Dépouillements

Nanomechanics modeling and simulation of carbon nanotubes / Xi Chen in Journal of engineering mechanics, Vol. 134 N°3 (Mars 2008) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 134 N°3 (Mars 2008) . - pp.211–216. Titre : Nanomechanics modeling and simulation of carbon nanotubes Type de document : texte imprimé Auteurs : Xi Chen, Auteur ; Yonggang Huang, Auteur Année de publication : 2008 Article en page(s) : pp.211–216. Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Simulation  Models  Mechanical  properties Résumé : nanoelectronic and nanomechanical devices. Recent advances of modeling and simulation at the nanoscale have led to a better understanding of the mechanical behaviors of carbon nanotubes. The modeling efforts incorporate atomic features into the continuum or structural mechanics theories, and the numerical simulations feature quantum mechanical approach and classical molecular dynamics. Multiscale and multiphysics modeling and simulation tools have also been developed to effectively bridge the different lengths and time scales, and to link basic scientific research with engineering application. The general approaches of the theoretical and numerical nanomechanics of CNTs are briefly reviewed. This paper is not intended to be a comprehensive review, but to introduce readers (especially those with traditional civil engineering or engineering mechanics backgrounds) to the new, interdisciplinary, or emerging fields in engineering mechanics, in this case the rapidly growing frontier of nanomechanics through the example of carbon nanotubes. ISSN : 0733-9399 En ligne : http://ascelibrary.org/action/showAbstract?page=211&volume=134&issue=3&journalCo [...] [article] Nanomechanics modeling and simulation of carbon nanotubes [texte imprimé] / Xi Chen, Auteur ; Yonggang Huang, Auteur . - 2008 . - pp.211–216. Mécanique appliquée Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 134 N°3 (Mars 2008) . - pp.211–216. Mots-clés : Simulation  Models  Mechanical  properties Résumé : nanoelectronic and nanomechanical devices. Recent advances of modeling and simulation at the nanoscale have led to a better understanding of the mechanical behaviors of carbon nanotubes. The modeling efforts incorporate atomic features into the continuum or structural mechanics theories, and the numerical simulations feature quantum mechanical approach and classical molecular dynamics. Multiscale and multiphysics modeling and simulation tools have also been developed to effectively bridge the different lengths and time scales, and to link basic scientific research with engineering application. The general approaches of the theoretical and numerical nanomechanics of CNTs are briefly reviewed. This paper is not intended to be a comprehensive review, but to introduce readers (especially those with traditional civil engineering or engineering mechanics backgrounds) to the new, interdisciplinary, or emerging fields in engineering mechanics, in this case the rapidly growing frontier of nanomechanics through the example of carbon nanotubes. ISSN : 0733-9399 En ligne : http://ascelibrary.org/action/showAbstract?page=211&volume=134&issue=3&journalCo [...]

