Ponències/Comunicacions de congressos
http://hdl.handle.net/2117/3555
Thu, 19 Apr 2018 23:58:32 GMT2018-04-19T23:58:32ZFurther developments in stress initialization in geomechanics via FEM and a two-step procedure involving Airy functions
http://hdl.handle.net/2117/115098
Further developments in stress initialization in geomechanics via FEM and a two-step procedure involving Airy functions
Rafels Ybern, Carles; Jaqués Adell, Irene; Aliguer Piferrer, Ignasi; Carol, Ignacio; Prat Catalán, Pere; Lakshmikantha, Ramasesha Mookanahallipatna; Segura Segarra, José María
The in-situ stress field in rock masses is a key aspect when a numerical analysis of a rock mass is carried out in any area of geo-engineering, such as civil, mining, or Oil & Gas. A method for the numerical generation of the in-situ stress state in the FE context, based on Airy stress functions was previously introduced. It involves two steps: 1) an estimate of the stress state at each Gauss point is generated, and 2) global equilibrium is verified and re-balancing nodal forces are applied as needed. In this paper, new developments towards improving the accuracy of the stress proposal are discussed. A real application example has been used to illustrate the results achieved with the new implementation.
Tue, 13 Mar 2018 11:48:10 GMThttp://hdl.handle.net/2117/1150982018-03-13T11:48:10ZRafels Ybern, CarlesJaqués Adell, IreneAliguer Piferrer, IgnasiCarol, IgnacioPrat Catalán, PereLakshmikantha, Ramasesha MookanahallipatnaSegura Segarra, José MaríaThe in-situ stress field in rock masses is a key aspect when a numerical analysis of a rock mass is carried out in any area of geo-engineering, such as civil, mining, or Oil & Gas. A method for the numerical generation of the in-situ stress state in the FE context, based on Airy stress functions was previously introduced. It involves two steps: 1) an estimate of the stress state at each Gauss point is generated, and 2) global equilibrium is verified and re-balancing nodal forces are applied as needed. In this paper, new developments towards improving the accuracy of the stress proposal are discussed. A real application example has been used to illustrate the results achieved with the new implementation.Coupled H-M fracture interaction using FEM with zero-thickness interface elements
http://hdl.handle.net/2117/115096
Coupled H-M fracture interaction using FEM with zero-thickness interface elements
Garolera Vinent, Daniel; Segura Serra, Josep Maria; Carol, Ignacio; Lakshmikantha, Ramasesha Mookanahallipatna; Alvarellos Iglesias, José
Massive treatments of hydraulic fracturing is a procedure employed for low permeability reservoirs stimulation. This technique consists in generating a series of parallel spaced fractures parallel (multi-stage fracturing). The generation of a fracture involves the modification of the local stress state, so in the case of a multi-stage treatment, the fracture propagation can be modified by the injection sequence, as it is observed with microseismicity monitoring [1]. This work proposes the study of this technique by means of the finite element method with zerothickness interface elements for the geo-mechanical modelling of discontinuities [2]. The technique consists in inserting interface elements in between standard elements to allow jumps in the displacement solution fields. For the mechanical problem, their kinematic constitutive variables are relative displacements, and the corresponding static variables are stress tractions. The relationship
between variables is controlled via a fracture-based constitutive law with elasto-plastic structure [3]. Concerning the hydraulic problem, the interface formulation includes both the longitudinal flow (with a longitudinal conductivity parameter strongly dependent on the fracture aperture), as well as and the transversal flow across the element (seepage)[4]. Previous works by the authors focused on the validation of the method, the analysis a single fracture plane problem [5,6]. In this case the method is extended to allow free propagation of fractures in any direction, by means of inserting interface elements between all continuum elements. The results presented in this paper analyse the effect of material properties, in particular fracture characterization, in the propagation and the effect of fracture job sequenc.
