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Ajouter le résultat dans votre panierStability analysis of direct integration algorithms applied to MDOF nonlinear structural dynamics / Cheng Chen in Journal of engineering mechanics, Vol. 134 n°9 (Septembre 2008)
Titre : Stability analysis of direct integration algorithms applied to MDOF nonlinear structural dynamics Type de document : texte imprimé Auteurs : Cheng Chen, Auteur ; James M. Ricles, Auteur Année de publication : 2008 Article en page(s) : pp.485–495. Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Algorithm Dynamics MDOF Transfer function Stability Nonlinear Résumé : Direct integration algorithms are typically used to solve temporally discretized equations of motion to evaluate the performance of structures under dynamic loading. The stability of these direct integration algorithms are usually investigated for linear elastic structures. However integration algorithms are often applied to structures with nonlinear behavior. This paper presents a procedure based on discrete control theory to investigate the stability of direct integration algorithms applied to multidegree-of-freedom (MDOF) nonlinear structures. The discrete root locus approach is used to investigate properties of the poles of the discrete transfer function matrix representing the nonlinear structural dynamics and to assess the stability of the integration algorithm. The procedure is illustrated using a nonlinear shear building MDOF system to investigate the stability of popular direct integration algorithms, including the Newmark family of integration algorithms, the Hilber-Hughes-Taylor α -method, and two newly developed explicit integration algorithms. Stability limits are derived for the direct integration algorithms that are found to be conditionally stable. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%29EM.1943-7889.0000083?journalCod [...]
in Journal of engineering mechanics > Vol. 134 n°9 (Septembre 2008) . - pp.485–495.[article] Stability analysis of direct integration algorithms applied to MDOF nonlinear structural dynamics [texte imprimé] / Cheng Chen, Auteur ; James M. Ricles, Auteur . - 2008 . - pp.485–495.
Mécanique appliquée
Langues : Anglais (eng)
in Journal of engineering mechanics > Vol. 134 n°9 (Septembre 2008) . - pp.485–495.
Mots-clés : Algorithm Dynamics MDOF Transfer function Stability Nonlinear Résumé : Direct integration algorithms are typically used to solve temporally discretized equations of motion to evaluate the performance of structures under dynamic loading. The stability of these direct integration algorithms are usually investigated for linear elastic structures. However integration algorithms are often applied to structures with nonlinear behavior. This paper presents a procedure based on discrete control theory to investigate the stability of direct integration algorithms applied to multidegree-of-freedom (MDOF) nonlinear structures. The discrete root locus approach is used to investigate properties of the poles of the discrete transfer function matrix representing the nonlinear structural dynamics and to assess the stability of the integration algorithm. The procedure is illustrated using a nonlinear shear building MDOF system to investigate the stability of popular direct integration algorithms, including the Newmark family of integration algorithms, the Hilber-Hughes-Taylor α -method, and two newly developed explicit integration algorithms. Stability limits are derived for the direct integration algorithms that are found to be conditionally stable. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%29EM.1943-7889.0000083?journalCod [...] Exemplaires
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Titre : General realization algorithm for modal identification of linear dynamic systems Type de document : texte imprimé Auteurs : R. A. De Callafon, Auteur ; Randy C. West, Auteur Année de publication : 2008 Article en page(s) : pp.496–505. Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Modal analysis Linear systems Earthquakes Algorithms Dynamic loads Résumé : The general realization algorithm (GRA) is developed to identify modal parameters of linear multi-degree-of-freedom dynamic systems subjected to measured (known) arbitrary dynamic loading from known initial conditions. The GRA extends the well known eigensystem realization algorithm (ERA) based on Hankel matrix decomposition by allowing an arbitrary input signal in the realization algorithm. This generalization is obtained by performing a weighted Hankel matrix decomposition, where the weighting is determined by the loading. The state-space matrices are identified in a two-step procedure that includes a state reconstruction followed by a least-squares optimization to get the minimum prediction error for the response. The statistical properties (i.e., bias, variance, and robustness to added output noise introduced to model measurement noise and modeling errors) of the modal parameter estimators provided by the GRA are investigated through numerical simulation based on a benchmark problem with nonclassical damping. ISSN : 0733-9399 En ligne : Modal analysis, Linear systems, Earthquakes, Algorithms, Dynamic loads Read More [...]
in Journal of engineering mechanics > Vol. 134 n°9 (Septembre 2008) . - pp.496–505.[article] General realization algorithm for modal identification of linear dynamic systems [texte imprimé] / R. A. De Callafon, Auteur ; Randy C. West, Auteur . - 2008 . - pp.496–505.