Coupled creep and seepage model for hybrid media / Daoping Lai in Journal of engineering mechanics, Vol. 134 N°3 (Mars 2008) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 134 N°3 (Mars 2008) . - pp.217–223. Titre : Coupled creep and seepage model for hybrid media Type de document : texte imprimé Auteurs : Daoping Lai, Auteur ; Robert Liang, Auteur Année de publication : 2008 Article en page(s) : pp.217–223. Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Coupling  Creep  Seepage  Hybrid  methods Résumé : The permeability coefficient of a rock mass depends mainly on the aperture of the joint and the porosity of the block, which may alter with time when creep of the rock mass is taken into account. Therefore, a coupled creep and seepage model for hybrid media is proposed in this paper. Large-scale and strongly permeable joints are simulated according to their spatial distributions, while other discontinuities are treated as equivalent continuum. Based on the fundamental mechanism of creep effects on the permeability of the rock mass, together with empirical equations for hydraulic conductivity, coupled creep and seepage equations for filled joints, rough joints, and equivalent continuum are proposed. By application of these equations, governing equations for the coupled creep and seepage model are deduced. A simplified numerical solution is proposed to solve the coupled creep and seepage model. The coupled model is shown to simulate the evolvement of seepage, deformation, and stress field in a gravity dam. By comparing the results derived by coupled and uncoupled models, it is concluded that the coupling between creep and seepage should be taken into account when performing engineering design of large dams. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9399%282008%29134%3A3%2821 [...] [article] Coupled creep and seepage model for hybrid media [texte imprimé] / Daoping Lai, Auteur ; Robert Liang, Auteur . - 2008 . - pp.217–223. Mécanique appliquée Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 134 N°3 (Mars 2008) . - pp.217–223. Mots-clés : Coupling  Creep  Seepage  Hybrid  methods Résumé : The permeability coefficient of a rock mass depends mainly on the aperture of the joint and the porosity of the block, which may alter with time when creep of the rock mass is taken into account. Therefore, a coupled creep and seepage model for hybrid media is proposed in this paper. Large-scale and strongly permeable joints are simulated according to their spatial distributions, while other discontinuities are treated as equivalent continuum. Based on the fundamental mechanism of creep effects on the permeability of the rock mass, together with empirical equations for hydraulic conductivity, coupled creep and seepage equations for filled joints, rough joints, and equivalent continuum are proposed. By application of these equations, governing equations for the coupled creep and seepage model are deduced. A simplified numerical solution is proposed to solve the coupled creep and seepage model. The coupled model is shown to simulate the evolvement of seepage, deformation, and stress field in a gravity dam. By comparing the results derived by coupled and uncoupled models, it is concluded that the coupling between creep and seepage should be taken into account when performing engineering design of large dams. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9399%282008%29134%3A3%2821 [...]

Comparison of far-field turbulent structure of a rectangular surface jet to three-dimensional free and wall jets / Soheil Gholamreza-Kashi in Journal of engineering mechanics, Vol. 134 N°3 (Mars 2008) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 134 N°3 (Mars 2008) . - pp.224–233. Titre : Comparison of far-field turbulent structure of a rectangular surface jet to three-dimensional free and wall jets Type de document : texte imprimé Auteurs : Soheil Gholamreza-Kashi, Auteur ; Robert J. Martinuzzi, Auteur ; Raouf E. Baddour, Auteur Année de publication : 2008 Article en page(s) : pp.224–233. Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Surface  jets  Submerged  jets  Shear  flow  Three-dimensional  flow  Turbulent  flow Résumé : The turbulence structure of a rectangular surface jet is compared to that of the three-dimensional free and wall jets. The surface jet turbulence quantities are mapped using laser Doppler velocimetry. In general, the turbulence structure of these three jets is found to be significantly different. For the surface jet, the free surface kinematic condition has a predominant effect on the whole structure, while for the wall jet, the influence of wall kinematic constraint is contained in the wall layer. A surface current with a higher lateral spreading rate than the submerged portion of the jet is developed, which does not exist for the wall jet because of the no-slip boundary condition. Unlike free jets, the submerged portion of the rectangular surface jet is characterized by two length scales. The Prandtl hypothesis with constant eddy viscosity provides a good estimate for the shear stresses in the lateral direction, but fails in the vertical direction, where the velocity profiles are much flatter, due to the free surface condition, than those for the free and wall jets. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9399%282008%29134%3A3%2822 [...] [article] Comparison of far-field turbulent structure of a rectangular surface jet to three-dimensional free and wall jets [texte imprimé] / Soheil Gholamreza-Kashi, Auteur ; Robert J. Martinuzzi, Auteur ; Raouf E. Baddour, Auteur . - 2008 . - pp.224–233. Mécanique appliquée Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 134 N°3 (Mars 2008) . - pp.224–233. Mots-clés : Surface  jets  Submerged  jets  Shear  flow  Three-dimensional  flow  Turbulent  flow Résumé : The turbulence structure of a rectangular surface jet is compared to that of the three-dimensional free and wall jets. The surface jet turbulence quantities are mapped using laser Doppler velocimetry. In general, the turbulence structure of these three jets is found to be significantly different. For the surface jet, the free surface kinematic condition has a predominant effect on the whole structure, while for the wall jet, the influence of wall kinematic constraint is contained in the wall layer. A surface current with a higher lateral spreading rate than the submerged portion of the jet is developed, which does not exist for the wall jet because of the no-slip boundary condition. Unlike free jets, the submerged portion of the rectangular surface jet is characterized by two length scales. The Prandtl hypothesis with constant eddy viscosity provides a good estimate for the shear stresses in the lateral direction, but fails in the vertical direction, where the velocity profiles are much flatter, due to the free surface condition, than those for the free and wall jets. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9399%282008%29134%3A3%2822 [...]

