• Geomechanics and Engineering
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• v.32 no.6
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• pp.615-625
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• 2023

Initial geometrical imperfection is an important factor affecting the structural characteristics of plate and shell structures. Studying the effect of geometrical imperfection on the structural characteristics of cylindrical shell is beneficial to explore the thermal post-buckling response characteristics of cylindrical shell. Therefore, we devote to investigating the thermal post-buckling behavior of graphene platelets reinforced mental foam (GPLRMF) cylindrical shells with geometrical imperfection. The properties of GPLRMF material with considering three types of graphene platelets (GPLs) distribution patterns are introduced firstly. Subsequently, based on Donnell nonlinear shell theory, the governing equations of cylindrical shell are derived according to Eulerian-Lagrange equations. Taking into account two different boundary conditions namely simply supported (S-S) and clamped supported (C-S), the Galerkin principle is used to solve the governing equations. Finally, the impact of initial geometrical imperfections, the GPLs distribution types, the porosity distribution types, the porosity coefficient as well as the GPLs mass fraction on the thermal post-buckling response of the cylindrical shells are analyzed.

• Steel and Composite Structures
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• v.46 no.5
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• pp.649-658
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• 2023

Although some scholars have studied the thermal post-buckling of graphene platelets strengthened metal foams (GPLRMFs) plates, they have not considered the influence of initial geometrical imperfection. Inspired by this fact, the present paper studies the thermal post-buckling characteristics of GPLRMFs plates with initial geometrical imperfection. Three kinds of graphene platelets (GPLs) distribution patterns including three patterns have been considered. The governing equations are derived according to the first-order plate theory and solved with the help of the Galerkin method. According to the comparison with published paper, the accuracy and correctness of the present research are verified. In the end, the effects of material properties and initial geometrical imperfection on the thermal post-buckling response of the GPLRMFs plates are examined. It can be found that the presence of initial geometrical imperfection reduces the thermal post-buckling strength. In addition, the present study indicates that GPL-A pattern is best way to improve thermal post-buckling strength for GPLRMFs plates, and the presence of foams can improve the thermal post-buckling strength of GPLRMFs plates, the Foam- II and Foam- I patterns have the lowest and highest thermal post-buckling strength. Our research can provide guidance for the thermal stability analysis of GPLRMFs plates.

• Smart Structures and Systems
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• v.25 no.5
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• pp.619-630
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• 2020

This paper studies nonlinear free vibration characteristics of nonlocal magneto-electro-elastic (MEE) nanobeams resting on nonlinear elastic substrate having geometrical imperfection by considering piezoelectric reinforcement scheme. The piezoelectric reinforcement can cause an enhanced vibration behavior of smart nanobeams under magnetic field. All of previously reported studies on MEE nanobeams ignore the influences of geometric imperfections which are very substantial due to the reason that a nanobeam cannot be always perfect. Nonlinear governing equations of a smart nanobeam are derived based on classical beam theory and an analytical trend is provided to obtained nonlinear vibration frequency. This research shows that changing the volume fraction of piezoelectric constituent in the material has a great influence on vibration behavior of smart nanobeam under electric and magnetic fields. Also, it can be seen that nonlinear vibration behaviors of smart nanobeam are dependent on the magnitude of exerted electric voltage, magnetic potential, hardening elastic foundation and geometrical imperfection.

• Bulletin of the Korean Chemical Society
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• v.29 no.3
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• pp.627-640
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• 2008

The geometrical structures, atomic charges, and relative energies of tetracoordinated Pd complexes [PdCl3Z (Z = Cl-, Br-, OH?-, H2O, NH3, PH3), PdCl2Z2 (Z = Br-, OH?-, H2O, NH3, PH3), PdZ?2X (Z = Cl-, OH?-, H2O, NH3, PH3; X = oxalate, O2-?CCO2-), and PdZ2Y (Z = Cl?-, OH?-, H2O, NH3, PH3; Y = succinate, CO2-?CHCHCO2-?)] and the ligand exchange reactions of the Pd complexes were investigated using the ab initio second order Mller-Plesset perturbation (MP2) and Density Functional Theory (DFT) methods. The geometrical characteristics of the tetracoordinated Pd(II) complexes with mono- and bidentate ligands, the effects of the atomic charges for the charged and uncharged ligands, the (dz2-p ) interactions between the dz2-orbital of Pd(II) and the p -orbital of bidentates, and the relative stabilities between the isomers of PdCl2Z2 and PdZ2Y were investigated in detail. The potential energy surfaces for the ligand exchange reactions used for the conversions of {[PdCl2(NH3)2] + H2O} to {[PdCl(NH3)2(H2O)]+ + Cl?-?} and {[PdCl2(PH3)2] + H2O} to {[PdCl(PH3)2(H2O)]+ + Cl?-?]} were investigated. The geometrical structure variations, molecular orbital variations (HOMO and LUMO), and relative stabilities for the ligand exchange processes were also examined quantitatively.