Mécanique appliquée
Langues : Anglais (eng)
in Journal of engineering mechanics > Vol. 134 n°9 (Septembre 2008) . - pp.496–505.
Mots-clés : Modal analysis Linear systems Earthquakes Algorithms Dynamic loads Résumé : The general realization algorithm (GRA) is developed to identify modal parameters of linear multi-degree-of-freedom dynamic systems subjected to measured (known) arbitrary dynamic loading from known initial conditions. The GRA extends the well known eigensystem realization algorithm (ERA) based on Hankel matrix decomposition by allowing an arbitrary input signal in the realization algorithm. This generalization is obtained by performing a weighted Hankel matrix decomposition, where the weighting is determined by the loading. The state-space matrices are identified in a two-step procedure that includes a state reconstruction followed by a least-squares optimization to get the minimum prediction error for the response. The statistical properties (i.e., bias, variance, and robustness to added output noise introduced to model measurement noise and modeling errors) of the modal parameter estimators provided by the GRA are investigated through numerical simulation based on a benchmark problem with nonclassical damping. ISSN : 0733-9399 En ligne : Modal analysis, Linear systems, Earthquakes, Algorithms, Dynamic loads Read More [...] Exemplaires
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Titre : Ultimate state of samples of ellipsoids under different stress paths Type de document : texte imprimé Auteurs : Tang-Tat Ng, Auteur Année de publication : 2008 Article en page(s) : pp.723–729. Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Void ratio Granular materials Soil mechanics Stress strain relations Sampling Résumé : The ultimate state of granular material was investigated by the discrete element method. This paper discusses a series of numerical triaxial tests on samples of two kinds of ellipsoids. Samples of three different densities were loaded along various stress paths. The ellipsoids were mixed in the proportions 50:50 by weight. The longer particles have an aspect ratio (major length/minor length) of 1.5 and the other particles have an aspect ratio of 1.2. The samples were generated by deposition under gravity to simulate the air-pluviation sample preparation technique. Then they were consolidated isotropically. Fourteen stress-path controlled triaxial tests were conducted numerically for each sample. They are sheared to the ultimate state to determine the friction angle and void ratio at the ultimate state. When samples of different densities were sheared along the same loading path, a unique ultimate state was observed. The initial density does not affect the ultimate state. However, when different loading paths are applied to the same numerical specimen, they do not always arrive at the same critical state in the void-mean stress space. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9399%282008%29134%3A9%2872 [...]
in Journal of engineering mechanics > Vol. 134 n°9 (Septembre 2008) . - pp.723–729.[article] Ultimate state of samples of ellipsoids under different stress paths [texte imprimé] / Tang-Tat Ng, Auteur . - 2008 . - pp.723–729.
Mécanique appliquée
Langues : Anglais (eng)
in Journal of engineering mechanics > Vol. 134 n°9 (Septembre 2008) . - pp.723–729.