Effects of train characteristics on the rate of deterioration of track roughness / Haitham M. Hawari in Journal of engineering mechanics, Vol. 134 N°3 (Mars 2008) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 134 N°3 (Mars 2008) . - pp.234–239. Titre : Effects of train characteristics on the rate of deterioration of track roughness Type de document : texte imprimé Auteurs : Haitham M. Hawari, Auteur ; Martin H. Murray, Auteur Année de publication : 2008 Article en page(s) : pp.234–239. Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Railroad  tracks  Degradation  Vertical  forces  Roughness  Mass  Suspension  Damping Résumé : Track roughness describes in part the up and down waves in the longitudinal geometry of a railway track. A train passing over rough track experiences a degree of bouncing that generates oscillations in the forces exerted by the train’s wheels on the top of the rail, which in turn cause this roughness to worsen. The rate at which the track roughness deteriorates depends on the response of the track to the weight of the train and to the dynamic oscillations in wheel/rail forces, which in turn are affected by the properties of the train vehicles’ components and the speed of the train. The paper develops relationships between the severity of track roughness and the dynamic wheel/rail forces generated by a moving train using field data, and between those forces and the specific vehicle characteristics of speed, total mass, unsprung mass, suspension stiffness, and damping, using NUCARS simulations. These two relationships in turn are combined to show how the speed of the train and the design of the train vehicle’s bogie suspension can worsen or improve the rate of deterioration of track roughness. The relationships also provide a firm basis for the owner of track to set more representative charges levied on the train operator for using the track. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9399%282008%29134%3A3%2823 [...] [article] Effects of train characteristics on the rate of deterioration of track roughness [texte imprimé] / Haitham M. Hawari, Auteur ; Martin H. Murray, Auteur . - 2008 . - pp.234–239. Mécanique appliquée Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 134 N°3 (Mars 2008) . - pp.234–239. Mots-clés : Railroad  tracks  Degradation  Vertical  forces  Roughness  Mass  Suspension  Damping Résumé : Track roughness describes in part the up and down waves in the longitudinal geometry of a railway track. A train passing over rough track experiences a degree of bouncing that generates oscillations in the forces exerted by the train’s wheels on the top of the rail, which in turn cause this roughness to worsen. The rate at which the track roughness deteriorates depends on the response of the track to the weight of the train and to the dynamic oscillations in wheel/rail forces, which in turn are affected by the properties of the train vehicles’ components and the speed of the train. The paper develops relationships between the severity of track roughness and the dynamic wheel/rail forces generated by a moving train using field data, and between those forces and the specific vehicle characteristics of speed, total mass, unsprung mass, suspension stiffness, and damping, using NUCARS simulations. These two relationships in turn are combined to show how the speed of the train and the design of the train vehicle’s bogie suspension can worsen or improve the rate of deterioration of track roughness. The relationships also provide a firm basis for the owner of track to set more representative charges levied on the train operator for using the track. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9399%282008%29134%3A3%2823 [...]

