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Model uncertainty in finite-element analysis / T. Haukaas in Journal of engineering mechanics, Vol. 137 N° 8 (Août 2011) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 137 N° 8 (Août 2011) . - pp.519-526 Titre : Model uncertainty in finite-element analysis : bayesian finite elements Type de document : texte imprimé Auteurs : T. Haukaas, Auteur ; P. Gardoni, Auteur Année de publication : 2011 Article en page(s) : pp.519-526 Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Probabilistic  models  Model  uncertainty  Finite  elements  Bayesian  updating Résumé : In this paper, probabilistic models for structural analysis are put forward, with particular emphasis on model uncertainty. Context is provided by the finite-element method and the need for probabilistic prediction of structural performance in contemporary engineering. Sources of model uncertainty are identified and modeled. A Bayesian approach is suggested for the assessment of new model parameters within the element formulations. The expressions are formulated by means of numerical “sensors” that influence the model uncertainty, such as element distortion and degree of nonlinearity. An assessment procedure is proposed to identify the sensors that are most suitable to capture model uncertainty. This paper presents the general methodology and specific implementations for a general-purpose structural element. Two numerical examples are presented to demonstrate the methodology and its implications for probabilistic prediction of structural response. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.org/emo/resource/1/jenmdt/v137/i8/p519_s1?isAuthorized=no [article] Model uncertainty in finite-element analysis : bayesian finite elements [texte imprimé] / T. Haukaas, Auteur ; P. Gardoni, Auteur . - 2011 . - pp.519-526. Mécanique appliquée Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 137 N° 8 (Août 2011) . - pp.519-526 Mots-clés : Probabilistic  models  Model  uncertainty  Finite  elements  Bayesian  updating Résumé : In this paper, probabilistic models for structural analysis are put forward, with particular emphasis on model uncertainty. Context is provided by the finite-element method and the need for probabilistic prediction of structural performance in contemporary engineering. Sources of model uncertainty are identified and modeled. A Bayesian approach is suggested for the assessment of new model parameters within the element formulations. The expressions are formulated by means of numerical “sensors” that influence the model uncertainty, such as element distortion and degree of nonlinearity. An assessment procedure is proposed to identify the sensors that are most suitable to capture model uncertainty. This paper presents the general methodology and specific implementations for a general-purpose structural element. Two numerical examples are presented to demonstrate the methodology and its implications for probabilistic prediction of structural response. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.org/emo/resource/1/jenmdt/v137/i8/p519_s1?isAuthorized=no

Analysis of soft fibers with kinematic constraints and cross-links by finite deformation beam theory / Franck Vernerey in Journal of engineering mechanics, Vol. 137 N° 8 (Août 2011) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 137 N° 8 (Août 2011) . - pp.527-536 Titre : Analysis of soft fibers with kinematic constraints and cross-links by finite deformation beam theory Type de document : texte imprimé Auteurs : Franck Vernerey, Auteur ; Ronald Y. S. Pak, Auteur Année de publication : 2011 Article en page(s) : pp.527-536 Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Flexible  fibers  Fibrous  networks  Beams  Structures  Cross-links  Large  deformation Résumé : This paper presents a hybrid analytical–computational mechanics formulation for an arbitrarily curved Timoshenko beam undergoing planar finite deformation and subjected to kinematic constraints in the form of fixed displacement and cross-linking. On the basis of an analytical reduction of the governing equations, the system reduced to a single nonlinear differential equation coupled with integral equations associated with translational constraints. An effective numerical formulation of the problem with general distributed and pointwise constraints is shown to be possible by using a simple finite-element procedure. To illustrate the efficiency and accuracy of the method, several examples are introduced to study both stable and bifurcation problems and a system of interacting fibers with different types of cross-link constraints. Because of the reduction of discretization error and the dimension of the matrix system, the proposed formulation is likely to be an attractive computational platform for modeling large-scale multifiber problems, as in fibrous microstructure simulations and other applications. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.org/emo/resource/1/jenmdt/v137/i8/p527_s1?isAuthorized=no [article] Analysis of soft fibers with kinematic constraints and cross-links by finite deformation beam theory [texte imprimé] / Franck Vernerey, Auteur ; Ronald Y. S. Pak, Auteur . - 2011 . - pp.527-536. Mécanique appliquée Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 137 N° 8 (Août 2011) . - pp.527-536 Mots-clés : Flexible  fibers  Fibrous  networks  Beams  Structures  Cross-links  Large  deformation Résumé : This paper presents a hybrid analytical–computational mechanics formulation for an arbitrarily curved Timoshenko beam undergoing planar finite deformation and subjected to kinematic constraints in the form of fixed displacement and cross-linking. On the basis of an analytical reduction of the governing equations, the system reduced to a single nonlinear differential equation coupled with integral equations associated with translational constraints. An effective numerical formulation of the problem with general distributed and pointwise constraints is shown to be possible by using a simple finite-element procedure. To illustrate the efficiency and accuracy of the method, several examples are introduced to study both stable and bifurcation problems and a system of interacting fibers with different types of cross-link constraints. Because of the reduction of discretization error and the dimension of the matrix system, the proposed formulation is likely to be an attractive computational platform for modeling large-scale multifiber problems, as in fibrous microstructure simulations and other applications. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.org/emo/resource/1/jenmdt/v137/i8/p527_s1?isAuthorized=no

Two-stage extended kalman filters with derivative-free local linearizations / Nilanjan Saha in Journal of engineering mechanics, Vol. 137 N° 8 (Août 2011) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 137 N° 8 (Août 2011) . - pp.537546 Titre : Two-stage extended kalman filters with derivative-free local linearizations Type de document : texte imprimé Auteurs : Nilanjan Saha, Auteur ; D. Roy, Auteur Année de publication : 2011 Article en page(s) : pp.537546 Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Two-stage  filter  Extended  Kalman  filters  Model  uncertainty  Derivative-free  local  linearizations  Parameter  estimations Résumé : This paper proposes a derivative-free two-stage extended Kalman filter (2-EKF) especially suited for state and parameter identification of mechanical oscillators under Gaussian white noise. Two sources of modeling uncertainties are considered: (1) errors in linearization, and (2) an inadequate system model. The state vector is presently composed of the original dynamical/parameter states plus the so-called bias states accounting for the unmodeled dynamics. An extended Kalman estimation concept is applied within a framework predicated on explicit and derivative-free local linearizations (DLL) of nonlinear drift terms in the governing stochastic differential equations (SDEs). The original and bias states are estimated by two separate filters; the bias filter improves the estimates of the original states. Measurements are artificially generated by corrupting the numerical solutions of the SDEs with noise through an implicit form of a higher-order linearization. Numerical illustrations are provided for a few single- and multidegree-of-freedom nonlinear oscillators, demonstrating the remarkable promise that 2-EKF holds over its more conventional EKF-based counterparts. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.org/emo/resource/1/jenmdt/v137/i8/p537_s1?isAuthorized=no [article] Two-stage extended kalman filters with derivative-free local linearizations [texte imprimé] / Nilanjan Saha, Auteur ; D. Roy, Auteur . - 2011 . - pp.537546. Mécanique appliquée Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 137 N° 8 (Août 2011) . - pp.537546 Mots-clés : Two-stage  filter  Extended  Kalman  filters  Model  uncertainty  Derivative-free  local  linearizations  Parameter  estimations Résumé : This paper proposes a derivative-free two-stage extended Kalman filter (2-EKF) especially suited for state and parameter identification of mechanical oscillators under Gaussian white noise. Two sources of modeling uncertainties are considered: (1) errors in linearization, and (2) an inadequate system model. The state vector is presently composed of the original dynamical/parameter states plus the so-called bias states accounting for the unmodeled dynamics. An extended Kalman estimation concept is applied within a framework predicated on explicit and derivative-free local linearizations (DLL) of nonlinear drift terms in the governing stochastic differential equations (SDEs). The original and bias states are estimated by two separate filters; the bias filter improves the estimates of the original states. Measurements are artificially generated by corrupting the numerical solutions of the SDEs with noise through an implicit form of a higher-order linearization. Numerical illustrations are provided for a few single- and multidegree-of-freedom nonlinear oscillators, demonstrating the remarkable promise that 2-EKF holds over its more conventional EKF-based counterparts. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.org/emo/resource/1/jenmdt/v137/i8/p537_s1?isAuthorized=no