Tue, 13 Mar 2018 11:29:44 GMThttp://hdl.handle.net/2117/1150962018-03-13T11:29:44ZGarolera Vinent, DanielSegura Serra, Josep MariaCarol, IgnacioLakshmikantha, Ramasesha MookanahallipatnaAlvarellos Iglesias, JoséMassive treatments of hydraulic fracturing is a procedure employed for low permeability reservoirs stimulation. This technique consists in generating a series of parallel spaced fractures parallel (multi-stage fracturing). The generation of a fracture involves the modification of the local stress state, so in the case of a multi-stage treatment, the fracture propagation can be modified by the injection sequence, as it is observed with microseismicity monitoring [1]. This work proposes the study of this technique by means of the finite element method with zerothickness interface elements for the geo-mechanical modelling of discontinuities [2]. The technique consists in inserting interface elements in between standard elements to allow jumps in the displacement solution fields. For the mechanical problem, their kinematic constitutive variables are relative displacements, and the corresponding static variables are stress tractions. The relationship
between variables is controlled via a fracture-based constitutive law with elasto-plastic structure [3]. Concerning the hydraulic problem, the interface formulation includes both the longitudinal flow (with a longitudinal conductivity parameter strongly dependent on the fracture aperture), as well as and the transversal flow across the element (seepage)[4]. Previous works by the authors focused on the validation of the method, the analysis a single fracture plane problem [5,6]. In this case the method is extended to allow free propagation of fractures in any direction, by means of inserting interface elements between all continuum elements. The results presented in this paper analyse the effect of material properties, in particular fracture characterization, in the propagation and the effect of fracture job sequenc.Modelling of heat and moisture transfer in concrete at high temperature
http://hdl.handle.net/2117/115095
Modelling of heat and moisture transfer in concrete at high temperature
Rodríguez, Mariana; López Garello, Carlos María; Carol, Ignacio
Moisture diffusion and related fluid pressures play a key role in cracking and spalling of concrete subject to high temperatures. This paper describes recent developments of a mode for moisture and heat transfer in porous materials, to be combined with an existing and well tested meso-mechanical model for concrete. Liquid and gas flows are formulated separately, yet later they can be combined in terms of s single variable, Pv. The material pore distribution curve is taken as the basis for developing a new physically-based desorption isotherm alternative to the traditional Bazant & Thonguthai’s model. A simple academic example for temperatures between 27 and 800ºC is presented to show the behaviour of the model.
Tue, 13 Mar 2018 11:26:04 GMThttp://hdl.handle.net/2117/1150952018-03-13T11:26:04ZRodríguez, MarianaLópez Garello, Carlos MaríaCarol, IgnacioMoisture diffusion and related fluid pressures play a key role in cracking and spalling of concrete subject to high temperatures. This paper describes recent developments of a mode for moisture and heat transfer in porous materials, to be combined with an existing and well tested meso-mechanical model for concrete. Liquid and gas flows are formulated separately, yet later they can be combined in terms of s single variable, Pv. The material pore distribution curve is taken as the basis for developing a new physically-based desorption isotherm alternative to the traditional Bazant & Thonguthai’s model. A simple academic example for temperatures between 27 and 800ºC is presented to show the behaviour of the model.Diffusion-reaction modelling of the degradation of oil-well cement exposed to carbonated brine
http://hdl.handle.net/2117/115087
Diffusion-reaction modelling of the degradation of oil-well cement exposed to carbonated brine
Martínez Estévez, Ariadna; Liaudat, Joaquín; López Garello, Carlos María; Carol, Ignacio
The essential aspects of a diffusion-reaction model in development for the degradation process of oil-well cement exposed to carbonated brine are presented in this paper. The formulation consists of two main diffusion/reaction field equations for the concentrations of aqueous calcium and carbon species in the hardened cement paste pore solution, complemented by a number of chemical kinetics and chemical equilibrium equations. The volume fraction distribution of the solid constituents of the hardened cement paste and the reaction products evolve with the progress of the reaction, determining the diffusivity properties of the material. A sensitivity analysis of some parameters of the model is presented to illustrate the capabilities to reproduce realistically some aspects of the degradation process.
