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1
Zhang, Ting Ting, E. Chuan Yan, Xian Ming Hu et Yang Bing Cao. « Fractal Description of Rock Mass Structure Representative Elementary Volume ». Advanced Materials Research 594-597 (novembre 2012) : 439–45. http://dx.doi.org/10.4028/www.scientific.net/amr.594-597.439.
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The mechanical parameters of the rock masses are scale dependent because of the existence of the discontinuities. The self-similarity of the discontinuities makes the application of fractal theory in the description of the rock mass structure possible. The novel point in this study is that the structure representative elementary volume (SREV) of rock mass is proposed. Rock mass structures were obtained through the two-dimensional discontinuity network simulation results, from which ten pieces of square rock mass specimens were chosen. The side lengths of the specimens were increased in turn from 1m to 10m. And the fractal dimension of each specimen with different sizes was calculated by the box-counting principal of the fractal geometry. The fractal dimensions of the rack mass structures became larger with their side lengths increasing, and finally stable. And the SREV of the rock mass was determined based on the variation rule of the fractal dimensions. Further, the relation between the structure representative elementary volume (SREV) and mechanical parameter representative elementary volume (REV) was qualitatively analyzed from the strength differences between the discontinuities and intact rock. And the conclusion was inferred that the size of the SREV was the upper limit of mechanical parameter REV. Meanwhile, the conclusion was verified by the results of the finite element method. This study can provided a referring value for the estimation of the mechanical parameter REV in future.
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Gasmi, H., M. Touahmia, A. Torchani, E. Hamdi et A. Boudjemline. « Determination of Fractured Rock’s Representative Elementary Volume by a Numerical Simulation Method ». Engineering, Technology & ; Applied Science Research 9, no 4 (10 août 2019) : 4448–51. http://dx.doi.org/10.48084/etasr.2854.
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The present study aims at developing a numerical program called DISSIM which can analyze the homogenization of rock massifs using a new subroutine which calculates Representative Elementary Volume (REV). The DISSIM methodology consists of two steps. The first step involves the modeling of the fractured network in order to provide a surface simulation that represents the real fracture of the examined front. The second step is to numerically model the wave propagation through the simulated fracture network while characterizing the attenuation of vibrations due to the effect of discontinuities. This part allows us to determine in particular the wave propagation velocity through the fractured mass, from which we can determine the homogenized Young's modulus. However, after extensive bibliographic research, it was realized that a third step appeared to be necessary. In fact, it is necessary to look for a representative elementary volume on which we apply the proposed homogenization method. Two types of the representative elementary volume are proposed in this article, the geometric REV and the mechanical REV. The presentation of these two types of REV and the DISSIM methodology are detailed in this paper. Then, this methodology was applied to the study of a real case. The present research provides a method allowing the calculation of both types of REV for fissured rocks. The case study yielded comparable results between the mechanical REV and the geometric REV, which is compatible with previous research studies.
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Perreux, Dominique M., et W. Steven Johnson. « A Model for Prediction of Bone Stiffness Using a Mechanical Approach of Composite Materials ». Journal of Biomechanical Engineering 129, no 4 (22 janvier 2007) : 494–502. http://dx.doi.org/10.1115/1.2746370.
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A model to predict the bone stiffness is presented in this paper. The objective is to obtain a description of bone stiffness of a representative elementary volume (REV) based on a small set of physical parameters. The main idea is to use measurable information related to the orientation and the density of a basic elementary submicrostructure (ESMS). This ESMS is the first arrangement of the basic components. A simple rule-of-mixtures approach is used to provide the elastic properties for the ESMS. The basic properties are dependent on the volume fraction of the mineralized phase. The orientation and the density of the ESMS is described by a tensor and a scalar, respectively. The model is used to obtain the elastic properties of both the cortical and trabecular bones. Data from femoral bone are used to verify this approach.
4
Huang, Xiao, Siyuan Li, Jionghao Jin et Chong Shi. « Determining Digital Representation and Representative Elementary Volume Size of Broken Rock Mass Using the Discrete Fracture Network–Discrete Element Method Coupling Technique ». Applied Sciences 14, no 2 (10 janvier 2024) : 606. http://dx.doi.org/10.3390/app14020606.
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Obtaining the digital characterization and representative elementary volume (REV) of broken rock masses is an important foundation for simulating their mechanical properties and behavior. In this study, utilizing the broken surrounding rock of the main powerhouse at the Liyang pumped storage power station as an engineering background, a three-dimensional fracture network generation program is first developed based on the theories of discrete fracture network (DFN) and discrete element method (DEM). The program is then integrated with a distinct element modelling platform to generate equivalent rock mass models for broken rock masses based on the DFN–DEM coupling technique. Numerical compression tests are conducted on cylindrical rock specimens produced using the proposed modelling approach, aiming to determining the REV size of the target rock masses at the Liyang power station. A comparative validation is also performed to examine the REV result obtained from the proposed approach, which adopted a REV measuring scale index (RMSI) to determine the REV size. Results indicate that the organic integration of DFN simulation techniques and DEM platforms can effectively construct numerical models for actual broken rock masses, with structural surface distributions statistically similar to the real ones. The results also show that the REV size of the investigated rock masses determined by the cylindrical rock models is 5 m × 10 m, which aligns with the size determined by the cubic rock models, as the target cubes show the same height as the cylindrical specimens. This study provides a model and parameter basis for the numerical calculation of the mechanical behavior of broken rock mass.
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Li, H., A. Levy et G. Ben-Dor. « Analytical prediction of regular reflection over rigid porous surfaces in pseudo-steady flows ». Journal of Fluid Mechanics 282 (10 janvier 1995) : 219–32. http://dx.doi.org/10.1017/s0022112095000115.
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An analytical model for solving the flow field associated with regular reflections of straight shock waves over porous layers has been developed. The governing equations of the gas inside the porous material were obtained by simplifying the general macroscopic balance equations which were obtained by an averaging process over a representative elementary volume of the microscopic balance equations as originally done by Bear & Bachmat (1990). The analytical predictions of the proposed model were compared to experimental results of Skews (1992) and Kobayashi, Adachi & Suzuki (1993). Very good to excellent agreement was evident.
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Baek, Y., O. I. Kweon, Y. S. Seo, K. S. Kim et G. W. K im. « Analysis of elastic behaviour of granite using homogenisation theory ». Journal of Nepal Geological Society 34 (9 octobre 2006) : 25–28. http://dx.doi.org/10.3126/jngs.v34i0.31875.
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We carried out photographic analysis of randomly distributed discrete elements in the lnada granite. The modal analysis of granite was also conducted simultaneously with the above photographic analysis. The results show that quartz and feldspar including mica occupy 99.4% of the total volume of the fine-grained granite. Based on the results of previous studies, an elastic homogenisation method is applied to analyse the macro-level stress distribution in the lnada granite, which is a composite material of rock-forming minerals with micro discontinuities.
For proper rock sampling and specimen preparation, the representative elementary volume (REV) should be determined in rock mechanical tests and numerical analyses. We determined the REV of the lnada granite using a stereoscopic microscope and applying a homogenisation numerical analysis.
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Buonsanti, Michele, Fortunato Ceravolo, Giovanni Leonardi et Francesco Scopelliti. « Interfaces Behavior in Glued Granular Materials ». Key Engineering Materials 665 (septembre 2015) : 113–16. http://dx.doi.org/10.4028/www.scientific.net/kem.665.113.
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In this paper a micro-scale model to investigate the structural integrity of a runway surface has been developed. By performing stress analysis on a representative volume element (RVE), our model specification has been focalized on two elementary mixture constituents, two rigid components glued together by asphalt. The analysis is performed under thermo-mechanical actions, as those produced by landing gear impact and variable high surface temperatures. Three different interfaces (rigid to rigid, rigid to soft and soft to soft), three different asphalt density and two different values of surface temperature have been considered in the simulation. Resulting stress and strain fields are compared to define the greater critical conditions and to evaluate the micro-scale structural integrity
8
Li, MY, YJ Cao, WQ Shen et JF Shao. « A damage model of mechanical behavior of porous materials : Application to sandstone ». International Journal of Damage Mechanics 27, no 9 (5 janvier 2017) : 1325–51. http://dx.doi.org/10.1177/1056789516685379.
