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Gianluca Cusatis - One of the best experts on this subject based on the ideXlab platform.
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multiphysics lattice discrete particle modeling m ldpm for the simulation of shale fracture permeability
Rock Mechanics and Rock Engineering, 2018Co-Authors: Xinwei Zhou, William J Carey, L P Frash, Gianluca CusatisAbstract:A three-dimensional multiphysics lattice discrete particle model (M-LDPM) framework is formulated to investigate the fracture permeability behavior of shale. The framework features a dual lattice system mimicking the mesostructure of the material and simulates coupled mechanical and flow behavior. The mechanical lattice model simulates the granular internal structure of shale, and describes heterogeneous deformation by means of discrete compatibility and equilibrium equations. The network of flow lattice elements constitutes a dual graph of the mechanical lattice system. A discrete formulation of mass balance for the flow elements is presented to model fluid flow along cracks and intact materials. The overall computational framework is implemented with a mixed explicit–Implicit Integration Scheme and a staggered coupling method that makes use of the dual lattice topology enabling the seamless two-way coupling of the mechanical and flow behaviors. The proposed model is used for the computational analysis of shale fracture permeability behavior by simulating triaxial direct shear tests on Marcellus shale specimens under various confining pressures. The simulated mechanical response is calibrated against the experimental data, and the predicted permeability values are also compared with the experimental measurements. Furthermore, the paper presents the scaling analysis of both the mechanical response and permeability measurements based on simulations performed on geometrically similar specimens with increasing size. The simulated stress strain curves show a significant size effect in the post-peak due to the presence of localized fractures. The scaling analysis of permeability measurements enables prediction of permeability for large specimens by extrapolating the numerical results of small ones.
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multiphysics lattice discrete particle modeling m ldpm for the simulation of shale fracture permeability
arXiv: Geophysics, 2018Co-Authors: Xinwei Zhou, William J Carey, L P Frash, Gianluca CusatisAbstract:A three-dimensional Multiphysics Lattice Discrete Particle Model (M-LDPM) framework is formulated to investigate the fracture permeability behavior of shale. The framework features a dual lattice system mimicking the mesostructure of the material and simulates coupled mechanical and flow behavior. The mechanical lattice model simulates the granular internal structure of shale and describes heterogeneous deformation by means of discrete compatibility and equilibrium equations. The network of flow lattice elements constitutes a dual graph of the mechanical lattice system. A discrete formulation of mass balance for the flow elements is formulated to model fluid flow along cracks. The overall computational framework is implemented with a mixed explicit-Implicit Integration Scheme and a staggered coupling method that makes use of the dual lattice topology enabling the seamless two-way coupling of the mechanical and flow behaviors. The proposed model is used for the computational analysis of shale fracture permeability behavior by simulating triaxial direct shear tests on Marcellus shale specimens under various confining pressures. The simulated mechanical response is calibrated against the experimental data, and the predicted permeability values are also compared with the experimental measurements. Furthermore, the paper presents the scaling analysis of both the mechanical response and permeability measurements based on simulations performed on geometrically similar specimens with increasing size. The simulated stress-strain curves show a significant size effect in the post-peak due to the presence of localized fractures. The scaling analysis of permeability measurements enables prediction of permeability for large specimens by extrapolating the numerical results of small ones.
David L Mcdowell - One of the best experts on this subject based on the ideXlab platform.
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a semi Implicit Integration Scheme for rate independent finite crystal plasticity
International Journal of Plasticity, 2006Co-Authors: R D Mcginty, David L McdowellAbstract:An efficient new numerical Integration Scheme is presented for rate independent crystal plasticity theory. A key feature of this approach is the ability to identify active slip systems prior to determining their shearing rate. Options are described for various cases of slip system hardening, including self hardening and latent hardening. Alternatives for the constitutive update are explored, including hyperelasticity based on the multiplicative decomposition of the deformation gradient as well as application of the consistency condition in a much more efficient hypoelastic formulation. Several conclusions are drawn concerning the influences of elastic and plastic properties on the activation of slip systems and their subsequent shearing rates. Key among these is the fact that, once activated, shearing rates are independent of the levels of shear flow resistance on the slip systems, provided that the plastic hardening moduli are much less in magnitude than the elastic moduli, as is usually the case. Determination of active slip systems and their shearing rates depend on the degree of elastic anisotropy of the crystal, but not on the magnitude of elastic stiffness.