Seismic Response control of building structures with superelastic shape memory alloy wire dampers / Yunfeng Zhang in Journal of engineering mechanics, Vol. 134 N°3 (Mars 2008) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 134 N°3 (Mars 2008) . - pp.240–251. Titre : Seismic Response control of building structures with superelastic shape memory alloy wire dampers Type de document : texte imprimé Auteurs : Yunfeng Zhang, Auteur ; Songye Zhu, Auteur Année de publication : 2008 Article en page(s) : pp.240–251. Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Bench  marks  Damping  Hysteresis  Seismic  effects  Structural  control  Shape  memory  effect Résumé : This paper presents a simulation-based benchmark control study in which shape memory alloy (SMA) wire dampers are utilized to control the seismic response of a three-story nonlinear steel frame building. The SMA wire damper uses superelastic Nitinol wires for energy dissipation because of its high fatigue life and large recoverable strain. An analytical model which considers the training effect of SMA wires is used to describe the stress-strain relationship of superelastic SMA wires. The performance of SMA wire dampers is investigated in the framework of the third-generation benchmark problem on structural control. A comparative study of the seismic response control performance of SMA wire dampers with either unprestrained or prestrained SMA wires was also conducted. The results of this simulation-based benchmark control study show that SMA wire dampers, as a passive structure control measure, can effectively reduce the seismic responses of the three-story nonlinear benchmark building structure and has the potential to withstand several design earthquakes without the need for repair. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9399%282008%29134%3A3%2824 [...] [article] Seismic Response control of building structures with superelastic shape memory alloy wire dampers [texte imprimé] / Yunfeng Zhang, Auteur ; Songye Zhu, Auteur . - 2008 . - pp.240–251. Mécanique appliquée Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 134 N°3 (Mars 2008) . - pp.240–251. Mots-clés : Bench  marks  Damping  Hysteresis  Seismic  effects  Structural  control  Shape  memory  effect Résumé : This paper presents a simulation-based benchmark control study in which shape memory alloy (SMA) wire dampers are utilized to control the seismic response of a three-story nonlinear steel frame building. The SMA wire damper uses superelastic Nitinol wires for energy dissipation because of its high fatigue life and large recoverable strain. An analytical model which considers the training effect of SMA wires is used to describe the stress-strain relationship of superelastic SMA wires. The performance of SMA wire dampers is investigated in the framework of the third-generation benchmark problem on structural control. A comparative study of the seismic response control performance of SMA wire dampers with either unprestrained or prestrained SMA wires was also conducted. The results of this simulation-based benchmark control study show that SMA wire dampers, as a passive structure control measure, can effectively reduce the seismic responses of the three-story nonlinear benchmark building structure and has the potential to withstand several design earthquakes without the need for repair. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9399%282008%29134%3A3%2824 [...]

State estimation in structural systems with model uncertainties / Eric M. Hernandez in Journal of engineering mechanics, Vol. 134 N°3 (Mars 2008) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 134 N°3 (Mars 2008) . - pp.252–257. Titre : State estimation in structural systems with model uncertainties Type de document : texte imprimé Auteurs : Eric M. Hernandez, Auteur ; Dionisio Bernal, Auteur Année de publication : 2008 Article en page(s) : pp.252–257. Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Filters  Estimation  Structural  behavior  Earthquake  engineering  Measurement Résumé : This paper presents an observer designed under the assumption that differences between predicted and measured outputs arise from discrepancies between the real structural system and the nominal model used to represent it. The observer gain is independent of the assumed model error parametrization and proves to be the transpose of the state to output matrix of a state space formulation. The estimated state with the proposed observer is shown to be identical to that obtained by exciting the nominal model with the known input while adjusting the measured portion of the state to match the measurements at the start of every step. Numerical experiments suggest that the proposed observer can provide state estimates that are substantially more accurate than results predicted by projecting the measurements in a truncated modal space. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9399%282008%29134%3A3%2825 [...] [article] State estimation in structural systems with model uncertainties [texte imprimé] / Eric M. Hernandez, Auteur ; Dionisio Bernal, Auteur . - 2008 . - pp.252–257. Mécanique appliquée Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 134 N°3 (Mars 2008) . - pp.252–257. Mots-clés : Filters  Estimation  Structural  behavior  Earthquake  engineering  Measurement Résumé : This paper presents an observer designed under the assumption that differences between predicted and measured outputs arise from discrepancies between the real structural system and the nominal model used to represent it. The observer gain is independent of the assumed model error parametrization and proves to be the transpose of the state to output matrix of a state space formulation. The estimated state with the proposed observer is shown to be identical to that obtained by exciting the nominal model with the known input while adjusting the measured portion of the state to match the measurements at the start of every step. Numerical experiments suggest that the proposed observer can provide state estimates that are substantially more accurate than results predicted by projecting the measurements in a truncated modal space. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9399%282008%29134%3A3%2825 [...]