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In this work, a multiscale model based on the Fast Fourier Transform (FFT) technique is applied to describe the mechanical behavior of porous materials. The effects of the microstructures (such as pore shape, number, size, distribution and orientation) on the overall strength of the porous medium and its microstress distribution are fully studied. The elastoplastic model is further extended by including a damage process. The influences of microstructure on the damage evolution of the porous medium are discussed and illustrated numerically. Then the proposed multiscale damage model is applied to study the macroscopic behavior of porous sandstone. According to the microstructure of the studied material, a representative elementary volume with randomly distributed spherical pores is considered. The solid phase of the sandstone is assumed to obey the Drucker–Prager criterion. Taking advantage of the FFT-based method, the evolution of generated damage is clearly illustrated during the loading process at the microscopic level. Comparisons between numerical results and experimental data show the efficiency of the proposed numerical model.
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Zhao, Tianyi, Huawei Zhao, Zhengfu Ning, Xiangfang Li et Qing Wang. « Permeability prediction of numerical reconstructed multiscale tight porous media using the representative elementary volume scale lattice Boltzmann method ». International Journal of Heat and Mass Transfer 118 (mars 2018) : 368–77. http://dx.doi.org/10.1016/j.ijheatmasstransfer.2017.11.004.
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Sadat, Salima, Allel Mokaddem, Bendouma Doumi, Mohamed Berber et Ahmed Boutaous. « Investigation of the effect of thermal stress on the interface damage of hybrid biocomposite materials ». Mechanics and Mechanical Engineering 23, no 1 (10 juillet 2019) : 253–58. http://dx.doi.org/10.2478/mme-2019-0034.
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Abstract In this paper, we have studied the effect of thermal stress on the damage of fiber-matrix interface of a hybrid biocomposite composed of two natural fibers, Hemp, Sisal, and Starch matrix. Our genetic modeling used the nonlinear acoustic technique based on Cox’s analytical model, Weibull’s probabilistic model, and Lebrun’s model describing the thermal stress by the two coefficients of expansion. The stress applied to our representative elementary volume is a uni-axial tensile stress. The numerical simulation shows that the Hemp- Sisal/Starch hybrid biocomposite is most resistant to thermal stresses as compared with Hemp/Starch biocomposite. It also shows that hybrid biocomposite materials have a high resistance to applied stresses (mechanical and thermal) compared to traditional materials and biocomposite materials. The results obtained in our study coincide perfectly with the results of Antoine et al., which showed through experimental tests that natural fibers perfectly improve the mechanical properties of biocomposite materials.
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Wan, R. G., et P. J. Guo. « Effect of microstructure on undrained behaviour of sands ». Canadian Geotechnical Journal 38, no 1 (1 février 2001) : 16–28. http://dx.doi.org/10.1139/t00-088.
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This paper presents a mathematical modelling of the effects of initial fabric on the mechanical behaviour of sand. A stress-dilatancy model that incorporates microstructural aspects of sand is hereby obtained while writing energy conservation for an ensemble of particles over a representative elementary volume at micro- and macro-scales. The resulting stress-dilatancy model, when used within an elastoplastic framework, successfully reproduces certain aspects of sand behaviour that are reflective of its microstructure under both drained and undrained conditions. The role of microstructure in relation to the characterization of steady, quasi-steady, and phase-transformation states is discussed within the framework of the model. Numerical simulations obtained from the proposed model are generally very consistent with experimental observations and provide insightful information.Key words: sand, liquefaction, fabric, dilatancy, constitutive laws, granular materials, plasticity.
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Liu, Haifeng, Chenghao Ma et Changqi Zhu. « X-ray Micro CT Based Characterization of Pore-Throat Network for Marine Carbonates from South China Sea ». Applied Sciences 12, no 5 (3 mars 2022) : 2611. http://dx.doi.org/10.3390/app12052611.
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The pore-throat network of rock exerts a vital influence on the permeability and mechanical properties of the rock. Resorting to X-ray micro-CT scanning, the present work investigates the pore-throat structure of marine biogenic carbonate samples from the South China Sea and compares them to terrigenous sedimentary sandstone. With the help of the maximum ball (MB) algorithm, the pore-throat networks inside representative elementary volumes of rock samples are revealed by stick-and-ball diagrams, which enables quantitative analyses afterwards. Higher and more deviant cross sectional porosity was observed for the carbonate samples compared to the sandstone sample, indicating relatively heterogeneous pores in the carbonate. Over 85% of pores in the carbonate samples were classified as mesopores. Irregular triangular cross sections can be inferred for the pores and throats of the carbonate. The type of rock and the porosity seem to have little effect on the shapes of the pores and throats. In the studied carbonate, the average volume of the throat was approximately one order of magnitude smaller than the average volume of a pore. The distribution of throat radius differed significantly between the studied carbonate samples. The average coordination number of the carbonate was measured to be 1.
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Rashidi, Mehdi, Andrew Tompson, Tom Kulp et Loni Peurrung. « 3-D Microscopic Measurement and Analysis of Chemical Flow and Transport in Porous Media ». Journal of Fluids Engineering 118, no 3 (1 septembre 1996) : 470–80. http://dx.doi.org/10.1115/1.2817782.
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Chemical flow and transport have been studied at the pore-scale in an experimental porous medium. Measurements have been taken using a novel nonintrusive fluorescence imaging technique. The experimental setup consists of a cylindrical column carved out of a clear plastic block, packed with clear beads of the same material. A refractive index-matched fluid was pumped under laminar, slow-flow conditions through the column. The fluid was seeded with tracer particles or a solute organic dye for flow and chemical transport measurements, respectively. The system is automated to image through the porous medium for collecting microscopic values of velocity, concentration, and pore geometry at high-accuracy and high-resolution. Various geometric, flow, and transport quantities have been obtained in a full three-dimensional volume within the porous medium. These include microscopic (pore-scale) medium geometry, velocity and concentration fields, dispersive solute fluxes, and reasonable estimates of a representative elementary volume (REV) for the porous medium. The results indicate that the range of allowable REV sizes, as measured from averaged velocity, concentration, and pore volume data, varies among the different quantities, however, a common overlapping range, valid for all quantities, can be determined. For our system, this common REV has been estimated to be about two orders of magnitude larger than the medium’s particle volume. Furthermore, correlation results show an increase in correlation of mean-removed velocity and concentration values near the concentration front in our experiments. These results have been confirmed via 3-D plots of concentration, velocity, pore geometry, and microscopic flux distributions in these regions.
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Loyola, Ana Carolina, Jean-Michel Pereira et Manoel Porfírio Cordão Neto. « General Statistics-Based Methodology for the Determination of the Geometrical and Mechanical Representative Elementary Volumes of Fractured Media ». Rock Mechanics and Rock Engineering 54, no 4 (3 février 2021) : 1841–61. http://dx.doi.org/10.1007/s00603-021-02374-6.
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Hu, Shuiqing, Daobing Wang, Yipeng Li, Xiongfei Liu, Fujian Zhou, Meng Wang, Chunming He et Bo Yu. « Thermo-Hydro-Mechanical Coupling Numerical Simulation on Mechanical Heterogeneity of Coal Rock ». Geofluids 2022 (9 août 2022) : 1–24. http://dx.doi.org/10.1155/2022/9410245.