Mots-clés : Void ratio Granular materials Soil mechanics Stress strain relations Sampling Résumé : The ultimate state of granular material was investigated by the discrete element method. This paper discusses a series of numerical triaxial tests on samples of two kinds of ellipsoids. Samples of three different densities were loaded along various stress paths. The ellipsoids were mixed in the proportions 50:50 by weight. The longer particles have an aspect ratio (major length/minor length) of 1.5 and the other particles have an aspect ratio of 1.2. The samples were generated by deposition under gravity to simulate the air-pluviation sample preparation technique. Then they were consolidated isotropically. Fourteen stress-path controlled triaxial tests were conducted numerically for each sample. They are sheared to the ultimate state to determine the friction angle and void ratio at the ultimate state. When samples of different densities were sheared along the same loading path, a unique ultimate state was observed. The initial density does not affect the ultimate state. However, when different loading paths are applied to the same numerical specimen, they do not always arrive at the same critical state in the void-mean stress space. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9399%282008%29134%3A9%2872 [...] Exemplaires
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Titre : Simple model for directional distortional hardening in metal plasticity within thermodynamics Type de document : texte imprimé Auteurs : Feigenbaum, Heidi P., Auteur ; Dafalias, Yannis F., Auteur Année de publication : 2008 Article en page(s) : pp.730-738 Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Plasticity Elastoplasticity Yield Thermal factors Anisotropy Résumé : Directional distortion, observed in many experiments on various types of metals, refers to the formation of a region of high curvature (sharpening) on the yield surface approximately in the direction of loading, and a region of low curvature (flattening) approximately in the opposite direction. Constitutive modeling of directional distortion was recently presented by the writers where an evolving fourth-order tensor-valued internal variable was introduced. In the current paper a much simpler mathematical formulation describing directional distortional hardening is presented without the use of a fourth-order tensor, in conjunction with kinematic and isotropic hardening. Two versions of the model in ascending level of complexity follow similar lines of development, which include derivation of all hardening rules on the basis of conditions sufficient to satisfy the thermodynamic dissipation inequality. As a tradeoff for its simplicity the present model does not fit experimental data as well as the model with the evolving fourth-order tensor, but it still captures the salient features of directional distortion in a rather satisfactory way. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9399%282008%29134%3A9%2872 [...]
in Journal of engineering mechanics > Vol. 134 n°9 (Septembre 2008) . - pp.730-738[article] Simple model for directional distortional hardening in metal plasticity within thermodynamics [texte imprimé] / Feigenbaum, Heidi P., Auteur ; Dafalias, Yannis F., Auteur . - 2008 . - pp.730-738.
Mécanique appliquée
Langues : Anglais (eng)
in Journal of engineering mechanics > Vol. 134 n°9 (Septembre 2008) . - pp.730-738
Mots-clés : Plasticity Elastoplasticity Yield Thermal factors Anisotropy Résumé : Directional distortion, observed in many experiments on various types of metals, refers to the formation of a region of high curvature (sharpening) on the yield surface approximately in the direction of loading, and a region of low curvature (flattening) approximately in the opposite direction. Constitutive modeling of directional distortion was recently presented by the writers where an evolving fourth-order tensor-valued internal variable was introduced. In the current paper a much simpler mathematical formulation describing directional distortional hardening is presented without the use of a fourth-order tensor, in conjunction with kinematic and isotropic hardening. Two versions of the model in ascending level of complexity follow similar lines of development, which include derivation of all hardening rules on the basis of conditions sufficient to satisfy the thermodynamic dissipation inequality. As a tradeoff for its simplicity the present model does not fit experimental data as well as the model with the evolving fourth-order tensor, but it still captures the salient features of directional distortion in a rather satisfactory way. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9399%282008%29134%3A9%2872 [...] Exemplaires
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Titre : Advanced boundary element analysis of three-dimensional elastic solids with fiber reinforcements Type de document : texte imprimé Auteurs : J. Chatterjee, Auteur ; F. Ma, Auteur ; P. K. Banerjee, Auteur Année de publication : 2008 Article en page(s) : pp.739-749 Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Boundary element method Composite materials Fiber reinforced Reinforcement ElasticityRead More: http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9399%282008%29134%3A9%28739%29 Résumé : An advanced boundary element methodology for the analysis of three-dimensional fiber-reinforced elastic solids using the concept of fiber elements has been presented in this paper as an extension of the earlier work of Banerjee and co-workers. The previous simplified formulation was based on the assumption that the Poisson ratios of the matrix and the fiber are equal. However, this may not be a valid assumption for all values of elastic stiffness ratios and fiber to matrix volume ratios. Moreover, such restrictions do not allow for any future extensions to nonlinear analysis. Also, because of limiting computing power available at that time, their implementation was restricted to only a small number of fiber elements in a given analysis. The new algorithm proposed in this work does not make any such assumptions. In this algorithm, the fibers are semianalytically integrated and the resulting equations are back-substituted into the equations for the composite matrix without any further approximation. The present work has been implemented in a general purpose multiregion boundary element computer program and is capable of handling very large numbers of fiber elements in a given analysis. Several numerical examples are presented to validate the proposed method of fiber composite analysis and its applicability is demonstrated via practical engineering problems. ISSN : 0733-9399
in Journal of engineering mechanics > Vol. 134 n°9 (Septembre 2008) . - pp.739-749[article] Advanced boundary element analysis of three-dimensional elastic solids with fiber reinforcements [texte imprimé] / J. Chatterjee, Auteur ; F. Ma, Auteur ; P. K. Banerjee, Auteur . - 2008 . - pp.739-749.