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a semi Implicit Integration Scheme for rate dependent and rate independent plasticity
Computers & Structures, 1997Co-Authors: E B Marin, David L McdowellAbstract:Abstract A semi-Implicit constitutive Integration procedure for rate-independent and rate-dependent inelastic flow of metals is presented. This Integration Scheme, originally proposed by Moran et al. [Formulation of Implicit finite element methods for multiplicative finite deformation plasticity. Int. J. Numer. Meth. Engng 29 , 483–514 (1990)], has the feature of being explicit in the plastic flow direction and hardening moduli but Implicit in the incremental plastic strain. Two approaches to this Scheme are devised for rate-dependent constitutive relations, denoted herein as the kinetic equation and the dynamic yield condition approaches. Details of the Integration Scheme are developed and applied to both incompressible and compressible inelasticity, including pure isotropic and combined kinematic-isotropic hardening theories. Both rate- and temperature-dependent and rate and temperature-independent constitutive laws are considered. In addition, the explicit version of this Scheme is obtained, resulting in the rate tangent modulus method.
Clive Temperton - One of the best experts on this subject based on the ideXlab platform.
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an efficient two time level semi lagrangian semi Implicit Integration Scheme
Quarterly Journal of the Royal Meteorological Society, 2007Co-Authors: Clive Temperton, Andrew StaniforthAbstract:The semi-Implicit semi-Lagrangian Integration technique enables numerical weather prediction models to be run with much longer timesteps than permitted by a semi-Implicit Eulerian Scheme. the choice of timestep can then be made on the basis of accuracy rather than stability requirements. to realize the full potential of the technique, it is important to maintain second-order accuracy in time; this has previously been achieved by applying it in the context of a three-time-level Integration Scheme. In this paper we present a two-time-level version of the technique which yields the same level of accuracy for half the computational effort. Unlike other efficient two-time-level Schemes, ours does not rely on operator splitting. We apply this Scheme to a variable-resolution barotropic finite-element regional model with a minimum gridlength of 100 km, using timesteps of up to three hours. the results are verified against a control run with uniformly high resolution, and are shown to be of similar accuracy to those of a semi-Implicit Eulerian Integration with a timestep of 10 minutes.
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stability of a two time level semi Implicit Integration Scheme for gravity wave motion
Monthly Weather Review, 1997Co-Authors: A J Simmons, Clive TempertonAbstract:Abstract A study is made of the computational stability of semi-Implicit treatments of gravity wave motion suitable for use with two-time-level advection Schemes. The analysis is for horizontally uniform reference values of temperature and surface pressure, and for hybrid pressure-based vertical coordinates. Stability requires the use of reference temperatures that are warmer than those that can be used safely with the corresponding three-time-level Scheme. The reference surface pressure should also be higher. When stable, the two-time-level Scheme is damping, although the largest scales are damped less than by the three-time-level Scheme if the latter uses a typical time filtering. The first-order decentered averaging of gravity wave tendencies used in a number of semi-Lagrangian models reduces the need for a relatively warm reference temperature profile but causes a quite substantial damping of otherwise well-represented low-wavenumber modes. The low-wavenumber damping can be avoided by using an alterna...
Xinwei Zhou - One of the best experts on this subject based on the ideXlab platform.