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Coal rock is a porous medium composed of organic matter and inorganic minerals, and it is very complex and highly heterogeneous. Coal bed methane (CBM) production is a thermo-hydro-mechanical (THM) coupling process in heterogeneous coal rock. THM coupling numerical simulation on the coal rock by considering the effect of mechanical heterogeneity is rarely reported. We use Weibull’s probability density distribution function to characterize the heterogeneity in elastic modulus of the coal rock, establish a THM coupling 3D finite element model of the coal rock by considering the variation in pore pressure caused by methane desorption, the linear thermal expansion effect, and coal rock skeleton shrinkage and deformation, and analyze variation in permeability, porosity, stress, temperature, and pore pressure within the coal rock representative elementary volume (REV) of variable mechanical heterogeneity with the cross-coupling correlation between permeability and porosity, and thermal field, stress field, and pressure field. The results show that the evolution of porosity and permeability in the coal rock is a THM coupling process related to mechanical heterogeneity, thermal expansion effect, pore pressure change caused by CBM desorption, and stressed deformation in the coal rock skeleton. The permeability and porosity fluctuate within the heterogeneous coal rock. The permeability and porosity fluctuate more frequently in the coal rock with stronger mechanical heterogeneity. The mechanical heterogeneity promotes local stress concentration. The time for variation in the stress through the whole the coal rock REV and the value of the first principal stress increase when the coal rock heterogeneity is enhanced. Under the THM coupling effect, the strong heterogeneity of the coal rock causes fluctuation in the thermal field. The evolution of coal porosity and permeability is a THM coupling process. This study provides theoretical guidance for CBM exploitation.
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Teruel, Federico E., et Rizwan-uddin. « Numerical computation of macroscopic turbulence quantities in representative elementary volumes of the porous medium ». International Journal of Heat and Mass Transfer 53, no 23-24 (novembre 2010) : 5190–98. http://dx.doi.org/10.1016/j.ijheatmasstransfer.2010.07.041.
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García-Salaberri, Pablo A., Iryna V. Zenyuk, Andrew D. Shum, Gisuk Hwang, Marcos Vera, Adam Z. Weber et Jeff T. Gostick. « Analysis of representative elementary volume and through-plane regional characteristics of carbon-fiber papers : diffusivity, permeability and electrical/thermal conductivity ». International Journal of Heat and Mass Transfer 127 (décembre 2018) : 687–703. http://dx.doi.org/10.1016/j.ijheatmasstransfer.2018.07.030.
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Zhang, M. Z., G. Ye et K. Van Breugel. « Un método numérico-estadístico para determinar el volumen elemental representativo (VER) de la pasta de cemento en la medición de la difusividad ». Materiales de Construcción 60, no 300 (15 décembre 2010) : 7–20. http://dx.doi.org/10.3989/mc.2010.60810.
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Pestrenin, V. M., I. V. Pestrenina, L. V. Landik, A. R. Fagalov et A. G. Pelevin. « REPRESENTATIVE VOLUME AND EFFECTIVE MATERIAL CHARACTERISTICS OF PERIODIC AND STATISTICALLY UNIFORMLY REINFORCED FIBER COMPOSITES ». PNRPU Mechanics Bulletin, no 1 (15 décembre 2023) : 103–10. http://dx.doi.org/10.15593/perm.mech/2023.1.10.
Texte intégralRésumé :
In the deformable solid mechanics, there are concepts associated with continuum points (displacements, relative elongations, shifts) and a set of continuum points – an elementary volume (mass, energy, stresses). The role of such volume in the mechanics of composite materials is played by the representative volume element (RVE).This concept was first introduced by R. Hill (1963). Modern authors use the W.J. Drugan, J.R. Willis (1996) formulation. Based on the analysis of the RVE concept, we formulated its essential features: RVE is the minimum possible sample for numerical tests to determine the effective material parameters of the composite; under any RVE loading, its macroscopic stress-strain state is uniform. Its significance for the mechanics of composite materials is revealed: the existence of RVE for a composite is a criterion for applying the effective modulus theory to the analysis of its stress-strain state; the dehomogenization of a stressed-state composite material at a point is a solution to the micromechanics problem of the RVE stress-strain state determination; the characteristic size of RVE limits the size of the sampling grid in the numerical study. An iterative algorithm for constructing a representative volume of a periodic structure composite and its effective material thermoelastic characteristics is proposed. It is shown that the geometric shape of such a composition is a rectangular parallelepiped. The RVE construction algorithm for periodic compositions is extended to the composites statistically uniformly reinforced with continuous fibers. A method for modeling such materials with a following regular structure is suggested described: in the section perpendicular to the fibers, fiber centers should be located at the vertices of regular triangles. Examples of constructing RVE and thermoelastic material characteristics of specific compositions are given. The calculation results are compared with the data obtained using certified software products.
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Akhzouz, Hajar, Hassan El Minor, Amine Bendarma et Hanane El Minor. « Multi-scale physico-chemical characterization of CEB/ANS bio-composites ». MATEC Web of Conferences 348 (2021) : 01008. http://dx.doi.org/10.1051/matecconf/202134801008.
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In a vision to identify the non-linear behaviour of the compressed earth blocks (CEB) reinforced by the Argan nut shells particles (ANS) influenced by many parameters like the shape, the distribution and the quantity of the stabilizers, as well as the interactions between both phases: matrix and reinforcement. The use of numerical models seems to be indispensable. Yet, simulations of heterogeneous structures quickly become unaffordable by direct calculations on finite element software. Therefore, a homogenization of the experimental, analytical, and numerical macrostructure is performed. Thus, an overall micro-mesomacro approach to modelling the mechanical behaviour of CEB/CNA bio-composites has been established. It is mainly based on the notion of the representative elementary volume with two different structures (periodic structure and structure with a poisson distribution). The numerical and analytical homogenization results were validated by the Young’s modulus values resulting from the experimental compression test and the corresponding stress-strain curves.
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Gherissi, Abderraouf Omar. « Failure study of the woven composite material : 2.5 D carbon fabric/ resin epoxy ». Journal of Mechanical Engineering and Sciences 13, no 3 (27 septembre 2019) : 5390–406. http://dx.doi.org/10.15282/jmes.13.3.2019.12.0438.
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In this paper an experimental analysis of the failure of a single layer woven fabric composite 2.5 D G1151/ Resin Epoxy through a tensile tests at 0°, 45° and 90° is investigated. In addition a FE simulation of failure were elaborated through multiscale modeling method, micro then meso then macro scale. The microscale simulation was elaborated on ABAQUS standard simulation of a 3D unit cell of random fibers distribution of a single yarn. The meso scale simulation developed on MATLAB. The meso approach based to the extraction of the behavior of representative volume elementary (RVE) of the 2.5 D woven composite. The macroscale simulation was elaborated on ABAQUS standard simulation. With reference to the numerical and experimental study, the results shows a good agreement. The present investigation is an important preliminary study in process forming of single woven carbon 2.5 D composite.
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Kfoury, Moussa, Rachid Ababou, Benoît Noetinger et Michel Quintard. « Upscaling Fractured Heterogeneous Media : Permeability and Mass Exchange Coefficient ». Journal of Applied Mechanics 73, no 1 (8 mai 2005) : 41–46. http://dx.doi.org/10.1115/1.1991864.
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In order to optimize oil recuperation, to secure waste storage, CO2 sequestration and describe more precisely many environmental problems in the underground, we need to improve some homogenization methods that calculate petrophysical parameters. In this paper, we discuss the upscaling of fluid transport equations in fractured heterogeneous media consisting of the fractures themselves and a heterogeneous porous matrix. Our goal is to estimate precisely the fluid flow parameters like permeability and fracture/matrix exchange coefficient at large scale. Two approaches are possible. The first approach consists in calculating the large-scale equivalent properties in one upscaling step, starting with a single continuum flow model at the local scale. The second approach is to perform upscaling in two sequential steps: first, calculate the equivalent properties at an intermediate scale called the ”unit scale,” and, second, average the flow equations up to the large scale. We have implemented the two approaches and applied them to randomly distributed fractured systems. The results allowed us to obtain valuable information in terms of sizes of representative elementary volume associated to a given fracture distribution.
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Charon, Willy, Marie-Christine Iltchev et Jean-François Blachot. « Mechanical simulation of a Proton Exchange Membrane Fuel Cell stack using representative elementary volumes of stamped metallic bipolar plates ». International Journal of Hydrogen Energy 39, no 25 (août 2014) : 13195–205. http://dx.doi.org/10.1016/j.ijhydene.2014.06.125.