Mécanique appliquée
Langues : Anglais (eng)
in Journal of engineering mechanics > Vol. 134 n°9 (Septembre 2008) . - pp.739-749
Mots-clés : Boundary element method Composite materials Fiber reinforced Reinforcement ElasticityRead More: http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9399%282008%29134%3A9%28739%29 Résumé : An advanced boundary element methodology for the analysis of three-dimensional fiber-reinforced elastic solids using the concept of fiber elements has been presented in this paper as an extension of the earlier work of Banerjee and co-workers. The previous simplified formulation was based on the assumption that the Poisson ratios of the matrix and the fiber are equal. However, this may not be a valid assumption for all values of elastic stiffness ratios and fiber to matrix volume ratios. Moreover, such restrictions do not allow for any future extensions to nonlinear analysis. Also, because of limiting computing power available at that time, their implementation was restricted to only a small number of fiber elements in a given analysis. The new algorithm proposed in this work does not make any such assumptions. In this algorithm, the fibers are semianalytically integrated and the resulting equations are back-substituted into the equations for the composite matrix without any further approximation. The present work has been implemented in a general purpose multiregion boundary element computer program and is capable of handling very large numbers of fiber elements in a given analysis. Several numerical examples are presented to validate the proposed method of fiber composite analysis and its applicability is demonstrated via practical engineering problems. ISSN : 0733-9399 Exemplaires
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Titre : Probabilistic models and simulation of irregular masonry walls Type de document : texte imprimé Auteurs : Seymour M. J. Spence, Auteur ; Massimiliano Gioffrè, Auteur ; Mircea D. Grigoriu, Auteur Année de publication : 2008 Article en page(s) : pp. 750–762. Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Probability Masonry Microstructures Stochastic models Random processes Monte Carlo method Simulation Walls Résumé : A method is proposed for generating samples of irregular masonry walls that capture the essential statistics of a given population. The method first entails characterizing the geometry of scaled star-like inclusions by means of a non-Gaussian random field model and second packing these inclusions together to form a virtual material specimen. The model used in the first step is a nonlinear memoryless mapping of a sum of harmonic functions with Gaussian coefficients while in the second step the model proposed transforms Poisson fields into a domain of inclusions with a sieving curve that matches the sample specimen. The two random field models are used to develop Monte Carlo algorithms which produce virtual material specimens that include two levels of probabilistic characterization, a first level that is correlated to the inclusion geometry, and a second that is dictated by the global morphology of the sample material specimen. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9399%282008%29134%3A9%2875 [...]
in Journal of engineering mechanics > Vol. 134 n°9 (Septembre 2008) . - pp. 750–762.[article] Probabilistic models and simulation of irregular masonry walls [texte imprimé] / Seymour M. J. Spence, Auteur ; Massimiliano Gioffrè, Auteur ; Mircea D. Grigoriu, Auteur . - 2008 . - pp. 750–762.
Mécanique appliquée
Langues : Anglais (eng)
in Journal of engineering mechanics > Vol. 134 n°9 (Septembre 2008) . - pp. 750–762.
