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CONTENTS
Volume 3, Number 2, June 2010
 

Abstract
Dynamic analysis of nano/micro bio-sensors based on a multiscale atomistic/continuum theory is introduced. We use a generalized atomistic finite element method (GAFEM) to analyze a biosensor which has 3 x Na x Np degrees of freedom, where Np is the number of representative unit cells and Na is the number of atoms per unit cell. The stiffness matrix is derived from interatomic potential between pairs of atoms. This work contains two studies: (1) the resonance analysis of nano bio-sensors with different amount of target analyte and (2) the dependence of resonance frequency on finite element mesh. We also examine the Courant-Friedrichs-Lewy (CFL) condition based on the highest resonance frequency. The CFL condition is the criterion for the time step used in the dynamic analysis by GAFEM. Our studies can be utilized to predict the performance of micro/nano bio-sensors from atomistic perspective.

Key Words
atomistic field theory; nanosensor; resonance frequency; courant condition.

Address
James Chen and James D. Lee: Dept. of Mechanical and Aerospace Engineering, The George Washington University, Washington DC 20052, USA

Abstract
The essential idea of the element-free Galerkin method (EFG) is that moving least-squares (MLS) approximation are used for the trial and test functions with the variational principle (weak form). By using the weighted orthogonal basis function to construct the MLS interpolants, we derive the formulae for an improved element-free Galerkin (IEFG) method for solving three-dimensional problems in linear elasticity. There are fewer coefficients in improved moving least-squares (IMLS) approximation than in MLS approximation. Also fewer nodes are selected in the entire domain with the IEFG method than is the case with the conventional EFG method. In this paper, we selected a few example problems to demonstrate the applicability of the method.

Key Words
weighted orthogonal function; Improved moving least-squares (IMLS) approximation; Element-free Galerkin (EFG) method; Improved element-free Galerkin (IEFG) method; 3D elastic problem.

Address
Zan Zhang: Shanghai Institute of Applied Mathematics and Mechanics, Shanghai University, Shanghai 200072, China
K.M. Liew: Department of Building and Construction, City University of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong SAR

Abstract
The propagation of waves in a micropolar transversely isotropic half space in the theory of thermoelasticity without energy dissipation are discussed. After developing the solution, the phase velocities and attenuation quality factor has been obtained. The expressions for amplitudes of stresses, displacements, microrotation and temperature distribution have been derived and computed numerically. The numerical results have been plotted graphically.

Key Words
micropolar; transversely isotropic; amplitude ratios; without energy dissipation.

Address
Rajneesh Kumar and Rajani Rani Gupta: Dept. of Mathematics, Kurukshetra University, Kurukshetra, Haryana-136 119, India

Abstract
In this paper, a theoretical method has been developed for the electric double layer interaction under condition of the variable dielectric permittivity of water. Using Poisson-Boltzmann equation (PBE), for one plate and two plates having similar or dissimilar constant charge or constant potential, we have investigated the electric double layer potential, its gradient and the disjoining pressure as well as the effect of variation of dielectric permittivity on these parameters. It has been assumed that plates are separated by a specific distance and contain a liquid solution in between. It is shown that reduction of the dielectric permittivity near the interfaces results in compression of electric double layers and affects the potential and its gradient which leads to a decreased electrostatic repulsion. In addition, it is shown that variation of dielectric permittivity in the case of higher electrolyte concentration, leads to a greater change in potential distribution between two plates.

Key Words
electric double layer; dielectric permittivity; poisson-boltzmann equation.

Address
Amir Farrokh Payam and Morteza Fathipour: Nano-Electronics Center of Excellence, Faculty of Electrical and Computer Engineering, Campus #2, University of Tehran, North Kargar St., P.O. BOX 14395-515, Tehran, Iran

Abstract
Damage detection plays a very important role to the maintenance of bridge structures. Traditional damage detection methods are usually based on structural dynamic properties, which are acquired from pre-installed sensors on the bridge. This is not only time-consuming and costly, but also suffers from poor sensitivity to damage if only natural frequencies and mode shapes are concerned in a noisy environment. Recently, the idea of using the dynamic responses of a passing vehicle shows a convenient and economical way for damage detection of bridge structures. Inspired by this new idea and the well-established tap test in the field of non-destructive testing, this paper proposes a new method for obtaining the damage information through the acceleration of a passing vehicle enhanced by a tapping device. Since no finger-print is required of the intact structure, this method can be easily implemented in practice. The logistics of this method is illustrated by a vehicle-bridge interaction model, along with the sensitivity analysis presented in detail. The validity of the method is proved by some numerical examples, and remarks are given concerning the potential implementation of the method as well as the directions for future research.

Key Words
bridge; damage; non-destructive testing; sensitivity; tap-scan method; vehicle.

Address
Zhihai Xiang, Xiaowei Dai, Yao Zhang and Qiuhai Lu:
Applied Mechanics Laboratory, Department of Engineering Mechanics, Tsinghua University, Beijing, 100084, P. R. China

Abstract
In most framed structures the nonlinearities and the damages are localized, extending over a limited length of the structural member. In order to capture the details of the local damage, the segments of a member that have entered the nonlinear range may need to be analyzed using the three-dimensional element (3D) model whereas the rest of the member can be analyzed using the simpler one-dimensional (1D) element model with fewer degrees of freedom. An Element-Coupling model was proposed to couple the small scale solid 3D elements with the large scale 1D beam elements. The mixed dimensional coupling is performed imposing the kinematic coupling hypothesis of the 1D model on the interfaces of the 3D model. The analysis results are compared with test results of a reinforced concrete pipe column and a structure consisting of reinforced concrete columns and a steel space truss subjected to static and dynamic loading. This structure is a reduced scale model of a direct air-cooled condenser support platform built in a thermal power plant. The reduction scale for the column as well as for the structure was 1:8. The same structures are also analyzed using 3D solid elements for the entire structure to demonstrate the validity of the Element-Coupling model. A comparison of the accuracy and the computational effort indicates that by the proposed Element-Coupling method the accuracy is almost the same but the computational effort is significantly reduced.

Key Words
element-coupling structural model; mixed dimensional elements; kinematic coupling; nonlinear analysis.

Address
Jianguang Yue: State Key Laboratory of Disaster Reduction in Civil Engineering, Tongji University, Shanghai 200092, China
Apostolos Fafitis: Dept. of Civil and Environmental Engineering, Arizona State University, Tempe AZ 85287, USA
Jiang Qian: State Key Laboratory of Disaster Reduction in Civil Engineering, Tongji University, Shanghai 200092, China



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