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Yujing Jiang - One of the best experts on this subject based on the ideXlab platform.
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a novel three dimensional discrete fracture network model for investigating the role of Aperture heterogeneity on fluid flow through fractured rock masses
International Journal of Rock Mechanics and Mining Sciences, 2019Co-Authors: Na Huang, Yujing Jiang, Richeng Liu, Satoshi SugimotoAbstract:Abstract Effect of anisotropic Aperture on the hydraulic properties of single rock fractures has been systematically investigated, yet the Aperture variability of individual fractures in 3D discrete fracture networks (DFNs) is commonly negligible by using parallel-plate fractures. The present study proposed a 3D DFN model with fractures having heterogeneous Apertures to estimate the influence of fracture variability on fluid flow. In total, a set of 1280 3D models with increasing fracture densities and fracture lengths are generated and the fluid flow through the models is simulated using a developed numerical code. The influences of Aperture heterogeneity and network topology on the flow pattern and permeability of 3D DFNs are estimated. The results show that the network topology provides a first-order frame of geometrical connectivity, and the heterogeneous Aperture further allows the flow to select some most transmissive channels within these connected fractures. The DFN model with identical Apertures generates a large number of medium-flow rate regions whereas the DFN model with fractures having heterogeneous Apertures results in extremely low- and high-flow rate regions. The permeability ratio of the two models is widely spread in terms of a small variation in the average Mechanical Aperture as a result of strong dependence on the Aperture distribution. The average permeability ratio increases significantly first and then approaches to 1.0 with increasing the average Mechanical Aperture. This allows for the definition of a critical Mechanical Aperture, above which the permeability can be properly predicted using the DFN model with fractures having identical Apertures and below which the permeability is much altered by the Aperture variability and the DFN model with fractures having heterogeneous Apertures should be employed.
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influences of hydraulic gradient surface roughness intersecting angle and scale effect on nonlinear flow behavior at single fracture intersections
Journal of Hydrology, 2016Co-Authors: Yujing Jiang, Richeng LiuAbstract:Summary Fluid flow tests were conducted on two crossed fracture models for which the geometries of fracture segments and intersections were measured by utilizing a visualization technique using a CCD (charged coupled device) camera. Numerical simulations by solving the Navier–Stokes equations were performed to characterize the fluid flow at fracture intersections. The roles of hydraulic gradient, surface roughness, intersecting angle, and scale effect in the nonlinear fluid flow behavior through single fracture intersections were investigated. The simulation results of flow rate agreed well with the experimental results for both models. The experimental and simulation results showed that with the increment of the hydraulic gradient, the ratio of the flow rate to the hydraulic gradient, Q / J , decreases and the relative difference of Q / J between the calculation results employing the Navier–Stokes equations and the cubic law, δ , increases. When taking into account the fracture surface roughness quantified by Z 2 ranging 0–0.42 for J = 1, the value of δ would increase by 0–10.3%. The influences of the intersecting angle on the normalized flow rate that represents the ratio of the flow rate in a segment to the total flow rate, R a , and the ratio of the hydraulic Aperture to the Mechanical Aperture, e / E , are negligible when J −3 , whereas their values change significantly when J > 10 −2 . Based on the regression analysis on simulation results, a mathematical expression was proposed to quantify e / E , involving variables of J and R r , where R r is the radius of truncating circles centered at an intersection. For E / R r > 10 −2 , e / E varies significantly and the scale of model has large impacts on the nonlinear flow behavior through intersections, while for E / R r −3 , the scale effect is negligibly small. Finally, a necessary condition to apply the cubic law to fluid flow through fracture intersections is suggested as J −3 , E / R r −3 , and Z 2 = 0.
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Experimental and Numerical Study of the Geometrical and Hydraulic Characteristics of a Single Rock Fracture during Shear
Seismic Safety Evaluation of Concrete Dams, 2013Co-Authors: Xiangbin Xiong, Yujing Jiang, Tomofumi Koyama, Chuhan ZhangAbstract:Abstract Coupled shear–flow tests were conducted on two artificial rock fractures with natural rock fracture characteristics under constant normal loading boundary conditions. Numerical simulations using three-dimensional Navier–Stokes equations taking account of the inertial effects of fluid were conducted using void space geometry models obtained from the coupled shear–flow tests. The test and numerical simulation results show that the evolution of geometric and hydraulic characteristics of rock fracture exhibit a three-stage behavior. Transmissivity of a certain void space geometry within a fracture is related to the Reynolds number of fluid flow due to the inertial effects of fluid, which can be represented by Navier–Stokes equations. The Mechanical Aperture is usually larger than the hydraulic Aperture back-calculated from measured flow rate, and the difference between them relates strongly to the geometric characteristics of fractures. A mathematical equation is proposed to describe the relation between hydraulic Aperture and Mechanical Aperture.
