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statistics of particle interactions in dense granular material under umaxial compression

JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS 2006年第7期54卷 1426-1448页

作者： Ma, Xia Zhang, Duan Z. Los Alamos Natl Lab Div Theoret Fluid Dynam Grp Los Alamos NM 87545 USA

Stress evolution in a dense granular material is closely related to interactions of contacting particles. We investigate statistics related to particle interactions and the relationship between the averaged local relative motion and the macroscopic motion. The validity of the Voigt and Reuss assumptions is examined, and extensions to these assumptions are proposed. Effects of history in the dense granular material are investigated. Statistical samples used in this paper are obtained using three-dimensional numerical simulations of dense granular media under uniaxial cyclical compression. The results show that stresses arise mostly from normal forces between particles, and direct contributions from frictional tangential forces between particles are small. Tangential friction, however, significantly increases the particle contact time, and thus reduces the rate of contact breakage. The contact breakage rate is demonstrated to be a stress relaxation rate. Therefore, stress increases significantly with friction between particles as a result of prolonged relaxation time. (c) 2006 Elsevier Ltd. All rights reserved.

关键词： granular material dense packing powder compaction probability and statistics constitutive behavior

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METHOD OF CALCULATING THE VULNERABILITY OF AN OVERHEAD TRANSMISSION-LINE TO FAULTS CAUSED BY GALLOPING

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IEE PROCEEDINGS-C GENERATION TRANSMISSION AND DISTRIBUTION 1981年第6期128卷 334-341页

作者： ROWBOTTOM, MD North Eastern Region Scientific Services Department Central Electricity Generating Board Harrogate UK

An attempt is made to identify the spans or sections of an overhead line route that are most vulnerable to galloping. Methods are presented for calculating from meteorological records the probability of the occurrence of galloping of clashing amplitude. The methods are perfectly general, given the necessary data. Using available data from meteorological stations, the methods are applied to two specific CEGB routes. The results give reasonable agreement on the relative vulnerability to clashing of different line designs, but poor agreement otherwise. Although a large number of remote automatic meteorological stations would be required to improve predictions, it is suggested that a better way to identify troublespots in the same timescale is to install distance-to-fault locators. The paper concludes that substantial numbers of ‘anti-galloping’ devices would be required if galloping to clashing amplitudes is a random event not restricted to specific ‘rogue’ spans

关键词： power overhead lines power transmission lines electrical faults overhead line route faults caused by galloping probability and statistics probability vulnerability Overhead power lines Network and transmission line calculations overhead transmission line

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Bounds on non-local effective relations for random composites loaded by configuration-dependent body force

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JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS 2000年第9期48卷 1827-1849页

作者： Luciano, R Willis, JR Dept Appl Math & Theoret Phys Cambridge CB3 9EW England Dept Ind Engn I-03043 Cassino FR Italy

An infinite domain occupied by composite material is considered. The composite is treated as random. The stress, strain and displacement fields within it are produced by body force with two types of components. One is deterministic while the other depends on the particular realisation of the medium as would be the case, for instance, under gravity loading, so that the distribution of a density (physical or otherwise) enters the problem, as well as the distribution of elastic constants. This feature introduces additional constitutive operators defining the mean response of the body. Besides the usual (non-local) effective modulus operator, there is another operator that provides a contribution to the mean stress from the fluctuating part of the density, and one more that accounts for the non-zero contribution to the mean energy from the interaction of the fluctuating part of the stress field with itself. Bounds of flashin-Shtrikman type are developed which provide restrictions on all these operators, in real space and in the transform domain. The formalism also provides direct Hashin-Shtrikman approximations for the non-local operators. (C) 2000 Elsevier Science Ltd. All rights reserved.

关键词： microstructures constitutive behaviour inhomogeneous material energy methods integral transforms probability and statistics

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Hybrid Factored Frontier Algorithm for Dynamic Bayesian Networks with a Biopathways Application

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IEEE-ACM TRANSACTIONS ON COMPUTATIONAL BIOLOGY AND BIOINFORMATICS 2012年第5期9卷 1352-1365页

作者： Palaniappan, Sucheendra K. Akshay, S. Liu, Bing Genest, Blaise Thiagarajan, P. S. Natl Univ Singapore Sch Comp Singapore 117417 Singapore IRISA ENS Cachan Bretagne Distribcom F-35042 Rennes France CNRS UMR IRISA F-35042 Rennes France

Dynamic Bayesian Networks (DBNs) can serve as succinct probabilistic dynamic models of biochemical networks [1]. To analyze these models, one must compute the probability distribution over system states at a given time point. Doing this exactly is infeasible for large models;hence one must use approximate algorithms. The Factored Frontier algorithm (FF) is one such algorithm [2]. However FF as well as the earlier Boyen-Koller (BK) algorithm [3] can incur large errors. To address this, we present a new approximate algorithm called the Hybrid Factored Frontier (HFF) algorithm. At each time slice, in addition to maintaining probability distributions over local states-as FF does-HFF explicitly maintains the probabilities of a number of global states called spikes. When the number of spikes is 0, we get FF and with all global states as spikes, we get the exact inference algorithm. We show that by increasing the number of spikes one can reduce errors while the additional computational effort required is only quadratic in the number of spikes. We validated the performance of HFF on large DBN models of biopathways. Each pathway has more than 30 species and the corresponding DBN has more than 3,000 nodes. Comparisons with FF and BK show that HFF is a useful and powerful approximate inferencing algorithm for DBNs.