• The Bulletin of The Korean Astronomical Society
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• v.23
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• pp.32-32
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• 1998

• Structural Engineering and Mechanics
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• v.45 no.3
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• pp.411-422
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• 2013

A well-designed mesh shape of the cable net is of essential significance to achieve high performance of cable-network antenna reflectors. This paper is concerned with the mesh design problem for such antenna reflector structure. Two new methods for creating the topological forms of the cable net are first presented. Among those, the cyclosymmetry method is useful to generate different polygon-faceted meshes, while the topological mapping method is suitable for acquiring triangle-faceted meshes with different mesh grid densities. Then, the desired spatial paraboloidal mesh geometrical configuration in the state of static equilibrium is formed by applying a simple mesh generation approach based on the force density method. The main contribution of this study is that a general technical guide for how to create the connectivities between the nodes and members in the cable net is provided from the topological point of view. With the new idea presented in this paper, multitudes of mesh configurations with different net patterns can be sought by a certain rule rather than by empiricism, which consequently gives a valuable technical reference for the mesh design of this type of cable-network structures in the engineering.

• Journal of Korean Association for Spatial Structures
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• v.18 no.4
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• pp.31-39
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• 2018

This paper analyse the mechanical characteristics of geometrical and material nonlinearity behavior of cylindrical shell roofs subjected to a concentrated load. The shell elements were modeled using 'NISA2016' software as 3D general shell element and 3D composite shell element. The 3D shell element includes deformation due to bending, membrane, membrane-bending coupling and shear perpendicular to the grain effects is suited for modeling moderately thick or thin general shells and laminated composite shells. And The 3D composite shell element consists of a number of layers of perfectly bonded anisotropic and orthotropic materials. The purpose of this research is to analysis the load-deflection curves considering the combined geometric and material nonlinearity of cylindrical shells. In a shallowed cylindrical shell, snap-through curve can be found.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.31 no.7 s.262
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• pp.792-799
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• 2007

A newly developed cellular metal based on kagome lattice is an ideal candidate for multifunctional materials achieving various optimal properties. Intensive efforts have been devoted to develop efficient techniques for mass production due to its wide potential applications. Since a variety of imperfections would be inevitably included in the realistic fabrication processes, it is highly important to examine the correlation between the imperfections and material strengths. Previous performance tests were mostly done by numerical simulations such as finite element method (FEM), but only for perfect structures without any imperfection. In this paper, we developed an efficient numerical framework using nonlinear random network analysis (RNA) to verify how the statistical imperfections (geometrical and material property) contribute to the performance of general truss structures. The numerical results for kagome truss structures are compared with experimental measurements on 3-layerd WBK (wire-woven bulk kagome). The mechanical strength of the kagome structures is shown relatively stable with the Gaussian types of imperfections.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.78-83
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• 2007

A newly developed cellular metal based on kagome lattice is an ideal candidate for multifunctional materials achieving various optimal properties. Intensive efforts have been devoted to develop efficient techniques for mass production due to its wide potential applications. Since a variety of imperfections would be inevitably included in the realistic fabrication processes, it is highly important to examine the correlation between the imperfections and material strengths. Previous performance tests were mostly done by numerical simulations such as finite element method (FEM), but only for perfect structures without any imperfection. In this paper, we developed an efficient numerical framework using nonlinear random network analysis (RNA) to verify how the statistical imperfections (geometrical and material property) contribute to the performance of general truss structures. The numerical results for kagome truss structures are compared with experimental measurements on 3-layerd WBK (wire-woven bulk kagome). The mechanical strength of the kagome structures is shown relatively stable with the Gaussian types of imperfections.

• Proceeding of EDISON Challenge
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• 2014.03a
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• pp.472-474
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• 2014

Carbon nanotubes (CNTs) have been intensively investigated since they have been considered as building blocks of nanoscience and nanotechnology. Theoretical and computational studies on CNTs have revealed their physical and chemical properties and helped researchers build various experimental devices to study them in depth. However, there have been only few systematic studies on detailed changes in electronic structures of CNTs due to geometrical structure modifications. In this regard, it is necessary to perform systematic investigations of the modifications in electronic structures of CNTs, as their geometrical configurations are altered, using the first-principles density functional theory. In other words, it is essential to determine the true equilibrium structure of CNTs. We are going to construct different atomic configurations of each nanotube by maintaining the original symmetries, but changing all the other bonding types one by one. Furthermore, as for CNTs, for example, the way the graphene sheet is wrapped is represented by a pair of indices (n,m) and electronic structures of CNTs vary depending on different indices. Therefore, we plan to study and discuss all the significant couplings between electronic and geometric structures in CNTs.