Dépouillements

Adaptive quadratic sum-squares error for structural damage identification / Yang, Jann N. in Journal of engineering mechanics, Vol. 135 N°2 (Février 2009) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 135 N°2 (Février 2009) . - pp. 67-77 Titre : Adaptive quadratic sum-squares error for structural damage identification Type de document : texte imprimé Auteurs : Yang, Jann N., Auteur ; Hongwei Huang, Auteur ; Shuwen Pan, Auteur Article en page(s) : pp. 67-77 Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Structural  behavior  Errors  Tracking  Damage. Résumé : The ability to detect damages online, based on vibration data measured from sensors, will ensure the reliability and safety of structures. Innovative data analysis techniques for the damage detection of structures have received considerable attention recently, although the problem is quite challenging. In this paper, we proposed a new data analysis method, referred to as the quadratic sum-squares error (QSSE) approach, for the online or almost online identification of structural parameters. Analytical recursive solution for the proposed QSSE method, which is not available in the previous literature, is derived and presented. Further, an adaptive tracking technique recently proposed is implemented in the proposed QSSE approach to identify the time-varying system parameters of the structure, referred to as the adaptive quadratic sum-squares error. The accuracy and effectiveness of the proposed approach are demonstrated using both linear and nonlinear structures. Simulation results using the finite-element models demonstrate that the proposed approach is capable of tracking the changes of structural parameters leading to the identification of structural damages DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JENMDT000 [...] [article] Adaptive quadratic sum-squares error for structural damage identification [texte imprimé] / Yang, Jann N., Auteur ; Hongwei Huang, Auteur ; Shuwen Pan, Auteur . - pp. 67-77. Mécanique appliquée Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 135 N°2 (Février 2009) . - pp. 67-77 Mots-clés : Structural  behavior  Errors  Tracking  Damage. Résumé : The ability to detect damages online, based on vibration data measured from sensors, will ensure the reliability and safety of structures. Innovative data analysis techniques for the damage detection of structures have received considerable attention recently, although the problem is quite challenging. In this paper, we proposed a new data analysis method, referred to as the quadratic sum-squares error (QSSE) approach, for the online or almost online identification of structural parameters. Analytical recursive solution for the proposed QSSE method, which is not available in the previous literature, is derived and presented. Further, an adaptive tracking technique recently proposed is implemented in the proposed QSSE approach to identify the time-varying system parameters of the structure, referred to as the adaptive quadratic sum-squares error. The accuracy and effectiveness of the proposed approach are demonstrated using both linear and nonlinear structures. Simulation results using the finite-element models demonstrate that the proposed approach is capable of tracking the changes of structural parameters leading to the identification of structural damages DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JENMDT000 [...]

Universal size effect law and effect of crack depth on quasi-brittle structure strength / Zdenek P. Bazant in Journal of engineering mechanics, Vol. 135 N°2 (Février 2009) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 135 N°2 (Février 2009) . - pp. 78-84 Titre : Universal size effect law and effect of crack depth on quasi-brittle structure strength Type de document : texte imprimé Auteurs : Zdenek P. Bazant, Auteur Article en page(s) : pp. 78-84 Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Size  effect  Fracture  Cracking  Notches  Structural  reliability  Concrete. Résumé : In cohesive fracture of quasi-brittle materials such as concrete, rock, fiber composites, tough ceramics, rigid foams, sea ice, and wood, one can distinguish six simple and easily modeled asymptotic cases: the asymptotic behaviors of very small and very large structures, structures failing at crack initiation from a smooth surface and those with a deep notch or preexisting deep crack, the purely statistical Weibull-type size effect, and the purely energetic (deterministic) size effect. Size effect laws governing the transition between some of these asymptotic cases have already been formulated. However, a general and smooth description of the complex transition between all of them has been lacking. Here, a smooth universal law bridging all of these asymptotic cases is derived and discussed. A special case of this law is a formula for the effect of notch or crack depth at fixed specimen size, which overcomes the limitations of a recently proposed empirical formula by Duan et al., 2003, 2004, 2006. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JENMDT000 [...] [article] Universal size effect law and effect of crack depth on quasi-brittle structure strength [texte imprimé] / Zdenek P. Bazant, Auteur . - pp. 78-84. Mécanique appliquée Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 135 N°2 (Février 2009) . - pp. 78-84 Mots-clés : Size  effect  Fracture  Cracking  Notches  Structural  reliability  Concrete. Résumé : In cohesive fracture of quasi-brittle materials such as concrete, rock, fiber composites, tough ceramics, rigid foams, sea ice, and wood, one can distinguish six simple and easily modeled asymptotic cases: the asymptotic behaviors of very small and very large structures, structures failing at crack initiation from a smooth surface and those with a deep notch or preexisting deep crack, the purely statistical Weibull-type size effect, and the purely energetic (deterministic) size effect. Size effect laws governing the transition between some of these asymptotic cases have already been formulated. However, a general and smooth description of the complex transition between all of them has been lacking. Here, a smooth universal law bridging all of these asymptotic cases is derived and discussed. A special case of this law is a formula for the effect of notch or crack depth at fixed specimen size, which overcomes the limitations of a recently proposed empirical formula by Duan et al., 2003, 2004, 2006. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JENMDT000 [...]

