• Steel and Composite Structures
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• v.50 no.4
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• pp.429-441
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• 2024

This paper studies the free vibration behavior of trapezoidal shaped coupled double-layered graphene sheets (DLGS) system using first-order shear deformation theory (FSDT) and incorporating nonlocal elasticity theory. Two nanoplates are assumed to be bonded by an interlayer van der walls force and surrounded by an external kelvin-voight viscoelastic medium. The governing equations together with related boundary condition are discretized using a mapping-differential quadrature method (DQM) in the spatial domain. Then the natural frequency of the system is obtained by solving the eigen value matrix equation. The validity of the current study is evaluated by comparing its numerical results with those available in the literature and then a parametric study is thoroughly performed, concentrating on the series effects of angles and aspect ratio of GS, viscoelastic medium, and nonlocal parameter. The model is used to study the vibration of DLGS for two typical deformation modes, the in-phase and out-of-phase vibrations, which are investigated. Numerical results indicate that due to Increasing the damping parameter of the viscoelastic medium has reduced the frequency of both modes and this medium has been able to overdamped the oscillations and by increasing stiffness parameters both in-phase and out-of-phase vibration frequencies increased.

• IEMEK Journal of Embedded Systems and Applications
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• v.5 no.1
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• pp.7-17
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• 2010

ITS(Intelligent Transport System) as things are used for Broadcast service using TDMB/TPEG/NAVI rather than personal seamless service. It is attaching weight to Traffic information gathering, Charging, Settlement service. This research is applied to improve DCCP(Datagram Congestion Control Protocol) which has function as protecting data and preserving message boundary. The improving method is like that we solve data trust in UDP because Connection and Transmission overhead in UDP is less than in TCP. We fix the data loss which is generated from unordered delivery section of IP base wireless service by using DCCP protocol. We guarantee of connection with OBE(On-Board Equipment) and reliance about transmission of data by complement to mapping table and multi-hoping. Finally, We evaluate the performance about transmission of IP based data. We constructed a test-bed near research center for this test.

• Advances in nano research
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• v.5 no.2
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• pp.179-192
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• 2017

The transverse vibration of double walled carbon nanotube (DWCNT) embedded in elastic medium with an initial imperfection is considered. In this paper, Timoshenko beam theory is employed. However the nonlocal theory is used for modeling the nano scale of nanotube. In addition, the governing Equations of motion are obtained utilizing the Hamilton's principle and simply-simply boundary conditions are assumed. Furthermore, the Navier method is used for determining the natural frequencies of DWCNT. Hence, some parameters such as nonlocality, curvature amplitude, Winkler and Pasternak elastic foundations and length of the curved DWCNT are analyzed and discussed. The results show that, the curvature amplitude causes to increase natural frequency. However, nonlocal coefficient and elastic foundations have important role in vibration behavior of DWCNT with imperfection.

• Journal of Hydrogen and New Energy
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• v.15 no.4
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• pp.257-265
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• 2004

Numerical analysis, as EAM(Embedded Atom Method), in the atomic level is necessary to analyze the relation between the hydrogen and hydrogen absorption metals. EAM established on density functional theory was developed as a new means for calculating various properties and phenomena of realistic metal systems. In this study, we had constructed the EAM program from constitutive formulae and parameters of the hydrogen, nickel and palladium for the purpose of predicting the expansion behavior on hydrogen absorbing. In result, not only the ground state properties of metals but also lattice constants and the volume expansion ratio of metal hydrides show good agreement with Daw's data and experiment data.

• Geomechanics and Engineering
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• v.12 no.2
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• pp.327-346
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• 2017

Laminated plates have many applications in different industrials. Buckling analysis of these structures with the nano-scale reinforcement has not investigated yet. However, buckling analysis of embedded laminated plates with nanocomposite layers is studied in this paper. Considering the single-walled carbon nanotubes (SWCNTs) as reinforcement of layers, SWCNTs agglomeration effects and nonlinear analysis using numerical method are the main contributions of this paper. Mori-Tanaka model is applied for obtaining the equivalent material properties of structure and considering agglomeration effects. The elastic medium is simulated by spring and shear constants. Based on first order shear deformation theory (FSDT), the governing equations are derived based on energy method and Hamilton's principle. Differential quadrature method (DQM) is used for calculating the buckling load of system. The effects of different parameters such as the volume percent of SWCNTs, SWCNTs agglomeration, number of layers, orientation angle of layers, elastic medium, boundary conditions and axial mode number of plate on the buckling of the structure are shown. Results indicate that increasing volume percent of SWCNTs increases the buckling load of the plate. Furthermore, considering agglomeration effects decreases the buckling load of system. In addition, it is found that the present results have good agreement with other works.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.1896-1901
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• 2008