Tue, 13 Mar 2018 08:11:51 GMThttp://hdl.handle.net/2117/1150872018-03-13T08:11:51ZMartínez Estévez, AriadnaLiaudat, JoaquínLópez Garello, Carlos MaríaCarol, IgnacioThe essential aspects of a diffusion-reaction model in development for the degradation process of oil-well cement exposed to carbonated brine are presented in this paper. The formulation consists of two main diffusion/reaction field equations for the concentrations of aqueous calcium and carbon species in the hardened cement paste pore solution, complemented by a number of chemical kinetics and chemical equilibrium equations. The volume fraction distribution of the solid constituents of the hardened cement paste and the reaction products evolve with the progress of the reaction, determining the diffusivity properties of the material. A sensitivity analysis of some parameters of the model is presented to illustrate the capabilities to reproduce realistically some aspects of the degradation process.Avoiding fracture instability in wedge splitting tests by means of numerical simulations
http://hdl.handle.net/2117/115086
Avoiding fracture instability in wedge splitting tests by means of numerical simulations
Liaudat, Joaquín; Garolera Vinent, Daniel; Martínez Estévez, Ariadna; Carol, Ignacio; Lakshmikantha, Ramasesha Mookanahallipatna; Alvarellos Iglesias, José
In this paper, unstable fracture propagation obtained in a in-house performed experimentalWedge Splitting Test (WST) is simulated by means of the FEM and fracture- based zero-thickness interface elements. In order to obtain a specimen geometry suitable for a stable WST without modifying the remaining significant parameters of the test (machine stiffness and control parameter), additional simulations were performed varying the length of the specimen notch, until a load-COD (Crack Opening Displacement) curve without snap-back was obtained. Finally, a new experimental WST with the modified geometry was carried out leading to a stable load-COD curve. In the simulations, elastic continuum elements were used to represent the rock, the steel loading plates and the test- ing machine compliance via an “equivalent spring”, whereas interface elements were used for the notch and along the potential crack path. The interface elements representing the notch were equipped with linear elastic constitutive law, with very low elastic stiffness Kn and Kt so that they do not oppose any significant resistance to opening. For the inter- face elements along the fracture path, an elastoplastic constitutive model with fracture energy-based evolution laws was used.
Tue, 13 Mar 2018 07:44:06 GMThttp://hdl.handle.net/2117/1150862018-03-13T07:44:06ZLiaudat, JoaquínGarolera Vinent, DanielMartínez Estévez, AriadnaCarol, IgnacioLakshmikantha, Ramasesha MookanahallipatnaAlvarellos Iglesias, JoséIn this paper, unstable fracture propagation obtained in a in-house performed experimentalWedge Splitting Test (WST) is simulated by means of the FEM and fracture- based zero-thickness interface elements. In order to obtain a specimen geometry suitable for a stable WST without modifying the remaining significant parameters of the test (machine stiffness and control parameter), additional simulations were performed varying the length of the specimen notch, until a load-COD (Crack Opening Displacement) curve without snap-back was obtained. Finally, a new experimental WST with the modified geometry was carried out leading to a stable load-COD curve. In the simulations, elastic continuum elements were used to represent the rock, the steel loading plates and the test- ing machine compliance via an “equivalent spring”, whereas interface elements were used for the notch and along the potential crack path. The interface elements representing the notch were equipped with linear elastic constitutive law, with very low elastic stiffness Kn and Kt so that they do not oppose any significant resistance to opening. For the inter- face elements along the fracture path, an elastoplastic constitutive model with fracture energy-based evolution laws was used.Analysis of vertical facing panel-joint gap in reinforced soil walls
http://hdl.handle.net/2117/115083
Analysis of vertical facing panel-joint gap in reinforced soil walls
Puig Damians, Ivan; Bathurst, Richard; Josa Garcia-Tornel, Alejandro; Lloret Morancho, Antonio; Lima, Juan
This paper extends the numerical parametric study previously reported by the writers for the vertical load distribution and vertical gap compression between facing panel units in steel reinforced soil walls ranging in height from 6 m to 24 m. The presented study demonstrates how gap compression and magnitude of vertical load transmitted between horizontal joints are influenced by joint location along the height of the wall, joint compressibility, and backfill, and foundation soil stiffness. The charts provided can be used to make a preliminary estimate of the number and type (stiffness) of the bearing pads to ensure a target minimum gap thickness at the end of construction, demonstrate the relative influence of wall height and different material component properties on vertical load levels and gap compression, or used as a benchmark to test numerical models used for project-specific design.