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Ben Ahmed, Amal, Ahmad Bahloul, Mohamed Iben Houria, Anouar Nasr et Raouf Fathallah. « Multiaxial fatigue life estimation of defective aluminum alloy considering the microstructural heterogeneities effect ». Proceedings of the Institution of Mechanical Engineers, Part L : Journal of Materials : Design and Applications 233, no 9 (16 août 2018) : 1830–42. http://dx.doi.org/10.1177/1464420718792024.
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The Al–Si–Mg high-cycle fatigue behavior is mainly affected by the microstructural heterogeneities and the presence of casting defects. This attempt aims to develop an analytical approach based on the evaluation of the highly stressed volume caused by local porosities and defined as the affected area methodology. The proposed approach is able to predict the aluminum alloy fatigue response by considering the effect of microstructure described by the secondary dendrite arm spacing and its correlation with the defect size effect. A representative elementary volume model is implemented to evaluate the stress distribution in the vicinity of the defect and to determine its impact on the high-cycle fatigue resistance. Work hardening due to cyclic loading is considered by applying the Lemaitre–Chaboche model. The Kitagawa–Takahashi diagrams corresponding to different microstructures and for two loading ratios: R σ = 0 and R σ = −1 were simulated based on the AA method. Simulations were compared to the experimental results carried out on cast aluminium alloy A356 with T6 post heat-treatment. The results show clearly that the proposed approach provides a good estimation of the A356-T6 fatigue limit and exhibits good ability in simulating the Kitagawa–Takahashi diagrams for fine and coarse microstructures.
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Peng, Chao, Qifeng Guo, Zhenxiong Yan, Minglong Wang et Jiliang Pan. « Investigating the Failure Mechanism of Jointed Rock Slopes Based on Discrete Element Method ». Advances in Civil Engineering 2020 (12 septembre 2020) : 1–19. http://dx.doi.org/10.1155/2020/8820158.
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This paper presents a comprehensive engineering method to investigate the failure mechanism of the jointed rock slopes. The field geology survey is first carried out to obtain the slope joint data. A joint network model considering the structural complexity of rock mass is generated in the PFC software. The synthetic rock mass (SRM) approach for simulating the mechanical behavior of jointed rock mass is employed, in which the flat-jointed bonded-particle model (FJM) and smooth joint contact model (SJM) represent intact rock and joints, respectively. Subsequently, the effect of microparameters on macromechanical properties of rock is investigated for parameter calibration. Moreover, the scale effect is analyzed by multiscale numerical tests, and the representative elementary volume (REV) size in the selected research area is found as 16 m × 16 m × 16 m. The microparameters of the SRM model are calibrated to match the mechanical properties of the engineering rock mass. Finally, an engineering case from Shuichang open-pit mine is analyzed and the failure process of the slope during the excavation process from micro- to macroscale is obtained. It has been found that failure occurs at the bottom of the slope and gradually develops upwards. The overall failure of the slope is dominated by the shallow local tension fracture and wedge failure.
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Sow, Libasse, Fabrice Bernard, Siham Kamali-Bernard et Cheikh Mouhamed Fadel Kébé. « Experiment-based modelling of the mechanical behaviour of non-hazardous waste incineration bottom ashes treated by hydraulic binder ». MATEC Web of Conferences 149 (2018) : 01038. http://dx.doi.org/10.1051/matecconf/201814901038.
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Instrumented indentation tests have been carried out on an isolated 25 mm diameter particle of Non-Hazardous Waste Incineration bottom ash. These tests have enabled one to assess the intrinsic mean reduced modulus of elasticity “Er” of the particles. This result is used as input data for a 3D numerical model of Representative Elementary Volumes (REV) of a road gravel made with this kind of by-products. This numerical model is based on a multi-scale hierarchical modelling strategy. The aggregates treated with cement have been decomposed into two REV at the sub-mesoscopic and mesoscopic scales. The numerical simulations campaign (“virtual laboratory”) lead to the following results. At the sub-mesoscopic scale, we determined the input parameters for the Concrete Damaged Plasticity Model (CDPM) used at the mesoscopic scale. At the mesoscopic scale, the mechanical characteristics of the road aggregates usually determined through experiments have been found. The non-hazardous waste incineration bottom ashes treated by hydraulic binder was classified into mechanical classe 3.
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Sow, Libasse, Fabrice Bernard et Siham Kamali-Bernard. « Mechanical Behaviour of Cement-Bound Gravels by Experiment-Based 3D Multi-Scale Modelling : Application to Non-Hazardous Waste Incineration Bottom Ashes Aggregates for Use in Road Engineering ». International Journal of Engineering Research in Africa 54 (juin 2021) : 71–85. http://dx.doi.org/10.4028/www.scientific.net/jera.54.71.
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This paper presents a hierarchical multi-scale modelling approach devoted to investigating the mechanical behaviour of cement-bound gravels. Material studied is based on Non-Hazardous Waste Incineration (NHWI) bottom ashes. The elastic moduli of NHWI particles have been previously determined by an original indentation campaign never conducted so far on these types of aggregates. The results of the experimental campaign serve as input data to the developed numerical strategy. The modelling is based on the definition of Representative Elementary Volumes (REV) considering all the heterogeneities of the material. The "virtual laboratory" set up made it possible to determine the mechanical parameters characterizing the gravel treated with 3% of cement. The high value obtained of the internal friction angle (76 °) gives the material a good bearing capacity. The classification in mechanical classes 3 and 4 when the Young's modulus of the NHWI particles varies from 20 to 80 GPa proves the feasibility of the reuse of this type of industrial by-products in this sector of activity. The present modelling approach is validated by means of comparisons with experimental results of the literature.
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Ahmed, Essam N., Sahrish B. Naqvi, Lorenzo Buda et Alessandro Bottaro. « A Homogenization Approach for Turbulent Channel Flows over Porous Substrates : Formulation and Implementation of Effective Boundary Conditions ». Fluids 7, no 5 (20 mai 2022) : 178. http://dx.doi.org/10.3390/fluids7050178.
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The turbulent flow through a plane channel bounded by a single permeable wall is considered; this is a problem of interest since a carefully chosen distribution of grains and voids in the porous medium can result in skin friction reduction for the flow in the channel. In the homogenization approach followed here, the flow is not resolved in the porous layer, but an effective velocity boundary condition is developed (and later enforced) at a virtual interface between the porous bed and the channel flow. The condition is valid up to order two in terms of a small gauge factor, the ratio of microscopic to macroscopic length scales; it contains slip coefficients, plus surface and bulk permeability coefficients, which arise from the solution of microscale problems solved in a representative elementary volume. Using the effective boundary conditions, free of empirical parameters, direct numerical simulations are then performed in the channel, considering a few different porous substrates. The results, examined in terms of mean values and turbulence statistics, demonstrate the drag-reducing effects of porous substrates with streamwise-preferential alignment of the solid grains.
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Mujtaba, Babar, Hana Hlaváčiková, Michal Danko, João L. M. P. de Lima et Ladislav Holko. « The role of stony soils in hillslope and catchment runoff formation ». Journal of Hydrology and Hydromechanics 68, no 2 (1 juin 2020) : 144–54. http://dx.doi.org/10.2478/johh-2020-0012.
Texte intégralRésumé :
AbstractThe role of stony soils in runoff response of mountain catchments is rarely studied. We have compared simulated response of stony soils with measured catchment runoff for events caused by rains of small and high intensities in the mountain catchment of the Jalovecký Creek, Slovakia. The soil water response was simulated for three sites with stoniness 10–65% using the Hydrus-2D single porosity model. Soil hydraulic parameters employed in the modelling, i. e. the saturated hydraulic conductivity and parameters of the soil water retention curves, were obtained by two approaches, namely by the Representative Elementary Volume approach (REVa) and by the inverse modelling with Hydrus-1D model (IMa). The soil water outflow hydrographs simulated by Hydrus-2D were compared to catchment runoff hydrographs by analysing their skewness and peak times. Measured catchment runoff hydrographs were similar to simulated soil water outflow hydrographs for about a half of rainfall events. Interestingly, most of them were caused by rainfalls with small intensity (below 2.5 mm/10 min). The REV approach to derive soil hydraulic parameters for soil water outflow modelling provided more realistic shapes of soil water outflow hydrographs and peak times than the IMa approach.