Single crystalline copper nanowires are subjected to bending tests using molecular dynamics simulations and the embedded atom method. To observe behaviors of nanowire, bending tests are performed for various rates of deflection and different boundary conditions: fixed-free and fixed-fixed. When the deflection of nanowire becomes large, twinnings and dislocations appear, and <100> crystal structure transforms to <110>. At high rates, phase transformation occurs in whole nanowire. But, at low rates, atomic structure changes to <110> phase partially. The final deformed structures are affected by the rate of deflection and boundary conditions. These effects can be important design parameters at nanoscale.

• Journal of the Korean Society of Safety
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• v.21 no.1 s.73
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• pp.15-20
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• 2006

The finite element alternating method is a convenient and efficient method to analyze three-dimensional cracks embedded in an infinite or a finite body because the method has the property that the uncracked body and cracks can be modeled independently. In this paper the method was applied for fatigue crack growth simulation. A surface crack in a cylinder was considered as an initial crack and the crack configurations and stress intensity factors during the crack growth were obtained. In this paper the finite element alternating method proposed by Nikishkov, Park and Atluri was used after modification. In the method, as the required solution for a crack in an infinite body, the symmetric Galerkin boundary element method formulated by Li and Mear was used. And a crack was modeled as distribution of displacement discontinuities, and the governing equation was formulated as singularity-reduced integral equations.

• Advances in nano research
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• v.4 no.3
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• pp.229-249
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• 2016

In this paper, buckling characteristics of nonhomogeneous functionally graded (FG) nanobeams embedded on elastic foundations are investigated based on third order shear deformation (Reddy) without using shear correction factors. Third-order shear deformation beam theory accounts for shear deformation effects by a parabolic variation of all displacements through the thickness, and verifies the stress-free boundary conditions on the top and bottom surfaces of the FG nanobeam. A two parameters elastic foundation including the linear Winkler springs along with the Pasternak shear layer is in contact with beam in deformation, which acts in tension as well as in compression. The material properties of FG nanobeam are supposed to vary gradually along the thickness and are estimated through the power-law and Mori-Tanaka models. The small scale effect is taken into consideration based on nonlocal elasticity theory of Eringen. Nonlocal equations of motion are derived through Hamilton's principle and they are solved applying analytical solution. Comparison between results of the present work and those available in literature shows the accuracy of this method. The obtained results are presented for the buckling analysis of the FG nanobeams such as the effects of foundation parameters, gradient index, nonlocal parameter and slenderness ratio in detail.

• Geomechanics and Engineering
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• v.19 no.1
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• pp.79-91
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• 2019

Renewed interest in the long-term pile foundations has been driven by the increase in offshore wind turbine installation to generate renewable energy. A monopile subjected to repetitive loads experiences an evolution of displacements, pile rotation, and stress redistribution along the embedded portion of the pile. However, it is not fully understood how the embedded pile interacts with the surrounding soil elements based on different pile geometries. This study investigates the long-term soil response around offshore monopiles using finite element method. The semi-empirical numerical approach is adopted to account for the fundamental features of volumetric strain (terminal void ratio) and shear strain (shakedown and ratcheting), the strain accumulation rate, and stress obliquity. The model is tested with different strain boundary conditions and stress obliquity by relaxing four model parameters. The parametric study includes pile diameter, embedded length, and moment arm distance from the surface. Numerical results indicate that different pile geometries produce a distinct evolution of lateral displacement and stress. In particular, the repetitive lateral load increases the global lateral load resistance. Further analysis provides insight into the propagation of the shear localization from the pile tip to the ground surface.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.20 no.6
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• pp.779-787
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• 2007

This paper presents a highly efficient moving least squares finite difference method (MLS FDM) for a heat transfer problem of bi-material with interfacial boundary. The MLS FDM directly discretizes governing differential equations based on a node set without a grid structure. In the method, difference equations are constructed by the Taylor polynomial expanded by moving least squares method. The wedge function is designed on the concept of hyperplane function and is embedded in the derivative approximation formula on the moving least squares sense. Thus interfacial singular behavior like normal derivative jump is naturally modeled and the merit of MLS FDM in fast derivative computation is assured. Numerical experiments for heat transfer problem of bi-material with different heat conductivities show that the developed method achieves high efficiency as well as good accuracy in interface problems.