351 research outputs found
DEM simulation of anisotropic granular materials:elastic and inelastic behavior
Full text linkIn this work, Discrete Elements Method simulations are carried out to investigate the effective stiffness of an assembly of frictional, elastic spheres under anisotropic loading. Strain probes, following both forward and backward paths, are performed at several anisotropic levels and the corresponding stress is measured. For very small strain perturbations, we retrieve the linear elastic regime where the same response is measured when incremental loading and unloading are applied. Differently, for a greater magnitude of the incremental strain a different stress is measured, depending on the direction of the perturbation. In the case of unloading probes, the behavior stays elastic until non-linearity is reached.Under forward perturbations, the aggregate shows an intermediate inelastic stiffness, in which the main contribution comes from the normal contact forces. That is, when forward incremental probes are applied the behavior of anisotropic aggregates is an incremental frictionless behavior. In this regime we show that contacts roll or slide so the incremental tangential contact forces are zero. Graphical Abstract: [Figure not available: see fulltext.].</p
Shear-induced phase transition of nanocrystalline hexagonal boron nitride to wurtzitic structure at room temperature and lower pressure
Full text linkDisordered structures of boron nitride (BN), graphite, boron carbide (BC), and boron carbon nitride (BCN) systems are considered important precursor materials for synthesis of superhard phases in these systems. However, phase transformation of such materials can be achieved only at extreme pressure–temperature conditions, which is irrelevant to industrial applications. Here, the phase transition from disordered nanocrystalline hexagonal (h)BN to superhard wurtzitic (w)BN was found at room temperature under a pressure of 6.7 GPa after applying large plastic shear in a rotational diamond anvil cell (RDAC) monitored by in situ synchrotron X-ray diffraction (XRD) measurements. However, under hydrostatic compression to 52.8 GPa, the same hBN sample did not transform to wBN but probably underwent a reversible transformation to a high-pressure disordered phase with closed-packed buckled layers. The current phase-transition pressure is the lowest among all reported direct-phase transitions from hBN to wBN at room temperature. Usually, large plastic straining leads to disordering and amorphization; here, in contrast, highly disordered hBN transformed to crystalline wBN. The mechanisms of strain-induced phase transformation and the reasons for such a low transformation pressure are discussed. Our results demonstrate a potential of low pressure–room temperature synthesis of superhard materials under plastic shear from disordered or amorphous precursors. They also open a pathway of phase transformation of nanocrystalline materials and materials with disordered and amorphous structures under extensive shear.This article is published as Ji, Cheng, Valery I. Levitas, Hongyang Zhu, Jharna Chaudhuri, Archis Marathe, and Yanzhang Ma. "Shear-induced phase transition of nanocrystalline hexagonal boron nitride to wurtzitic structure at room temperature and lower pressure." Proceedings of the National Academy of Sciences 109, no. 47 (2012): 19108-19112. 10.1073/pnas.1214976109. Posted with permission.</p
Human hand sign language recognition based on extreme learning machine
No full textAs machine learning algorithms and computer processing speed greatly advanced in recent years, real-time hand gesture recognition has become a promising topic in computer science and language technology. Some of the existing limits in achieving user-friendly experience are real-time recognition speed and accuracy. This project aims to realize practical dual hand real-time recognition and to develop new man-machine interaction functions. Based on senior Mr. Jiang Runzhou’s FYP work, Ms. Cai Xiao, Mr. Liu Hongyang and the author work closely to achieve the objective. Realizable functions include PowerPoint slide show control, music player control and Rock, Paper, Scissor game. Mr. Jiang Runzhou’s past gesture recognition is also enhanced to achieve more excellent accuracy.Bachelor of Engineerin
Additional file 5: of A manually annotated Actinidia chinensis var. chinensis (kiwifruit) genome highlights the challenges associated with draft genomes and gene prediction in plants
No full text‘Hongyang’ Gene models that align to Red5 genome.List of Actinidia chinensis ‘Hongyang’ genes that align to the Red5 whole genome sequence. Additional file 5A: models from original ‘Hongyang’ annotation [14]. Additional file 5B: models from revised ‘Hongyang’ annotation [18] (XLSX 19 kb
Trending topics in computational mechanics of granular materials: from fundamentals to applications
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マルチスケール手法によるジオテキスタイル補強地盤の特性評価
Full text link広島大学(Hiroshima University)博士(工学)Doctor of Engineeringdoctora
Simulation-guided optimization of granular phononic crystal structure using the discrete element method
Full text linkThe paper describes a novel methodology of designing granular phononic crystals for acoustic wave manipulations. A discrete element method is utilized to model the dynamics of a pulse wave propagating through the densely packed assembly of elastic spherical particles with an embedded phononic crystal — the region consisting of a certain arrangement of particles with varying densities. We suggest an optimization strategy that extremizes the useful properties of a granular phononic crystal, which are described in terms of a noise-proof functional based on frequency–wavenumber summation of spectral energy density. Few types of efficient phononic crystals are identified. The suggested methodology is of interest for a number of applications, in particular, for seismic shielding and selective sound absorption
Performance study of iterative Bayesian filtering to develop an efficient calibration framework for DEM
Full text linkThis work presents an efficient probabilistic framework for the Bayesian calibration of micro-mechanical parameters for Discrete Element Method (DEM) modelling. Firstly, the superior behaviour of the iterative Bayesian filter over the sequential Monte Carlo filter for calibrating micro-mechanical parameters is shown. The linear contact model with rolling resistance is used for simulating the triaxial responses of Toyoura sand under different confining pressures. Secondly, synthetic data from DEM simulations of triaxial compression are used to assess the reliability of iterative Bayesian filtering with respect to the user-defined parameters, such as the number of samples and predefined parameter ranges. Excellent calibration results with errors between 1 and 2% are obtained when the number of samples is chosen high enough. It is crucial that the sample size is representative for the distribution of individual parameters within the predefined parameter ranges. The wider the ranges, the more samples are required. The investigation also shows the necessity of including both stress and strain histories, at certain confidence levels, for estimation of the correct mechanical responses, especially the correct fabric responses. Finally, based on the findings of this work a fully-automated open-source calibration tool is developed and demonstrated for selected stress paths
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