elastic stiffness parameters. This contribution builds on earlier studies to assess whether the received signal characteristics can provide additional information about either the material’s behaviour or the nature of the material itself. Specifically it considers the maximum frequency that the material can transmit; it also assesses whether there is a simple link between the spectrum of the received signal and the natural frequencies of the sample. Discrete element method (DEM) simulations of planar compression wave propagation were performed to generate the data for the study. Restricting consideration to uniform (monodisperse) spheres, the material fabric was varied by considering face-centred cubic lattice packings as well as random configurations with different packing densities. Supplemental analyses, in addition to the DEM simulations, were used to develop a more comprehensive understanding of the system dynamics. The assembly stiffness and mass matrices were extracted from the DEM model and these data were used in an eigenmode analysis that provided significant insight into the observed overall dynamic response. The close agreement of the wave velocities estimated using eigenmode analysis with the DEM results confirms that DEM wave propagation simulations can reliably be used to extract material stiffness data. The data show that increasing either stress or density allows higher frequencies to propagate through the media, but the low-pass wavelength is a function of packing density rather than stress level. Prior research which had hypothesised that there is a simple link between the spectrum of the received signal and the natural sample frequencies was not substantiated.
24 citations
Cites background or result from "Micromechanics of seismic wave prop..."
...[13] showed that the system response observed in DEM simulations of dynamic tests gives a reasonable match to that observed in equivalent physical laboratory tests....
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...[13] found that the relationship between particle size and flow−pass differs from that proposed by Santamarina and Aloufi [10] and Santamarina et al....
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...13 confirms the observations based on data in [13] and shows that flow−pass increases with stress for the random dense packing (test cases 7 and 8)....
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References
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TL;DR: In this article, three parallel algorithms for classical molecular dynamics are presented, which can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors.
32,670 citations
01 May 1993
TL;DR: 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.
Abstract: 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.
29,323 citations
"Micromechanics of seismic wave prop..." refers methods in this paper
...The DEM specimens were created by first pluviating spherical particles, with a particle size distribution (PSD) corresponding to the laboratory measured PSD, under gravity loading using the DEM code Granular LAMMPS [19,20]....
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...LAMMPS is MPI parallelised and so well suited to simulating the computationally expensive pluviation process....
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TL;DR: In this paper, a numerical model for rock is proposed in which the rock is represented by a dense packing of non-uniform-sized circular or spherical particles that are bonded together at their contact points and whose mechanical behavior is simulated by the distinct element method using the two-and three-dimensional discontinuum programs PFC2D and PFC3D.
3,470 citations
"Micromechanics of seismic wave prop..." refers methods in this paper
...During pluviation, energy was dissipated using the local damping approach described by [21] with a coefficient of 0....
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TL;DR: In this article, the authors used the resonant column method to evaluate the longitudinal and shear wave velocities in specimens of Ottawa sand, crushed quartz sand, and crushed quartz silt.
Abstract: Laboratory tests, using the resonant column method, were conducted to evaluate the longitudinal and shear wave velocities in specimens of Ottawa sand, crushed quartz sand, and crushed quartz silt. The variables considered were the confining pressure, and the moisture content, void ratio, and grain characteristics of the materials. The wave velocities for the sands varied with approximately the 1/4 power of the confining pressure. At a given confining pressure, the velocity varied almost linearly with void ratio. A diagram is included that shows these relationships over a range of void ratio from 0.3 to 1.3 and confining pressures between 500 psf and 6,000 psf. The effects of relative density, grain size, and gradation entered only through their effects on void ratio. The wave velocities in the quartz silts were found to be greatly dependent on time.
958 citations
"Micromechanics of seismic wave prop..." refers background or methods in this paper
...The void ratio correction factor used was a modified version of the one obtained from [2] with a factor of 2....
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...Interpretation of data from dynamic tests based on response of resonant columns, [2], and the measurements of body wave (shear and compression wave) velocities within the soil element [3] presents a real challenge see [4,5]....
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TL;DR: In this article, the authors presented the results of a study concerning the accuracy of displacements caused by a single, harmonic, one-dimensional elastic wave propagating through a finite element mesh.
Abstract: The purpose of this paper is presentation of the results of a study concerning the accuracy of displacements caused by a single, harmonic, one-dimensional elastic wave propagating through a finite element mesh. Results are presented for the steady-state response of a finite model of the semi-infinite elastic constrained rod; both the homogeneous and two material cases were analyzed.
896 citations
"Micromechanics of seismic wave prop..." refers methods in this paper
...For continuum analyses of wave propagation using the finite element method [39] showed that the element size must be significantly smaller than the wave length associated with the highest frequency component of the inserted wave....
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