Mon, 12 Mar 2018 23:38:57 GMThttp://hdl.handle.net/2117/1150832018-03-12T23:38:57ZPuig Damians, IvanBathurst, RichardJosa Garcia-Tornel, AlejandroLloret Morancho, AntonioLima, JuanThis paper extends the numerical parametric study previously reported by the writers for the vertical load distribution and vertical gap compression between facing panel units in steel reinforced soil walls ranging in height from 6 m to 24 m. The presented study demonstrates how gap compression and magnitude of vertical load transmitted between horizontal joints are influenced by joint location along the height of the wall, joint compressibility, and backfill, and foundation soil stiffness. The charts provided can be used to make a preliminary estimate of the number and type (stiffness) of the bearing pads to ensure a target minimum gap thickness at the end of construction, demonstrate the relative influence of wall height and different material component properties on vertical load levels and gap compression, or used as a benchmark to test numerical models used for project-specific design.3D-mesomechanical analysis of external sulfate attack in concrete
http://hdl.handle.net/2117/114869
3D-mesomechanical analysis of external sulfate attack in concrete
Pérez Carreras, Adrià; Riera Bayo, Celia; López Garello, Carlos María; Carol, Ignacio
The present study focuses on degradation of concrete by external sulfate attack. The numerical model developed by the MECMAT/UPC group, incorporates coupled C-M analysis using a meso-mechanical approach with discrete cracking, using the MEF and zero thickness interface elements with a constitutive law based on nonlinear fracture mechanics concepts. Examples of application are run on 2D and 3D samples, with geometries and FE meshes generated with a code developed also in-house. The numerical analysis is carried out using two independent codes and a “staggered” procedure. The first code performs the mechanical analysis and the second the diffusive/reaction chemical problem. 2D uncoupled and coupled analysis are presented and discussed. Preliminary coupled 3D results are also presented and compared with equivalent 2D results, and the differences are detected and analyzed.
Tue, 06 Mar 2018 16:30:16 GMThttp://hdl.handle.net/2117/1148692018-03-06T16:30:16ZPérez Carreras, AdriàRiera Bayo, CeliaLópez Garello, Carlos MaríaCarol, IgnacioThe present study focuses on degradation of concrete by external sulfate attack. The numerical model developed by the MECMAT/UPC group, incorporates coupled C-M analysis using a meso-mechanical approach with discrete cracking, using the MEF and zero thickness interface elements with a constitutive law based on nonlinear fracture mechanics concepts. Examples of application are run on 2D and 3D samples, with geometries and FE meshes generated with a code developed also in-house. The numerical analysis is carried out using two independent codes and a “staggered” procedure. The first code performs the mechanical analysis and the second the diffusive/reaction chemical problem. 2D uncoupled and coupled analysis are presented and discussed. Preliminary coupled 3D results are also presented and compared with equivalent 2D results, and the differences are detected and analyzed.Modeling concrete expansions via couped C-M mesoscale analysis with zero-thickness interface elements, and lab experiments
http://hdl.handle.net/2117/114208
Modeling concrete expansions via couped C-M mesoscale analysis with zero-thickness interface elements, and lab experiments
Carol, Ignacio; Liaudat, Joaquín; López Garello, Carlos María
This paper briefly summarizes ongoing developments on C-M coupled modelling of concrete swelling due to external sulfate attack and due to alkali-silica reaction. Both models are based on a meso-mechanical model for concrete, previously developed for purely mechanical actions, that has been also used as the basis for modelling other coupled phenomena such as drying shrinkage and mechanical effects of high temperatures. Additionally, two new experimental setups are presented. One devoted to the study of ASR expansions at the level of a single aggregate-matrix (cement paste or mortar) interface and the other devoted to study ASR expansions in concrete under triaxial confinement.
Fri, 16 Feb 2018 15:02:07 GMThttp://hdl.handle.net/2117/1142082018-02-16T15:02:07ZCarol, IgnacioLiaudat, JoaquínLópez Garello, Carlos MaríaThis paper briefly summarizes ongoing developments on C-M coupled modelling of concrete swelling due to external sulfate attack and due to alkali-silica reaction. Both models are based on a meso-mechanical model for concrete, previously developed for purely mechanical actions, that has been also used as the basis for modelling other coupled phenomena such as drying shrinkage and mechanical effects of high temperatures. Additionally, two new experimental setups are presented. One devoted to the study of ASR expansions at the level of a single aggregate-matrix (cement paste or mortar) interface and the other devoted to study ASR expansions in concrete under triaxial confinement.Application of configurational mechanics to crack propagation
http://hdl.handle.net/2117/108747
Application of configurational mechanics to crack propagation
Crusat Codina, Laura; Carol, Ignacio
Crack initiation and propagation is an essential aspect in the mechanical behavior of a large variety of materials and structures in all fields of Engineering and, in particular, the prediction of crack trajectories is one of the major challenges of existing numerical methods. Classical procedures to fix crack direction have been based on local criteria such as maximum (tensile) hope stress. However, Fracture Mechanics principles suggest that global criteria should be used instead, such as maximizing structural energy release rates. An emerging trend along this way is based on Configurational Mechanics, which describes a dual version of the mechanical problem in terms of configurational pseudo-stresses, pseudo-forces, etc. all with a physical meaning related to the change in global structural elastic energy caused by changes in the structural geometry (configuration). In the FEM context, these concepts are applied to optimize the total energy of the mesh with respect to reference coordinates using the discrete configurational forces. Configurational stresses given by Eshelby’s energy-momentum tensor may be integrated using standard expressions to give configurational nodal forces. Adequate treatment of these forces in the context of iterative FE calculations, may lead to prediction of crack trajectories in terms of global structural energy.