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Experimental and numerical study of the geometrical and hydraulic characteristics of a single rock fracture during shear
International Journal of Rock Mechanics and Mining Sciences, 2011Co-Authors: Xiangbin Xiong, Yujing Jiang, Tomofumi Koyama, Chuhan ZhangAbstract:Abstract Coupled shear-flow tests were conducted on two artificial rock fractures with natural rock fracture characteristics under constant normal loading boundary conditions. Numerical simulations using the 3-D Navier–Stokes equations taking account of the inertial effects of fluid were conducted using the void space geometry models obtained from the coupled shear-flow tests. The test and numerical simulation results show that the evolutions of geometrical and hydraulic characteristics of rock fracture exhibit a three-stage behavior. Transmissivity of a certain void space geometry within a fracture is related to the Reynolds number of fluid flow due to the inertial effects of fluid, which can be represented by the Navier–Stokes equations, but cannot be represented by some simplified equations, such as the cubic law, the Reynolds equation or the Stokes equations. The Mechanical Aperture is usually larger than the hydraulic Aperture back-calculated from measured flow rate, and the difference between them is found strongly related to the geometrical characteristics of the fractures. A mathematical equation is proposed to describe the relation between hydraulic Aperture and Mechanical Aperture by means of the ratio of the standard deviation of local Mechanical Aperture to its mean value, the standard deviation of local slope of fracture surface and Reynolds number.
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experimental study of the hydro Mechanical behavior of rock joints using a parallel plate model containing contact areas and artificial fractures
International Journal of Rock Mechanics and Mining Sciences, 2008Co-Authors: Yujing Jiang, Tomofumi Koyama, Lanru Jing, Yoshihiko TanabashiAbstract:In recent years, geological disposal of radioactive wastes is considered to be the most promising option, which requires the understanding of the coupled Mechanical, hydraulic and thermal properties of the host rock masses and rock fractures. The hydro-Mechanical behavior and properties of rock fractures are usually determined by laboratory experiments on fracture specimens that serve as the basic building block of the constitutive models of fractured rock masses. Laboratory testing of rock fractures involve a number of technical issues that may have significant impacts on the reliability and applicability of the testing results, chief among them are the quantitative estimation of the evolutions of hydraulic transmissivity fields of fractures during shear under different normal constraint conditions, and the sealing techniques when fluid flow during shear is involved. In this study, a new shear-flow testing apparatus with specially designed fluid sealing techniques for rock fractures were developed, under constant normal load (CNL) or constant normal stiffness (CNS) constraint. The topographical data of all fracture specimens were measured before testing to constitute the geometrical models for simulating the change of Mechanical Aperture distributions during shearing. A number of shear-flow coupling tests were carried out on three kinds of rock fracture specimens to evaluate the influence of morphological properties of rock fractures on their hydro-Mechanical behaviour. Some empirical relations were proposed to evaluate the effects of contact area and surface roughness on the behavior of fluid flow through rock fractures.
Huidong Wang - One of the best experts on this subject based on the ideXlab platform.
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heat extraction mechanism in a geothermal reservoir with rough walled fracture networks
International Journal of Heat and Mass Transfer, 2018Co-Authors: Yun Chen, Huidong WangAbstract:Abstract This study aims at understanding the mechanism of heat extraction from a geothermal reservoir characterized by rough-walled fracture networks. A unified pipe-network method (UPM) which simplifies both fractures and the rock matrix as pipes is developed considering the local thermal non-equilibrium (LTNE) theory, and it is verified against an analytical solution. Three-dimensional simulations of macroscopic fluid flow and heat transfer in a fractured geothermal reservoir are conducted to take account of fracture roughness. The channeling effect and the heterogeneous distribution of fluid temperature in a core-scale model with a rough-walled fracture surface are simulated. An equivalent heat transfer coefficient (EHTC) is obtained from numerical experiments with respect to the flow rate, Mechanical Aperture and the equivalent hydraulic Aperture. A representative element volume is then used to investigate the flow and heat transfer process in a geothermal reservoir with rough-walled fracture networks by applying the obtained EHTC. Results demonstrate that it is essential to use the proposed EHTC since the constant heat transfer coefficient (HTC) recommended in previous studies underestimates the final outlet fluid temperature in cases with rough-walled fractures.
Geneva Switzerland - One of the best experts on this subject based on the ideXlab platform.
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BPM calibration independent LHC optics correction DISCLAIMER BPM Calibration Independent LHC Optics Correction *
2020Co-Authors: R Tomas, Cern F Zimmerman, Geneva Switzerland, R Calaga, Cern F ZimmermannAbstract:The tight Mechanical Aperture for the LHC imposes severe constraints on both the beta and dispersion beating. Robust techniques to compensate these errors are critical for operation of high intensity beams in the LHC. We present simulations using realistic errors from magnet measurements and alignment tolerances in the presence of BPM noise. Correction reveals that the use of BPM calibration and model independent observables are key ingredients to accomplish optics correction. Experiments at RHIC to verify the algorithms for optics correction are also presented
Chuangbing Zhou - One of the best experts on this subject based on the ideXlab platform.