Random lattice-particle simulation of statistical size effect in quasi-brittle Structures failing at crack initiation / Peter Grassl in Journal of engineering mechanics, Vol. 135 N°2 (Février 2009) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 135 N°2 (Février 2009) . - pp. 85-92 Titre : Random lattice-particle simulation of statistical size effect in quasi-brittle Structures failing at crack initiation Type de document : texte imprimé Auteurs : Peter Grassl, Auteur ; Zdenek P. Bazant, Auteur Article en page(s) : pp. 85-92 Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Concrete  Material  properties  Size  effect  Cracking  Statistics  Structural  reliability. Résumé : The modeling of statistical size effect of concrete structures that fail at crack initiation is studied, with special attention to the interaction between the autocorrelation length and the size of the failure zone. The mechanical failure of concrete is modeled by a network of axial springs with degrading stiffness. The heterogeneity of concrete is idealized by spatial variation of the tensile strength and fracture energy. As an example, the direct tensile test in plane stress, with the size range of 1:20, is simulated. Furthermore, simulations of a four-point bending test with varying bending span are compared to the experimental results reported in the literature. The interaction of the autocorrelation length and the size of the failure zone is identified as a key parameter for the modeling of statistical size effect DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JENMDT000 [...] [article] Random lattice-particle simulation of statistical size effect in quasi-brittle Structures failing at crack initiation [texte imprimé] / Peter Grassl, Auteur ; Zdenek P. Bazant, Auteur . - pp. 85-92. Mécanique appliquée Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 135 N°2 (Février 2009) . - pp. 85-92 Mots-clés : Concrete  Material  properties  Size  effect  Cracking  Statistics  Structural  reliability. Résumé : The modeling of statistical size effect of concrete structures that fail at crack initiation is studied, with special attention to the interaction between the autocorrelation length and the size of the failure zone. The mechanical failure of concrete is modeled by a network of axial springs with degrading stiffness. The heterogeneity of concrete is idealized by spatial variation of the tensile strength and fracture energy. As an example, the direct tensile test in plane stress, with the size range of 1:20, is simulated. Furthermore, simulations of a four-point bending test with varying bending span are compared to the experimental results reported in the literature. The interaction of the autocorrelation length and the size of the failure zone is identified as a key parameter for the modeling of statistical size effect DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JENMDT000 [...]