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Ding, Changdong, Zhenjiang Liu, Xiancheng Mei et Shaoming Ouyang. « Size-Dependent Mechanical Properties and Excavation Responses of Basalt with Hidden Cracks at Baihetan Hydropower Station through DFN–FDEM Modeling ». Applied Sciences 14, no 19 (8 octobre 2024) : 9069. http://dx.doi.org/10.3390/app14199069.
Texte intégralRésumé :
Basalt is an important geotechnical material for engineering construction in Southwest China. However, it has complicated structural features due to its special origin, particularly the widespread occurrence of hidden cracks. Such discontinuities significantly affect the mechanical properties and engineering stability of basalt, and related research is lacking and unsystematic. In this work, taking the underground caverns in the Baihetan Hydropower Station as the engineering background, the size-dependent mechanical behaviors and excavation responses of basalt with hidden cracks were systematically explored based on a synthetic rock mass (SRM) model combining the finite-discrete element method (FDEM) and discrete fracture network (DFN) method. The results showed that: (1) The DFN–FDEM model generated based on the statistical characteristics of the geometric parameters of hidden cracks can consider the real structural characteristics of basalt, whereby the mechanical behaviors found in laboratory tests and at the engineering site could be exactly reproduced. (2) The representative elementary volume (REV) size of basalt blocks containing hidden cracks was 0.5 m, and the mechanical properties obtained at this size were considered equivalent continuum properties. With an increase in the sample dimensions, the mechanical properties reflected in the stress–strain curves changed from elastic–brittle to elastic–plastic or ductile, the strength failure criterion changed from linear to nonlinear, and the failure modes changed from fragmentation failure to local structure-controlled failure and then to splitting failure. (3) The surrounding rock mass near the excavation face of underground caverns typically showed a spalling failure mode, mainly affected by the complex structural characteristics and high in situ stresses, i.e., a tensile fracture mechanism characterized by stress–structure coupling. The research findings not only shed new light on the failure mechanisms and size-dependent mechanical behaviors of hard brittle rocks represented by basalt but also further enrich the basic theory and technical methods for multi-scale analyses in geotechnical engineering, which could provide a reference for the design optimization, construction scheme formulation, and disaster prevention of deep engineering projects.
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Sabet, Safa, Moghtada Mobedi, Murat Barisik et Akira Nakayama. « Numerical determination of interfacial heat transfer coefficient for an aligned dual scale porous medium ». International Journal of Numerical Methods for Heat & ; Fluid Flow 28, no 11 (5 novembre 2018) : 2716–33. http://dx.doi.org/10.1108/hff-03-2018-0097.
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Purpose Fluid flow and heat transfer in a dual scale porous media is investigated to determine the interfacial convective heat transfer coefficient, numerically. The studied porous media is a periodic dual scale porous media. It consists of the square rods which are permeable in an aligned arrangement. It is aimed to observe the enhancement of heat transfer through the porous media, which is important for thermal designers, by inserting intra-pores into the square rods. A special attention is given to the roles of size and number of intra-pores on the heat transfer enhancement through the dual scale porous media. The role of intra-pores on the pressure drop of air flow through porous media is also investigated by calculation and comparison of the friction coefficient. Design/methodology/approach To calculate the interfacial convective heat transfer coefficient, the governing equations which are continuity, momentum and energy equations are solved to determine velocity, pressure and temperature fields. As the dual scale porous structure is periodic, a representative elementary volume is generated, and the governing equations are numerically solved for the selected representative volume. By using the obtained velocity, pressure and temperature fields and using volume average definition, the volume average of aforementioned parameters is calculated and upscaled. Then, the interfacial convective heat transfer coefficient and the friction coefficient is numerically determined. The interparticle porosity is changed between 0.4 and 0.75, while the intraparticle varies between 0.2 and 0.75 to explore the effect of intra-pore on heat transfer enhancement. Findings The obtained Nusselt number values are compared with corresponding mono-scale porous media, and it is found that heat transfer through a porous medium can be enhanced threefold (without the increase of pressure drop) by inserting intraparticle pores in flow direction. For the porous media with low values of interparticle porosity (i.e. = 0.4), an optimum intraparticle porosity exists for which the highest heat transfer enhancement can be achieved. This value was found around 0.3 when the interparticle porosity was 0.4. Research limitations/implications The results of the study are interesting, especially from heat transfer enhancement point of view. However, further studies are required. For instance, studies should be performed to analyze the rate of the heat transfer enhancement for different shapes and arrangements of particles and a wider range of porosity. The other important parameter influencing heat transfer enhancement is the direction of pores. In the present study, the intraparticle pores are in flow direction; hence, the enhancement rate of heat transfer for different directions of pores must also be investigated. Practical implications The application of dual scale porous media is widely faced in daily life, nature and industry. The flowing of a fluid through a fiber mat, woven fiber bundles, multifilament textile fibers, oil filters and fractured porous media are some examples for the application of the heat and fluid flow through a dual scale porous media. Heat transfer enhancement. Social implications The enhancement of heat transfer is a significant topic that gained the attention of researchers in recent years. The importance of topic increases day-by-day because of further demands for downsizing of thermal equipment and heat recovery devices. The aim of thermal designers is to enhance heat transfer rate in thermal devices and to reduce their volume (and/or weight in some applications) by using lower mechanical power for cooling. Originality/value The present study might be the first study on determination of thermal transport properties of dual scale porous media yielded interesting results such as considerable enhancement of heat transfer by using proper intraparticle channels in a porous medium.
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Jiang, LiJuan, HongGuang Sun et Yan Wang. « Modeling immiscible fluid flow in fractal pore medium by multiphase lattice Boltzmann flux solver ». Physics of Fluids 35, no 2 (février 2023) : 023334. http://dx.doi.org/10.1063/5.0137360.
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In this paper, the multiphase lattice Boltzmann flux solver (MLBFS), where the phase field model and the apparent liquid permeability model are built-in, is developed to simulate incompressible multiphase flows in fractal pore structure at the representative elementary volume scale. MLBFS takes advantage of the traditional Navier–Stokes solver (e.g., geometric flexibility and direct handling of complex boundary conditions) and lattice Boltzmann method (e.g., intrinsically kinetic nature, simplicity, and parallelism). It is easily applied to simulate multiphase flows transport in the porous medium with large density ratios and high Reynolds numbers. This study focuses on the fluid flow in fractal pore structures and provides an in-depth discussion of the effects of non-Newtonian index, fractal parameters, and density ratios on multiphase flow. The proposed model is validated with benchmark problems to test the applicability and reliability of the MLBFS in describing fluid flow in fractal pore structures with large density ratios and viscosity ratios. Simulation results show that the fractal parameters (i.e., fractal dimension, tortuous fractal dimension, porosity, and capillary radius ratio) can accurately characterize fractal pore structure and significantly affect the apparent liquid permeability. In addition, the flow rate increases with the fractal dimension and decreases with the tortuous fractal dimension, while both flow rate and apparent liquid permeability decrease as the capillary radius ratio. It is also noteworthy that the effect of nonlinear drag forces cannot be neglected for shear-thickened flows.
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ARSON, CHLOE, YANNICK YASOTHAN, ROMAIN JEANNERET, AURELIE BENOIT, NICOLAS ROUBIER et ELSA VENNAT. « AN ALTERNATIVE TO PERIODIC HOMOGENIZATION FOR DENTIN ELASTIC STIFFNESS ». Journal of Mechanics in Medicine and Biology 20, no 02 (mars 2020) : 1950081. http://dx.doi.org/10.1142/s0219519419500817.