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multiphysics lattice discrete particle modeling m ldpm for the simulation of shale fracture permeability
Rock Mechanics and Rock Engineering, 2018Co-Authors: Xinwei Zhou, William J Carey, L P Frash, Gianluca CusatisAbstract:A three-dimensional multiphysics lattice discrete particle model (M-LDPM) framework is formulated to investigate the fracture permeability behavior of shale. The framework features a dual lattice system mimicking the mesostructure of the material and simulates coupled mechanical and flow behavior. The mechanical lattice model simulates the granular internal structure of shale, and describes heterogeneous deformation by means of discrete compatibility and equilibrium equations. The network of flow lattice elements constitutes a dual graph of the mechanical lattice system. A discrete formulation of mass balance for the flow elements is presented to model fluid flow along cracks and intact materials. The overall computational framework is implemented with a mixed explicit–Implicit Integration Scheme and a staggered coupling method that makes use of the dual lattice topology enabling the seamless two-way coupling of the mechanical and flow behaviors. The proposed model is used for the computational analysis of shale fracture permeability behavior by simulating triaxial direct shear tests on Marcellus shale specimens under various confining pressures. The simulated mechanical response is calibrated against the experimental data, and the predicted permeability values are also compared with the experimental measurements. Furthermore, the paper presents the scaling analysis of both the mechanical response and permeability measurements based on simulations performed on geometrically similar specimens with increasing size. The simulated stress strain curves show a significant size effect in the post-peak due to the presence of localized fractures. The scaling analysis of permeability measurements enables prediction of permeability for large specimens by extrapolating the numerical results of small ones.
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multiphysics lattice discrete particle modeling m ldpm for the simulation of shale fracture permeability
arXiv: Geophysics, 2018Co-Authors: Xinwei Zhou, William J Carey, L P Frash, Gianluca CusatisAbstract:A three-dimensional Multiphysics Lattice Discrete Particle Model (M-LDPM) framework is formulated to investigate the fracture permeability behavior of shale. The framework features a dual lattice system mimicking the mesostructure of the material and simulates coupled mechanical and flow behavior. The mechanical lattice model simulates the granular internal structure of shale and describes heterogeneous deformation by means of discrete compatibility and equilibrium equations. The network of flow lattice elements constitutes a dual graph of the mechanical lattice system. A discrete formulation of mass balance for the flow elements is formulated to model fluid flow along cracks. The overall computational framework is implemented with a mixed explicit-Implicit Integration Scheme and a staggered coupling method that makes use of the dual lattice topology enabling the seamless two-way coupling of the mechanical and flow behaviors. The proposed model is used for the computational analysis of shale fracture permeability behavior by simulating triaxial direct shear tests on Marcellus shale specimens under various confining pressures. The simulated mechanical response is calibrated against the experimental data, and the predicted permeability values are also compared with the experimental measurements. Furthermore, the paper presents the scaling analysis of both the mechanical response and permeability measurements based on simulations performed on geometrically similar specimens with increasing size. The simulated stress-strain curves show a significant size effect in the post-peak due to the presence of localized fractures. The scaling analysis of permeability measurements enables prediction of permeability for large specimens by extrapolating the numerical results of small ones.
Fabio Mazza - One of the best experts on this subject based on the ideXlab platform.