Damage localization from transmission zeros of delta systems / Dionisio Bernal in Journal of engineering mechanics, Vol. 135 N°2 (Février 2009) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 135 N°2 (Février 2009) . - pp. 93-99 Titre : Damage localization from transmission zeros of delta systems Type de document : texte imprimé Auteurs : Dionisio Bernal, Auteur Article en page(s) : pp. 93-99 Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Damage  Parameters  Localization. Résumé : Conditioning difficulties often thwart the characterization of damage by model updating. Methods that can provide information on damage location without explicit selection of free parameters are important for improving the likelihood of success. A technique that satisfies this objective known as the dynamic damage locating vector method locates damage as regions where a stress field that is computed in a model of the reference state, using loads extracted from changes in the transfer matrix, is identically zero. Central to the present paper is the fact that existence of the noted loads requires that the change in the transfer matrix be rank deficient everywhere in [openface C]. Specifically, the paper examines the situation where the change in the transfer matrix is full normal rank and shows that although zero stress excitations are not generally feasible, useful surrogates can often be obtained from conditions defined by the invariant zero triplets (i.e., zero, zero direction, and zero input) of a mathematical structure, designated as the delta system, which maps inputs to changes in the output. The paper discusses the formulation of the delta system, the extraction of the invariant zeros, and the computation of the associated stress fields. Selection of the potentially damaged set of elements is based on a decision logic that uses the aggregate information from all (or any subset) of the identified zeros. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JENMDT000 [...] [article] Damage localization from transmission zeros of delta systems [texte imprimé] / Dionisio Bernal, Auteur . - pp. 93-99. Mécanique appliquée Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 135 N°2 (Février 2009) . - pp. 93-99 Mots-clés : Damage  Parameters  Localization. Résumé : Conditioning difficulties often thwart the characterization of damage by model updating. Methods that can provide information on damage location without explicit selection of free parameters are important for improving the likelihood of success. A technique that satisfies this objective known as the dynamic damage locating vector method locates damage as regions where a stress field that is computed in a model of the reference state, using loads extracted from changes in the transfer matrix, is identically zero. Central to the present paper is the fact that existence of the noted loads requires that the change in the transfer matrix be rank deficient everywhere in [openface C]. Specifically, the paper examines the situation where the change in the transfer matrix is full normal rank and shows that although zero stress excitations are not generally feasible, useful surrogates can often be obtained from conditions defined by the invariant zero triplets (i.e., zero, zero direction, and zero input) of a mathematical structure, designated as the delta system, which maps inputs to changes in the output. The paper discusses the formulation of the delta system, the extraction of the invariant zeros, and the computation of the associated stress fields. Selection of the potentially damaged set of elements is based on a decision logic that uses the aggregate information from all (or any subset) of the identified zeros. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JENMDT000 [...]

Effects of bed roughness on flow around bed-mounted cylinders in open channels / M. A. F. Sadeque in Journal of engineering mechanics, Vol. 135 N°2 (Février 2009) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 135 N°2 (Février 2009) . - pp. 100-110 Titre : Effects of bed roughness on flow around bed-mounted cylinders in open channels Type de document : texte imprimé Auteurs : M. A. F. Sadeque, Auteur ; N. Rajaratnam, Auteur ; M. R. Loewen, Auteur Article en page(s) : pp. 100-110 Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Open  channel  flow  Boundary  layers  Flow  visualization  Shear  stress  Bed  roughness  Fish  management. Résumé : This paper presents the results of an experimental study of flow around cylindrical objects on a rough bed in an open channel. This is an extension of a previous study of flow around cylinders on a smooth bed. The purpose of this study is to explore the effects of bed roughness on the characteristics of the deflected flow around cylindrical objects and the resulting bed-shear stress distributions. Similar to the previous study cylindrical objects of equal diameter and four heights were tested under similar flow conditions producing four different levels of submergence. Bed shear stress and deflected flow velocities were measured by a thin yaw-type Preston probe after a set of flow visualization tests. Flow visualization tests showed that the horse-shoe vortex systems on the rough bed occupy a relatively greater width compared to the smooth bed. Unlike smooth bed observations, the flow separation point upstream of the cylinder was not dependent on the level of submergence as the separation points were found to appear within a short range of x=−1D to −1.2D. Bed shear stress has been found to increase significantly near the shoulder of the cylinders, and its ratio with respect to the approach bed-shear stress was twice as large compared to the smooth bed case. Mean velocity profiles were analyzed in terms of three-dimensional turbulent boundary layer theories. Bed roughness was found to oppose the effect of the lateral pressure gradient that causes skewing in the boundary layer. Perry and Joubert's model has been found to be equally accurate on smooth and rough beds for predicting the deflected velocity magnitudes around cylinders. The present study will enhance the knowledge of hydraulics of flow around bed-mounted objects (e.g. fish-rocks) in natural streams. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JENMDT000 [...] [article] Effects of bed roughness on flow around bed-mounted cylinders in open channels [texte imprimé] / M. A. F. Sadeque, Auteur ; N. Rajaratnam, Auteur ; M. R. Loewen, Auteur . - pp. 100-110. Mécanique appliquée Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 135 N°2 (Février 2009) . - pp. 100-110 Mots-clés : Open  channel  flow  Boundary  layers  Flow  visualization  Shear  stress  Bed  roughness  Fish  management. Résumé : This paper presents the results of an experimental study of flow around cylindrical objects on a rough bed in an open channel. This is an extension of a previous study of flow around cylinders on a smooth bed. The purpose of this study is to explore the effects of bed roughness on the characteristics of the deflected flow around cylindrical objects and the resulting bed-shear stress distributions. Similar to the previous study cylindrical objects of equal diameter and four heights were tested under similar flow conditions producing four different levels of submergence. Bed shear stress and deflected flow velocities were measured by a thin yaw-type Preston probe after a set of flow visualization tests. Flow visualization tests showed that the horse-shoe vortex systems on the rough bed occupy a relatively greater width compared to the smooth bed. Unlike smooth bed observations, the flow separation point upstream of the cylinder was not dependent on the level of submergence as the separation points were found to appear within a short range of x=−1D to −1.2D. Bed shear stress has been found to increase significantly near the shoulder of the cylinders, and its ratio with respect to the approach bed-shear stress was twice as large compared to the smooth bed case. Mean velocity profiles were analyzed in terms of three-dimensional turbulent boundary layer theories. Bed roughness was found to oppose the effect of the lateral pressure gradient that causes skewing in the boundary layer. Perry and Joubert's model has been found to be equally accurate on smooth and rough beds for predicting the deflected velocity magnitudes around cylinders. The present study will enhance the knowledge of hydraulics of flow around bed-mounted objects (e.g. fish-rocks) in natural streams. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JENMDT000 [...]