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Dentin, the main tissue of the tooth, is made of tubules surrounded by peri-tubular dentin (PTD), embedded in a matrix of inter-tubular dentin (ITD). The PTD and the ITD have different relative fractions of collagen and hydroxyapatite crystals. The ITD is typically less rigid than the PTD, which can be seen as a set of parallel hollow cylindrical reinforcements in the ITD matrix. In this paper, we extend Hashin and Rozen’s homogenization scheme to a nonuniform distribution of hollow PTD cylinders, determined from image analysis. We relate the transverse isotropic elastic coefficients of a Representative Elementary Volume (REV) of dentin to the elastic and topological properties of PTD and ITD. The model is calibrated against experimental data. Each sample tested is consistently characterized by Environmental Scanning Electron Microscopy (ESEM), nanoindentation and Resonant Ultrasound Spectroscopy (RUS), which ensures that macroscopic mechanical properties measured are correlated with microstructure observations. Despite the high variability of microstructure descriptors and mechanical properties, statistical analyses show that Hashin’s bounds converge and that the proposed model can be used for back-calculating the microscopic Poisson’s ratios of dentin constituents. Three-point bending tests conducted in the laboratory were simulated with the Finite Element Method (FEM). Elements were assigned transverse isotropic elastic parameters calculated by homogenization. The tubule orientation and the pdf of the ratio inner/outer tubule radius were determined in several zones of the beams before testing. The remainder of the micro-mechanical parameters were taken equal to those calibrated by RUS. The horizontal strains found experimentally by Digital Image Correlation (DIC) were compared to those found by FEM. The DIC and FEM horizontal strain fields showed a very good agreement in trend and order of magnitude, which verifies the calibration of the homogenization model. By contrast with previous studies of dentin, we fully calibrated a closed form mechanical model against experimental data and we explained the testing procedures. In elastic conditions, the proposed homogenization scheme gives a better account of microstructure variability than micro–macro dentin models with periodic microstructure.
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Wang, Hao, Xueyan Guo, Xinrong Liu, Xiaohan Zhou et Bin Xu. « Shear Mechanical Behaviours and Size Effect of Band–Bedrock Interface : Discrete Element Method Simulation Insights ». Applied Sciences 14, no 20 (17 octobre 2024) : 9481. http://dx.doi.org/10.3390/app14209481.
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The shear band is a prominent feature within the Banbiyan hazardous rock mass located in the Wushan section of the Three Gorges Reservoir area. This band constitutes a latent risk, as the potential for the rock mass to slide along the region threatens the safety of lives and property. Presently, the understanding of the shear mechanisms and the impact of shear band size on the band–bedrock interface is incomplete. In this study, based on band–bedrock shear laboratory tests, DEM simulation is used to investigate the shear-induced coalescence mechanism, stress evolution, and crack-type characteristics of the band–bedrock interface. In addition, the shear mechanical properties of samples considering specimen size, rock step height, and step width are further studied. The results show that the crack initiation and failure crack types observed in the first rock step are predominantly tensile. In contrast, the failure cracks in the remaining rock slabs and steps are primarily characterised by shear mode in addition to other mixed modes. The stress condition experienced by the first step is very near to the position of the applied point load, whereas the stress distribution across the remaining steps shows a more complex state of compressive–tensile stress. The relationship between shear parameters and sample size is best described by a negative exponential function. The representative elementary volume (REV) for shear parameters is suggested to be a sample with a geometric size of 350 mm. Notably, the peak shear strength and shear elastic modulus demonstrate a progressive increase with the rise in rock step height, with the amplifications reaching 91.37% and 115.83%, respectively. However, the residual strength exhibits an initial decline followed by a gradual ascent with increasing rock step height, with the amplitude of reduction and subsequent amplification being 23.73% and 116.94%, respectively. Additionally, a narrower rock step width is found to diminish the shear parameter values, which then tend to stabilise within a certain range as the step width increases.
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Kulatilake, Pinnaduwa H. S. W., Hasan Ucpirti et Ove Stephansson. « Effects of finite-size joints on the deformability of jointed rock at the two-dimensional level ». Canadian Geotechnical Journal 31, no 3 (1 juin 1994) : 364–74. http://dx.doi.org/10.1139/t94-044.
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A numerical decomposition technique, which has resulted from a linking between joint-geometry modeling and generation schemes, and a distinct element code (UDEC), is used to study the effect of joint-geometry parameters of finite-size joints on the deformability properties of jointed rock at the two-dimensional (2D) level. The influence of joint-geometry parameters such as joint density, ratio of joint size to block size, and joint orientation on the deformability of jointed rock is shown. Relations are established between deformability properties of jointed rock and fracture-tensor parameters. An incrementally linear elastic, anisotropic constitutive model is developed to represent the prefailure mechanical behaviour of jointed rock at the 2D level. This constitutive model has captured the anisotropic, scale-dependent behaviour of jointed rock. In this model, the effect of the joint-geometry network in the rock mass is incorporated in terms of fracture-tensor components. Some insight is given related to estimation of representative elementary volumes for deformability properties of jointed rock. Key words : rock masses, deformability, distinct element method, fracture tensor, anisotropy, scale effects.
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Pan’kov, A. A. « Diagnostics of impregnation defects of reinforcing filaments of polymer composite with built-in fibre-optic sensor with distributed Bragg grating ». PNRPU Mechanics Bulletin, no 3 (15 décembre 2020) : 60–72. http://dx.doi.org/10.15593/perm.mech/2020.3.07.
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Mathematical model of unidirectional fibrous polymer composite material with optical fiber sensor built into reinforcing fiber (filament of elementary fibers) with distributed Bragg grating is developed in order to diagnoste defects of filament impregnation - finding probability of impregnation defect as relative length of local sections of filament without impregnation, i.e. without filling binder of space between its elementary fibers. The technique of digital processing of reflection spectrum according to the solution of the integral Fredholm equation of the 1st kind is used in order to find the desired informative function of density of distribution of axial strains along the length of the sensitive section of the fibre-optic sensor. The approach assumes that the optical fiber sensor is embedded in the composite material at the stage of its manufacture, wherein the low-reflective nature of the sensitive portion of the optical fiber allows linear summation of reflection coefficients from its various local portions regardless of their mutual positions. Algorithm of numerical processing of strain distribution density function is developed for finding of sought probability of presence of impregnation defects along filament length. It has been revealed that the distribution density function has pronounced informative pulses, from the location and value of which the sought-after values of probability of presence of impregnation defects along the length of the filament can be found. The results of diagnostics of different values of the sought probability of the filament impregnation defect are presented based on the results of numerical simulation of the measured reflection spectra and the sought function of strain distribution density along the length of the sensitive section of the optical fiber sensor at different values of the volume fraction of the filaments, combinations of transverse and longitudinal loads of the representative domain of the unidirectional fibrous composite material in comparison with graphs for the case without load.
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Zhang, Chuangye, Wenyong Liu, Chong Shi, Shaobin Hu et Jin Zhang. « Experimental Investigation and Micromechanical Modeling of Hard Rock in Protective Seam Considering Damage–Friction Coupling Effect ». Sustainability 14, no 23 (6 décembre 2022) : 16296. http://dx.doi.org/10.3390/su142316296.