关键词： probability and statistics symbolic and algebraic manipulation-algorithms life and medical sciences-biology and genetics

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Feature-based reverse modeling strategies

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COMPUTER-AIDED DESIGN 2006年第5期38卷 485-506页

作者： Ke, Yinling Fan, Shuqian Zhu, Weidong Li, An Liu, Fengshan Shi, Xiquan Zhejiang Univ Dept Engn Mech Hangzhou 310027 Peoples R China Delaware State Univ Dept Math Dover DE 19901 USA

We presented two integrated solution schemes, sectional feature based strategy and surface feature based strategy, for modeling industrial components from point cloud to surfaces without using triangulation. For the sectional feature based strategy, slicing, curve feature recognition and constrained fitting are introduced. This strategy emphasizes the advanced feature architecture patterns from 2D to 3D in reverse engineering. The surface feature based strategy relies on differential geometric attributes estimation and diverse feature extraction techniques. The methods and algorithms such as attributes estimation based on 4D Shepard surface, symmetry plane extraction, quadric surface recognition and optimization, extruded and rotational surface extraction, and blend feature extraction with probability and statistic theory are proposed. The reliable three-dimensional feature fabricated the valid substratum of B-rep model faultlessly. All the algorithms are implemented in RE-SOFT, a reverse engineering software developed by Zhejiang University. The proposed strategies can be used to capture the original design intention accurately and to complete the reverse modeling process conveniently. Typical industrial components are used to illustrate the validation of our feature-based strategies. (C) 2006 Elsevier Ltd. All rights reserved.

关键词： reverse engineering feature recognition geometric constraints constrained fitting probability and statistics

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On the probabilistic-deterministic transition involved in a fragmentation process of brittle materials

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COMPUTERS & STRUCTURES 2003年第12期81卷 1241-1253页

作者： Hild, F Denoual, C Forquin, P Brajer, X Univ Paris 06 CNRS UMR 8535 LMT Cachan ENS Cachan F-94235 Cachan France CEA DAM Dept PTA F-91680 Bruyeres Le Chatel France DGA CTA Dept MSP F-94114 Arcueil France St Gobain Res F-93303 Aubervilliers France

Dynamic loadings produce high stress waves leading to the fragmentation of brittle materials such as ceramics, concrete, glass and rocks. The main mechanism used to explain the change of the number of fragments with stress rate is a shielding phenomenon. However, under quasi-static loading conditions, a weakest link hypothesis may be applicable. Therefore, depending on the local strain or stress rate, different fragmentation regimes are observed. One regime corresponds to single fragmentation for which a probabilistic approach is needed. Conversely, the multiple fragmentation regime may be described by a deterministic approach. The transition between the two fragmentation regimes is discussed for high performance concrete, glass and SiC ceramics. (C) 2003 Elsevier Science Ltd. All rights reserved.

关键词： brittle materials continuum damage mechanics discrete modeling dynamic fracture probability and statistics single and multiple fragmentation stress relaxation Weibull model

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Modeling of thermally activated dislocation glide and plastic flow through local obstacles

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INTERNATIONAL JOURNAL OF PLASTICITY 2003年第9期19卷 1271-1296页

作者： Hiratani, M Zbib, HM Khaleel, MA Washington State Univ Sch Mech & Mat Engn Pullman WA 99164 USA Pacific NW Natl Lab Richland WA 99352 USA

A unified phenomenological model is developed to study the dislocation glide through weak obstacles during the first stage of plastic deformation in metals. This model takes into account both the dynamical responses of dislocations during the flight process and thermal activations while dislocations are bound by obstacle arrays. The average thermal activation rate is estimated using an analytical model based on the generalized Friedel relations. Then, the average flight velocity after an activation event is obtained numerically by discrete dislocation dynamics (DD). To simulate the dynamical dislocation behavior, the inertia term is implemented into the equation of dislocation motion within the DD code. The results from the DD simulations, coupled with the analytical model, determine the total dislocation velocity as a function of the stress and temperatures. By choosing parameters typical of the face centered cubic metals, the model reproduces both obstacle control and drag control motion in low and high velocity regimes, respectively. As expected by other string models, dislocation overshoots of obstacles caused by the dislocation inertia at the collisions are enhanced as temperature goes down. (C) 2002 Elsevier Science Ltd. All rights reserved.