Tue, 17 Oct 2017 11:40:27 GMThttp://hdl.handle.net/2117/1087472017-10-17T11:40:27ZCrusat Codina, LauraCarol, IgnacioCrack initiation and propagation is an essential aspect in the mechanical behavior of a large variety of materials and structures in all fields of Engineering and, in particular, the prediction of crack trajectories is one of the major challenges of existing numerical methods. Classical procedures to fix crack direction have been based on local criteria such as maximum (tensile) hope stress. However, Fracture Mechanics principles suggest that global criteria should be used instead, such as maximizing structural energy release rates. An emerging trend along this way is based on Configurational Mechanics, which describes a dual version of the mechanical problem in terms of configurational pseudo-stresses, pseudo-forces, etc. all with a physical meaning related to the change in global structural elastic energy caused by changes in the structural geometry (configuration). In the FEM context, these concepts are applied to optimize the total energy of the mesh with respect to reference coordinates using the discrete configurational forces. Configurational stresses given by Eshelby’s energy-momentum tensor may be integrated using standard expressions to give configurational nodal forces. Adequate treatment of these forces in the context of iterative FE calculations, may lead to prediction of crack trajectories in terms of global structural energy.Comparison of discrete and equivalent continuum approaches to simulate the mechanical behavior of jointed rock masses
http://hdl.handle.net/2117/103373
Comparison of discrete and equivalent continuum approaches to simulate the mechanical behavior of jointed rock masses
Gonzalez, Nubia Aurora; Vargas, P.E.; Carol, Ignacio; Das, K. C.; Sandha, S.S.; Rodrigues, E.; Mello,, U.; Segura Segarra, José María; Lakshmikantha, Ramasesha Mookanahallipatna
Modeling of rock masses is of major importance to assess the Geomechanical behaviour of oil &gas reservoirs, especially for fractured tight reservoirs. The presence of discontinuities will significantly influence the general behavior of the rock masses, in particular introducing strength reduction, enhanced/reduction permeability, anisotropic behavior and a non-linear response. In the present study, Discrete and Equivalent continuum approaches have been used to simulate the mechanical behavior of jointed rock masses. Discrete approach uses the eXtended Finite Element Method (XFEM) and the Zero-thickness interface elements, while the Equivalent continuum approaches uses an elastic-viscoplastic constitutive model of the multilaminate type to represent the rock mass behavior. Advantages and limitations of each approach are identified and some hints for their practical use are given. Although the discrete approach is sometimes preferred for being based on a mature theory, the equivalent continuum analysis seems to be more often applicable for usual geomechanical analyses from engineering practice.
Tue, 04 Apr 2017 16:54:07 GMThttp://hdl.handle.net/2117/1033732017-04-04T16:54:07ZGonzalez, Nubia AuroraVargas, P.E.Carol, IgnacioDas, K. C.Sandha, S.S.Rodrigues, E.Mello,, U.Segura Segarra, José MaríaLakshmikantha, Ramasesha MookanahallipatnaModeling of rock masses is of major importance to assess the Geomechanical behaviour of oil &gas reservoirs, especially for fractured tight reservoirs. The presence of discontinuities will significantly influence the general behavior of the rock masses, in particular introducing strength reduction, enhanced/reduction permeability, anisotropic behavior and a non-linear response. In the present study, Discrete and Equivalent continuum approaches have been used to simulate the mechanical behavior of jointed rock masses. Discrete approach uses the eXtended Finite Element Method (XFEM) and the Zero-thickness interface elements, while the Equivalent continuum approaches uses an elastic-viscoplastic constitutive model of the multilaminate type to represent the rock mass behavior. Advantages and limitations of each approach are identified and some hints for their practical use are given. Although the discrete approach is sometimes preferred for being based on a mature theory, the equivalent continuum analysis seems to be more often applicable for usual geomechanical analyses from engineering practice.