On-line learning failure-tolerant neural-aided controller for earthquake excited structures / Sriram Narasimhan in Journal of engineering mechanics, Vol. 134 N°3 (Mars 2008) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 134 N°3 (Mars 2008) . - pp.258–268. Titre : On-line learning failure-tolerant neural-aided controller for earthquake excited structures Type de document : texte imprimé Auteurs : Sriram Narasimhan, Auteur ; Sundaram Suresh, Auteur ; Satish Nagarajaiah, Auteur Année de publication : 2008 Article en page(s) : pp.258–268. Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Active  control  Neutral  networks  Failures  Earthquake  resistant  structures Résumé : This paper presents an on-line learning failure-tolerant neural controller capable of controlling buildings subjected to severe earthquake ground motions. In the proposed scheme the neural controller aids a conventional H∞ controller designed to reduce the response of buildings under earthquake excitations. The conventional H∞ controller is designed to reduce the structural responses for a suite of severe earthquake excitations using specially designed frequency domain weighting filters. The neural controller uses a sequential learning radial basis function neural network architecture called extended minimal resource allocating network. The parameters of the neural network are adapted on-line with no off-line training. The performance of the proposed neural-aided controller is illustrated using simulation studies for a two degree of freedom structure equipped with one actuator on each floor. Results are presented for the cases of no failure and failure of the actuator on each of the two floors under several earthquake excitations. The study indicates that the performance of the proposed neural-aided controller is superior to that of the H∞ controller under no actuator failure conditions. In the presence of actuator failures, the performance of the primary H∞ controller degrades considerably, since actuator failures have not been considered for the design. Under these circumstances, the neural-aided controller is capable of controlling the acceleration and displacement structural responses. In many cases, using the neural-aided controller, the response magnitudes under failure conditions are comparable to the performance of the H∞ controller under no-failure conditions. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9399%282008%29134%3A3%2825 [...] [article] On-line learning failure-tolerant neural-aided controller for earthquake excited structures [texte imprimé] / Sriram Narasimhan, Auteur ; Sundaram Suresh, Auteur ; Satish Nagarajaiah, Auteur . - 2008 . - pp.258–268. Mécanique appliquée Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 134 N°3 (Mars 2008) . - pp.258–268. Mots-clés : Active  control  Neutral  networks  Failures  Earthquake  resistant  structures Résumé : This paper presents an on-line learning failure-tolerant neural controller capable of controlling buildings subjected to severe earthquake ground motions. In the proposed scheme the neural controller aids a conventional H∞ controller designed to reduce the response of buildings under earthquake excitations. The conventional H∞ controller is designed to reduce the structural responses for a suite of severe earthquake excitations using specially designed frequency domain weighting filters. The neural controller uses a sequential learning radial basis function neural network architecture called extended minimal resource allocating network. The parameters of the neural network are adapted on-line with no off-line training. The performance of the proposed neural-aided controller is illustrated using simulation studies for a two degree of freedom structure equipped with one actuator on each floor. Results are presented for the cases of no failure and failure of the actuator on each of the two floors under several earthquake excitations. The study indicates that the performance of the proposed neural-aided controller is superior to that of the H∞ controller under no actuator failure conditions. In the presence of actuator failures, the performance of the primary H∞ controller degrades considerably, since actuator failures have not been considered for the design. Under these circumstances, the neural-aided controller is capable of controlling the acceleration and displacement structural responses. In many cases, using the neural-aided controller, the response magnitudes under failure conditions are comparable to the performance of the H∞ controller under no-failure conditions. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9399%282008%29134%3A3%2825 [...]

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