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CONTENTS
Volume 1, Number 3, September 2012
 

Abstract
Tuned vibration control in aeroelasticity of slender wood bridges is treated in present paper. The approach suggested takes into account multiple functions in aeroelastic analysis and flutter of slender wood bridges subjected to laminar and turbulent wind flow. Tuned vibration control approach is presented with application on actual bridge. Some results obtained are discussed.

Key Words
Bernoulli equation; damping; flutter response; mechanics of turbulent wind motion; slender wood bridge; tuned vibration control; wind model

Address
Alexander Tesar : Institute of Construction and Architecture, Slovak Academy of Sciences, Dubravska cesta 9,
845 03 Bratislava 45, Slovak Republic

Abstract
The nonlinear resonant response of an axially moving beam is investigated in this paper via two different numerical techniques: the pseudo-arclength continuation technique and direct time integration. In particular, the response is examined for the system in the neighborhood of a three-to-one internal resonance between the first two modes as well as for the case where it is not. The equation of motion is reduced into a set of nonlinear ordinary differential equation via the Galerkin technique. This set is solved using the pseudo-arclength continuation technique and the results are confirmed through use of direct time integration. Vibration characteristics of the system are presented in the form of frequency-response curves, time histories, phase-plane diagrams, and fast Fourier transforms (FFTs).

Key Words
axially moving beams; vibrations; stability; bifurcation; internal resonance

Address
Mergen H. Ghayesh and Marco Amabili : Department of Mechanical Engineering, McGill University, Montreal, Quebec, Canada H3A 0C3

Abstract
A finite element model is developed for dynamic response prediction of floating offshore wind turbine systems considering coupling of wind turbine, floater and mooring system. The model employs Morison\'s equation with Srinivasan\'s model for hydrodynamic force and a non-hydrostatic model for restoring force. It is observed that for estimation of restoring force of a small floater, simple hydrostatic model underestimates the heave response after the resonance peak, while non-hydrostatic model shows good agreement with experiment. The developed model is used to discuss influence of heave plates and modeling of mooring system on floater response. Heave plates are found to influence heave response by shifting the resonance peak to longer period, while response after resonance is unaffected. The applicability of simplified linear modeling of mooring system is investigated using nonlinear model for Catenary and Tension Legged mooring. The linear model is found to provide good agreement with nonlinear model for Tension Leg mooring while it overestimates the surge response for Catenary mooring system. Floater response characteristics under different wave directions for the two types of mooring system are similar in all six modes but heave, pitch and roll amplitudes is negligible in tension leg due to high restraint. The reduced amplitude shall lead to reduction in wind turbine loads.

Key Words
floating offshore wind turbine; coupled system; Morison equation; finite element

Address
Muhammad Bilal Waris : Department of Civil and Architectural Engineering, Sultan Qaboos University, P.O.Box 33, Muscat 123, Sultanate of Oman
Takeshi Ishihara : Department of Civil Engineering, School of Engineering, University of Tokyo, 7-3-1, Hongo,
Bunkyo-ku, Tokyo 113-8656, Japan

Abstract
In the present paper, a multilevel approach for the local nanobuckling analysis of carbon nanotube (CNT) based composite materials is proposed and described. The approach comprises four levels, all of them at nanoscale. The first level aims to propose the potential that describes the interatomic forces between carbon atoms. In the second level, molecular dynamics simulations are performed to extract the elastic properties of the CNT. The third level aims to determine the stiffness of the material that surrounds the CNT (matrix), using the annular membrane analysis. In the fourth level, finite strip analysis of the CNT elastically restrained by the matrix is performed to calculate the critical strain at which the CNT buckles locally. In order to achieve accurate results and take the CNT-matrix interaction into account, the 3rd and 4th steps may be repeated iteratively until convergence is achieved. The proposed multilevel approach is applied to several CNTs embedded in a cylindrical representative volume element and illustrated in detail. It shows that (i) the interaction between the CNT and the matrix should be taken into account and (ii) the buckling at nanoscale is sensitive to several types of local buckling modes.

Key Words
carbon nanotube (CNT); composite material; CNT-matrix interaction; molecular dynamics; membrane analysis; finite strip analysis; local buckling

Address
N. Silvestre, B. Faria and A. Duarte : Department of Civil Engineering, ICIST, Instituto Superior Tecnico, Technical University of Lisbon, Portugal

Abstract
In this paper, two types of porous burners with radial and axial flow have been modeled numerically and compared. For this purpose, governing equations were solved one-dimensionally for methane-air premix gas. The mechanism used in simulating combustion phenomenon was 15 stage reduced mechanism based on GRI3.0. In order to compare the two burners, the inlet flow rate and fuel-air ratio have been assumed equal for the two burners. The results of the study indicated that reduction in speed and increase in cross-section area in the direction of flow have a considerable influence on the behavior of radial burner in comparison to axial burner. Regarding temperature distribution inside the burner, it was observed that the two above mentioned factors can be influential in temperature of flame propagation region. Also, regarding distribution of CO and NO emission, the results indicate that the porous radial burner has lower emissions in comparison to the axial once. The output radiative heat transfer efficiency of the two burners was also compared and in this case also even the radial porous burner was found to be preferable.

Key Words
radial porous burner; axial porous burner; emissions; speed reduction

Address
N. Ghiasi Tabari, M.R. Astaraki and A.H. Arabi : Islamic Azad University-Dashtestan branch, Dashtestan, Bushehr, Iran


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