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The hard rock in the protective coal seam of the Pingdingshan Mine in China is a typical quasi-brittle material exhibiting complex mechanical characteristics. According to available research on the mechanical property, the inelastic deformation and development of damage are considered related with crack initiation and propagation, which are main causes of the material degradation. In the present study, an original experimental investigation on the rock sample of the Pingdingshan coal mine is firstly carried out to obtain the basic mechanical responses in a conventional triaxial compression test. Based on the homogenization method and thermodynamic theory, a damage–friction coupled model is proposed to simulate the non-linear mechanical behavior. In the framework of micromechanics, the hard rock in a protective coal seam is viewed as a heterogeneous material composed of a homogeneous solid matrix and a large number of randomly distributed microcracks, leading to a Representative Elementary Volume (REV), i.e., the matrix–cracks system. By the use of the Mori–Tanaka homogenization scheme, the effective elastic properties of cracked material are obtained within the framework of micromechanics. The expression of free energy on the characteristic unitary is derived by homogenization methods and the pairwise thermodynamic forces associated with the inelastic strain and damage variables. The local stress tensor is decomposed to hydrostatic and deviatoric parts, and the effective tangent stiffness tensor is derived by considering both the plastic yield law and a specific damage criterion. The associated generalized Coulomb friction criterion and damage criterion are introduced to describe the evolution of inelastic strain and damage, respectively. Prepeak and postpeak triaxial response analysis is carried out by coupled damage–friction analysis to obtain analytical expressions for rock strength and to clarify the basic characteristics of the damage resistance function. Finally, by the use of the returning mapping procedure, the proposed damage–friction constitutive model is applied to simulate the deformation of Pingdingshan hard rock in triaxial compression with respect to different confining pressures. It is observed that the numerical results are in good agreement with the experimental data, which can verify the accuracy and show the obvious advantages of the micromechanic-based model.
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Gallegos Mayorga, Linamaría, Stéphane Sire, Sylvain Calloch, Suzhe Yang, Luc Dieleman et Jean Luc Martin. « A Self-Heating Approach to Characterize Anisotropy Effects in Fatigue Behaviour : Application to a Nineteenth Century Puddled Iron from a French Railway Bridge ». Advanced Materials Research 891-892 (mars 2014) : 136–42. http://dx.doi.org/10.4028/www.scientific.net/amr.891-892.136.
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The puddled iron is known for its extended use in monumental construction during the second half of the nineteenth century; among the structures built with such material are about half of French railway metallic bridges, most of them with over a century of service life. This scenario rises several concerns about the resistance of this material to cyclic loadings and therefore its fatigue behaviour. However, the puddled iron possesses several properties that make its mechanical characterization particularly difficult. Due to the puddling process this metal contains an important number of non-metallic inclusions that not only will turn out in a heterogeneous material but also (due to the rolling process) into an anisotropic one. In this paper a fast characterization of fatigue properties is proposed by using the self-heating method. The experimental self-heating curves obtained from specimens of the bridge of Toles (Chaumont, France) showed a scatter that was not observed in homogeneous materials (modern steel for example), this phenomenon is explained by the lack of determination of the representative elementary volume of the puddled iron. However, this data gives us important information such as the minimum and maximum boundaries of the mean fatigue limit for several orientations. An anisotropic two-scale probabilistic model for high cycle fatigue is also used to represent the orientation dependency of the results and the scatter found on the experimental data by using Hills elasto-plastic law and Weibulls distribution law to describe several characteristics of each site where the microplasticity occurs. The influence of such parameters and the limitations of the model are also discussed.
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Kolegov, Grigoriy A., et Aleksey Yu Krainov. « Simulation of the coal mine ventilation with account for gob areas ». Vestnik Tomskogo gosudarstvennogo universiteta. Matematika i mekhanika, no 79 (2022) : 78–88. http://dx.doi.org/10.17223/19988621/79/7.
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Mine ventilation network models are widely used in underground coal mining in Russia. The models cover a variety of practical problems ranging from simple air distribution in active mine workings to changes in the static air pressure gradient associated with complex technological or hazardous processes occurring in mines. Isolated gob areas are integral parts of ventilation networks in coal mines. The most commonly used underground coal extraction technology in Russia is the longwall mining. A gob forms when a coal seam is extracted, and the upper layers of the rock cave in. Gobs are isolated from active mine entries with seals, but there is always air leakages from active faces inducing the air circulation in isolated areas. Gobs join different coal seams and often become the sources of underground fires. Therefore, the inclusion of gobs in mine ventilation network models would help contain accidents and eliminate the caused damage. The study uses the method of representative elementary volumes to incorporate a porous medium into mine ventilation network models. Quadratic resistances are assigned to the edges of the model, where Kirchhoffs laws are valid. The aerodynamic resistances of the gob edges are calculated using the Ergun equation. The proposed method has been used to evaluate pressure gradients in the gob area of the Raspadskaya mine. Several scenarios of the aerodynamic resistance variation in the active mine workings surrounding the gob area, such as partial flooding and drilling of boreholes from the surface, have been simulated, and the corresponding changes in pressure gradients have been analyzed.
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Wang, Yajuan, Jun’an Zhang, Tianle Zhang, Zhiwei Lu et Hao Dong. « Analysis and Experiment of Heat Transfer Performance of Straight-Channel Grid Regenerator ». International Journal of Heat and Technology 40, no 3 (30 juin 2022) : 781–91. http://dx.doi.org/10.18280/ijht.400317.
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The design of heat transfer performance of regenerator is the key technology of Stirling machine and is of great significance to ensure the operation efficiency of equipment. In this study the temperature difference between the two ends of regenerator at room temperature is less than 50K. This paper attempts to study the heat transfer performance of the straight channel grid regenerator at room temperature and verify its accuracy. At first, a straight-channel grid regenerator was designed in this study by analyzing the influence of structural parameters on the regenerator in order to reduce the flow resistance loss. The Pore Scale method and Representative Elementary Volume methods were combined to analyze the heat transfer characteristics of the grid regenerator. Compared with the wire mesh regenerator under the same condition, the straight-channel grid regenerator’s flow resistance could reduce by 96.2%. When the length-diameter ratio is 2:1 and the porosity is between 0.4 and 0.5, the heat transfer performance of the grid regenerator is satisfactory when it is applied in Stirling heat pump at room temperature. Then, A segmented variable porosity grid regenerator was designed based on the grid regenerator, and its performance was proved to be better than that of the grid regenerator. Finally, the two regenerators were developed based on additive manufacturing technology, and a single blow experiment platform was built. The experimental results fit well with the simulation results, with the maximum error being less than 1.5%. The experimental results prove the correctness of the model, which lays a foundation for the subsequent analysis of the periodic heat transfer characteristics of the straight-channel grid regenerator.
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Steinbrecher, Ivo, Alexander Popp et Christoph Meier. « Consistent coupling of positions and rotations for embedding 1D Cosserat beams into 3D solid volumes ». Computational Mechanics 69, no 3 (28 novembre 2021) : 701–32. http://dx.doi.org/10.1007/s00466-021-02111-4.
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AbstractThe present article proposes a mortar-type finite element formulation for consistently embedding curved, slender beams into 3D solid volumes. Following the fundamental kinematic assumption of undeformable cross-section s, the beams are identified as 1D Cosserat continua with pointwise six (translational and rotational) degrees of freedom describing the cross-section (centroid) position and orientation. A consistent 1D-3D coupling scheme for this problem type is proposed, requiring to enforce both positional and rotational constraints. Since Boltzmann continua exhibit no inherent rotational degrees of freedom, suitable definitions of orthonormal triads are investigated that are representative for the orientation of material directions within the 3D solid. While the rotation tensor defined by the polar decomposition of the deformation gradient appears as a natural choice and will even be demonstrated to represent these material directions in a $$L_2$$ L 2 -optimal manner, several alternative triad definitions are investigated. Such alternatives potentially allow for a more efficient numerical evaluation. Moreover, objective (i.e. frame-invariant) rotational coupling constraints between beam and solid orientations are formulated and enforced in a variationally consistent manner based on either a penalty potential or a Lagrange multiplier potential. Eventually, finite element discretization of the solid domain, the embedded beams, which are modeled on basis of the geometrically exact beam theory, and the Lagrange multiplier field associated with the coupling constraints results in an embedded mortar-type formulation for rotational and translational constraint enforcement denoted as full beam-to-solid volume coupling (BTS-FULL) scheme. Based on elementary numerical test cases, it is demonstrated that a consistent spatial convergence behavior can be achieved and potential locking effects can be avoided, if the proposed BTS-FULL scheme is combined with a suitable solid triad definition. Eventually, real-life engineering applications are considered to illustrate the importance of consistently coupling both translational and rotational degrees of freedom as well as the upscaling potential of the proposed formulation. This allows the investigation of complex mechanical systems such as fiber-reinforced composite materials, containing a large number of curved, slender fibers with arbitrary orientation embedded in a matrix material.