Mots-clés : Probability Masonry Microstructures Stochastic models Random processes Monte Carlo method Simulation Walls Résumé : A method is proposed for generating samples of irregular masonry walls that capture the essential statistics of a given population. The method first entails characterizing the geometry of scaled star-like inclusions by means of a non-Gaussian random field model and second packing these inclusions together to form a virtual material specimen. The model used in the first step is a nonlinear memoryless mapping of a sum of harmonic functions with Gaussian coefficients while in the second step the model proposed transforms Poisson fields into a domain of inclusions with a sieving curve that matches the sample specimen. The two random field models are used to develop Monte Carlo algorithms which produce virtual material specimens that include two levels of probabilistic characterization, a first level that is correlated to the inclusion geometry, and a second that is dictated by the global morphology of the sample material specimen. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9399%282008%29134%3A9%2875 [...] Exemplaires
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Titre : Finite elements on generalized elastic foundation in Timoshenko beam theory Type de document : texte imprimé Auteurs : Gelu Onu, Auteur Année de publication : 2008 Article en page(s) : pp.763–776. Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Elastic foundations Parameters Finite element method Beam columns Shear deformation Résumé : Using the Vlasov foundation model, a modified approach of the continuous beam on elastic supports, leading to both a mechanical model and the proper foundation parameters of the generalized foundation is shown. Two formulations of the beam finite-element with shear deformation effect, resting on a two-parameter elastic foundation, characterized by distinct contributions of normal and rotary reactions are presented. The behavior of the second foundation parameter in the two formulations is governed by the bending cross section rotation of a beam. The first formulation, yielding a free-of-meshing stiffness matrix and equivalent nodal load vector, is based on the transcendental or “exact” solution of the governing differential equation of the beam resting on the elastic layer of constant thickness. Considering a linear variation of the layer thickness along the beam, the second formulation is based on the assumed polynomial displacement field. Numerical comparisons with the exact approach show that the cubic formulation leads to better results when the foundation parameters are variables. The practical utility of the analogy between a tensile axial force and the second foundation parameter is exemplified, too. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9399%282008%29134%3A9%2876 [...]
in Journal of engineering mechanics > Vol. 134 n°9 (Septembre 2008) . - pp.763–776.[article] Finite elements on generalized elastic foundation in Timoshenko beam theory [texte imprimé] / Gelu Onu, Auteur . - 2008 . - pp.763–776.
Mécanique appliquée
Langues : Anglais (eng)
in Journal of engineering mechanics > Vol. 134 n°9 (Septembre 2008) . - pp.763–776.
Mots-clés : Elastic foundations Parameters Finite element method Beam columns Shear deformation Résumé : Using the Vlasov foundation model, a modified approach of the continuous beam on elastic supports, leading to both a mechanical model and the proper foundation parameters of the generalized foundation is shown. Two formulations of the beam finite-element with shear deformation effect, resting on a two-parameter elastic foundation, characterized by distinct contributions of normal and rotary reactions are presented. The behavior of the second foundation parameter in the two formulations is governed by the bending cross section rotation of a beam. The first formulation, yielding a free-of-meshing stiffness matrix and equivalent nodal load vector, is based on the transcendental or “exact” solution of the governing differential equation of the beam resting on the elastic layer of constant thickness. Considering a linear variation of the layer thickness along the beam, the second formulation is based on the assumed polynomial displacement field. Numerical comparisons with the exact approach show that the cubic formulation leads to better results when the foundation parameters are variables. The practical utility of the analogy between a tensile axial force and the second foundation parameter is exemplified, too. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9399%282008%29134%3A9%2876 [...] Exemplaires
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Titre : Asymmetric dynamic green’s functions in a two-layered transversely isotropic half-space Type de document : texte imprimé Auteurs : Ali Khojasteh, Auteur ; Mohammad Rahimian, Auteur ; Ronald Y. S. Pak, Auteur Année de publication : 2008 Article en page(s) : pp.777–787. Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Greens function Layered systems Wave propagation Elasticity Anisotropy Boundaries Half space Résumé : By virtue of a complete representation using two displacement potentials, an analytical derivation of the elastodynamic Green’s functions for a transversely isotropic layer underlain by a transversely isotropic half-space is presented. Three-dimensional point-load and patch-load Green’s functions for stresses and displacements are given in the complex-plane line-integral representations. The formulation includes a complete set of transformed stress-potential and displacement-potential relations in the framework of Fourier expansions and Hankel integral transforms, that is useful in a variety of elastodynamic as well as elastostatic problems. For the numerical computation of the integrals, a robust and effective methodology is laid out. Comparisons with the existing numerical solutions for a two-layered transversely isotropic half-space under static surface load, and a homogeneous transversely isotropic half-space subjected to buried time-harmonic load are made to confirm the accuracy of the present solutions. Selected numerical results for displacement and stress Green’s functions are presented to portray the dependence of the response of the two-layered half-space on the frequency of excitation and the role of the upper layer. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9399%282008%29134%3A9%2877 [...]
in Journal of engineering mechanics > Vol. 134 n°9 (Septembre 2008) . - pp.777–787.[article] Asymmetric dynamic green’s functions in a two-layered transversely isotropic half-space [texte imprimé] / Ali Khojasteh, Auteur ; Mohammad Rahimian, Auteur ; Ronald Y. S. Pak, Auteur . - 2008 . - pp.777–787.