Distant damage-assessment method for multilayer composite systems using electromagnetic waves / Tzu-Yang Yu in Journal of engineering mechanics, Vol. 137 N° 8 (Août 2011) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 137 N° 8 (Août 2011) . - pp.547-560 Titre : Distant damage-assessment method for multilayer composite systems using electromagnetic waves Type de document : texte imprimé Auteurs : Tzu-Yang Yu, Auteur Année de publication : 2011 Article en page(s) : pp.547-560 Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Damage  assessment  Concrete  Radar  Fiber-reinforced  polymers  Tomographic  reconstruction Résumé : In this paper, a damage assessment method for remotely inspecting the near-surface condition of multilayer composite systems is proposed. The method utilizes far-field steady-state electromagnetic waves reflected from the surface of multilayer composite systems and generates the in-depth profile of the inspected composite systems using inverse synthetic aperture radar (ISAR) imaging technique. Spatial imagery of the system can be reconstructed with the structural and geometric features of the multilayer system. These features are revealed by discrete scatterers in the imagery. Reconstructed imagery can be used for detecting construction defects and structural damages in the near-surface region of the system. The theoretical background of the method is described, followed by experimental measurements on glass-fiber-reinforced polymer (GFRP)-confined concrete cylinders with an artificial defect as an example of multilayer composite systems. Continuous waves in the frequency range of 8 to 12 GHz were used. The imaging results show that the proposed method can reveal the location and size of the embedded defect in the GFRP-concrete composite system, indicating the potential use of the method as a basis for distant radar/microwave nondestructive testing/evaluation techniques in civil engineering. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.org/emo/resource/1/jenmdt/v137/i8/p547_s1?isAuthorized=no [article] Distant damage-assessment method for multilayer composite systems using electromagnetic waves [texte imprimé] / Tzu-Yang Yu, Auteur . - 2011 . - pp.547-560. Mécanique appliquée Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 137 N° 8 (Août 2011) . - pp.547-560 Mots-clés : Damage  assessment  Concrete  Radar  Fiber-reinforced  polymers  Tomographic  reconstruction Résumé : In this paper, a damage assessment method for remotely inspecting the near-surface condition of multilayer composite systems is proposed. The method utilizes far-field steady-state electromagnetic waves reflected from the surface of multilayer composite systems and generates the in-depth profile of the inspected composite systems using inverse synthetic aperture radar (ISAR) imaging technique. Spatial imagery of the system can be reconstructed with the structural and geometric features of the multilayer system. These features are revealed by discrete scatterers in the imagery. Reconstructed imagery can be used for detecting construction defects and structural damages in the near-surface region of the system. The theoretical background of the method is described, followed by experimental measurements on glass-fiber-reinforced polymer (GFRP)-confined concrete cylinders with an artificial defect as an example of multilayer composite systems. Continuous waves in the frequency range of 8 to 12 GHz were used. The imaging results show that the proposed method can reveal the location and size of the embedded defect in the GFRP-concrete composite system, indicating the potential use of the method as a basis for distant radar/microwave nondestructive testing/evaluation techniques in civil engineering. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.org/emo/resource/1/jenmdt/v137/i8/p547_s1?isAuthorized=no

Quasi-static axial damping of poroviscoelastic cylinders / Zachary C. Grasley in Journal of engineering mechanics, Vol. 137 N° 8 (Août 2011) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 137 N° 8 (Août 2011) . - pp.561-570 Titre : Quasi-static axial damping of poroviscoelastic cylinders Type de document : texte imprimé Auteurs : Zachary C. Grasley, Auteur ; Chin Leung, Auteur Année de publication : 2011 Article en page(s) : pp.561-570 Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Viscoelasticity  Cyclic  tests  Concrete  Cylinder  Poroelasticity Résumé : Design of infrastructure materials with inherent material damping may help dissipate energy during dynamic loading events such as earthquakes, thereby reducing structural damage and risk of collapse. One possible method to enhance damping of cementitious materials such as concrete is to utilize poromechanical damping. To evaluate the potential damping associated with the poromechanical effect and to aid in the design of high damping porous materials such as concrete, approximate closed-form solutions have been derived for poromechanical damping as a function of frequency, maximum damping, and critical damping frequency for axially loaded solid and hollow cylinders. The effect of inherent viscoelastic damping of the porous material body was included in the analysis, which indicated that inherent viscoelastic damping could be superposed on poromechanical damping to predict overall damping capacity. Simulations indicate that poromechanical damping may be significant for cementitious materials if designed appropriately. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.org/emo/resource/1/jenmdt/v137/i8/p561_s1?isAuthorized=no [article] Quasi-static axial damping of poroviscoelastic cylinders [texte imprimé] / Zachary C. Grasley, Auteur ; Chin Leung, Auteur . - 2011 . - pp.561-570. Mécanique appliquée Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 137 N° 8 (Août 2011) . - pp.561-570 Mots-clés : Viscoelasticity  Cyclic  tests  Concrete  Cylinder  Poroelasticity Résumé : Design of infrastructure materials with inherent material damping may help dissipate energy during dynamic loading events such as earthquakes, thereby reducing structural damage and risk of collapse. One possible method to enhance damping of cementitious materials such as concrete is to utilize poromechanical damping. To evaluate the potential damping associated with the poromechanical effect and to aid in the design of high damping porous materials such as concrete, approximate closed-form solutions have been derived for poromechanical damping as a function of frequency, maximum damping, and critical damping frequency for axially loaded solid and hollow cylinders. The effect of inherent viscoelastic damping of the porous material body was included in the analysis, which indicated that inherent viscoelastic damping could be superposed on poromechanical damping to predict overall damping capacity. Simulations indicate that poromechanical damping may be significant for cementitious materials if designed appropriately. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.org/emo/resource/1/jenmdt/v137/i8/p561_s1?isAuthorized=no

Attenuation and damping of multireflected transient elastic waves in a pile / Yih-Hsing Pao in Journal of engineering mechanics, Vol. 137 N° 8 (Août 2011) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 137 N° 8 (Août 2011) . - pp.571-579 Titre : Attenuation and damping of multireflected transient elastic waves in a pile Type de document : texte imprimé Auteurs : Yih-Hsing Pao, Auteur ; Yun-Yan Yu, Auteur Année de publication : 2011 Article en page(s) : pp.571-579 Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Impact  loading  on  a  pile  Damped  wave  equation  Reverberation-ray  matrix  analysis  Attenuation  and  damping  of  waves  Ultrasonic  inspection  of  piles Résumé : Early time transient waves multireflected in a finite pile, governed by a damped wave equation, are analyzed by a reverberation-ray matrix. The pile is surrounded by compacted soil, and the composite is modeled by elastic springs and viscous dampers distributed along the length and at the tip of an elastic rod. Steady-state waves with complex frequencies and wave numbers that are generated by a source of harmonic time function at the top and reverberated between the top and bottom surface of the pile are sorted in matrix form into ray-groups, arriving at a receiver in successive orders of reflections from the bottom. The steady-state ray groups are synthesized into a series of nonsingular Fourier integrals that can be evaluated accurately with a fast Fourier-transform algorithm. The first integral (zeroth-order) has also been reduced by complex contour integration to the well-known closed-form solution in Bessel functions for a semi-infinite pile. Detailed time records of velocity response received at the top after three reflections are calculated to illustrate attenuation and damping; arrival times and amplitude-phase change on each reflection for various lateral and base supports. The calculated records resemble ultrasonic nondestructive testing data. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.org/emo/resource/1/jenmdt/v137/i8/p571_s1?isAuthorized=no [article] Attenuation and damping of multireflected transient elastic waves in a pile [texte imprimé] / Yih-Hsing Pao, Auteur ; Yun-Yan Yu, Auteur . - 2011 . - pp.571-579. Mécanique appliquée Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 137 N° 8 (Août 2011) . - pp.571-579 Mots-clés : Impact  loading  on  a  pile  Damped  wave  equation  Reverberation-ray  matrix  analysis  Attenuation  and  damping  of  waves  Ultrasonic  inspection  of  piles Résumé : Early time transient waves multireflected in a finite pile, governed by a damped wave equation, are analyzed by a reverberation-ray matrix. The pile is surrounded by compacted soil, and the composite is modeled by elastic springs and viscous dampers distributed along the length and at the tip of an elastic rod. Steady-state waves with complex frequencies and wave numbers that are generated by a source of harmonic time function at the top and reverberated between the top and bottom surface of the pile are sorted in matrix form into ray-groups, arriving at a receiver in successive orders of reflections from the bottom. The steady-state ray groups are synthesized into a series of nonsingular Fourier integrals that can be evaluated accurately with a fast Fourier-transform algorithm. The first integral (zeroth-order) has also been reduced by complex contour integration to the well-known closed-form solution in Bessel functions for a semi-infinite pile. Detailed time records of velocity response received at the top after three reflections are calculated to illustrate attenuation and damping; arrival times and amplitude-phase change on each reflection for various lateral and base supports. The calculated records resemble ultrasonic nondestructive testing data. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.org/emo/resource/1/jenmdt/v137/i8/p571_s1?isAuthorized=no