关键词： creep dislocations strengthening mechanisms metallic materials probability and statistics

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A stochastic constitutive model for disordered cellular materials: Finite-strain uni-axial compression

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INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES 2006年第11-12期43卷 3542-3568页

作者： Schraad, MW Harlow, FH Los Alamos Natl Lab Div Theoret Fluid Dynam Grp Los Alamos NM 87545 USA

A stochastic constitutive model is developed for describing the continuum-scale mechanical response of disordered cellular materials. In the present work, attention is restricted to finite-strain uni-axial compression under quasi-static loading conditions. The development begins with an established cellular-scale mechanical model, but departs from traditional modeling approaches by generalizing the cellular-scale model to accommodate finite strain. The continuum-scale model is obtained by averaging the cellular-scale mechanical response over an ensemble of foam cells. Various stochastic material representations are considered through the use of probability density functions for the relevant material parameters, and the effects of the various representations on the continuum-scale response are investigated. Combining cellular-scale mechanics with a stochastic material representation to derive a continuum-scale constitutive model offers a promising new approach for simulating the finite-strain response of cellular materials. Results demonstrate that increasing a material's degree of polydispersity can produce the same stiffening effects as increasing the initial solid-volume fraction. Additionally, particular stochastic material representations are shown to provide upper and lower bounds on the mechanical response of the cellular materials under investigation, while suitable choices for the stochastic representation are shown to accurately reproduce experimental stress-strain data through the large deformations associated with densification. Published by Elsevier Ltd.

关键词： microstructures constitutive behavior finite strain foam material probability and statistics

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Principal Uncertainty Quantification With Spatial Correlation for Image Restoration Problems

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IEEE TRANSACTIONS ON PATTERN ANALYSIS AND MACHINE INTELLIGENCE 2024年第5期46卷 3321-3333页

作者： Belhasin, Omer Romano, Yaniv Freedman, Daniel Rivlin, Ehud Elad, Michael Verily Life Sci South San Francisco CA 94080 USA Technion Israel Inst Technol Dept Comp Sci IL-3200003 Haifa Israel

Uncertainty quantification for inverse problems in imaging has drawn much attention lately. Existing approaches towards this task define uncertainty regions based on probable values per pixel, while ignoring spatial correlations within the image, resulting in an exaggerated volume of uncertainty. In this paper, we propose PUQ (Principal Uncertainty Quantification) - a novel definition and corresponding analysis of uncertainty regions that takes into account spatial relationships within the image, thus providing reduced volume regions. Using recent advancements in generative models, we derive uncertainty intervals around principal components of the empirical posterior distribution, forming an ambiguity region that guarantees the inclusion of true unseen values with a user-defined confidence probability. To improve computational efficiency and interpretability, we also guarantee the recovery of true unseen values using only a few principal directions, resulting in more informative uncertainty regions. Our approach is verified through experiments on image colorization, super-resolution, and inpainting;its effectiveness is shown through comparison to baseline methods, demonstrating significantly tighter uncertainty regions.

关键词： Uncertainty Task analysis Inverse problems Correlation Superresolution Image restoration Standards Uncertainty and probabilistic reasoning probability and statistics restoration inverse problems stochastic processes correlation and regression analysis

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Particle fracture in high-volume-fraction ceramic-reinforced metals: Governing parameters and implications for composite failure

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JOURNAL OF THE MECHANICS AND PHYSICS OF SOLIDS 2009年第11期57卷 1781-1800页

作者： Hauert, Aude Rossoll, Andreas Mortensen, Andreas Ecole Polytech Fed Lausanne Lab Mech Met Stn 12 CH-1015 Lausanne Switzerland

Weibull parameters of angular alumina particles are determined from experimental tensile test data on high-ceramic-content metal matrix composites using a micromechanical model that accounts for internal damage in the form of particle cracking, the dominant damage mode in these composites. The fraction of broken particles is assessed from the drop of Young's modulus and particle fracture is assumed to be stress controlled. Two extreme load-sharing modes, namely a purely local and a global load-sharing mode, are considered to account for the load redistribution due to particle fracture. Consistent powder strength parameters can be thus "back-calculated" for particles that are embedded in different Al-Cu matrices. On the other hand, this calculation fails for pure Al matrix composites, which exhibit a much larger strain to failure than Al-Cu matrix composites. It is shown that for Al matrix composites, the role of plastic (composite) strain on particle fracture constitutes a second parameter governing particle damage. This finding is rationalized by particle-particle interactions in these tightly packed ceramic particle-reinforced composites, and by the increase of matrix stress heterogeneity that is brought with increasing plastic strain. Failure of the alloyed matrix composites is well described by the (lower bound) local load-sharing micromechanical model, which predicts a catastrophic failure due to an avalanche of damage. The same model predicts failure of pure aluminium matrix composites to occur at the onset of tensile instability, also in agreement with experimental results once the role of plastic strain on damage accumulation is accounted for. (C) 2009 Elsevier Ltd. All rights reserved.

关键词： Fracture mechanisms Particulate-reinforced material Mechanical testing probability and statistics Weibull strength distribution

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