Mécanique appliquée
Langues : Anglais (eng)
in Journal of engineering mechanics > Vol. 134 n°9 (Septembre 2008) . - pp.777–787.
Mots-clés : Greens function Layered systems Wave propagation Elasticity Anisotropy Boundaries Half space Résumé : By virtue of a complete representation using two displacement potentials, an analytical derivation of the elastodynamic Green’s functions for a transversely isotropic layer underlain by a transversely isotropic half-space is presented. Three-dimensional point-load and patch-load Green’s functions for stresses and displacements are given in the complex-plane line-integral representations. The formulation includes a complete set of transformed stress-potential and displacement-potential relations in the framework of Fourier expansions and Hankel integral transforms, that is useful in a variety of elastodynamic as well as elastostatic problems. For the numerical computation of the integrals, a robust and effective methodology is laid out. Comparisons with the existing numerical solutions for a two-layered transversely isotropic half-space under static surface load, and a homogeneous transversely isotropic half-space subjected to buried time-harmonic load are made to confirm the accuracy of the present solutions. Selected numerical results for displacement and stress Green’s functions are presented to portray the dependence of the response of the two-layered half-space on the frequency of excitation and the role of the upper layer. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9399%282008%29134%3A9%2877 [...] Exemplaires
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Titre : Experimental investigation of flow past a square cylinder at an angle of incidence Type de document : texte imprimé Auteurs : Sushanta Dutta, Auteur ; P. K. Panigrahi, Auteur ; K. Muralidhar, Auteur Année de publication : 2008 Article en page(s) : pp.788–803. Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Cylinders Drag Coefficients Experimentation Résumé : Flow past a square cylinder placed at an angle to the incoming flow is experimentally investigated using particle image velocimetry, hot wire anemometry, and flow visualization. The Reynolds number based on cylinder size and the average incoming velocity is set equal to 410. Data for four cylinder orientations ( θ=0 , 22.5, 30, and 45°) and two aspect ratios [ AR=16 and 28] are reported. Results are presented in terms of drag coefficient, Strouhal number, time averaged velocity, stream traces, turbulence intensity, power spectra, and vorticity field. In addition, flow visualization images in the near wake of the cylinder are discussed. The shape and size of the recirculation bubble downstream of the cylinder are strong functions of orientation. A minimum in drag coefficient and maximum in Strouhal number is observed at a cylinder orientation of 22.5°. The v -velocity profile and time-average stream traces show that the wake and the separation process are asymmetric at orientations of 22.5 and 30°. The corresponding power spectra show additional peaks related to secondary vortical structures that arise from nonlinear interaction between the Karman vortices. The flow visualization images show the streamwise separation distance between the alternating vortices to be a function of cylinder orientation. Further, the flow approaches three dimensionality early, i.e., closer to the cylinder surface for the 22.5° orientation. The drag coefficient decreases with an increase in aspect ratio, while the Strouhal number is seen to increase with aspect ratio. The turbulence intensity is higher for the large aspect ratio cylinder and the maximum turbulence intensity appears at an earlier streamwise location. The overall dependence of drag coefficient and Strouhal number on orientation is preserved for the two aspect ratios studied. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9399%282008%29134%3A9%2878 [...]
in Journal of engineering mechanics > Vol. 134 n°9 (Septembre 2008) . - pp.788–803.[article] Experimental investigation of flow past a square cylinder at an angle of incidence [texte imprimé] / Sushanta Dutta, Auteur ; P. K. Panigrahi, Auteur ; K. Muralidhar, Auteur . - 2008 . - pp.788–803.
Mécanique appliquée
Langues : Anglais (eng)
in Journal of engineering mechanics > Vol. 134 n°9 (Septembre 2008) . - pp.788–803.