Meandering instability of a vertical plume / Albert Dai in Journal of engineering mechanics, Vol. 135 N°2 (Février 2009) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 135 N°2 (Février 2009) . - pp. 111-114 Titre : Meandering instability of a vertical plume Type de document : texte imprimé Auteurs : Albert Dai, Auteur ; Marcelo H. Garcia, Auteur Article en page(s) : pp. 111-114 Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Plumes  Boundary  layer  flow  Wavelength. Résumé : The meandering instability of a two-dimensional vertical plume is considered in this paper. The base flow profile is derived using boundary layer approximation and similarity hypothesis, in the spirit of Blasius boundary layer solution. Using linear stability analysis, we derive a modified version of the Orr-Sommerfeld equation governing the disturbances. The resulting eigenvalue problem is solved by the Galerkin method. It is found that a vertical plume is unstable to meandering, and in particular, three different wavelengths of meanders exist. A meandering instability of long wavelength ensues at the lowest portion of a vertically rising plume, where R<94. Beyond R=94 and R=192, the most unstable wavelength shifts to an intermediate and to a short wavelength meandering during the course of rising motion. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JENMDT000 [...] [article] Meandering instability of a vertical plume [texte imprimé] / Albert Dai, Auteur ; Marcelo H. Garcia, Auteur . - pp. 111-114. Mécanique appliquée Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 135 N°2 (Février 2009) . - pp. 111-114 Mots-clés : Plumes  Boundary  layer  flow  Wavelength. Résumé : The meandering instability of a two-dimensional vertical plume is considered in this paper. The base flow profile is derived using boundary layer approximation and similarity hypothesis, in the spirit of Blasius boundary layer solution. Using linear stability analysis, we derive a modified version of the Orr-Sommerfeld equation governing the disturbances. The resulting eigenvalue problem is solved by the Galerkin method. It is found that a vertical plume is unstable to meandering, and in particular, three different wavelengths of meanders exist. A meandering instability of long wavelength ensues at the lowest portion of a vertically rising plume, where R<94. Beyond R=94 and R=192, the most unstable wavelength shifts to an intermediate and to a short wavelength meandering during the course of rising motion. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=JENMDT000 [...]

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