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a forchheimer equation based flow model for fluid flow through rock fracture during shear
Rock Mechanics and Rock Engineering, 2018Co-Authors: Guan Rong, Chuangbing Zhou, Jie Yang, Long Cheng, Jie Tan, Jun PengAbstract:Shear deformation-induced hydraulic conductivity change in fracture has been studied for decades. However, the existing models to link shear deformation and hydraulic behaviors are less accurate due to complex flow in rock fractures. This study presents an improved flow model for calculating nonlinear flow behaviors in rock fractures during shear. In this model, the linear and nonlinear coefficients in the Forchheimer equation were determined using Mechanical Aperture and fracture roughness coefficients. The Mechanical Aperture was equal to the initial Aperture plus the change of the Aperture due to shear-induced dilation. The dilation curve was divided into three stages and analytical expressions for modeling the dilation curve were established by incorporating the joint roughness coefficient (JRC) and the mobilized roughness coefficient (JRCmob). In addition, shear-flow tests were conducted on marble and granite fractures with normal stress between 0.5 and 3.0 MPa. The experimental data were used to verify the proposed model. The results show that the proposed model predicts flow in rock fractures well.
Richeng Liu - One of the best experts on this subject based on the ideXlab platform.
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a novel three dimensional discrete fracture network model for investigating the role of Aperture heterogeneity on fluid flow through fractured rock masses
International Journal of Rock Mechanics and Mining Sciences, 2019Co-Authors: Na Huang, Yujing Jiang, Richeng Liu, Satoshi SugimotoAbstract:Abstract Effect of anisotropic Aperture on the hydraulic properties of single rock fractures has been systematically investigated, yet the Aperture variability of individual fractures in 3D discrete fracture networks (DFNs) is commonly negligible by using parallel-plate fractures. The present study proposed a 3D DFN model with fractures having heterogeneous Apertures to estimate the influence of fracture variability on fluid flow. In total, a set of 1280 3D models with increasing fracture densities and fracture lengths are generated and the fluid flow through the models is simulated using a developed numerical code. The influences of Aperture heterogeneity and network topology on the flow pattern and permeability of 3D DFNs are estimated. The results show that the network topology provides a first-order frame of geometrical connectivity, and the heterogeneous Aperture further allows the flow to select some most transmissive channels within these connected fractures. The DFN model with identical Apertures generates a large number of medium-flow rate regions whereas the DFN model with fractures having heterogeneous Apertures results in extremely low- and high-flow rate regions. The permeability ratio of the two models is widely spread in terms of a small variation in the average Mechanical Aperture as a result of strong dependence on the Aperture distribution. The average permeability ratio increases significantly first and then approaches to 1.0 with increasing the average Mechanical Aperture. This allows for the definition of a critical Mechanical Aperture, above which the permeability can be properly predicted using the DFN model with fractures having identical Apertures and below which the permeability is much altered by the Aperture variability and the DFN model with fractures having heterogeneous Apertures should be employed.
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influences of hydraulic gradient surface roughness intersecting angle and scale effect on nonlinear flow behavior at single fracture intersections
Journal of Hydrology, 2016Co-Authors: Yujing Jiang, Richeng LiuAbstract:Summary Fluid flow tests were conducted on two crossed fracture models for which the geometries of fracture segments and intersections were measured by utilizing a visualization technique using a CCD (charged coupled device) camera. Numerical simulations by solving the Navier–Stokes equations were performed to characterize the fluid flow at fracture intersections. The roles of hydraulic gradient, surface roughness, intersecting angle, and scale effect in the nonlinear fluid flow behavior through single fracture intersections were investigated. The simulation results of flow rate agreed well with the experimental results for both models. The experimental and simulation results showed that with the increment of the hydraulic gradient, the ratio of the flow rate to the hydraulic gradient, Q / J , decreases and the relative difference of Q / J between the calculation results employing the Navier–Stokes equations and the cubic law, δ , increases. When taking into account the fracture surface roughness quantified by Z 2 ranging 0–0.42 for J = 1, the value of δ would increase by 0–10.3%. The influences of the intersecting angle on the normalized flow rate that represents the ratio of the flow rate in a segment to the total flow rate, R a , and the ratio of the hydraulic Aperture to the Mechanical Aperture, e / E , are negligible when J −3 , whereas their values change significantly when J > 10 −2 . Based on the regression analysis on simulation results, a mathematical expression was proposed to quantify e / E , involving variables of J and R r , where R r is the radius of truncating circles centered at an intersection. For E / R r > 10 −2 , e / E varies significantly and the scale of model has large impacts on the nonlinear flow behavior through intersections, while for E / R r −3 , the scale effect is negligibly small. Finally, a necessary condition to apply the cubic law to fluid flow through fracture intersections is suggested as J −3 , E / R r −3 , and Z 2 = 0.