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Dentz, M., M. Icardi et J. J. Hidalgo. « Mechanisms of dispersion in a porous medium ». Journal of Fluid Mechanics 841 (1 mars 2018) : 851–82. http://dx.doi.org/10.1017/jfm.2018.120.
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This paper studies the mechanisms of dispersion in the laminar flow through the pore space of a three-dimensional porous medium. We focus on preasymptotic transport prior to the asymptotic hydrodynamic dispersion regime, in which solute motion may be described by the average flow velocity and a hydrodynamic dispersion coefficient. High-performance numerical flow and transport simulations of solute breakthrough at the outlet of a sand-like porous medium evidence marked deviations from the hydrodynamic dispersion paradigm and identify two distinct regimes. The first regime is characterised by a broad distribution of advective residence times in single pores. The second regime is characterised by diffusive mass transfer into low-velocity regions in the wake of solid grains. These mechanisms are quantified systematically in the framework of a time-domain random walk for the motion of marked elements (particles) of the transported material quantity. Particle transitions occur over the length scale imprinted in the pore structure at random times given by heterogeneous advection and diffusion. Under globally advection-dominated conditions, i.e., Péclet numbers larger than 1, particles sample the intrapore velocities by diffusion and the interpore velocities through advection. Thus, for a single transition, particle velocities are approximated by the mean pore velocity. In order to quantify this advection mechanism, we develop a model for the statistics of the Eulerian velocity magnitude based on Poiseuille’s law for flow through a single pore and for the distribution of mean pore velocities, both of which are linked to the distribution of pore diameters. Diffusion across streamlines through immobile zones in the wake of solid grains gives rise to exponentially distributed residence times that decay on the diffusion time over the pore length. The trapping rate is determined by the inverse diffusion time. This trapping mechanism is represented by a compound Poisson process conditioned on the advective residence time in the proposed time-domain random walk approach. The model is parameterised with the characteristics of the porous medium under consideration and captures both preasymptotic regimes. Macroscale transport is described by an integro-differential equation for solute concentration, whose memory kernels are given in terms of the distribution of mean pore velocities and trapping times. This approach quantifies the physical non-equilibrium caused by a broad distribution of mass transfer time scales, both advective and diffusive, on the representative elementary volume (REV). Thus, while the REV indicates the scale at which medium properties like porosity can be uniquely defined, this does not imply that transport can be characterised by hydrodynamic dispersion.
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de Araújo, O. M. O., K. V. Sharma, A. S. Machado, T. M. P. Santos, C. G. Ferreira, R. Straka, F. W. Tavares et R. T. Lopes. « Representative elementary volume in limestone sample ». Journal of Instrumentation 13, no 10 (25 octobre 2018) : C10003. http://dx.doi.org/10.1088/1748-0221/13/10/c10003.
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Puyguiraud, Alexandre, Philippe Gouze et Marco Dentz. « Is There a Representative Elementary Volume for Anomalous Dispersion ? » Transport in Porous Media 131, no 2 (16 novembre 2019) : 767–78. http://dx.doi.org/10.1007/s11242-019-01366-z.
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Xue, Yufang, Zhongxian Cai, Heng Zhang, Qingbing Liu, Lanpu Chen, Jiyuan Gao et Fangjie Hu. « Insights into Heterogeneity and Representative Elementary Volume of Vuggy Dolostones ». Energies 15, no 16 (10 août 2022) : 5817. http://dx.doi.org/10.3390/en15165817.
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Carbonate reservoirs commonly have significant heterogeneity and complex pore systems due to the multi-scale characteristic. Therefore, it is quite challenging to predict the petrophysical properties of such reservoirs based on restricted experimental data. In order to study the heterogeneity and size of the representative elementary volume (REV) of vuggy dolostones, a total of 26 samples with pore sizes ranging from micrometers to centimeters were collected from the Cambrian Xiaoerbulake Formation at the Kalping uplift in the Tarim Basin of northwestern China. In terms of the distribution of pore size and contribution of pores to porosity obtained by medical computed tomography testing, four types of pore systems (Types I–IV) were identified. The heterogeneity of carbonate reservoirs was further quantitatively evaluated by calculating the parameters of pore structure, heterogeneity, and porosity cyclicity. The results indicate that different pore systems yield variable porosities, pore structures, and heterogeneity. The porosity is relatively higher in Type-II and Type-IV samples compared to those of Type-I and Type-III. It is caused by well-developed large vugs in the former two types of samples, which increase porosity and reduce heterogeneity. Furthermore, the REV was calculated by deriving the coefficient of variation. Nine of the twenty-six samples reach the REV within the volume of traditional core plugs, which indicates that the REV sizes of vuggy dolostones are commonly much larger than the volume of traditional core plugs. Finally, this study indicates that REV sizes are affected by diverse factors. It can be effectively predicted by a new model established based on the relationship between REV sizes and quantitative parameters. The correlated coefficient of this model reaches 0.9320. The results of this study give more insights into accurately evaluating the petrophysical properties of vuggy carbonate reservoirs.
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Rong, Guan, Jun Peng, Xiaojiang Wang, Guang Liu et Di Hou. « Permeability tensor and representative elementary volume of fractured rock masses ». Hydrogeology Journal 21, no 7 (7 septembre 2013) : 1655–71. http://dx.doi.org/10.1007/s10040-013-1040-x.
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Li, J. H., L. M. Zhang, Y. Wang et D. G. Fredlund. « Permeability tensor and representative elementary volume of saturated cracked soil ». Canadian Geotechnical Journal 46, no 8 (août 2009) : 928–42. http://dx.doi.org/10.1139/t09-037.
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Cracks are prevalent in near-ground-surface soils and provide preferential pathways for fluid flow. Cracks increase water infiltration or contaminant solute transport into soils. This paper studies the development of a permeability tensor and a representative elementary volume (REV) for saturated cracked soils. First, a method of generating random crack networks based on the statistical parameters of the crack geometry is presented. Then, the permeability tensor and REV for a crack network are studied by modeling water flow through the generated random crack networks. Finally, the permeability tensor for a cracked soil is obtained by combining the crack network and the soil matrix, and the properties of the permeability tensor and the REV for the cracked soils are investigated. Results show that the permeability tensor can be used to represent the permeability anisotropy of a cracked soil. An REV can be readily established when the crack network is relatively dense. An REV can be defined and the contribution of the crack network to permeability is small when a crack network exists in homogeneous sands. An REV is harder to establish and the hydraulic conductivity is dominated by the random crack network when a sparse crack network exists in clays.
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Ukrainczyk, N., et E. A. B. Koenders. « Representative elementary volumes for 3D modeling of mass transport in cementitious materials ». Modelling and Simulation in Materials Science and Engineering 22, no 3 (28 février 2014) : 035001. http://dx.doi.org/10.1088/0965-0393/22/3/035001.
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Wang, Da Yong, Hu Shan Xu et Xiao Jing Ma. « Computed Tomography Analysis of Representative Elementary Volume (REV) of Porous Medium ». Advanced Materials Research 868 (décembre 2013) : 234–37. http://dx.doi.org/10.4028/www.scientific.net/amr.868.234.
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Representative Elementary Volume (REV) is not only a necessary measure for studying heterogeneous pore structure of reservoir rocks but also an important parameter for core-scale numerical modeling. In this paper, we accordingly analyze the REV for different porous media with different grain sizes based on computed tomography (CT) measurement. Our results show that that CT measurement is a relible method for REV analysis and that there is an appropriate linear relationship between grain size and REV.
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Sedaghat, Mohammad H., et Siroos Azizmohammadi. « Representative-Elementary-Volume Analysis of Two-Phase Flow in Layered Rocks ». SPE Reservoir Evaluation & ; Engineering 22, no 03 (1 août 2019) : 1075–83. http://dx.doi.org/10.2118/194014-pa.
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