In this work, quantum molecular dynamics simulations (QMD) are preformed to study the hydrogen molecules in three types of carbon nanostructures, C60 fullerene, (5,5) and (9,0) carbon nanotubes and graphene layers. Interactions between hydrogen and the nanostructures is of importance to understand hydrogen storage for the development of hydrogen economy. The QMD method overcomes the difficulties with empirical interatomic potentials to model the interaction among hydrogen and carbon atoms in the confined geometry. In QMD, the interatomic forces are calculated by solving the Schrodinger\'s equation with the density functional theory (DFT) formulation, and the positions of the atomic nucleus are calculated with the Newton\'s second law in accordance with the Born-Oppenheimer approximation. It is found that the number of hydrogen atoms that is less than 58 can be stored in the C60 fullerene. With larger carbon
fullerenes, more hydrogen may be stored. For hydrogen molecules passing though the fullerene, a particular
orientation is required to obtain least energy barrier. For carbon nanotubes and graphene, adsorption may
adhere hydrogen atoms to carbon atoms. In addition, hydrogen molecules can also be stored inside the
nanotubes or between the adjacent layers in graphite, multi-layer graphene.
A significant problem met in engineering practice when designing cable-stayed bridges is the failure of cables. Many different factors can lead to sudden failure of cables, such as corrosion, continuous friction or abrasion, progressive and extended crevice created by fatigue and finally an explosion caused by sabotage or accident, are some of the causes that can lead to the sudden failure of one or more cables. This paper deals with the sudden failure of cables in a special form of cable-stayed bridges with a single line of cables anchored at the central axis of the deck\'s cross-section. The analysis is carried out by the modal superposition technique where an analytical method developed by the authors in a previous work has been employed.
cable-stayed bridges; dynamic response; cable failure; sudden failure
I.G. Raftoyiannis, T.G. Konstantakopoulos and G.T. Michaltsos: Department of Civil Engineering, National Technical University of Athens, Greece
The study deals with the physical modeling of a typical single storeyed building frame resting on pile foundation and embedded in cohesive soil mass using the finite element based software SAP-IV. Two groups of piles comprising two and three piles, with series and parallel arrangement thereof, are considered. The slab provided at top and bottom of the frame along with the pile cap is idealized as four noded and two dimensional thin shell elements. The beams and columns of the frame, and piles are modeled using two noded one dimensional beam-column element. The soil is modeled using closely spaced discrete linear springs. A parametric study is carried out to investigate the effect of various parameters of the pile foundation, such as spacing in a group and number of piles in a group, on the response of superstructure. The response considered includes the displacement at the top of the frame and bending moment in columns. The soil-structure interaction effect is found to increase the displacement in the range of 38 -133% and to increase the absolute maximum positive and negative moments in the column in the range of 2-12% and 2-11%. The effect of the soil- structure interaction is observed to be significant for the type of foundation and soil considered in this study. The results obtained are compared further with those of Chore et al. (2010), wherein different idealizations were used for modeling the superstructure frame and sub-structure elements (foundation). While fair agreement is observed in the results in either study, the trend of the results obtained in both studies is also same.
soil-structure interaction; pile groups; pile spacing; top displacement; bending moment
H.S. Chore: Department of Civil Engineering Datta Meghe College of Engineering, Sector-3, Airoli,
Navi Mumbai- 400 708, India
In this paper, the forced vibration problem of an Euler-Bernoulli beam that is joined with a semi-infinite field of a compressible fluid is considered as a boundary value problem (BVP). This BVP includes two partial differential equations (PDE) and some boundary conditions (BC), which are introduced comprehensively. After that, the closed-form solution of this fluid-structure interaction problem is obtained in the frequency domain. Some mathematical techniques are utilized, and two unknown functions of the BVP, including the beam displacement at each section and the fluid dynamic pressure at all points, are attained. These functions are expressed as an infinite series and evaluated quantitatively for a real example in the results section. In addition, finite element analysis is carried out for comparison.
fluid-structure interaction; closed-form solution; dynamic analysis; frequency domain; finite element method; compressible fluid
Amirhossein Keivani and Ahmad Shooshtari: Civil Engineering Faculty, Ferdowsi University of Mashhad, Mashhad, Iran
Ahmad Aftabi Sani: Civil Engineering Department, Mashhad Branch, Islamic Azad University, Mashhad, Iran