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nonlinear dynamic response of rc buildings with different base isolation systems subjected to horizontal and vertical components of near fault ground motions
The Open Construction and Building Technology Journal, 2012Co-Authors: Fabio Mazza, Alfonso Vulcano, Mirko MazzaAbstract:Near-fault ground motions are characterized by long-duration horizontal pulses and high values of the peak vertical acceleration, which can become critical for a base-isolated structure. In order to check if current code provisions can be considered adequate for the design of base-isolated structures located in a near-fault area, base-isolated five-storey r.c. framed buildings with elastomeric bearings acting alone ("Base Isolation" system) or combined in parallel or in series with sliding bearings ("Base Isolation and in-Parallel Sliding", BIPS, or "Base Isolation and in-Series Sliding", BISS, sys- tems) are studied. The base-isolated structures are designed assuming the same values for the fundamental vibration pe- riod and equivalent viscous damping in the horizontal direction. Different values of the stiffness ratio, defined as the ratio between the vertical and horizontal stiffness of the elastomeric bearings, are considered; moreover, different values of the sliding ratio, defined as the global sliding force corresponding to an examined BIPS or BISS system divided by the maxi- mum sliding force (in the case of a sliding bearing under each column), are also assumed. The nonlinear analysis of the test structures subjected to strong near-fault ground motions is performed using a step-by-step procedure based on a two- parameter Implicit Integration Scheme and an initial-stress-like iterative procedure. At each step of the analysis, plastic conditions are checked at the potential critical sections of the girders (i.e. end sections of the sub-elements in which a girder is discretized) and columns (i.e. end sections), where a bilinear moment-curvature law is adopted. The response of an elastomeric bearing is simulated by a model with variable stiffness properties in the horizontal and vertical directions, depending on the axial force and lateral deformation, and linear viscous damping. Finally, a rigid-plastic (with friction variability) law is assumed to simulate the behaviour of a sliding bearing.
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effects of near fault ground motions on the nonlinear dynamic response of base isolated r c framed buildings
Earthquake Engineering & Structural Dynamics, 2012Co-Authors: Fabio Mazza, Alfonso VulcanoAbstract:SUMMARY Near-fault ground motions are characterized by long-period horizontal pulses and high values of the ratio between the peak value of the vertical acceleration, PGAV, and the analogous value of the horizontal acceleration, PGAH, which can become critical for base-isolated (BI) structures. The objective of the present work is to check the effectiveness of the base isolation of framed buildings when using High-Damping-Rubber Bearings (HDRBs), taking into consideration the combined effects of the horizontal and vertical components of near-fault ground motions. To this end, a numerical investigation is carried out with reference to BI reinforced concrete buildings designed according to the European seismic code (Eurocode 8). The design of the test structures is carried out in a high-risk region considering (besides the gravity loads) the horizontal seismic loads acting alone or in combination with the vertical ones and assuming different values of the ratio between the vertical and horizontal stiffnesses of the HDRBs. The nonlinear seismic analysis is performed using a step-by-step procedure based on a two-parameter Implicit Integration Scheme and an initial-stress-like iterative procedure. At each step of the analysis, plastic conditions are checked at the potential critical sections of the girders (i.e. end sections of the sub-elements in which a girder is discretized) and columns (i.e. end sections), where a bilinear moment–curvature law is adopted; the effect of the axial load on the ultimate bending moment (M-N interaction) of the columns is also taken into account. The response of an HDRB is simulated by a model with variable stiffness properties in the horizontal and vertical directions, depending on the axial force and lateral deformation, and linear viscous damping. Copyright © 2011 John Wiley & Sons, Ltd.
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nonlinear analysis of spatial framed structures by a lumped plasticity model based on the haar karman principle
Computational Mechanics, 2010Co-Authors: Fabio Mazza, Mirko MazzaAbstract:A lumped plasticity model is proposed for the nonlinear static and dynamic analyses of three-dimensional reinforced concrete (r.c.) frames. A bilinear moment-curvature law and an interaction surface axial force-biaxial bending moment are considered. The nonlinear dynamic analysis is performed using a two-parameter Implicit Integration Scheme and an initial-stress like iterative strategy, adopting the Haar–Karman principle. As a preliminary, two cantilever steel beams, one with box-section and one with tubular section, are used for validating the proposed model under monotonic and cyclic loadings. Moreover single-storey r.c. three-dimensional frames, with square and rectangular cross-sections, subjected to bi-directional ground motions, are assumed as test structures for studying the sensitivity of the model to changes in strength and stiffness input parameters. Comparisons with more refined fibre models prove the reliability of the proposed model.