Size-effect testing of cohesive fracture parameters and nonuniqueness of work-of-fracture method / Bažant, Zdeněk P. in Journal of engineering mechanics, Vol. 137 N° 8 (Août 2011) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 137 N° 8 (Août 2011) . - pp.580-588 Titre : Size-effect testing of cohesive fracture parameters and nonuniqueness of work-of-fracture method Type de document : texte imprimé Auteurs : Bažant, Zdeněk P., Auteur ; Qiang Yu, Auteur Année de publication : 2011 Article en page(s) : pp.580-588 Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Quasibrittle  fracture  Cohesive  crack  model  Fracture  mechanics  Cracks  Quasibrittle  materials  Concrete  Scaling  Testing  Brittleness Résumé : The cohesive crack model has been widely accepted as the best compromise for the analysis of fracture of concrete and other quasibrittle materials. The softening stress-separation law of this model is now believed to be best described as a bilinear curve characterized by four parameters: the initial and total fracture energies Gf and GF, the tensile strength ft′, and the knee-point ordinate σ1. The classical work-of-fracture test of a notched beam of one size can deliver a clear result only for GF. Here it is shown computationally that the same complete load-deflection curve can be closely approximated with stress-separation curves in which the ft′ values differ by 77% and Gf values by 68%. It follows that the work-of-fracture test alone cannot provide an unambiguous basis for quasibrittle fracture analysis. It is found, however, that if this test is supplemented by size-effect testing, all four cohesive crack model parameters can be precisely identified and the fracture analysis of structures becomes unambiguous. It is shown computationally that size-effect tests do not suffice for determining GF and ft′, which indicates that they provide a sufficient basis for computing neither the postpeak softening of fracturing structures nor the peak loads of a very large structure. However, if the size-effect tests are supplemented by one complete softening load-deflection curve of a notched specimen, an unambiguous calculation of peak loads and postpeak response of structures becomes possible. To this end, the notched specimen tests must be conducted in a certain size range, whose optimum is here established by extending a previous analysis. Combination of the work-of-fracture and size-effect testing could be avoided only if the ratios GF/Gf and σ1/ft′ were known a priori, but unfortunately their estimates are far too uncertain. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.org/emo/resource/1/jenmdt/v137/i8/p580_s1?isAuthorized=no [article] Size-effect testing of cohesive fracture parameters and nonuniqueness of work-of-fracture method [texte imprimé] / Bažant, Zdeněk P., Auteur ; Qiang Yu, Auteur . - 2011 . - pp.580-588. Mécanique appliquée Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 137 N° 8 (Août 2011) . - pp.580-588 Mots-clés : Quasibrittle  fracture  Cohesive  crack  model  Fracture  mechanics  Cracks  Quasibrittle  materials  Concrete  Scaling  Testing  Brittleness Résumé : The cohesive crack model has been widely accepted as the best compromise for the analysis of fracture of concrete and other quasibrittle materials. The softening stress-separation law of this model is now believed to be best described as a bilinear curve characterized by four parameters: the initial and total fracture energies Gf and GF, the tensile strength ft′, and the knee-point ordinate σ1. The classical work-of-fracture test of a notched beam of one size can deliver a clear result only for GF. Here it is shown computationally that the same complete load-deflection curve can be closely approximated with stress-separation curves in which the ft′ values differ by 77% and Gf values by 68%. It follows that the work-of-fracture test alone cannot provide an unambiguous basis for quasibrittle fracture analysis. It is found, however, that if this test is supplemented by size-effect testing, all four cohesive crack model parameters can be precisely identified and the fracture analysis of structures becomes unambiguous. It is shown computationally that size-effect tests do not suffice for determining GF and ft′, which indicates that they provide a sufficient basis for computing neither the postpeak softening of fracturing structures nor the peak loads of a very large structure. However, if the size-effect tests are supplemented by one complete softening load-deflection curve of a notched specimen, an unambiguous calculation of peak loads and postpeak response of structures becomes possible. To this end, the notched specimen tests must be conducted in a certain size range, whose optimum is here established by extending a previous analysis. Combination of the work-of-fracture and size-effect testing could be avoided only if the ratios GF/Gf and σ1/ft′ were known a priori, but unfortunately their estimates are far too uncertain. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.org/emo/resource/1/jenmdt/v137/i8/p580_s1?isAuthorized=no

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