Mots-clés : Cylinders Drag Coefficients Experimentation Résumé : Flow past a square cylinder placed at an angle to the incoming flow is experimentally investigated using particle image velocimetry, hot wire anemometry, and flow visualization. The Reynolds number based on cylinder size and the average incoming velocity is set equal to 410. Data for four cylinder orientations ( θ=0 , 22.5, 30, and 45°) and two aspect ratios [ AR=16 and 28] are reported. Results are presented in terms of drag coefficient, Strouhal number, time averaged velocity, stream traces, turbulence intensity, power spectra, and vorticity field. In addition, flow visualization images in the near wake of the cylinder are discussed. The shape and size of the recirculation bubble downstream of the cylinder are strong functions of orientation. A minimum in drag coefficient and maximum in Strouhal number is observed at a cylinder orientation of 22.5°. The v -velocity profile and time-average stream traces show that the wake and the separation process are asymmetric at orientations of 22.5 and 30°. The corresponding power spectra show additional peaks related to secondary vortical structures that arise from nonlinear interaction between the Karman vortices. The flow visualization images show the streamwise separation distance between the alternating vortices to be a function of cylinder orientation. Further, the flow approaches three dimensionality early, i.e., closer to the cylinder surface for the 22.5° orientation. The drag coefficient decreases with an increase in aspect ratio, while the Strouhal number is seen to increase with aspect ratio. The turbulence intensity is higher for the large aspect ratio cylinder and the maximum turbulence intensity appears at an earlier streamwise location. The overall dependence of drag coefficient and Strouhal number on orientation is preserved for the two aspect ratios studied. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9399%282008%29134%3A9%2878 [...] Exemplaires
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Titre : Question of tension softening versus tension stiffening in plain and reinforced concrete Type de document : texte imprimé Auteurs : Bernd Koeberl, Auteur ; Kaspar Willam, Auteur Année de publication : 2008 Article en page(s) : pp.804–808. Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Bonding Reinforced concrete Cracking Computer models Failure modes Shear failure Tension Résumé : Stress transfer from concrete into steel is one of the fundamental mechanisms behind the significant ductility of reinforced concrete. Considering the low value of cracking strain of plain concrete, it is the stress transfer that takes place during debonding when the steel strain approaches the yield limit at a level which is an order of magnitude larger than the cracking limit of concrete. This technical note examines the difference of “tension softening” of plain concrete versus “tension stiffening” of reinforced concrete which describes the stress transfer mechanism from concrete into the embedded reinforcing bars. Using three-dimensional finite-element simulations the fracture energy arguments of Mode I versus Mode II are reexamined when the axial response behavior of plain concrete in tension softening is compared with that of reinforced concrete exhibiting tension stiffening in long and short tension members. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9399%282008%29134%3A9%2880 [...]
in Journal of engineering mechanics > Vol. 134 n°9 (Septembre 2008) . - pp.804–808.[article] Question of tension softening versus tension stiffening in plain and reinforced concrete [texte imprimé] / Bernd Koeberl, Auteur ; Kaspar Willam, Auteur . - 2008 . - pp.804–808.
Mécanique appliquée
Langues : Anglais (eng)
in Journal of engineering mechanics > Vol. 134 n°9 (Septembre 2008) . - pp.804–808.
Mots-clés : Bonding Reinforced concrete Cracking Computer models Failure modes Shear failure Tension Résumé : Stress transfer from concrete into steel is one of the fundamental mechanisms behind the significant ductility of reinforced concrete. Considering the low value of cracking strain of plain concrete, it is the stress transfer that takes place during debonding when the steel strain approaches the yield limit at a level which is an order of magnitude larger than the cracking limit of concrete. This technical note examines the difference of “tension softening” of plain concrete versus “tension stiffening” of reinforced concrete which describes the stress transfer mechanism from concrete into the embedded reinforcing bars. Using three-dimensional finite-element simulations the fracture energy arguments of Mode I versus Mode II are reexamined when the axial response behavior of plain concrete in tension softening is compared with that of reinforced concrete exhibiting tension stiffening in long and short tension members. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9399%282008%29134%3A9%2880 [...] Exemplaires
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